USBR Engineering Geology Field Manual Volume 1 Chapter 1

Chapter 1

INTRODUCTION

This manual provides guidelines and instructions for performing and documenting field work. The manual is a ready reference for anyone engaged in field-oriented engineering geology or geotechnical engineering. The manual is written for general engineering geology use as well as to meet Reclamation needs. The application of geology to solving engineering problems is emphasized, rather than academic or other aspects of geology. The manual provides guidance for:

• Geologic classification and description of rock and rock discontinuities

• Engineering classification and description of soil and surficial deposits

• Application of standard indexes, descriptors, and terminology

• Geologic mapping, sampling, testing, and performing discontinuity surveys

• Exploratory drilling

• Soil and rock logging

• Acquisition of groundwater data

• Core logging

• Soil logging

• Investigation of hazardous waste sites FIELD MANUAL

Although the methods described in this manual are appropriate for most situations, complex sites, conditions, or design needs may require modification or expansion of the suggestions, criteria, and indices to fit specific requirements.

Many of the chapters in this manual will always need revision because they cover material that changes as technology changes. Critical comments, especially suggestions for improvement, are welcome from all users, not just the Bureau of Reclamation.

The appendix contains abbreviations and acronyms commonly used in engineering geology.

2 Chapter 2

GEOLOGIC TERMINOLOGY AND CLASSIFICATIONS FOR GEOLOGIC MATERIALS

Established References for Geological Terminology

Adaptations or refinements of the Bureau of Reclamation (Reclamation) standards presented in this and subsequent chapters may be established to meet specific design requirements or site-specific geologic complexity when justified.

The Glossary of Geology, Fourth Edition [1]1, published by the American Geological Institute (AGI), 1997, is accepted by Reclamation as the standard for definitions of geologic words and terms except for the nomenclature, definitions, or usage established in this chapter and chapters 3, 4, and 5.

The North American Stratigraphic Code (NASC) [2] is the accepted system for classifying and naming stratigraphic units. However, Reclamation's engineering geology programs are focused primarily on the engineering properties of geologic units, not on the details of formal stratigraphic classification. Stratigraphic names are not always consistent within the literature, often change from one locality to another, and do not necessarily convey engineering properties or rock types. Use of stratigraphic names in Reclamation documents normally will be informal (lower case) (see NASC for discussion of formal versus informal usage). Exceptions to informal usage are for names previously used formally in the area in discussions of geologic setting or regional geology. Normally,

1 Brackets refer to bibliography entries at end of each chapter. FIELD MANUAL the first use of formal names in a report should include a reference to a geologic map or publication in which the term is defined.

Geologic Classification of Materials

The following definitions of geologic materials more fully satisfy general usage and supersede those in the Glossary of Geology. These definitions are for geologic classification of materials. They should not be confused with engineering classifications of materials such as rock and soil or rock and common excavation.

• Bedrock is a general term that includes any of the generally indurated or crystalline materials that make up the Earth's crust. Individual stratigraphic units or units significant to engineering geology within bedrock may include poorly or nonindurated materials such as beds, lenses, or intercalations. These may be weak rock units or interbeds consisting of clay, silt, and sand (such as the generally soft and friable St. Peter Sandstone), or clay beds and bentonite partings in siliceous shales of the Morrison Formation.

•Surficial Deposits are the relatively younger materials occurring at or near the Earth's surface overlying bedrock. They occur as two major classes: (1) transported deposits generally derived from bedrock materials by water, wind, ice, gravity, and man's intervention and (2) residual deposits formed in place as a result of weathering processes. Surficial deposits may be stratified or unstratified such as soil profiles, basin fill, alluvial or fluvial deposits, landslides, or talus. The material may be partially indurated or cemented by silicates, oxides, carbonates, or other chemicals (caliche or hardpan). This term is often used interchangeably with the imprecisely

4 TERMINOLOGY defined word “overburden.” “Overburden” is a mining term meaning, among other things, material overlying a useful material that has to be removed. “Surficial deposit” is the preferred term.

In some localities, where the distinction between bedrock and surficial deposits is not clear, even if assigned a stratigraphic name, a uniform practice should be established and documented and that definition followed for the site or study.

Guidelines for the collection of data pertaining to bedrock and surficial deposits are presented in chapter 6.

Engineering Classification of Geologic Materials

General

Geologic classification of materials as surficial deposits or bedrock is insufficient for engineering purposes. Usually, surficial deposits are described as soil for engineering purposes, and most bedrock is described as rock; however, there are exceptions. Contract documents often classify structure excavations as to their ease of excavation. Also, classification systems for tunneling in geologic materials have been established.

Classification as Soil or Rock

In engineering applications, soil may be defined as generally unindurated accumulations of solid particles produced by the physical and/or chemical disintegration of bedrock and which may or may not contain organic matter. Surficial deposits, such as colluvium, alluvium, or residual soil, normally are described using Recla-

5 FIELD MANUAL mation Procedure 5005, Determining Unified Soil Classification (Visual Method) [3]. American Society for Testing and Materials (ASTM) Standards D2487-85, Standard Test Method for Classification of Soils for Engineering Purposes or D2488-84, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), which are based on Reclamation 5000 and 5005 [3] also may be used. Instructions for the description and classification of soils are provided in chapter 3. Chapter 11 provides instructions for the logging of soils in geologic explorations. In some cases, partially indurated soils may have rock-like characteristics and may be described as rock.

The United States Department of Agriculture (USDA) Agricultural Soils Classification System is used for drainage and land classification and some detailed Quaternary geology studies, such as for seismotectonic investigations.

Rock as an engineering material is defined as lithified or indurated crystalline or noncrystalline materials. Rock is encountered in masses and as large fragments which have consequences to design and construction differing from those of soil. Field classification of igneous, metamorphic, sedimentary, and pyroclastic rocks are provided in chapter 4. Chapter 4 also presents a suggested description format, standard descriptors, and descriptive criteria for the lithologic and engineering physical properties of rock. Nonindurated materials within bedrock should be described using the Reclamation soil classification standards and soil descriptors presented in chapter 3. Engineering and geological classification and description of discontinuities which may be present in either soil or rock are discussed in chapter 5.

6 TERMINOLOGY

Classification of Excavations

The engineering classification of excavation as either rock excavation or common excavation or the definition of rock in specifications must be evaluated and determined for each contract document and should be based on the physical properties of the materials (induration and other characteristics), quantity and method of excavation, and equipment constraints and size.

Classification of Materials for Tunneling

Classification systems are used for data reports, specifications, and construction monitoring for tunnel designs and construction. When appropriate for design, other load prediction and classification systems may be used such as the Q system developed by the Norwegian Geo- technical Institute (NGI), Rock Mass Rating System Geomechanics Classification (RMR), and Rock Structure Rating (RSR).

The following terms for the classification of rock [4] for tunneling are suggested:

• Intact rock contains neither joints nor hairline cracks. If it breaks, it breaks across sound rock. On account of damage to the rock due to blasting, spalls may drop off the roof several hours or days after blasting. This is known as spalling condition. Hard, intact rock may also be encountered in the popping condition (rock burst) involving the spontaneous and violent detachment of rock slabs from sides or roof.

• Stratified rock consists of individual strata with little or no resistance against separation along the boundaries

7 FIELD MANUAL between strata. The strata may or may not be weakened by transverse joints. In such rock, the spalling condition is quite common.

• Moderately jointed rock contains joints and hairline cracks, but the blocks between joints are locally grown together or so intimately interlocked that vertical walls do not require lateral support. In rocks of this type, both the spalling and the popping condition may be encountered.

• Blocky and seamy rock consists of chemically intact or almost intact rock fragments which are entirely separated from each other and imperfectly interlocked. In such rock, vertical walls may require support.

• Crushed but chemically intact rock has the character of a crusher run. If most or all of the fragments are as small as fine sand and no recementation has taken place, crushed rock below the water table exhibits the properties of a water-bearing sand.

• Squeezing rock slowly advances into the tunnel without perceptible volume increase. Movement is the result of overstressing and plastic failure of the rock mass and not due to swelling.

• Swelling rock advances into the tunnel chiefly on account of expansion. The capacity to swell is generally limited to those rocks which contain smectite, a montmorillonite group of clay minerals, with a high swelling capacity.

Although the terms are defined, no distinct boundaries exist between rock categories. Wide variations in the physical properties of rocks classified by these terms and rock loading are often the case.

8 TERMINOLOGY

Table 2-1, Ground behavior for earth tunneling with steel supports, provides ground classifications for different reactions of ground to tunneling operations.

Application and Use of Standard Indexes, Terminology, and Descriptors

This section and subsequent chapters 3, 4, and 5 provide definitions and standard descriptors for physical properties of geologic materials which are of engineering significance. The ability of a foundation to support loads imposed by various structures depends primarily on the deformability and stability of the foundation materials and the groundwater conditions. Description of geologic and some manmade materials (embankments) is one of the geologist's direct contributions to the design process. Judgment and intuition alone are not adequate for the safe and economical design of large complex engineering projects. Preparation of geologic logs, maps and sections, and detailed descriptions of observed material is the least expensive aspect and most continuous record of a subsurface exploration program. It is imperative to develop design data properly because recent advances in soil and rock mechanics have enabled engineers and geologists to analyze more conditions than previously possible. These analyses rely on physical models that are developed through geologic observation and which must be described without ambiguity.

The need for standard geologic terminology, indexes, and descriptors has long been recognized because it is important that design engineers and contractors, as well as geologists, be able to have all the facts and qualitative information as a common basis to arrive at conclusions from any log of exploration, report, or drawing, regardless of the preparer. Geologic terminology,

9 FIELD MANUAL

Table 2-1.—Ground behavior for earth tunneling with steel supports (after Terzaghi, 1977) [4] Ground classification Reaction of ground to tunneling operation

HARD Tunnel heading may be advanced without roof support. FIRM Ground in which a roof section of a tunnel can be left unsupported for several days without inducing a perceptible movement of the ground. RAVELING Chunks or flakes of soil begin to drop out of roof at some point during the ground-movement period. SLOW RAVELING The time required to excavate 5 feet of tunnel and install a rib set and lagging in a small tunnel is about 6 hours. Therefore, if the stand-up time of raveling ground is more than 6 hours, by using ribs and lagging, the steel rib sets may be spaced on 5-foot centers. Such a soil would be classed as slow raveling. FAST RAVELING If the stand-up time is less than 6 hours, set spacing must be reduced to 4 feet, 3 feet, or even 2 feet. If the stand-up time is too short for these smaller spacings, liner plates should be used, either with or without rib sets, depending on the tunnel size. SQUEEZING Ground slowly advances into tunnel without any signs of fracturing. The loss of ground caused by squeeze and the resulting settlement of the ground surface can be substantial. SWELLING Ground slowly advances into the tunnel partly or chiefly because of an increase in the volume of the ground. The volume increase is in response to an increase of water content. In every other respect, swelling ground in a tunnel behaves like a stiff non-squeezing, or slowly squeezing, non-swelling clay. RUNNING The removal of lateral support on any surface rising at an angle of more than 34E (to the horizontal) is immediately followed by a running movement of the soil particles. This movement does not stop until the slope of the moving soil becomes roughly equal to 34E• if running ground has a trace of cohesion, then the run is preceded by a brief period of progressive raveling. VERY SOFT SQUEEZING Ground advances rapidly into tunnel in a plastic flow. FLOWING Ground supporting a tunnel cannot be classified as flowing ground unless water flows or seeps through it toward the tunnel. For this reason, a flowing condition is encountered only in free air tunnels below the watertable or under compressed air when the pressure is not high enough in the tunnel to dry the bottom. A second prerequisite for flowing is low cohesion of soil. Therefore, conditions for flowing ground occur only in inorganic silt, fine silty sand, clean sand or gravel, or sand-and-gravel with some clay binder. Organic silt may behave either as a flowing or as a very soft, squeezing ground.

10 TERMINOLOGY standard descriptors, and descriptive criteria for physical properties have been established so that geologic data are recorded uniformly, objectively, consistently, and accurately. The application of these indexes, terminology, descriptors, and various manual and visual tests must be applied consistently by all geologists for each particular project. The need to calibrate themselves with others performing similar tests and descriptions is imperative to ensure that data are recorded and interpreted uniformly. The use of these standard descriptors and terminology is not intended to replace the geologist's or engineer's individual judgment. The established standard qualitative and quantitative descriptors will assist newly employed geologists and engineers in understanding Reclamation terminology and procedures, permit better analysis of data, and permit better understanding by other geologists and engineers, and by contractors. Most of the physical dimensions established for the descriptive criteria pertaining to rock and discontinuity characteristics have been established using a 1-3-10-30-100 progression for consistency, ease of memory, conversion from English to metric (30 millimeters [mm] = 0.1 foot [ft]) units, and to conform to many established standards used throughout the world. Their use will improve analysis, design and construction considerations, and specifications preparation. Contractor claims also should be reduced due to consistent and well defined terminology and descriptors.

Alphanumeric values for many physical properties have been established to enable the geotechnical engineer and engineering geologist to readily analyze the geologic data. These alphanumeric descriptors also will assist in compilation of data bases and computer searches when using computer generated logs. For consistency, the lower the alphanumeric value, the more favorable the condition being described. However, alphanumeric codes do not replace a complete description of what is observed. A

11 FIELD MANUAL complete description provides physical dimensions including a range and/or average in size, width, length or other physical property, and/or descriptive information.

It is important to start physical testing of the geologic materials as early as possible in an exploration program; descriptors alone are not sufficient. As data are interpreted, index properties tests can be performed in the field to obtain preliminary strength estimates for representative materials or materials requiring special consideration. The scope of such a program must be tailored to each feature. Tests which are to be considered include point load, Schmidt hammer, sliding tilt, and pocket Torvane or penetrometer tests. These tests are described briefly in chapters 4 and 5. Indexes to be considered include rock hardness, durability (slaking), and Rock Quality Designation (RQD). The type of detailed laboratory studies can be formulated better and the amount of sampling and testing may be reduced if results from field tests are available.

Units of Measurements for Geologic Logs of Exploration, Drawings, and Reports

Metric Units

For metric specifications and studies, metric (Interna- tional System of Units) should be used from the start of work if possible. Logs of exploration providing depth measurements should be given to tenths or hundredths of meters. All linear measurements such as particle or crystal sizes, ranges or averages in thickness, openness, and spacing, provided in descriptor definitions in chapters 3, 4, and 5, should be expressed in millimeters or meters as appropriate. Pressures should be given in pascals (Pa). Permeability (hydraulic conductivity)

12 TERMINOLOGY should be in centimeters per second (cm/s). In some cases, local usage of other units such as kilogram per square centimeter (kg/cm2) for pressure or centimeters (cm) may be used.

English Units (U.S. Customary)

For specifications and studies using United States customary or English units (inch-pound), depth measurements should be given in feet and tenths of feet. Ranges in thickness, openness, and spacing, are preferred in tenths or hundredths of a foot, or feet as shown in the descriptor definitions in chapters 4 and 5. Pressure should be in pound-force per square inch (lbf/in2 or PSI). Permeability should be in feet per year (ft/yr). The exceptions to the use of English units (inch-pound) are for describing particle and grain sizes and age dating. Particle sizes for soils classified using American Society for Testing and Materials/Unified Soil Classification Systems (ASTM/USCS) should be in metric units on all logs of exploration. For description of bedrock, particle and grain sizes are to be in millimeters.

Age Dates

If age dates are abbreviated, the North American Strati- graphic Commission (NASC) recommends ka for thousand years and Ma for million years, but my or m.y. (million years) for time intervals (for example, ". . . during a period of 40 my . . .").

Conversion of Metric and English (U.S. Customary) Units

Table 2-2 provides many of the most frequently used metric and English (U.S. Customary) units for geotechnical work.

13 FIELD MANUAL

Table 2-2.—Useful conversion factors—metric and English units (inch-pound)

To convert units in column 1 to units in column 4, multiply column 1 by the factor in column 2. To convert units in column 4 to units in column 1, multiply column 4 by the factor in column 3. Column 1 Column 2 Column 3 Column 4

Length inch (in) 2.540 X 10 1 3.937 X 10-2 millimeter (mm) hundredths of feet 3.048 X 102 3.281 X 10 -3 millimeter (mm) foot (ft) 3.048 X 10 -1 3.281 meter (m) mile (mi) 1.6093 6.2137 X 10-1 kilometer (km) Area square inch (in2) 6.4516 X 10-4 1.550 X 10-3 square meter (m2) square foot (ft2) 9.2903 X 10 -2 1.0764 X 101 square meter (m2) acre 4.0469 X 10 -1 2.4711 hectare square mile (mi2) 0.386 X 10 -2 259.0 hectares Volume cubic inch (in3) 1.6387 X 10-2 6.102 X 10-2 cubic centimeter (cm2) cubic feet (ft3) 2.8317 X 10-2 3.5315 x 101 cubic meter (m3) cubic yard (yd3) 7.6455 X 101 1.3079 cubic meter (ms) cubic feet (ft3) 7.4805 1.3368 x 10-1 gallon (gal) gallon (gal) 3.7854 2.6417 X 10-1 liter (L) acre-feet (acre-ft) 1.2335 X 103 8.1071 X 10 -4 cubic meter (m3) Flow gallon per minute (gal/min) 6.309 X 10-2 1.5850 X 101 liter per second (L/s) cubic foot per second (ft3/s) 4.4883 X 102 2.228 X 10-3 gallons per minute (gal/min) 1.9835 5.0417 X 10-1 acre-feet per day (acre-ft/d) cubic foot per second (ft3/s) 7.2398 X 102 1.3813 X 10-3 acre-feet per year (acre-ft/yr) 2.8317 X 10-2 3.531 X 101 cubic meters per second (m3/s) 8.93 X 105 1.119 X 10-6 cubic meters per year (m3/yr) Permeability k, feet/year 9.651 X 10-7 1.035 X 106 k, centimeter per second (cm/sec) Density pound-mass per cubic foot 1.6018 X 101 6.2429 X 10-2 kilogram per cubic meter (lb/ft3) (kg/m3) Unit Weight pound force per cubic foot 0.157 6.366 kilonewton per cubic meter (lb/ft3) (kN/m3) Pressure pounds per square inch (psi) 7.03 X 10-2 1.4223 X 101 kilogram per square centimeter (kg/cm3) 6.8948 0.145 kiloPascal (kPa) Force ton 8.89644 1.12405 X 10-1 kilonewton (kN) pound-force 4.4482 X 10-3 224.8096 kilonewton (kN) Temperature EC = 5/9 (EF - 32 E) EF = (9/5 EC) + 32 E Grouting Metric bag cement per meter 3.0 0.33 U.S. bag cement per foot Water:cement ratio 0.7 1.4 water:cement ratio by weight by volume pounds per square inch 0.2296 4.3554 kilogram per square centi- per foot meter per meter (kg/cm2/m) k, feet/year 0.1 10 Lugeon

14 TERMINOLOGY

BIBLIOGRAPHY

[1] The Glossary of Geology, 4th edition, American Geologic Institute, Alexandria, VA, 1997.

[2] The American Association of Petroleum Geologists Bulletin, v. 67, No. 5, pp. 841-875, May 1983.

[3] Bureau of Reclamation, Earth Manual, 3rd edition, part 2, Denver, CO, 1990.

[4 ] Proctor, Robert V., and Thomas L. White, "Earth Tunneling with Steel Supports," Commercial Shearing, Inc., 1775 Logan Avenue, Youngstown, OH 44501, 1977.

15 Chapter 3

ENGINEERING CLASSIFICATION AND DESCRIPTION OF SOIL

General

Application

Soil investigations conducted for engineering purposes that use test pits, trenches, auger and drill holes, or other exploratory methods and surface sampling and mapping are logged and described according to the Unified Soil Classification System (USCS) as presented in Bureau of Reclamation (Reclamation) standards USBR 5000 [1] and 5005 [2]. Also, bedrock materials with the engineering properties of soils are described using these standards (chapter 2). The Reclamation standards are consistent with the American Society for Testing Materials (ASTM) Designation D2487 and 2488 on the USCS system [3,4]. Descriptive criteria and terminology presented are primarily for the visual classification and manual tests. The identification portion of these methods in assigning group symbols is limited to soil particles smaller than 3 inches (in) (75 millimeters [mm]) and to naturally occurring soils. Provisions are also made to estimate the percentages of cobbles and boulders by volume. This descriptive system may also be applied to shale, shells, crushed rock, and other materials if done according to criteria established in this section. Chapter 11 addresses the logging format and criteria for describing soil in test pits, trenches, auger holes, and drill hole logs.

All investigations associated with land classification for irrigation suitability, data collection, analyses of soil and substratum materials related to drainage investigations, and Quaternary stratigraphy (e.g., fault and paleoflood studies) are logged and described using the FIELD MANUAL U.S. Department of Agriculture terminology outlined in appendix I to Agriculture Handbook No. 436 (Soil Taxonomy), dated December 1975 [5].

All soil classification descriptions for particle sizes less than No. 4 sieve size are to be in metric units.

Performing Tests and Obtaining Descriptive Information

The USCS groups soils according to potential engineering behavior. The descriptive information assists with estimating engineering properties such as shear strength, compressibility, and permeability. These guidelines can be used not only for identification of soils in the field but also in the office, laboratory, or wherever soil samples are inspected and described.

Laboratory classification of soils [1] is not always required but should be performed as necessary and can be used as a check of visual-manual methods. The descriptors obtained from visual-manual inspection provide valuable information not obtainable from laboratory testing. Visual-manual inspection is always required. The visual-manual method has particular value in identifying and grouping similar soil samples so that only a minimum number of laboratory tests are required for positive soil classification. The ability to identify and describe soils correctly is learned more readily under the guidance of experienced personnel, but can be acquired by comparing laboratory test results for typical soils of each type with their visual and manual characteristics. When identifying and describing soil samples from an area or project, all the procedures need not be followed. Similar soils may be grouped together; for example, one sample should be identified and described completely, with the others identified as similar based on performing only a few of the identification and descriptive procedures.

18 SOIL Descriptive information should be evaluated and reported on every sample.

The sample used for classification must be representative of the stratum and be obtained by an appropriate accepted or standard procedure. The origin of the material must be correctly identified. The origin description may be a boring number and depth and/or sample number, a geologic stratum, a pedologic horizon, or a location description with respect to a permanent monument, a grid system, or a station number and offset.

Terminology for Soils

Definitions for soil classification and description are in accordance with USBR 3900 Standard Definitions of Terms and Symbols Relating to Soil Mechanics [6]:

Cobbles and boulders—particles retained on a 3-inch (75-mm) U.S. Standard sieve. The following terminology distinguishes between cobbles and boulders:

• Cobbles—particles of rock that will pass a 12-in (300-mm) square opening and be retained on a 3-in (75-mm) sieve.

• Boulders—particles of rock that will not pass a 12-in (300-mm) square opening.

Gravel—particles of rock that will pass a 3-in (75-mm) sieve and is retained on a No. 4 (4.75-mm) sieve. Gravel is further subdivided as follows:

• Coarse gravel—passes a 3-in (75-mm) sieve and is retained on 3/4-in (19-mm) sieve.

• Fine gravel—passes a ¾-in (19-mm) sieve and is retained on No. 4 (4.75-mm) sieve.

19 FIELD MANUAL

Sand—particles of rock that will pass a No. 4 (4.75-mm) sieve and is retained on a No. 200 (0.075-mm or 75-micrometer [µm]) sieve. Sand is further subdivided as follows:

• Coarse sand—passes No. 4 (4.75-mm) sieve and is retained on No. 10 (2.00-mm) sieve.

• Medium sand—passes No. 10 (2.00-mm) sieve and is retained on No. 40 (425-µm) sieve.

• Fine sand—passes No. 40 (425-µm) sieve and is retained on No. 200 (0.075-mm or 75-µm) sieve.

Clay—passes a No. 200 (0.075-mm or 75-µm) sieve. Soil has plasticity within a range of water contents and has considerable strength when air-dry. For classification, clay is a fine-grained soil, or the fine-grained portion of a soil, with a plasticity index greater than 4 and the plot of plasticity index versus liquid limit falls on or above the "A"-line (figure 3-5, later in this chapter).

Silt—passes a No. 200 (0.075-mm or 75-µm) sieve. Soil is nonplastic or very slightly plastic and that exhibits little or no strength when air-dry is a silt. For classification, a silt is a fine-grained soil, or the fine- grained portion of a soil, with a plasticity index less than 4 or the plot of plasticity index versus liquid limit falls below the "A"-line (figure 3-5).

Organic clay—clay with sufficient organic content to influence the soil properties is an organic clay. For classification, an organic clay is a soil that would be classified as a clay except that its liquid limit value after oven-drying is less than 75 percent of its liquid limit value before oven-drying.

20 SOIL Organic silt—silt with sufficient organic content to in- flu-ence the soil properties. For classification, an organic silt is a soil that would be classified as a silt except that its liquid limit value after oven-drying is less than 75 percent of its liquid limit value before oven-drying.

Peat—material composed primarily of vegetable tissues in various stages of decomposition, usually with an organic odor, a dark brown to black color, a spongy consistency, and a texture ranging from fibrous to amorphous. Classification procedures are not applied to peat.

Classifications of Soils

Group Names and Group Symbols

The identification and naming of a soil based on results of visual and manual tests is presented in a subsequent section. Soil is given an identification by assigning a group symbol(s) and group name. Important information about the soil is added to the group name by the term "with" when appropriate (figures 3-1, 3-2, 3-3, 3-4). The group name is modified using “with” to stress other significant components in the soil.

Figure 3-2 is a flow chart for assigning typical names and group symbols for inorganic fine-grained soils; figure 3-3 is a flow chart for organic fine-grained soils; figure 3-4 is a flow chart for coarse-grained soils. Refer to tables 3-1 and 3-2 for the basic group names without modifiers. If the soil has properties which do not distinctly place it in

21 FIELD MANUAL

FINE-GRAINED SOILS

Sandy BASIC with sand

GROUP NAME Gravelly with gravel

COARSE-GRAINED SOILS

with silt BASIC with sand

GROUP NAME with clay with gravel

Figure 3-1.—Modifiers to basic soil group names (for visual classification). a specific group, borderline symbols may be used. There is a distinction between dual symbols and borderline symbols.

Dual Symbols.—Dual symbols separated by a hyphen are used in laboratory classification of soils and in visual classification when soils are estimated to contain 10 percent fines. A dual symbol (two symbols separated by a hyphen, e.g., GP-GM, SW-SC, CL-ML) should be used to indicate that the soil has the properties of a classification where two symbols are required. Dual symbols are required when the soil has between 5 and 12 percent fines from laboratory tests (table 3-2), or fines are estimated as 10 percent by visual classification. Dual symbols are also required when the liquid limit and plasticity index values plot in the CL-ML area of the plasticity chart (figure 3-5, later in this chapter).

22 SOIL Figure 3-2.—Flow chart for inorganic fine-grained soils, visual method.

23 FIELD MANUAL Figure 3-3.—Flow chart for organic soils, visual method.

24 SOIL Figure 3-4.—Flow chart for coarse-grained soils, visual method.

25 FIELD MANUAL

Table 3-1.—Basic group names, primary groups

Coarse-grained soils Fine-grained soils GW - Well graded gravel CL - Lean clay GP - Poorly graded gravel ML - Silt GM - Silty gravel OL - Organic clay (on or GC - Clayey gravel sand above A-line SW - Well graded sand - Organic silt (below A-line) SP - Poorly graded sand CH - Fat clay SM - Silty sand MH - Elastic silt SC - Clayey sand OH - Organic clay (on or above A-line) - Organic silt (below A-line) Basic group name—hatched area on Plasticity Chart (Laboratory Classification) CL-ML - Silty clay GC-GM - Silty, clayey gravel SC-SM - Silty, clayey sand

Table 3-2.—Basic group names, 5 to 12 percent fines (Laboratory Classification)

GW-GM - Well graded gravel with silt GW-GC - Well graded gravel with clay (if fines = CL-ML) Well graded gravel with silty clay GP-GM - Poorly graded gravel with silt GP-GC - Poorly graded gravel with clay (if fines = CL-ML) Poorly graded gravel with silty clay SW-SM - Well graded sand with silt SW-SC - Well graded sand with clay (if fines = CL-ML) Well graded sand with silty clay SP-SM - Poorly graded sand with silt SP-SC - Poorly graded sand with clay (if fines = CL-ML) Poorly graded sand with silty clay

26 SOIL Borderline Symbols.—Borderline symbols are used when soil properties indicate the soil is close to another classification group. Two symbols separated by a slash, such as CL/CH, SC/CL, GM/SM, CL/ML, should be used to indicate that the soil has properties that do not distinctly place the soil into a specific group. Because the visual classification of soil is based on estimates of particle-size distribution and plasticity characteristics, it may be difficult to clearly identify the soil as belonging to one category. To indicate that the soil may fall into one of two possible basic groups, a borderline symbol may be used with the two symbols separated by a slash. A borderline classification symbol should not be used indiscriminately. Every effort should be made first to place the soil into a single group. Borderline symbols can also be used in laboratory classification, but less frequently.

A borderline symbol may be used when the percentage of fines is visually estimated to be between 45 and 55 percent. One symbol should be for a coarse-grained soil with fines and the other for a fine-grained soil. For example: GM/ML, CL/SC.

A borderline symbol may be used when the percentage of sand and the percentage of gravel is estimated to be about the same, for example, GP/SP, SC/GC, GM/SM. It is practically impossible to have a soil that would have a borderline symbol of GW/SW. However, a borderline symbol may be used when the soil could be either well graded or poorly graded. For example: GW/GP, SW/SP.

A borderline symbol may be used when the soil could be either a silt or a clay. For example: CL/ML, CH/MH, SC/SM.

27 FIELD MANUAL A borderline symbol may be used when a fine-grained soil has properties at the boundary between a soil of low compressibility and a soil of high compressibility. For example: CL/CH, MH/ML.

The order of the borderline symbol should reflect similarity to surrounding or adjacent soils. For example, soils in a borrow area have been predominantly identified as CH. One sample has the borderline symbol of CL and CH. To show similarity to the adjacent CH soils, the borderline symbol should be CH/CL.

The group name for a soil with a borderline symbol should be the group name for the first symbol, except for:

CL/CH - lean to fat clay ML/CL - clayey silt CL/ML - silty clay

Preparation for Identification and Visual Classification

A usually dark-brown to black material composed primarily of vegetable tissue in various stages of decomposition with a fibrous to amorphous texture and organic odor is a highly organic soil and classified as peat, PT. Plant forms may or may not be readily recognized. In general, the greater the organic content, the greater the water content, void ratio, and compressibility of peat. Organic soils are often identified by their odor. To check for organic content, the soil can be subjected to the laboratory classification liquid limit test criteria. Organic soils can also be identified through laboratory loss-on- ignition tests. Materials identified as peat are not subjected to the following identification procedures.

28 SOIL Soil identification procedures are based on the minus 3-in (75-mm) particle sizes. All plus 3-in (75-mm) particles must be manually removed from a loose sample, or mentally for an intact sample, before classifying the soil. Estimate and note the percent by volume of the plus 3-in (75-mm) particles, both the percentage of cobbles and the percentage of boulders.

Note: Because the percentages of the particle- size distribution in laboratory classification (ASTM: D 2487) are by dry weight and the estimates of percentages for gravel, sand, and fines are by dry weight, the description should state that the percentages of cobbles and boulders are by volume, not weight, for visual classification. Estimation of the volume of cobbles and boulders is not an easy task. Accurate estimating requires experience. While experienced loggers may be able to successfully estimate the minus 3-in fraction to within 5 percent, the margin of error could be larger for oversize particles. Estimates can be confirmed or calibrated with large scale field gradation tests on critical projects. Given the large possible errors in these estimates, the estimates should not be used as the sole basis for design of processing equipment. Large scale gradations should be obtained as part of the process plant designs.

In most cases, the volume of oversize is estimated in three size ranges, 3 to 5, 5 to 12, and 12 inches and larger. Cobbles are often divided into two size ranges, because in roller compacted fill of 6-in compacted lift thickness, the maximum size cobble is 5 inches. If the purpose of the investigation is not for roller compacted fill, a single size range for cobbles can be estimated.

29 FIELD MANUAL Estimate and note the percentage by dry weight of the gravel, sand, and fines of the fraction of the soil smaller than 3 in (75-mm). The percentages are estimated to the closest 5 percent. The percentages of gravel, sand, and fines must add up to 100 percent, excluding trace amounts. The presence of a component not in sufficient quantity to be considered 5 percent in the minus 3-in (75-mm) portion, is indicated by the term "trace." For example: trace of fines. A trace is not considered in the total of 100 percent for the components.

The first step in the identification procedure is to determine the percentages of fine-grained and coarse- grained materials in the sample. The soil is fine-grained if it contains 50 percent or more fines. The soil is coarse- grained if it contains less than 50 percent fines. Procedures for the description and classification of these two preliminary identification groups follow.

Procedures and Criteria for Visual Classification of Fine-Grained Soils

Select a representative sample of the material for examination and remove particles larger than the No. 40 sieve (medium sand and larger) until a specimen equivalent to about a handful of representative material is available. Use this specimen for performing the identification tests.

Identification Criteria for Fine-Grained Soils.—The tests for identifying properties of fines are dry strength, dilatency, toughness, and plasticity.

1. Dry strength.—Select from the specimen enough material to mold into a ball about 1 in (25 mm) in diameter. Mold or work the material until it has the consistency of putty, adding water if necessary.

30 SOIL From the molded material, make at least three test specimens. Each test specimen should be a ball of material about ½ in (12 mm) in diameter. Allow the test specimens to dry in air or sun, or dry by artificial means, as long as the temperature does not exceed 60 degrees Centigrade (EC). In most cases, it will be necessary to prepare specimens and allow them to dry over night. If the test specimen contains natural dry lumps, those that are about ½ in (12 mm) in diameter may be used in place of molded balls. (The process of molding and drying usually produces higher strengths than are found in natural dry lumps of soil). Test the strength of the dry balls or lumps by crushing them between the fingers and note the strength as none, low, medium, high, or very high according to the criteria in table 3-3. If natural dry lumps are used, do not use the results of any of the lumps that are found to contain particles of coarse sand.

Table 3-3.—Criteria for describing dry strength None The dry specimen crumbles with mere pressure of handling.

Low The dry specimen crumbles with some finger pressure.

Medium The dry specimen breaks into pieces or crumbles with considerable finger pressure. High The dry specimen cannot be broken with finger pressure. Specimen will break into pieces between thumb and a hard surface. Very High The dry specimen cannot be broken between thumb and a hard surface.

31 FIELD MANUAL The presence of high-strength, water-soluble cementing materials, such as calcium carbonate, may cause exceptionally high dry strengths. The presence of calcium carbonate can usually be detected from the intensity of the reaction with dilute hydrocloric acid (HCl). Criteria for reaction with HCl are presented in a subsequent paragraph.

2. Dilatancy.—Select enough material from the specimen to mold into a ball about ½ in (12 mm) in diameter. Mold the material, adding water if necessary, until it has a soft, but not sticky, consistency. Smooth the soil ball in the palm of one hand with the blade of a knife or spatula. Shake horizontally (the soil ball), striking the side of the hand vigorously against the other hand several times. Note the reaction of the water appearing on the surface of the soil. Squeeze the sample by closing the hand or pinching the soil between the fingers and note reaction as none, slow, or rapid according to the criteria in table 3-4. The reaction criteria are the speeds with which water appears while shaking and disappears while squeezing.

Table 3-4.—Criteria for describing dilatancy None No visible change in the specimen. Slow Water slowly appears on the surface of the specimen during shaking and does not disap- pear or disappears slowly upon squeezing. Rapid Water quickly appears on the surface of the specimen during shaking and disappears upon squeezing.

32 SOIL 3. Toughness.—Following completion of the dilatancy test, the specimen is shaped into an elongated pat and rolled by hand on a smooth surface or between the palms into a thread about c in (3 mm) diameter. (If the sample is too wet to roll easily, spread the sample out into a thin layer and allow some water loss by evaporation). Fold the sample threads and reroll repeatedly until the thread crumbles at a diameter of about c in (3 mm) when the soil is near the plastic limit. Note the time required to reroll the thread to reach the plastic limit. Note the pressure required to roll the thread near the plastic limit. Also, note the strength of the thread. After the thread crumbles, the pieces should be lumped together and kneaded until the lump crumbles. Note the toughness of the material during kneading.

Describe the toughness of the thread and lump as low, medium, or high according to the criteria in table 3-5.

Table 3-5.—Criteria for describing toughness

Low Only slight pressure is required to roll the thread near the plastic limit. The thread and the lump are weak and soft.

Medium Medium pressure is required to roll the thread to near the plastic limit. The thread and the lump have medium stiffness.

High Considerable pressure is required to roll the thread to near the plastic limit. The thread and the lump have very high stiffness.

33 FIELD MANUAL 4. Plasticity.—On the basis of observations made during the toughness test, describe the plasticity of the material according to the criteria given in table 3-6 (figure 3-5).

Table 3-6.—Criteria for describing plasticity

Nonplastic A 3-mm thread cannot be rolled at any water content.

Low The thread can barely be rolled, and the lump cannot be formed when drier than the plastic limit.

Medium The thread is easy to roll, and not much time is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. The lump crumbles when drier than the plastic limit.

High It takes considerable time rolling and kneading to reach the plastic limit. The thread can be rolled several times after reaching the plastic limit. The lump can be formed without crumbling when drier than the plastic limit.

After the dry strength, dilatency, toughness, and plasticity tests have been performed, decide on whether the soil is an organic or an inorganic fine- grained soil.

34 SOIL Figure 3-5.—Plasticity chart.

35 FIELD MANUAL Identification of Inorganic Fine-Grained Soils.— Classify the soils using the results of the manual tests and the identifying criteria shown in table 3-7. Possible inorganic soils include lean clay (CL), fat clay (CH), silt (ML), and elastic silt (MH). The properties of an elastic silt are similar to those for a lean clay. However, the silt will dry quickly on the hand and have a smooth, silky feel when dry. Some soils which classify as MH according to the field classification criteria are difficult to distinguish from lean clays, CL. It may be necessary to perform laboratory testing to ensure proper classification.

Table 3-7.—Identification of inorganic fine-grained soils from manual tests

Group Dry symbol strength Dilatancy Toughness ML None to low Slow to Low or thread rapid cannot be formed CL Medium to high None to slow Medium MH Low to medium None to slow Low to medium CH High to very None High high

Some soils undergo irreversible changes upon air drying. These irreversible processes may cause changes in atterberg limits and other index tests. Even unsuspected soils such as low plasticity silts may have differing atterberg limits due to processes like disaggregation. When tested at natural moisture, clay particles cling to silt particles resulting in less plasticity. When dried, the clay disaggregates, making a finer and more well graded mix of particles with increased plasticity.

36 SOIL For foundation studies of existing or new structures, natural moisture atterberg limits are preferred because the in-place material will remain moist. Natural moisture atterberg limits are especially important in critical studies, such as earthquake liquefaction evaluation of silts. On some foundation studies, such as for pumping plant design, consolidation tests will govern, and natural moisture atterbergs are not required. For borrow studies, soils will likely undergo moisture changes, and natural moisture atterberg limits are not required unless unusual mineralogy is encountered.

Identification of Organic Fine-Grained Soils.—If the soil contains enough organic particles to influence the soil properties, classify the soil as an organic soil, OL or OH. Organic soils usually are dark brown to black and usually have an organic odor. Often organic soils will change color, (black to brown) when exposed to air. Organic soils normally do not have high toughness or plasticity. The thread for the toughness test is spongy. In some cases, further identification of organic soils as organic silts or organic clays, OL or OH is possible. Correlations between the dilatancy, dry strength, and toughness tests with laboratory tests can be made to classify organic soils in similar materials.

Modifiers for Fine-Grained Soil Classifications.—If based on visual observation, the soil is estimated to have 15 to 25 percent sand and/or gravel, the words "with sand and/or gravel" are added to the group name, for example, LEAN CLAY WITH SAND, (CL); SILT WITH SAND AND GRAVEL (ML). Refer to figures 3-2 and 3-3. If the soil is visually estimated to be 30 percent or more sand and/or gravel, the words "sandy" or "gravelly" are added to the group name. Add the word "sandy" if there appears to be more sand than gravel. Add the word "gravelly" if there appears to be more gravel than sand, for example, SANDY LEAN CLAY (CL); GRAVELLY FAT CLAY (CH);

37 FIELD MANUAL SANDY SILT (ML). Refer to figures 3-2 and 3-3. Note that the Laboratory Classification follows different criteria.

Procedures and Criteria for Visual Classification of Coarse-Grained Soils

A representative sample containing less than 50 percent fines is identified as a coarse-grained soil.

The soil is a gravel if the percentage by weight of gravel is estimated to be more than the percentage of sand.

The soil is a sand if the percentage by weight of sand is estimated to be more than the percentage of gravel.

The soil is a clean gravel or clean sand if the percentages of fines are visually estimated to be 5 percent or less. A clean gravel or sand is further classified by grain size distribution.

The soil is classified as a WELL GRADED GRAVEL (GW), or as a WELL GRADED SAND (SW), if a wide range of particle sizes and substantial amounts of the intermediate particle sizes are present. The soil is classified as a POORLY GRADED GRAVEL (GP) or as a POORLY GRADED SAND (SP) if the material is predominantly one size (uniformly graded) or the soil has a wide range of sizes with some intermediate sizes obviously missing (gap or skip graded).

The soil is identified as either gravel with fines or sand with fines if the percentage of fines is visually estimated to be 15 percent or more.

38 SOIL Classify the soil as a CLAYEY GRAVEL (GC) or a CLAYEY SAND (SC) if the fines are clayey as determined by the procedures for fine-grained soil identification.

Identify the soil as a SILTY GRAVEL (GM) or a SILTY SAND (SM) if the fines are silty as determined by the procedures for fine-grained soil identification.

If the soil is visually estimated to contain 10 percent fines, give the soil a dual classification using two group symbols. The first group symbol should correspond to a clean gravel or sand (GW, GP, SW, SP), and the second symbol should correspond to a gravel or sand with fines (GC, GM, SC, SM). The typical name is the first group symbol plus "with clay" or "with silt" to indicate the plasticity characteristics of the fines. For example, WELL GRADED GRAVEL WITH CLAY (GW-GC); POORLY GRADED SAND WITH SILT (SP-SM). Refer to figure 3-4.

If the specimen is predominantly sand or gravel but contains an estimated 15 percent or more of the other coarse-grained constituent, the words "with gravel" or "with sand" are added to the group name. For example: POORLY GRADED GRAVEL WITH SAND (GP); CLAY- EY SAND WITH GRAVEL (SC). Refer to figure 3-4.

If the field sample contained any cobbles and/or boulders, the words "with cobbles" or "with cobbles and boulders" are added to the group name, for example, SILTY GRA- VEL WITH COBBLES (GM).

Abbreviated Soil Classification Symbols

If space is limited, an abbreviated system may be used to indicate the soil classification symbol and name such as in logs, data bases, tables, etc. The abbreviated system

39 FIELD MANUAL is not a substitute for the full name and descriptive information but can be used in supplementary presentations. The abbreviated system consists of the soil classification system based on this chapter, with prefixes and suffixes as listed below.

Prefix: s = sandy g = gravelly Suffix: s = with sand g = with gravel c = with cobbles b = with boulders

The soil classification symbol is enclosed in parentheses. Examples are:

CL, sandy lean clay s(CL) SP-SM, poorly graded sand (SP-GM)g with silt and gravel GP, poorly graded gravel with sand, (GP)scb cobbles, and boulders ML, gravelly silt with sand g(ML)sc and cobbles

Description of the Physical Properties of Soil

Descriptive information for classification and reporting soil properties such as angularity, shape, color, moisture conditions, and consistency are presented in the following paragraphs.

Angularity

Angularity is a descriptor for coarse-grained materials only. The angularity of the sand (coarse sizes only), gravel, cobbles, and boulders, are described as angular,

40 SOIL subangular, subrounded, or rounded as indicated by the criteria in table 3-8. A range of angularity may be stated, such as: sub-rounded to rounded.

Table 3-8.—Criteria for describing angularity of coarse-grained particles

Angular Particles have sharp edges and relatively planar sides with unpolished surfaces.

Subangular Particles are similar to angular description but have rounded edges.

Subrounded Particles have nearly planar sides but well- rounded corners and edges.

Rounded Particles have smoothly curved sides and no edges.

Shape

Describe the shape of the gravel, cobbles, and boulders as “flat, elongated” or “flat and elongated” if they meet the criteria in table 3-9. Indicate the fraction of the particles that have the shape, such as: one-third of gravel particles are flat. If the material is to be processed or used as aggregate for concrete, note any unusually shaped particles.

Color

Color is an especially important property in identifying organic soils and is often important in identifying other types of soils. Within a given locality, color may also be useful in identifying materials of similar geologic units. Color should be described for moist samples. Note if color

41 FIELD MANUAL

Table 3-9.—Criteria for describing particle shape

The particle shape is described as follows, where length, width, and thickness refer to the greatest, intermediate, and least dimensions of a particle, respectively.

Flat Particles with width/thickness >3.

Elongated Particles with length/width >3.

Flat and Particles meet criteria for both flat and elongated elongated. represents a dry condition. If the sample contains layers or patches of varying colors, this should be noted, and representative colors should be described. The Munsel Color System may be used for consistent color descriptions.

Odor

Describe the odor if organic or unusual. Soils containing a significant amount of organic material usually have a distinctive odor of decaying vegetation. This is especially apparent in fresh samples, but if the samples are dried, the odor often may be revived by heating a moistened sample. If the odor is unusual, such as that of a petroleum product or other chemical, the material should be described and identified if known. The material may be hazardous, and combustion or exposure should be considered.

Moisture Conditions

Describe the moisture condition as dry, moist, or wet, as indicated by the criteria in table 3-10.

42 SOIL

Table 3-10.—Criteria for describing moisture condition

Dry Absence of moisture, dusty, dry to the touch.

Moist Damp but no visible water.

Wet Visible free water, usually soil is below water table.

Reaction with HCl

Describe the reaction with HCl as none, weak, or strong, as indicated by the criteria in table 3-11. Calcium carbonate is a common cementing agent. The reaction with dilute hydrochloric acid is important in determining the presence and abundance of calcium carbonate.

Table 3-11.—Criteria for describing reaction with HCl

None No visible reaction.

Weak Some reaction, with bubbles forming slowly.

Strong Violent reaction, with bubbles forming immediately.

Consistency

Describe consistency (degree of firmness) for intact fine- grained soils as very soft, soft, firm, hard, or very hard, as indicated by the criteria in table 3-12. This observation is inappropriate for soils with significant amounts of gravel. Pocket penetrometer or torvane testing may supplement this data.

43 FIELD MANUAL Table 3-12.—Criteria for describing consistency of in-place or undisturbed fine-grained soils

Very soft Thumb will penetrate soil more than 1 in (25 mm). Soft Thumb will penetrate soil about 1 in (25 mm). Firm Thumb will indent soil about 1/4 in (5 mm). Hard Thumb will not indent soil but readily indented with thumbnail. Very hard Thumbnail will not indent soil.

Cementation

Describe the cementation of intact soils as weak, moderate, or strong, as indicated by the criteria in table 3-13.

Table 3-13.—Criteria for describing cementation

Weak Crumbles or breaks with handling or little finger pressure.

Moderate Crumbles or breaks with considerable finger pressure.

Strong Will not crumble or break with finger pressure.

Structure (Fabric)

Describe the structure of the soil according to criteria described in table 3-14. The descriptors presented are for soils only; they are not synonymous with descriptors for rock.

44 SOIL

Table 3-14.—Criteria for describing structure

Stratified Alternating layers of varying material or color; note thicknesses.

Laminated1 Alternating layers of varying material or color with layers less than 6 mm thick; note thicknesses.

Fissured1 Breaks along definite planes with little resistance to fracturing.

Slickensided1 Fracture planes appear polished or glossy, sometimes striated.

Blocky1 Cohesive soil that can be broken down into small angular lumps which resist further breakdown.

Lenses Inclusion of small pockets of different soils, such as small lenses of sand scattered through a mass of clay; note thicknesses.

Homogeneous Same color and textural or structural appearance throughout.

1 Do not use for coarse-grained soils with the exception of fine sands which can be laminated.

Particle Sizes

For gravel and sand-size components, describe the range of particle sizes within each component as defined in the previous terminology paragraph. Descriptive terms, sizes, and examples of particle sizes are shown in table 3-15.

45 FIELD MANUAL

Table 3-15.—Particle sizes

Descriptive Familiar example within term Size the size range Boulder 300 mm or more Larger than a volleyball Cobble 300 mm to 75 mm Volleyball - grapefruit - orange Coarse gravel 75 mm to 20 mm Orange - grape Fine gravel 20 mm to No. 4 Grape - pea sieve (5 mm) Coarse sand No. 4 sieve to Sidewalk salt No. 10 sieve Medium sand No. 10 sieve to Openings in window No. 40 sieve screen Fine sand No. 40 sieve to Sugar - table salt, grains No. 200 sieve barely visible

Describe the maximum particle size found in the sample. For reporting maximum particle size, use the following descriptors and size increments:

Fine sand Medium sand Coarse sand 5-mm increments from 5 mm to 75 mm 25-mm increments from 75 mm to 300 mm 100-mm increments over 300 mm

For example: "maximum particle size 35 mm" "maximum particle size 400 mm"

If the maximum particle size is sand size, describe as fine, medium, or coarse sand; for example, maximum particle size, medium sand.

46 SOIL If the maximum particle size is gravel size, describe the maximum particle size as the smallest sieve opening that the particle would pass.

If the maximum particle size is cobble or boulder size, describe the maximum dimension of the largest particle.

Particle Hardness

Describe the hardness of coarse sand and larger particles as hard, or state what happens when the particles are hit by a hammer; e.g., gravel-size particles fracture with considerable hammer blow, some gravel-size particles crumble with hammer blow. Hard means particles do not fracture or crumble when struck with a hammer. Remember that the larger the particle, the harder the blow required to fracture it. A good practice is to describe the particle size and the method that was used to determine the hardness.

Additional Descriptive Information

Additional descriptive information may include unusual conditions, geological interpretation or other classification methods, such as:

Presence of roots or root holes or other organic material or debris; Degree of difficulty in drilling or augering hole or excavating a pit; or Raveling or caving of the trench, hole, pit, or exposure; or Presence of mica or other predominant minerals.

A local or commercial name and/or a geologic interpretation should be provided for the soil.

47 FIELD MANUAL A classification or identification of the soil according to other classification systems may be added.

Narrative Descriptions and Examples

The description should include the information shown in tables 3-16 and 3-17, a checklist for the description of soils. Example descriptions follow.

Table 3-16.—Checklist for the description of soil classification and identification

1. Group name and symbol 2. Percent gravel, sand, and/or fines 3. Percent by volume of cobbles and boulders 4. Particle size Gravel - fine, coarse Sand - fine, medium, coarse 5. Particle angularity angular subangular subrounded rounded 6. Particle shape flat elongated flat and elongated 7. Maximum particle size or dimension 8. Hardness of coarse sand and larger particles 9. Plasticity of fines nonplastic low medium high 10. Dry strength none low medium high very high 11. Dilatancy none slow rapid 12. Toughness low medium high 13. Color (when moist) 14. Odor (if organic or unusual) 15. Moisture dry moist wet 16. Reaction with HCL none weak strong

48 SOIL Table 3-17.—Checklist for the description of in-place conditions

In-place conditions:

1. Consistency (fine-grained soils only) very soft soft firm hard very hard 2. Cementation weak moderate strong 3. Structure stratified laminated fissured slickened lensed homogeneous 4. Geologic interpretation and/or local name, if any 5. Additional comments and description Presence of roots or root holes Presence of mica, gypsum, etc. Surface coatings Caving or sloughing of excavation Excavation difficulty

Example 1: CLAYEY GRAVEL WITH SAND AND COB- BLES (GC)—Approximately 50 percent fine to coarse, sub-rounded to subangular gravel; approximately 30 percent fine to coarse, subrounded sand; approximately 20 per-cent fines with medium plasticity, high dry strength, no dilatancy, medium toughness; weak reaction with HCl; original field sample had about 5 percent (by volume) subrounded cobbles, maximum size 150 mm.

IN-PLACE CONDITIONS: firm, homogeneous, dry, brown.

GEOLOGIC INTERPRETATION: alluvial fan.

Abbreviated symbol is (GC)sc.

Example 2: WELL GRADED GRAVEL WITH SAND (GW)—Approximately 75 percent fine to coarse, hard, sub-angular gravel; approximately 25 percent fine to

49 FIELD MANUAL coarse, hard, subangular sand; trace of fines; maximum size 75 mm, brown, dry; no reaction with HCl.

Abbreviated symbol is (GW)s

Example 3: SILTY SAND WITH GRAVEL (SM)—Ap- proximately 60 percent predominantly fine sand; approximately 25 percent silty fines with low plasticity, low dry strength, rapid dilatancy, and low toughness; approximately 15 percent fine, hard, subrounded gravel, a few gravel-size particles fractured with hammer blow; maximum size 25 mm; no reaction with HCl.

IN-PLACE CONDITIONS: firm, stratified, and contains lenses of silt 1- to 2-in thick, moist, brown to gray; in-place density was 106 pounds per cubic foot (lb/ft3), and in-place moisture was 9 percent.

GEOLOGIC INTERPRETATION: ALLUVIUM

Abbreviated symbol is (SM)g.

Example 4: ORGANIC SOIL (OL/OH)—Approximately 100 percent fines with low plasticity, slow dilatancy, low dry strength, and low toughness; wet, dark brown, organic odor, weak reaction with HCl.

Abbreviated symbol is (OL/OH).

Example 5: SILTY SAND WITH ORGANIC FINES (SM)—Approximately 75 percent fine to coarse, hard, subangular reddish sand, approximately 25 percent organic and silty dark-brown nonplastic fines with no dry strength and slow dilatancy; wet; maximum size, coarse sand; weak reaction with HCl.

Abbreviated symbol is (SM)

50 SOIL Example 6: POORLY GRADED GRAVEL WITH SILT, SAND, COBBLES, AND BOULDERS (GP-GM)—Approx- imately 75 percent fine to coarse, hard, subrounded to subangular gravel; approximately 15 percent fine, hard, subrounded to subangular sand; approximately 10 percent silty nonplastic fines; moist, brown; no reaction with HCl; original field sample had approximately 5 percent (by volume) hard, subrounded cobbles and a trace of hard, subrounded boulders with a maximum dimension of 500 mm.

Abbreviated symbol is (GP-GM)scb.

Use of Soil Classification as Secondary Identification Method for Materials Other Than Natural Soils

General

Materials other than natural soils may be classified and their properties identified and described using the same procedures presented in the preceding subsections. The following materials are not considered soils and should not be given a primary USCS soil classification:

Partially lithified or poorly cemented materials

Shale Claystone Sandstone Siltstone Decomposed granite

Processed, manmade, or other materials

Crushed rock Slag Crushed sandstone Shells Cinders Ashes

51 FIELD MANUAL Identification criteria may be used for describing these materials, especially for describing particle sizes and shapes and identifying those materials which convert to soils after field or laboratory processing. Description format and classification for these materials are discussed individually in the following paragraphs.

Partially Lithified or Cemented Materials

Partially lithified or poorly cemented materials may need to be classified because the material will be excavated, processed, or manipulated for use as a construction material. When the physical properties are to be determined for these materials for classification, the material must be processed into a soil by grinding or slaking in water (shale, siltstone, poorly indurated ash deposits).

The physical properties and resulting classification describe the soil type as created by reworking the original material. Soil classifications can then be used as a secondary identification. However, the classification symbol and group name must be reported in quotation marks in any 1ogs, tables, figures, and reports. If laboratory tests are performed on these materials, the results must be reported as shown in figure 3-6.

An example of a written narrative for either a test pit or auger hole log based on visual classification is as follows: Symbol Description

Shale Fragments 3.4- to 7.8-foot (ft) Shale Fragments— Retrieved as 2- to 4-in pieces of shale from power auger hole, dry, brown, no reaction with HCl. After slaking in water for 24 hours, material classified as "SANDY CLAY (CH)"—

52 SOIL Figure 3-6.—Sample of test results summary.

53 FIELD MANUAL Approximately 60 percent fines with high plasticity, high dry strength, no dilatancy and high toughness; approximately 35 percent fine to medium, hard sand; approximately 5 percent gravel-size pieces of shale.

Processed or Manmade Materials

Processed, manmade, or other materials are also used as construction materials, and classification can be used as a secondary identification. However, for these processed materials, the group name and classification symbol are to be within quotation marks. If laboratory tests are performed on these materials, the results must be reported as shown in table 3-6.

An example of a written narrative for logs for visual classification is as follows:

Symbol Description

CRUSHED ROCK Stockpile No. 3 CRUSHED ROCK— processed gravel and cobbles from P.T. NO. 7; "POORLY GRADED GRAVEL (GP)"—approximately 90 percent fine, hard, angular, gravel-size particles; approximately 10 percent coarse, angular, sand- size particles; dry, tan, no reaction with HCl.

Special Cases for Classification

Some materials that require a classification and description according to USBR 5000 [1] or USBR 5005 [2] should not have a heading that is a classification group name.

54 SOIL When these materials will be used in, or influence, design and construction, they should be described according to the criteria for logs of test pits and auger holes and the classification symbol and typical name placed in quotation marks similar to the previous discussion on secondary identification method for materials other than natural soils. The heading should be as follows:

Topsoil Landfill Road surfacing Uncompacted or Compacted Fill

For example:

Classification

Symbol Description

TOPSOIL 0.0-0.8 meter (m) TOPSOIL—would be classified as "ORGANIC SILT (OL)." Approximately 80 percent fines with low plasticity, slow dilatancy, low dry strength, and low toughness; approximately 20 percent fine to medium sand; wet, dark brown, organic odor, weak reaction with HCl; roots present throughout.

Some material should be described but not given a classification symbol or group name, such as landfill (trash, garbage, etc.) or asphalt road. All of the above listed terms are only examples; this is not a complete list. If the above materials are not to be used and will not influence design or construction, only the basic term listed above need be shown on the logs without a complete description or classification.

55 FIELD MANUAL BIBLIOGRAPHY

[1] Bureau of Reclamation, U.S. Department of the Interior, USBR-5000, “Procedure for Determining Unified Soil Classification (Laboratory Method),” Earth Manual, Part II, 3rd edition, 1990.

[2] Bureau of Reclamation, U.S. Department of the Interior, USBR-5005, “Procedure for Determining Unified Soil Classification (Visual Method),” Earth Manual, Part II, 3rd edition, 1990.

[3] American Society for Testing and Materials, ASTM D-2487, “Standard Classification of Soils for Engineering Purposes,” ASTM Annual Book of Standards, Volume 04.08 on Soil and Rock, Section 4 - Construction, West Conshohocken, PA, 1996.

[4] American Society for Testing and Materials, ASTM D-2488, “Standard Practice for Description and Identification of soils (Visual-Manual Procedure),” ASTM Annual Book of Standards, Volume 04.08 on Soil and Rock, Section 4 - Construction, West Con- shohocken, PA, 1996.

[5] U.S. Department of Agriculture, Agriculture Hand- book No. 436, Appendix I (Soil Taxonomy), December 1975.

[6] Bureau of Reclamation, U.S. Department of the Interior, USBR 3900, “Standard Definitions of Terms and Symbols Relating to Soil Mechanics,” Earth Manual, Part II, 3rd edition, 1990.

56 Chapter 4

CLASSIFICATION OF ROCKS AND DESCRIPTION OF PHYSICAL PROPERTIES OF ROCK

Introduction

Uniformity of definitions, descriptors, and identification of rock units is important to maintain continuity in geologic logs, drawings, and reports from a project with multiple drilling sessions, different loggers and mappers. Also important is the recording of all significant observable parameters when logging or mapping. This chapter presents a system for the identification and classification of rocks and includes standard terminology and descriptive criteria for physical properties of engineering significance. The standards presented in this chapter may be expanded or modified to fit project requirements.

Rock Classification

Numerous systems are in use for field and petrographic classification of rocks. Many classifications require detailed petrographic laboratory tests and thin sections, while others require limited petrographic examination and field tests. The Bureau of Reclamation (Reclamation) has adopted a classification system which is modified from R.B. Travis [1]. While not based entirely on field tests or field identification of minerals, many of the classification categories are sufficiently broad that field identification is possible. Even where differences in the mineral constituents cannot be determined precisely in the field, differences usually are not significant enough to affect the engineering properties of the rock if classified somewhat incorrectly by lithologic name. Detailed mineralogical identification and petrographic classification can be performed on hand samples or core samples submitted to a petrographic laboratory. FIELD MANUAL

If samples are submitted to a petrographic laboratory, the petrographic classification generally will coincide with the classification according to Travis. The petrographic igneous rock classifications are somewhat more precise and include specialty rock types based upon mineral composition, texture, and occurrence. For example, a lamprophyric dike composed of green hornblende phenocrysts or clinopyroxene in the groundmass could be classified as spessartite, whereas a lamprophyre containing biotite with or without clinopyroxene could be classified as a kersantite. Sedimentary rock classifications generally include grain size, type of cement or matrix, mineral composition in order of increasing amounts greater than 15 percent, and the rock type, such as medium-grained, calcite-cemented, feldspathic- quartzose sandstone, and coarse- to fine-grained, lithic- feldspathic-quartzose gray-wacke with an argillaceous- ferruginous-calcareous matrix. Metamorphic rock classifications include specific rock types based upon crystal size, diagnostic accessory minerals, mineralogical composition in increasing amounts greater than 15 percent, and structure. Two examples of metamorphic rock descriptions are medium-grained, hornblende-biotite schist, or fine- to medium-grained, garnetiferous, muscovite-chlorite-feldspar-quartz gneiss. The above classification can be abbreviated by the deletion of mineral names from the left to right as desired. The mineral type immediately preceding the rock name is the most diagnostic.

The term "quartzite” is restricted to a metamorphic rock only. The sedimentary sandstone equivalent is termed a "quartz cemented quartzose sandstone."

Samples submitted to a petrographic laboratory should be representative of the in-place rock unit. For example, if a granitic gneiss is sampled but only the granite portion submitted, the rock will be petrographically classified as

58 ROCKS a granite since the gneissic portion cannot be observed or substantiated by the thin section and hand specimen. Petrographic classifications can be related to the engineering properties of rock units and are important.

Geologic rock unit names should be simple, and general rock names should be based on either field identification, existing literature, or detailed petrographic examination, as well as engineering properties. Overclassification is distracting and unnecessary. For example, use "hornblende schist" or "amphibolite" instead of "sericite- chlorite-calcite-hornblende schist." The term "granite" may be used as the rock name and conveys more to the designer than the petrographically correct term "nepheline-syenite porphyry." Detailed mineralogical descriptions may be provided in reports when describing the various rock units and may be required to correlate between observations, but mineralogical classifications are not desirable as a rock unit name unless the mineral constituents or fabric are significant to engineering properties.

The classification for igneous, sedimentary, metamorphic, and pyroclastic rocks is shown on figures 4-1, 4-2, 4-3, and 4-4, respectively. These figures are condensed and modified slightly from Travis' classifications, but the more detailed original classifications of Travis are acceptable. Figure 4-5 or appropriate American Geological Institute (AGI) data sheets are suggested for use when estimating composition percentages in classification.

Description of Rock

Adequate descriptors, a uniform format, and standard terminology must be used for all geologic investigations to properly describe rock foundation conditions. These

59 FIELD MANUAL Figure 4-1.—Field classification of igneous rocks (modified after R.B. Travis [1955]).

60 ROCKS Figure 4-2.—Field classification of sedimentary rocks (modified after R.B. Travis [1955]).

61 FIELD MANUAL Figure 4-3.—Field classification of metamorphic rocks (modified after R.B. Travis [1955]).

62 ROCKS

Figure 4-4.—Field classification of pyroclastic rocks. Blocks are angular to subangular clasts > 64 millimeters (mm); bombs are rounded to subrounded clasts > 64 mm. Determine percent of each size present (ash, lapilli, blocks, and bombs) and list in decreasing order after rock name. Preceed rock name with the term "welded" for pyroclastic rocks which retained enough heat to fuse after deposition. Rock names for such deposits are usually selected from the lower right portion of the classification diagram above. (Modified from Fisher, 1966 [2] and Williams and McBirney, 1979 [3]).

paragraphs provide descriptors for those physical characteristics of rock that are used in logs of exploration, in narratives of reports, and on preconstruction geologic maps and cross sections, as well as construction or "as- built" drawings. The alphanumeric descriptors provided may be used in data-field entries of computer generated

63 FIELD MANUAL Figure 4-5.—Charts for estimating percentage of composition rocks and sediments.[4]

64 ROCKS logs. Chapter 5 establishes descriptors for the physical characteristics of discontinuities in rock required for engineering geologic studies.

All descriptors should be defined and included in a legend when submitting data for design and/or records of construction. An example of a legend and explanation is figure 4-6, Reclamation standard drawing 40-D-6493, may be used for geologic reports and specifications where the standard descriptors and terminology established for rock are used during data collection.

Format for Descriptions of Rock

Engineering geology rock descriptions should include generalized lithologic and physical characteristics using qualitative and quantitative descriptors. A general format for describing rock in exploration logs and legends on general note drawings is:

• Rock unit (member or formation) name • Lithology with lithologic descriptors composition (mineralogy) grain/particle size texture color • Bedding/foliation/flow texture • Weathering • Hardness/strength • Contacts • Discontinuities (includes fracture indexes) • Permeability data (as available from testing) • Moisture conditions

Example descriptions are presented in a later section.

65 FIELD MANUAL

Rock Unit Names and Identification

Rock unit names not only are required for identification purposes but may also provide indicators of depositional environment and geologic history, geotechnical characteristics, and correlations with other areas. A simple descriptive name and map symbol should be assigned to provide other users with possible engineering characteristics of the rock type. The rock unit names may be stratigraphic, lithologic, genetic, or a combination of these, such as Navajo Sandstone (Jn), Tertiary shale (Tsh), Jurassic chlorite schist (Jcs), Precambrian granite (Pcgr), or metasediments (ms). Bedrock units of similar physical properties should be delineated and identified as to their engineering significance as early as possible during each geologic study. Planning study maps and other large-scale drawings may require geologic formations or groups of engineering geologic units with descriptions of their engineering significance in accompanying discussions.

Units should be differentiated by engineering properties and not necessarily formal stratigraphic units where differences are significant. Although stratigraphic names are not required, units should be correlated to stratigraphic names in the data report or by an illustration, such as a stratigraphic column. Stratigraphic names and ages (formation, member) may be used as the rock unit name.

For engineering studies, each particular stratigraphic unit may require further subdivisions to identify engineering parameters. Examples of important engineering properties are:

• Susceptibility to weathering or presence of alteration

66 ROCKS

Figure 4-6.—Descriptor legend and explanation example.

67 FIELD MANUAL

68 ROCKS

• Dominant discontinuity characteristics

• Hardness and/or strength

• Deformability

• Deletereous minerals or beds (such as swelling susceptibility, sulfates, or clays)

For example, a Tertiary shale unit, Tsh, may be

differentiated as Tsh1 or Tsh2 if unit 2 contains bentonite interbeds and unit 1 does not, and Tshc could be used as a unit name for the bentonite beds. A chlorite schist unit,

Cs, may be differentiated as CsA or CsB where unit A contains higher percentages of chlorite or talc and is significantly softer (different deformation properties) than unit B. A metasediment unit, ms, may be further

differentiated on more detailed maps and logs as mssh (shale) or msls (limestone). All differentiated units should be assigned distinctive map symbols and should be described on the General Geologic Legend, Explanation, and Notes drawings.

Descriptors and Descriptive Criteria for Physical Characteristics of Rock

Lithologic Descriptors (Composition, Grain Size, and Texture).—Provide a brief lithologic description of the rock unit. This includes a general description of mineralogy, induration, cementation, crystal and grain sizes and shapes, textural adjectives, and color. Lithologic descriptors are especially important for the description of engineering geology subunits when rock unit names are not specific. Examples of rock unit names that are not specific are metasediments, Tertiary intrusives, or Quaternary volcanics.

69 FIELD MANUAL

1. Composition.—Use standard adjectives such as sandy, silty, calcareous, etc. Detailed mineral comp osition generally is not necessary or desirable unless useful in correlating units or indicating pertinent engineering physical properties. Note unique features such as fossils, large crystals, inclusions, concretions, and nodules which may be used as markers for correlations and interpretations.

2. Crystal or particle sizes and shapes.— Describe the typical crystal or grain shapes and provide a description of sizes present in the rock unit based on the following standards:

• Igneous and metamorphic rocks.—Table 4-1 is recommended for descriptions of crystal sizes in igneous and metamorphic rocks. Crystal sizes given in millimeters (mm) are preferred rather than fractional inch (in) equivalents.

Table 4-1.—Igneous and metamorphic rock grain size descriptors

Average crystal Descriptor diameter Very coarse-grained or pegmatitic > 10 mm (3/8 in) Coarse-grained 5-10 mm (3/16 - 3/8 in) Medium-grained 1-5 mm (1/32 - 3/16 in) Fine-grained 0.1-1 mm (0.04 - 1/32 in) Aphanitic (cannot be seen with <0.1 mm (<0.04 in) the unaided eye

• Sedimentary and pyroclastic rocks.—Terminology for particle sizes and their lithified products which form sedimentary and pyroclastic rocks is provided in table 4-2. The size

70 ROCKS

Table 4-2.—Sedimentary and pyroclastic rock particle-size descriptors (AGI Glossary)

Sedimentary (epiclastic) Rounded, subrounded, USGS Size subangular Volcanic (pyroclastic) (soils only) in Particle mm Particle or Lithified Frag- Lithified size (inches) fragment product ment product*

Boulder Boulder Boulder Block+ Volcanic 300 (12) conglomerate breccia+ 256 (10) Cobble Cobble Cobble Bomb Agglo- conglomerate merate 75 (3) 64 (2.5) Coarse 32 (1.3) gravel Pebble Lapilli Pebble conglomerate Lapilli 20 (0.8) tuff Fine gravel 4.75 (0.19) 4 (0.16) Coarse sand Granule Granule conglomerate 2 (0.08) Very coarse Coarse Coarse Medium sand Sandstone ash tuff 1 (0.04) sand 0.5 (0.02) Coarse sand (Very coarse, 0.42 Medium coarse, 0.25 sand medium fine, Fine sand 0.125 Fine sand or very fine) 0.074 Very fine Fines 0.0625 sand Non- Siltstone Fine ash Fine tuff plastic Silt Shale Silt 0.00391

Clay Claystone Plastic Shale Clay

+ Broken from previous igneous rock block shaped (angular to subangular). Solidified from plastic material while in flight, rounded clasts. * Refer to figure 4-4.

71 FIELD MANUAL

limits do not correspond to the Unified Soil Classification System for soil particle size but are used for the field description and petrographic classification of rocks. These limits are the accepted sizes in geologic literature and are used by petrographic laboratories.

3. Textural adjectives.—Texture describes the arrangements of minerals, grains, or voids. These microstructural features can affect the engineering properties of the rock mass. Use simple, standard, textural adjectives or phrases such as porphyritic, vesicular, scoriaceous, pegmatitic, granular, well developed grains, dense, fissile, slaty, or amorphous. Use of terms such as holohyaline, hypidiomorphic granular, and crystaloblastic is inappropriate.

Textural terms which identify solutioning, leaching, or voids in bedrock are useful for describing primary texture, weathering, alteration, permeability, and density.

The terminology which follows defines sizes of voids, or holes in bedrock. However, when describing pits, vugs, cavities, or vesicles, a complete description which includes the typical diameter, or the "mostly" range, and the maximum size observed is required. For example:

". . . randomly oriented, elliptically shaped vugs range mostly from 0.03 to 0.06 foot (ft) in diameter, maximum size 0.2 foot; decreases in size away from quartz-calcite vein; about 15 percent contain calcite crystals. . .” or ". . . cavity, 3.3 ft wide by 16.4 ft long by 2.3 ft high, striking N 45EW, dipping 85ESW was. . ..”

72 ROCKS

• Pit (pitted).—Pinhole to 0.03 ft [d in] (<1 to 10 mm) openings.

• Vug (vuggy).—Small opening (usually lined with crystals) ranging in diameter from 0.03 ft [d in] to 0.33 ft [4 in] (10 to 100 mm).

• Cavity.—An opening larger than 0.33 ft [4 in] (100 mm), size descriptions are required, and adjectives such as small, or large, may be used, if defined.

• Honeycombed.—Individual pits or vugs are so numerous that they are separated only by thin walls; this term is used to describe a cell-like form.

• Vesicle (vesicular).—Small openings in volcanic rocks of variable shape formed by entrapped gas bubbles during solidification.

4. Color.—As a minimum, provide the color of wet altered and unaltered or fresh rock. Reporting color for both wet and dry material is recommended since the colors may differ significantly and cause confusion. The Munsell Color System, as used in the Geologic Society of America Rock Color Chart [5], is used to provide standard color names and assist in correlation. The chart also provides uniform and identifiable colors to others. Color designators are optional unless necessary for clarity, e.g., light brown (5YR 5/6). Terms such as banded, streaked, mottled, speckled, and stained may be used to further describe color. Also describe colors of bands, etc.

Bedding, Foliation, and Flow Texture.—These features give the rock anisotropic properties or represent potential failure surfaces. Continuity and thickness of these features influence rock mass properties and cannot

73 FIELD MANUAL always be tested in the laboratory. Descriptors in table 4-3 are used to identify these thicknesses.

Table 4-3.—Bedding, foliation, or flow texture descriptors

Descriptors Thickness/spacing

Massive Greater than 10 ft (3 meters [m])

Very thickly, bedded, 3 to 10 ft (1 to 3 m) foliated, or banded

Thickly 1 to 3 ft (300 mm to 1 m)

Moderately 0.3 to 1 ft (100 to 300 mm)

Thinly 0.1 to 0.3 ft (30 to 100 mm)

Very thinly 0.03 [3/8 in] to 0.1 ft (10 to 30 mm)

Laminated (intensely Less than 0.03 ft [3/8 in] foliated or banded) (<10 mm)

Weathering and Alteration.—

1. Weathering.—Weathering, the process of chemical or mechanical degradation of rock, can significantly affect the engineering properties of the rock and rock mass. For engineering geology descriptions, the term "weathering" includes both chemical disintegration (decomposition) and mechanical disaggregation as agents of alteration.

Weathering effects generally decrease with depth, although zones of differential weathering can occur and may modify a simple layered sequence of weathering.

74 ROCKS

Examples are: (1) differential weathering within a single rock unit, apparently due to relatively higher permeability along fractures; (2) differential weathering due to compositional or textural differences; (3) differential weathering of contact zones associated with thermal effects such as interflow zones within volcanics; (4) directional weathering along permeable joints, faults, shears, or contacts which act as conduits along which weathering agents penetrate more deeply into the rock mass; and (5) topographic effects.

Weathering does not correlate directly with specific geotechnical properties used for many rock mass classifications. However, weathering is important because it may be the primary criterion for determining depth of excavation, cut slope design, method and ease of excavation, and use of excavated materials. Porosity, absorption, compressibility, shear and compressive strengths, density, and resistance to erosion are the major engineering parameters influenced by weathering. Weathering generally is indicated by changes in the color and texture of the body of the rock, color, and condition of fracture fillings and surfaces, grain boundary conditions, and physical properties such as hardness.

Weathering is reported using descriptors presented in table 4-4, which divides weathering into categories that reflect definable physical changes due to chemical and mechanical processes. This table summarizes general descriptions which are intended to cover ranges in bedrock conditions. Weathering tables are generally applicable to all rock types; however, they are easier to apply to crystalline rocks and rocks that contain ferromagnesian minerals. Weathering in many sedimentary rocks will not always conform to the criteria established in

75 FIELD MANUAL

table 4-4, and weathering categories may have to be modified for particular site conditions. However, the basic horizontal categories and descriptors presented can be used. Site-specific conditions, such as fracture openness, filling, and degree and depth of penetration of oxidation from fracture surfaces, should be identified and described.

2. Alteration.—Chemical alteration effects are distinct from chemical and mechanical degradation (weathering), such as hydrothermal alteration, may not fit into the horizontal suite of weathering categories portrayed in table 4-4. Oxides may or may not be present. Alteration is site-specific, may be either deleterious or beneficial, and may affect some rock units and not others at a particular site. For those situations where the alteration does not relate well to the weathering categories, adjusting the description within the framework of table 4-4 may be necessary. Many of the general characteristics may not change, but the degree of discoloration and oxidation in the body of the rock and on fracture surfaces could be very different. Appropriate descriptors, such as moderately altered or intensely altered, may be assigned for each alteration category. Alteration products, depths of alteration, and minerals should be described.

3. Slaking.—Slaking is another type of disintegration which affects engineering properties of rock. Terminology and descriptive criteria to identify this deleterious property are difficult to standardize because some materials air slake, many water slake, and some only slake after one or more wet-dry cycles. The Durability Index (DI) is a simplified method for describing slaking. Criteria for the index are based

76 ROCKS

Table 4-4.—Weathering descriptors

Diagnostic features Mechanical weathering - Grain boundary Descriptors Chemical weathering—Discoloration and/or oxidation conditions Texture and solutioning (disaggregation) Alpha- primarily for granitics numeric Fracture and some coarse- General characteristics descriptor Descriptive term Body of rock surfaces† grained sediments Texture Solutioning (strength, excavation, etc.)§ W1 Fresh. No discoloration, not oxidized. No discoloration or No separation, intact No change. No solutioning. Hammer rings when crystalline rocks oxidation. (tight). are struck. Almost always rock excavation except for naturally weak or weakly cemented rocks such as siltstones or shales. W2 Slightly weathered to fresh.* W3 Sllightly weathered. Discoloration or oxidation is limited Minor to complete No visible separation, Preserved. Minor leaching of Hammer rings when crystalline rocks to surface of, or short distance discoloration or intact (tight). some soluble are struck. Body of rock not from, fractures; some feldspar oxidation of most minerals may be weakened. With few exceptions, such crystals are dull. surfaces. noted. as siltstones or shales, classified as rock excavation. W4 Moderately to slightly weathered.* W5 Moderately Discoloration or oxidation extends All fracture surfaces Partial separation of Generally Soluble minerals Hammer does not ring when rock is weathered. from fractures, usually throughout; are discolored or boundaries visible. preserved. may be mostly struck. Body of rock is slightly weak- Fe-Mg minerals are “rusty,” oxidized. leached. ened. Depending on fracturing, feldspar crystals are “cloudy.” usually is rock excavation except in naturally weak rocks such as siltstone or shales. W6 Intensely to moderately weathered.* W7 Intensely weathered. Discoloration or oxidation All fracture surfaces Partial separation, rock Texture al- Leaching of soluble Dull sound when struck with throughout; all feldspars and Fe- are discolored or is friable; in semiarid tered by minerals may be hammer; usually can be broken with Mg minerals are altered to clay to oxidized, surfaces conditions granitics are chemical complete. moderate to heavy manual pressure some extent; or chemical alteration friable. disaggregated. disintegration or by light hammer blow without produces in situ disaggregation, see (hydration, reference to planes of weakness such grain boundary conditions. argillation). as incipient or hairline fractures, or veinlets. Rock is significantly weakened. Usually common excavation. W8 Very intensely weathered. W9 Decomposed. Discolored or oxidized throughout, Complete separation of Resembles a soil, partial or complete Can be granulated by hand. Always but resistant minerals such as grain boundaries remnant rock structure may be common excavation. Resistant quartz may be unaltered; all (disaggregated). preserved; leaching of soluble minerals such as quartz may be feldspars and Fe-Mg minerals are minerals usually complete. present as “stringers” or “dikes.” completely altered to clay. Note: This chart and its horizontal categories are more readily applied to rocks with feldspars and mafic minerals. Weathering in various sedimentary rocks, particularly limestones and poorly indurated sediments, will not always fit the categories established. This chart and weathering categories may have to be modified for particular site conditions or alteration such as hydrothermal effects; however, the basic framework and similar descriptors are to be used. * Combination descriptors are permissible where equal distribution of both weathering characteristics are present over significant intervals or where characteristics present are “in between” the diagnostic feature. However, dual descriptors should not be used where significant, identifiable zones can be delineated. When given as a range, only two adjacent terms may be combined (i.e., decomposed to lightly weathered or moderately weathered to fresh) are not acceptable. † Does not include directional weathering along shears or faults and their associated features. For example, a shear zone that carried weathering to great depths into a fresh rock mass would not require the rock mass to be classified as weathered. § These are generalizations and should not be used as diagnostic features for weathering or excavation classification. These characteristics vary to a large extent based on naturally weak materials or cementation and type of excavation.

77 FIELD MANUAL

78 ROCKS

on time exposed and effects noted in the field (see table 4-5). These simplified criteria do not specify whether the specimen or exposure is wetted, dried, or subjected to cyclic wetting and drying, and/or freeze-thaw. When reporting slaking or durability, a complete description includes the test exposure conditions. For example, the material could be classified as having "characteristics of DI 3 upon drying." Slaking is not the same as the effects of bedding separation or disaggregation produced by stress relief.

Table 4-5.—Durability index descriptors

Alpha- numeric descriptor Criteria

DI0 Rock specimen or exposure remains intact with no deleterious cracking after exposure longer than 1 year.

DI1 Rock specimen or exposure develops hairline cracking on surfaces within 1 month, but no disaggregation within 1 year of exposure.

DI2 Rock specimen or exposure develops hairline cracking on surfaces within 1 week and/or disaggregation within 1 month of exposure.

DI3 Specimen or exposure may develop hairline cracks in 1 day and displays pronounced separation of bedding and/or disaggregation within 1 week of exposure.

DI4 Specimen or exposure displays pronounced cracking and disaggregation within 1 day (24 hours) of exposure. Generally ravels and degrades to small fragments.

79 FIELD MANUAL

A field test suitable for evaluating the degree and rate of slaking for materials, primarily clayey materials and altered volcanics, is described below. The slaking test evaluates the disaggregation of an intact specimen in water and reflects the fabric of the material, internal stresses, and character of the interparticle bonds.

To evaluate slaking behavior, immerse two intact specimens (pieces of core or rock fragments consisting of a few cubic inches or centimeters) in water. One piece should be at natural water content (wrapped jar sample) and one piece from an air-dried sample. Test results should be photographed with labels to identify specimens and exposure times.

Results of the evaluation should be reported for each specimen. Describe the behavior of the specimens as follows:

a. Volume changes.—The volume of the material reduced to individual particles should be estimated and compared to the initial volume of material. The degree of disaggregation is described using the following descriptive criteria:

None No discernable disaggregation Slight Less than 5 percent of the volume disaggregated Moderate Between 5 and 25 percent of the volume disaggregated Intense More than 25 percent but less than the total volume disaggregated Complete No intact piece of the material remains

80 ROCKS

b. Rate of slaking.—The following descriptors are used to identify the time to slake:

Slow slaking Action continues for several hours Moderate Action completed within 1 hour slaking Rapid Action completed within slaking 2 minutes Sudden Complete reaction, action com- slaking pleted instantaneously

[Generally, slaking applies to rock; disaggregation applies to soils.]

4. Character of material.—The character of the remaining pieces of material after the test is completed is described as follows:

No change Material remains intact Plates remain Remaining material present as platy fragments of generally uniform thickness Flakes remain Remaining material present as flaky or wedge-shaped fragments Blocks remain Blocky fragments remain Grains remain Remaining material chiefly present as sand-size grains

No fragments Remaining material entirely disaggregated to clay-size particles

Hardness—Strength.—Hardness can be related to intact rock strength as a qualitative indication of density and/or resistance to breaking or crushing. Strength is a necessary engineering parameter for design that

81 FIELD MANUAL frequently is not assessed, but plays a role in engineering design and construction, such as tunnel support requirements, bit wear for drilling or tunnel boring machine (TBM) operations, allowable bearing pressures, excavation methods, and support.

The hardness and strength of intact rock is a function of the individual rock type but may be modified by weathering or alteration. Hardness and strength are described for each geologic unit when they are functions of the rock type and also for zones of alteration or weathering when there are various degrees of hardness and/or strength due to different degrees of weathering or chemical alteration. When evaluating strengths, it is important to note whether the core or rock fragments break around, along, or through grains; or along or across incipient fractures, bedding, or foliation.

Hardness and especially strength are difficult characteristics to assess with field tests. Two field tests can be used; one is a measure of the ability to scratch the surface of a specimen with a knife, and the other is the resistance to fracturing by a hammer blow. Results from both tests should be reported. The diameter and length of core or the fragment size will influence the estimation of strength and should be kept in mind when correlating strengths. A 5- to 8-inch (130- to 200-mm) length of N-size core or rock fragment, if available, should be used for hardness determinations to preclude erroneously reporting point, rather than average hardness, and to evaluate the tendency to break along incipient fractures and textural or structural features when struck with a rock pick. Standards (heavy, moderate, and light hammer blow) should be calibrated with other geologists mapping or logging core for a particular project. Descriptors used for rock hardness/strength are shown on table 4-6.

82 ROCKS

Table 4-6.—Rock hardness/strength descriptors

Alpha- numeric descriptor Descriptor Criteria H1 Extremely Core, fragment, or exposure cannot be hard scratched with knife or sharp pick; can only be chipped with repeated heavy hammer blows. H2 Very hard Cannot be scratched with knife or sharp pick. Core or fragment breaks with repeated heavy hammer blows. H3 Hard Can be scratched with knife or sharp pick with difficulty (heavy pressure). Heavy hammer blow required to break specimen. H4 Moderately Can be scratched with knife or sharp pick hard with light or moderate pressure. Core or fragment breaks with moderate hammer blow H5 Moderately Can be grooved 1/16 inch (2 mm) deep by soft knife or sharp pick with moderate or heavy pressure. Core or fragment breaks with light hammer blow or heavy manual pressure. H6 Soft Can be grooved or gouged easily by knife or sharp pick with light pressure, can be scratched with fingernail. Breaks with light to moderate manual pressure. H7 Very soft Can be readily indented, grooved or gouged with fingernail, or carved with a knife. Breaks with light manual pressure. Any bedrock unit softer than H7, very soft, is to be described using USBR 5000 consistency descriptors.

Note: Although "sharp pick" is included in these definitions, descriptions of ability to be scratched, grooved, or gouged by a knife is the preferred criteria

A few empirical and quantitative field techniques which are quick, easy, and inexpensive are available to provide strength estimates. Quantitative strength estimates can

83 FIELD MANUAL be obtained from the point load test. A lightweight and portable testing device is used to break a piece of core (with a minimum length at least 1.5 times the diameter) between two loading points. If a new fracture does not run from one loading point to the other upon completion of the test, or if the points sink into the rock surface causing excessive deformation or crushing, the test should not be recorded. Raw data are given with the reduced data (equations to empirically convert load data to compressive strengths are usually supplied with the equipment). The Schmidt (L) hammer may also be used for estimating rock strengths; refer to Field Index Tests in chapter 5. Each of these tests can be used to calibrate the manual index (empirical) properties described in table 4-6, and a range of compressive strengths can be assigned. Depending on the scope of the study and structure being considered, laboratory testing may be required and used to confirm the field test data.

Discontinuities.—Describe all discontinuities such as joints, fractures, shear/faults, and shear/fault zones, and significant contacts. These descriptions should include all observable characteristics such as orientation, spacing, continuity, openness, surface conditions, and fillings. Appropriate terminology, descriptive criteria and descriptors, and examples pertaining to discontinuities are presented in chapter 5.

Contacts.—Contacts between various rock units or rock/ soil units must be described. In addition to providing a geologic classification, describe the engineering characteristics such as the planarity or irregularity and other descriptors used for discontinuities.

Descriptors applicable to the geologic classification of contacts are:

84 ROCKS

• Conformable • Unconformable • Welded—contact between two lithologic units, one of which is igneous, that has not been disrupted tectonically • Concordant (intrusive rocks) • Discordant (intrusive rocks)

Descriptors pertinent to engineering classification of contacts are:

• Jointed—contact not welded, cemented, or healed—a fracture • Intact • Healed (by secondary process) • Sharp • Gradational • Sheared • Altered (baked or mineralized) • Solutioned

If jointed or sheared, additional discontinuity descriptors such as thickness of fillings, openness, moisture, and roughness, should be provided also (see discontinuity descriptors in chapter 5).

Permeability Data.—Permeability (hydraulic conductivity) is an important physical characteristic that must be described. Suggested methods for testing, terminology, and descriptors are available in the Earth Manual and Ground Water Manual. Numerical values for hydraulic conductivity (K) can be determined using any of several methods. These values may be shown on drill hole logs. For narrative discussions or summary descriptions, the numerical value and descriptors may be used. Descriptors to be used—such as low,

85 FIELD MANUAL moderate—are those shown on figure 4-7. Whether permeability is primary (through intact rock) or secondary (through fractures) should be indicated.

Example Descriptions

The examples which follow are in representative formats for describing bedrock in the physical conditions column of drill hole logs and on a legend, explanation, and notes drawing.

Core Log Narrative

Several examples of descriptions for core logs are presented. These examples illustrate format and the use of the lithologic descriptors but do not include a description of discontinuities.

Log with Alphanumeric Descriptors and English Units.— . . . 12.6 to 103.6: Amphibolite Schist (JKam). Fine- grained (0.5 to 1 mm); subschistose to massive; greenish-black (5G 2/1) with numerous blebs and stringers of white calcite to 0.02 ft thick with solution pits and vugs to 0.03 ft, mostly 0.01 ft, aligned subparallel to foliation; very thinly foliated, foliation dips 65E to 85E, steepening with depth. Moderately to slightly weathered (W4), iron oxide staining on all discontinuities. Hard (H3), can be scratched with knife with heavy pressure, core breaks parallel to foliation with heavy hammer blow. Slightly fractured (FD3),. . ..

86 ROCKS Figure 4-7.—Permeability conversion chart.

87 FIELD MANUAL

Log with Alphanumeric Descriptors Using Metric Units.—

103.60 to 183.22: Sandstone (TUsa). Ferruginous quartzose sandstone. Medium-grained (0.25 to 0.5 mm), well sorted, subrounded to rounded quartz grains are well cemented by silica; hematite occurs as minor cement agent and as thin coating on grains. Moderate reddish-brown (10R 6/6). Moderately bedded, beds 250 to 310 mm thick, bedding dips 15E to 29E, averages 18E. Slightly weathered. Hard, cannot be scratched with knife, core breaks with heavy hammer blow across bedding and through grains. Moderately fractured. Core recovered. . ..

172.41-176.30: Claystone (TUc2). Calcareous montmorillonitic clay with 20 percent subangular, fine sand-size quartz fragments. Strong reaction with hydrochloric acid (HCl), grayish pink (5R 8/2). Moderately to rapidly slaking when dropped in water. Very thinly bedded to laminated with bed thickness from 8 to 20 mm. Very intensely weathered. Very soft, can be gouged with fingernail, friable, core breaks with manual pressure, smaller fragments can be crushed with fingers. . . Upper contact is parallel to bedding, conformable, gradational, and intact; lower contact is unconformable, sharp and jointed but tight; dips 35E . . ..

Legend

The example which follows could be typical of a rock unit description on a general legend, explanation, and note drawing. The object is to describe as many physical properties as possible which apply to the entire rock unit at the site. If individual subunits can be differentiated, they could be assigned corresponding symbols and

88 ROCKS described below the undifferentiated description. Those characteristics in the subunits which are similar or are included in the undifferentiated unit do not need to be repeated for each subunit.

Amphibolite Schist - Undifferentiated.—Mineralogy variable but generally consists of greater than 30 percent amphibole. Contains varying percentages of feldspar, quartz, and epidote in numerous, thin, white and light green (5G 7/4), discontinuous stringers and blebs. Texture ranges from fine grained and schistose to medium grained and subschistose. Overall, color ranges from greenish black (5G 2/1) to olive black (5Y 2/1). Thinly foliated; foliation dips steeply 75E to 85E NE. Weathering is variable but generally moderately weathered to depths of 75 ft, slightly weathered to 120 ft, and fresh below. Where oxidized, moderate reddish-brown (10R 4/6), frequently with dendritic patterns of oxides on discontinuities. Hard, fresh rock can be scratched slightly with heavy knife pressure; fresh N-size core breaks along foliation with moderate to heavy hammer blow. Foliation joints are variably spaced and discontinuous, spaced more closely where weathered. Joint sets are prominent but discontinuous. (Joint sets are identified in the specifications paragraphs). Commonly altered 0.1 to 6 ft along contacts of dikes and larger shears with epidote and quartz ("altered amphibolite" on logs of exploration). When altered, harder than amphibolite. Based on drill hole permeability testing, hydraulic conductivity is very low to low, with values ranging from 0.09 to 130 feet per year (ft/yr) averages 1.5 ft/yr in slightly weathered and fresh rock.

89 FIELD MANUAL

BIBLIOGRAPHY

[1] Travis, Russell B., "Classification of Rocks," v. 50, No. 1, Quarterly of the Colorado School of Mines, Golden, CO, January 1955.

[2] Fisher, R.V., "Rocks Composed of Volcanic Frag- ments: Earth Science Review, v. I, pp. 287-298, 1966.

[3] Williams, H., and McBirney, A., Volcanology, published by Freeman, Cooper and Company, San Francisco, CA. 391 pp., 1979.

[4] Compton, Robert R., Geology in the Field, published by John Wiley & Sons, Inc., New York, NY, 1985.

[5] Geological Society of America Rock Color Chart, 8th printing, 1995.

90 Chapter 5

TERMINOLOGY AND DESCRIPTIONS FOR DISCONTINUITIES

General

Structural breaks or discontinuities generally control the mechanical behavior of rock masses. In most rock masses the discontinuities form planes of weakness or surfaces of separation, including foliation and bedding joints, joints, fractures, and zones of crushing or shearing. These discontinuities usually control the strength, deformation, and permeability of rock masses. Most engineering problems relate to discontinuities rather than to rock type or intact rock strength. Discontinuities must be carefully and adequately described. This chapter describes terminology, indexes, qualitative and quantitative descriptive criteria, and format for describing discontinuities. Many of the criteria contained in this chapter are similar to criteria used in other established sources which are accepted as international standards (for example, International Journal of Rock Mechanics, 1978 [1]).

Discontinuity Terminology

The use of quantitative and qualitative descriptors requires that what is being described be clearly identified. Nomenclature associated with structural breaks in geologic materials is frequently misunderstood. For example, bedding, bedding planes, bedding plane partings, bedding separations, and bedding joints may have been used to identify similar or distinctly different geological features. The terminology for discontinuities which is presented in this chapter should be used uniformly for all geology programs. Additional definitions for various types of discontinuities are presented in the Glossary of Geology [2]; these may be used to further describe structural breaks. The following basic definitions should not be modified unless clearly justified, and defined. FIELD MANUAL

Discontinuity.—A collective term used for all structural breaks in geologic materials which usually have zero to low tensile strength. Discontinuities also may be healed. Discontinuities comprise fractures (including joints), planes of weakness, shears/faults, and shear/fault zones. Depositional or erosional contacts between various geologic units may be considered discontinuities. For discussion of contacts, refer to chapter 4.

Fracture.—A term used to describe any natural break in geologic material, excluding shears and shear zones. Examples of the most common fractures are defined as follows:

1. Joint.—A fracture which is relatively planar along which there has been little or no obvious displacement parallel to the plane. In many cases, a slight amount of separation normal to the joint surface has occurred. A series of joints with similar orientation form a joint set. Joints may be open, healed, or filled; and surfaces may be striated due to minor movement. Fractures which are parallel to bedding are termed bedding joints or bedding plane joints. Those fractures parallel to metamorphic foliation are called foliation joints.

2. Bedding plane separation.—A separation along bedding planes after exposure due to stress relief or slaking.

3. Random fracture.—A fracture which does not belong to a joint set, often with rough, highly irregular, and nonplanar surfaces along which there has been no obvious displacement.

4. Shear.—A structural break where differential movement has occurred along a surface or zone of

92 DISCONTINUITIES failure; characterized by polished surfaces, striations, slickensides, gouge, breccia, mylonite, or any combination of these. Often direction of movement, amount of displacement, and continuity may not be known because of limited exposures or observations.

5. Fault.—A shear with significant continuity which can be correlated between observation locations; foundation areas, or regions; or is a segment of a fault or fault zone reported in the literature. The designation of a fault or fault zone is a site-specific determination.

6. Shear/fault zone.—A band of parallel or subparallel fault or shear planes. The zone may consist of gouge, breccia, or many fault or shear planes with fractured and crushed rock between the shears or faults, or any combination. In the literature, many fault zones are simply referred to as faults.

7. Shear/fault gouge.—Pulverized (silty, clayey, or clay-size) material derived from crushing or grinding of rock by shearing, or the subsequent decomposition or alteration. Gouge may be soft, uncemented, indurated (hard), cemented, or mineralized.

8. Shear/fault breccia.—Cemented or uncemented, predominantly angular (may be platy, rounded, or contorted) and commonly slickensided rock fragments resulting from the crushing or shattering of geologic materials during shear displacement. Breccia may range from sand-size to large boulder- size fragments, usually within a matrix of fault gouge. Breccia may consist solely of mineral grains.

9. Shear/fault-disturbed zone.—An associated zone of fractures and/or folds adjacent to a shear or

93 FIELD MANUAL

shear zone where the country rock has been subjected to only minor cataclastic action and may be mineralized. If adjacent to a fault or fault zone, the term is fault-disturbed zone. Occurrence, orientation, and areal extent of these zones depend upon depth of burial (pressure and temperature) during shearing, brittleness of materials, and the in- place stresses.

Terminology for joint (JT), foliation joint (FJ), bedding joint (BJ), incipient joint (IJ) or incipient fracture (IF), random fracture (RF), mechanical break (MB), and fracture zone (FZ) is given on figure 5-9 (drawing No. 40-D- 6499 following later in this chapter). Suggested abbreviations are in parentheses.

Indexes for Describing Fracturing

Fracture Density

Fracture density is based on the spacing between all natural fractures in an exposure or core recovery lengths from drill holes, excluding mechanical breaks, shears, and shear zones; however, shear-disturbed zones (fracturing outside the shear) are included. In this context, fracture is a general term and includes all natural breaks such as joints, bedding joints, foliation joints, and random fractures. Fracture density should always be described in physical measurements, but summary descriptive terms relating to these measurements are a convenient aid in communicating characteristics of the rock mass. Standard descriptors apply to all rock exposures, such as tunnel walls, dozer trenches, outcrops, or foundation cut slopes and inverts, as well as boreholes. Fracture

94 DISCONTINUITIES descriptors presented in table 5-1 and figure 5-9 are based on drill hole cores where lengths are measured along the core axis.

When describing fracture density, a percentage of the types of fractures should be provided. A complete description for fracture density might read: Slightly Fractured (FD3), recovered core in 0.8- to 4.7-feet (0.2- to 1.4-meter [m]) lengths, mostly 1.7 feet (520 millimeters [mm]), 25 percent bedding joints/75 percent joints.

Fracture Frequency

Fracture frequency is the number of fractures occurring within a unit length. The number of natural fractures is divided by the length and is reported as fractures per foot or fractures per meter.

Rock Quality Designation

Rock Quality Designation (RQD) [2] is a fracture index used in many rock classification systems. To determine the RQD value, add the total length of solid core that is 4 inches (100 mm) or more long regardless of core diameter. If the core is broken by handling or the drilling process (mechanical breaks), the broken pieces are fitted together and counted as one piece, provided that they form the requisite length of 4 inches (100 mm). The length of these pieces is measured along the centerline of the core. This sum is divided by the length of the run (drill interval) and recorded on the log as a percentage of each run. Figure 5-1 illustrates RQD measurements and procedures.

RQD estimates can be determined from outcrops. RQD = 115 - 3.3 where Jv equals the total number of joints in a cubic meter. RQD may also be estimated from an

95 FIELD MANUAL Figure 5-1.—Rock Quality Designation (RQD) computation.

96 DISCONTINUITIES

Table 5-1.—Fracture density descriptors

Alpha- numeric Criteria descriptor Descriptor (excludes mechanical breaks) FD0 Unfractured No observed fractures. FD1 Very slightly Core recovered mostly in lengths fractured greater than 3 feet (1 m). FD2 Slightly to very slightly fractured FD3 Slightly fractured Core recovered mostly in lengths from 1 to 3 feet (300 to 1,000 mm) with few scattered lengths less than 1 foot (300 mm) or greater than 3 feet (1,000 mm). FD4 Moderately to slightly fractured1 FD5 Moderately Core recovered mostly in lengths fractured from 0.33 to 1.0 foot (100 to 300 mm) with most lengths about 0.67 foot (200 mm). FD6 Intensely to moderately fractured1 FD7 Intensely fractured Lengths average from 0.1 to 0.33 foot (30 to 100 mm) with fragmented intervals. Core recovered mostly in lengths less than 0.33 foot (100 mm). FD8 Very intensely to intensely fractured1 FD9 Very intensely Core recovered mostly as chips and fractured fragments with a few scattered short core lengths. 1 Combinations of fracture densities are permissible where equal distribution of both fracture density characteristics are present over a significant core interval or exposure, or where characteristics are "in between" the descriptor definitions.

97 FIELD MANUAL outcrop by determining the sum of solid rock (fracture free) in lengths 4 inches long or greater along a line that simulates either a 5- or 10-foot "core run." Detail line surveys provide the data needed to calculate RQD. Orienting the lines in different directions reduces directional bias. Either of these methods offers an advantage over RQDs determined from drill core, because all fracture orientations are included. Also, these RQD values more realistically represent rock conditions.

Description of Fractures

An accurate description of fractures is as important as the physical characteristics of the rock mass. Fractures affect and usually control the strength, deformation, and permeability characteristics of a rock mass. Fractures are grouped into sets based on similar orientations, and each set is labeled and described. Along with the physical measurements, such as attitude, spacing, and continuity, include information such as composition, thickness, and hardness of fillings or coatings; characteristics of surfaces such as hardness, roughness, waviness, and alteration; healing; fracture openness; and presence of water or water flow. Joint and fracture properties also may be useful for correlating purposes. Cleavage (CL) in metamorphic rocks includes slaty cleavage, crenulation cleavage, phyllitic structure, and schistosity (after Davis [4]) and often can be used to evaluate the tectonic setting.

Figure 5-9 may be used for geologic reports or specifications where the standard descriptors and terminology established for discontinuities are used during data collection.

98 DISCONTINUITIES

Format for the Description of Fractures

Identifying and recording the physical characteristics of fractures during mapping and logging is the least expensive part of most geologic investigations. An accurate and concise description of these characteristics permits interpretation in geologic terms directly applicable to design and construction. As many of the characteristics should be described as possible, limited only by the type of observation. For example, continuity and waviness cannot be provided for joints observed in core. Examples of fracture descriptions recorded for a drill hole log and for an outcrop or exposure are in a following section. A general format for recording fracture descriptions follows:

• Orientation • Spacing • Continuity • Openness • Fillings Thickness Composition Weathering/alteration Hardness • Healing • Surfaces Roughness Waviness Weathering/alteration Hardness • Field index test results • Moisture

99 FIELD MANUAL

Descriptors for Fracture Characteristics

The following paragraphs present terminology, descriptor criteria, and descriptors for recording fracture data. Alphanumeric descriptors are amenable to computer sorting. Alphanumeric descriptors are not a substitute for a complete description of the fracture characteristics.

Orientation.—The orientation of all fractures with respect to applied loads can be critical to deformation or stability. Seepage or grouting also may be affected or controlled by orientation. Orientation is usually measured in the field, and the raw data tabulated and interpreted. The analysis typically includes stereonets, contour diagrams, fracture sets, and their areal distribution. A detailed statistical analysis of the fracture data may be necessary. Azimuths or quadrants may be used, but azimuths are becoming the standard, in part because they are easier to computerize. The American right-hand rule for dip direction notation is preferred. The method of measuring the dip of planar discontinuities, foliation, and bedding in cores is shown in figure 5-9. Figures 5-1 and 5-2 illustrate how inclination of a joint in core from an angle hole can be interpreted as a horizontal joint (A) or vertical joint (B) by rotating the core 180 degrees (E). If the core is oriented and the top of the core is known, the inclination can be recorded as positive (+) or negative (-) to avoid ambiguity and to assist in determining sets.

Fracture orientation is recorded as strike and dip, or as azimuth and dip, preferably using the right-hand rule. Orientation of planar features with undetermined strike can be measured directly and reported as dip in vertical holes. In angle holes, where true dip is not known, the angle of the plane should be measured from the core axis

100 DISCONTINUITIES and reported as inclination, i.e., "bedding plane joints inclined 65 degrees from the core axis."

Spacing.—Spacing affects block size and geometry in the rock mass. Spacing is a required input to several rock mass classification systems. When a set can be distinguished (parallel or subparallel joints), true spacing can be measured and is described for each joint set, as shown on figure 5-2 and in table 5-2. If apparent spacing is given, label as such.

Figure 5-2.—Comparison of true and apparent spacing.

Continuity.—A continuous joint or fracture is weaker and more deformable than a short discontinuous fracture bridged by intact bedrock. Recording trace lengths to describe continuity is useful in large exposures. Identification of the more continuous fractures is an important aspect of formulating rock stability input data, especially for high cut slopes and in large underground openings. Record the longest observable trace regardless of end type and note whether it is a strike (S), dip (D), or apparent (A) trace. Descriptors for continuity are provided in table 5-3.

101 FIELD MANUAL

Table 5-2.—Fracture spacing descriptors

Alpha- numeric Joint or fracture descriptor spacing descriptor True spacing SP1 Extremely widely Greater than 10 feet (ft) spaced (<3 m) SP2 Very widely spaced 3 to 10 ft (1 to 3 m) SP3 Widely spaced 1 to 3 ft (300 mm to 1 m) SP4 Moderately spaced 0.3 to 1 ft (100 to 300 mm) SP5 Closely spaced 0.1 to 0.3 ft (30 to 100 mm) SP6 Very closely spaced Less than 0.1 ft (<30 mm)

Table 5-3.—Fracture continuity descriptors

Alpha- numeric descriptor Descriptor Lengths C1 Discontinuous Less than 3 ft (>1 m) C2 Slightly continuous 3 to 10 ft (1 to 3 m) C3 Moderately continuous 10 to 30 ft (3 to 10 m) C4 Highly continuous 30 to 100 ft (10 to 30 m) C5 Very continuous Greater than 100 ft (>30 m)

This information alone is not sufficient to completely assess joint or fracture continuity because trace lengths may be partially obscured. When performing joint studies or surveys, record the number of ends (fracture terminations) that can be seen in the exposure using the alphanumeric descriptors shown in table 5-4. The size of the exposure should be noted because this is a determining factor when surveying for visible ends.

102 DISCONTINUITIES

Table 5-4.—Descriptors for recording fracture ends in joint surveys

Alpha- numeric descriptor Criteria E0 Zero ends leave the exposure (both ends of the fracture can be seen in the exposure). E1 One end can be seen (one end of the fracture terminates in the exposure). E2 Both ends cannot be observed (two fracture ends do not terminate in the exposure).

Openness.—The width or aperture is measured normal to the fracture surface. This aperture or openness affects the strength, deformability, and seepage characteristics. Describe fracture openness by the categories shown in table 5-5. For drill logs, if actual openness cannot be measured or estimated, use only open or tight and do not assign an alphanumeric descriptor.

Characteristics of Fracture Fillings.—Describing the presence or absence of coatings or fillings and distinguishing between types, alteration, weathering, and strength and hardness of the filling material may be as significant as fracture spatial relationships or planarity. Strength and permeability of fractures may be affected by fillings. Descriptions of fracture coatings and fillings are site specific but must address the following considerations:

1. Thickness of fillings.—Table 5-6 provides descriptors for recording the thickness of fracture fillings or coatings.

103 FIELD MANUAL

Table 5-5.—Fracture openness descriptors

Alpha- numeric descriptor Descriptor Openness O0 Tight No visible separation O1 Slightly open Less than 0.003 ft [1/32 inch (in)] (<1 mm) O2 Moderately open 0.003 to 0.01 ft [1/32 in to 1/8 in] (1 to 3 mm) O3 Open 0.01 to 0.03 ft [1/8 to 3/8 in] (3 to 10 mm) O4 Moderately wide 0.03 ft [3/8 in] to 0.1 ft (10 to 30 mm) O5 Wide Greater than 0.1 ft (>30 mm) (record actual openness)

Table 5-6.—Fracture filling thickness descriptors

Alpha- numeric descriptor Descriptor Thickness T0 Clean No film coating T1 Very thin Less than 0.003 ft [1/32 in] (<1 mm) T2 Moderately thin 0.003 to 0.01 ft [1/32 to 1/8 in] (1 to 3 mm) T3 Thin 0.01 to 0.03 ft [1/8 to 3/8 in] (3 to 10 mm) T4 Moderately thick 0.03 ft [3/8 in] to 0.1 ft (10 to 30 mm) T5 Thick Greater than 0.1 ft (>30 mm) (record actual thickness)

104 DISCONTINUITIES

2. Composition of fillings.—The mineralogical classification of fillings, such as quartz, gypsum, and carbonates, must be identified to convey physical properties of fractures that may be significant criteria for design. Soil materials in open fractures should be described and classified according to the Unified Soil Classification System (USCS) (see USBR 5000 and USBR 5005 [5]).

Fractures may be filled or "healed" entirely or over a significant portion of their areal extent by quartz, calcite, or other minerals. Veins may be present without healing the fracture or may have been broken again forming new surfaces. Soluble fillings, such as gypsum, may cause foundation or structural degradation during the facility's expected lifetime. Fracture fillings must be considered during design, construction investigations, and monitoring or potential long-term stability, deformability, and seepage problems may require expensive rehabilitation efforts.

Coatings or fillings of chlorite, talc, graphite, or other low-strength materials need to be identified because of their deleterious effects on strength, especially when wet. Some fillings, such as dispersive, erosive, or micaceous materials, can squeeze, pipe under fluid flow, and contribute to a loss of strength and stability. Montmorillonitic clays may swell or cause swelling pressures. Cohesionless materials, such as sands and silts, or materials which have been crushed or altered may run or flow into underground excavations or serve as seepage conduits.

105 FIELD MANUAL

3. Weathering or alteration.—Descriptors for weathering or alteration of fracture fillings (excluding soil materials) are the same as those used for rock weathering.

4. Hardness/strength.—Descriptors for hardness/ strength of fillings should be the same as those presented for bedrock hardness or soil consistency (chapters 3 and 4). Various field index tests may also be performed to determine strengths of fillings. Refer to the Field Index Tests in chapter 4.

5. Healing.—Fractures may be healed or recemented by one or more episodes of mineralization or precipitation of soluble materials. A description of fracture healing or rehealing should include not only the type of healing or cementing agent, but an estimate of the degree to which the fracture has been healed. The subjective criteria and descriptors shown in table 5-7 should be used to describe healing.

Characteristics of Fracture Surfaces.—The physical characteristics of fracture surfaces are very important for deformability and stability analyses. Dimensional characteristics such as roughness and waviness (see figure 5-3) and characteristics, such as weathering and hardness of the surfaces, are important in evaluating the shear strength of fractures. Fracture roughness descriptors are given in table 5-8. Surface characteristics are less important only when low-strength materials comprise fracture fillings.

The description of fracture asperities is divided into two categories: small-scale asperities, or roughness, and large-scale undulations, or waviness. Figure 5-3 shows .

106 DISCONTINUITIES

Table 5-7.—Fracture healing descriptors

Alpha- numeric descriptor Descriptor Criteria HL0 Totally healed Fracture is completely healed or recemented to a degree at least as hard as surrounding rock. HL2 Moderately Greater than 50 percent of fracture material, fracture surfaces, or healed filling is healed or recemented; and/or strength of the healing agent is less hard than surrounding rock. HL3 Partly healed Less than 50 percent of fractured material, filling, or fracture surface is healed or recemented. HL5 Not healed Fracture surface, fracture zone, or filling is not healed or recemented; rock fragments or filling (if present) is held in place by iits own angularity and/or cohesiveness. examples of these asperities. Descriptors for roughness and waviness and additional items related to fracture surfaces follow.

1. Roughness.—The roughness (small-scale asperities) of fracture surfaces is critical for evaluating shear strengths. Roughness descriptors such as striated or slickensided should be used whenever observed. For oriented core or outcrops, the orientation of striations or slickensides should be recorded. The rake of striations or slickensides should be recorded when observed in core from vertical drill holes which have not been oriented. In

107 FIELD MANUAL

Figure 5-3.—Examples of roughness and waviness of fracture surfaces, typical roughness profiles, and terminology. The length of each profile is in the range of 3 to 15 feet (1 to 5 m); the vertical and horizontal scales are equal.

Coulomb's equation for shear strength (S = C + N tan n), the large scale undulations (i) are entered into the equation as N tan (n + i).

2. Waviness.—Waviness (large-scale undulations) also should be recorded for fracture surveys along

108 DISCONTINUITIES

Table 5-8.—Fracture roughness descriptors Alpha- numeric descriptor Descriptor Criteria R1 Stepped Near-normal steps and ridges occur on the fracture surface. R2 Rough Large, angular asperities can be seen. R3 Moderately Asperities are clearly visible and rough fracture surface feels abrasive. R4 Slightly rough Small asperities on the fracture surface are visible and can be felt. R5 Smooth No asperities, smooth to the touch. R6 Polished Extremely smooth and shiny.

exposures. This is done by recording amplitude and wavelength, or as a minimum, describing as either planar or undulating.

3. Weathering/alteration.—Weathering or alteration of fracture surfaces is one of the criteria used for classifying rock mass weathering. Even though it is inherent in the weathering categories, the actual description of surface alteration and the associated loss of strength of the rock needs to be reported. Qualitative information can be presented when describing a particular joint set, joint, or fracture. The condition of the surface(s), such as depth of penetration and degree of staining or oxidation, should be recorded.

Moisture Conditions.—The presence of moisture or the potential for water flow along fractures may be an

109 FIELD MANUAL indicator of potential grout takes or seepage paths. Criteria and descriptors shown in table 5-9 describe moisture conditions for fractures. The presence or absence of moisture cannot be determined in core, but evidence of previous long-term water flow is found in leaching, color changes, oxidation, and dissolutioning.

Table 5-9.—Fracture moisture conditions descriptors

Alpha- numeric descriptor Criteria

M1 The fracture is dry, tight, or filling (where present) is of sufficient density or composition to impede water flow. Water flow along the fracture does not appear possible.

M2 The fracture is dry with no evidence of previous water flow. Water flow appears possible.

M3 The fracture is dry but shows evidence of water flow such as staining, leaching, and vegetation.

M4 The fracture filling (where present) is damp, but no free water is present.

M5 The fracture shows seepage and is wet with occasional drops of water.

M6 The fracture emits a continuous flow (estimate flow rate) under low pressure. Filling materials (where present) may show signs of leaching or piping.

M7 The fracture emits a continuous flow (estimate flow rate) under moderate to high pressure. Water is squirting, and/or filling material (where present) may be substantially washed out.

110 DISCONTINUITIES

Field Index Tests

Schmidt Hammer tests can be used to estimate the hardness/strength of the rock surfaces along a discontinuity (which may be weaker than the body of the rock). The rebound of a spring-actuated projectile is measured from the surface being tested. The sample should be large enough, preferably intact or securely fastened to a stable base (i.e., concrete), so that it does not move during tests. Unclamped specimens should measure at least 0.7 foot (200 mm) in each direction. Direct testing on rock outcrops is usually the best method. Results should be obtained from both wet and dry surfaces. Ten readings are taken at various locations on each surface. The five lowest readings are discounted, and the five highest readings are averaged to obtain a realistic rebound number (Schmidt hardness). The hammer is always oriented perpendicular to the surface being tested. A unit dry weight must also be determined for the material being tested. Using the Schmidt hardness and the unit dry weight, the uniaxial compressive strength of the sample can be estimated.

Tilt-type sliding-friction tests are also useful in estimating the shear strength of fractures. Samples can be obtained from outcrops or rock core. A representative sample is tilted, and the angle at which the top of the sample slides relative to the bottom is measured. This angle is an approximation of the friction angle. Both wet and dry surfaces should be tested. The weight, thickness, and approximate dimensions of the sample parts also are recorded. A friction angle can be estimated in a similar manner using three pieces of core. Two representative pieces of core are used as a base, and the third piece is placed on top. The base is then tilted until the top piece of core slides, and this angle is measured.

111 FIELD MANUAL

Pocket penetrometers may be used to estimate the strength of soil-like fillings or surfaces. The surface or a filling is penetrated by the penetrometer to the line on the penetrometer (about a quarter of an inch), and the approximate compressive strength is read directly from a calibrated scale on the penetrometer. Example Descriptions of Fractures

The examples which follow show a representative format for recording data. Actual descriptions vary and depend on whether the observations were recorded from exposures, drill core, or detailed joint surveys. Data report descriptions of discontinuities should be expanded to provide ranges and typical characteristics or additional significant data for each set or individual fractures from all observations.

Drill Core.—The following metric example is taken from a log of a rock core interval from a vertical drillhole; in an angle hole, orientation would be recorded as inclination from the core axis:

“. . . Moderately to slightly fractured (35% bedding joints, 65% joints). Core recovered in 210 to 730 mm lengths, mostly as 300 mm lengths. Bedding joints dip 30 to 35E, widely spaced (SP3) at 370 to 790 mm, avg 580 mm; 29 are tight, 6 are open; all are clean; 20 are moderately rough (R3), 15 are slightly rough (R4); oxidation penetrates 30 mm from surfaces (W4); all surfaces can be scratched by moderate knife pressure (H4). Joint set A dips 50 to 75E, mostly 60 to 65E, normal bedding; very widely spaced (SP2) at 0.9 to 1.2 m, avg 1 m; 3 are open, 1 is tight, and 9 are tight and healed by 3 to 30 mm thick, fresh (W1), very hard (H2), quartz- calcite fillings; the 3 open joints are clean, slightly rough (R4), oxidation stains penetrate

112 DISCONTINUITIES

60 mm from surfaces (W4) which can be scratched by light to moderate knife pressure, all 3 show evidence of water flow (W6) . . .. ”

Exposure Mapping.—An example of fracture descriptions for an exposure, using English units, follows:

“Joint set A-1 strikes N. 20-38E W., mostly N. 20- 25E W.; dips 50-65E NE, averages 54E NE. Very widely spaced (SP2), 3.8 to 7.3 ft apart, mostly 5 ft apart; most have moderately to highly continuous (C3 to C4) 25 to 55 ft trace lengths. Approx. 60% are open to moderately wide (O3 to O4), ranging in openness from 0.1 to 0.3 ft, remainder are tight to slightly open (O0 to O1). Approx. 10% of the joints contain thin, hard quartz fillings, 25% are clean, and 65% contain firm fat clay (CH) fillings which can be indented with thumbnail. All rock surfaces are moderately weathered with dendritic iron oxide staining which can be scratched with light to moderate knife pressure. Most surfaces are slightly rough (R4) and undulatory, approx. 20% are rough (R2) and planar. Undulations have wavelengths of 10 to 20 ft, average 15 ft, and amplitudes range from 0.2 to 0.5 ft. Clean joints are dry but show evidence of moisture flow (M3), most clay filled joints are damp but show no evidence of flow (M4).”

Fracture Survey.—Statistical evaluations are valuable, so it is important to collect joint properties for analysis. This can be readily accomplished using fracture survey techniques. Data sheets are prepared with appropriate columns for recording the data, a traverse distance and

113 FIELD MANUAL direction are established, and all pertinent data are measured and recorded. Data are analyzed using statistical methods. Refer to chapter 7 for detailed descriptions of discontinuity surveys.

Descriptions of Shears and Shear Zones

Shear, fault, and associated terminology are defined at the beginning of this chapter. The following describes a method to classify shears, shear zones, and their associated features. A format to describe and quantify shear and fault physical characteristics and example descriptions is provided. For each discussion, the word "fault" can be substituted for "shear."

Identification or Naming of Shears

Significant shears should be named for ease of identification in logs of exploration, mapping of exposures, interpretations on geologic drawings, discussion in reports, sample identification, and design treatment. Identifica- tion of a shear or shear zone by letter/number designation, such as S-9 (shear zone No. 9) or F-1 (fault zone No. 1), is recommended. Major splays may be identified by an appropriate combination of letters and numbers such as S-la or F-2c. Shears also may be named by their location such as "powerplant shear," "Salt Creek Shear zone," or "left abutment fault" if only a few shears are present in the study area.

Uniform and Structured Shear Zones

The identification and correlation of shears and shear zones from multiple but separate observations in boreholes, trenches, and limited outcrops are often difficult. The identification and description of shear and

114 DISCONTINUITIES

shear zone components and their physical characteristics are necessary to both assist in correlating observations and for design analyses. Together with physical measurements of attitude and thickness, the description of the component parts and internal structure of a shear may be used for correlation in much the same way that geophysical signatures or lithology are used to identify certain stratigraphic units. The composition of a shear or shear zone at each exposure can be described as either uniform or structured. Illustrated in figure 5-4 is a 0.5-foot (150-mm) thick uniform shear composed of 40 percent breccia distributed relatively uniformly throughout 60 percent clay gouge. Although the shear contains two components, clay gouge and brecciated fragments, the components are distributed uniformly throughout the 0.5-foot shear zone.

Figure 5-4.—Uniform shear zone.

In contrast, a structured shear zone is composed of two or more zones which differ significantly in composition or physical properties. A structured shear zone could consist of components similar to the uniform shear described above with an additional 0.2-foot (60-mm) thick quartz vein along one contact, as shown on figure 5-5.

A more complex structured shear zone might have a 0.1-foot (30-mm) thick chloritic gouge layer adjacent to the vein as shown on figure 5-6.

115 FIELD MANUAL

Figure 5-5.—Structured shear zone (two zones or layers).

Figure 5-6.—Structured shear zone (three layers).

Numerous small quartz-calcite or other mineral veinlets commonly occur irregularly distributed throughout shears. The veinlets do not form distinct layers; therefore, they should be considered a percentage component of a uniform shear as illustrated on figure 5-7.

Figure 5-7.—Uniform shear zone with veinlets.

116 DISCONTINUITIES

Shear zones may have minor or major lateral variations in the percentages of components within short distances at an exposure. The shear zone illustrated in figure 5-4 consists of 60 percent clay gouge and 40 percent rock fragments. Because the various components are not arranged in layers, the shear is of the uniform type. In an adjacent tunnel, the same shear zone may consist of 40 percent clay gouge and 60 percent rock fragments. If the exposure is limited, as in most tunnels or exploratory trenches, the percentages of the various components should be averaged, as illustrated on figure 5-8, and the average composition should be described.

Figure 5-8.—Uniform shear zone (composite).

Descriptors and Description Format for Shears and Shear Zones

For shears to be uniformly and adequately described, a brief discussion of each applicable item in the following list should be included. The recommended format for describing a shear or shear zone, either uniform or structured as follows:

• Attitude • Thickness

117 FIELD MANUAL

• Composition

Gouge Percent by volume Color Moisture content Consistency (hardness/strength) Composition Occurrence — layers or matrix Breccia Percent by volume Fragment size(s) Fragment shape(s) Fragment surface characteristics Lithology Hardness/strength

Other components (vein or dike materials) Percentage Thickness Composition (mineralogy, texture, fracturing, etc.)

• Healing

• Zone strength

• Direction of movement (if determinable)

Attitude.—Measure strike and dip in exposures and from oriented core, report dip in vertical core, and measure angle from core axis for inclined drill core. Report an average figure if only moderate variations are observed. Provide both a range and average if large variations in orientation are apparent.

Thickness.—Report the true thickness of the shear or shear zone. True thickness can be measured directly or computed. Indicate an average figure for minor variations, as well as a range and average for significant

118 DISCONTINUITIES

variations. Do not include associated features beyond the shear contacts (the shear-disturbed zone), or intact blocks of rock around which the shear has bifurcated as components of the thickness.

Composition.—Report an average percentage for each description-format component. The various layers or zones of structured shears may be indicated by use of bracketed numbers [i.e., shear 1(1), 1(2)]. Describe each individual layer or zone in the order it occurs as if each were a uniform shear.

1. Gouge.—

• Percentage.—Report an average percent by volume for each exposure or layer.

• Color.—Report color to help distinguish between several types of gouge or to indicate alteration. The Munsel Color System can be used to record both the wet and dry color.

• Moisture content.—Describe the apparent moisture content upon initial exposure, using the following terms: wet (visible free water); moist (damp but without visible water); and dry (absence of moisture, dusty, dry to the touch).

• Consistency (strength/hardness).—Report the ease with which gouge can be worked by hand: Very soft [thumb penetrates gouge more than 1 in (25 mm) if the gouge occurs in a sufficient quantity]; soft [easily molded, penetration of thumb about 1 in (25 mm)]; firm [easily crumbled, can be penetrated by thumb up to 1/4 in : (5 mm)]; hard (can be broken with finger pressure, no indentation with thumb, readily indented with

119 FIELD MANUAL

thumbnail); and very hard (cannot be indented with thumbnail). Use a pocket penetrometer to estimate gouge strength.

• Composition.—Report identifiable mineral types; talc, chlorite, mica. Otherwise, report the soil classification group name and/or symbol, such as CH, ML, lean clay, etc.

• Occurrence.—Describe how the gouge occurs, such as thin coatings on fragments, a matrix, or a layer.

2. Breccia.—

• Percentage.—Report an average percent by volume for each exposure or layer.

• Fragment size.—Estimate or measure the dimension of the most common fragment sizes and report as a range. Use fractions of an inch and tenths of a foot or metric equivalents.

• Fragment shape.—Unless the distribution of several shapes is nearly equal, report the most common shapes and degree of angularity as shown in figure 5-9.

• Fragment characteristics.—These should be included because they affect or provide an indication of the strength of the zone or help to identify a particular zone in several exposures or observations. Descriptions should include striated, slickensided, polished, rough, chloritic coatings, and weathering.

120 DISCONTINUITIES

Figure 5-9.—Standard descriptors and descriptive criteria for discontinuities.

121 FIELD MANUAL

122 DISCONTINUITIES

• Lithology.—The identification of rock fragments (rock type) is essential, particularly if different from the surrounding rock mass or if several rock types are present in the zone. Indicate if fragments within the zone are altered.

• Fragment hardness/strength.—Describe how the average-size fragment can be broken across its least dimension using the following format: can be broken with (light, moderate, heavy) manual pressure or hammer blow.

3. Other components (vein or dike material).— Describe any large veins or dikes which occur within the shear, either as a component of a uniform shear zone, usually occurring in the form of branching, discontinuous veinlets less than 1/2-inch (13-mm) thick, or as a layer (zone) within a structured shear. Dikes or large veins should be included as a single layer of a shear zone if they are bounded by shears. Also, they should be described as a rock unit. If a shear occurs only along one border of a dike or vein, the dike or vein should be described only as a rock unit.

• Percentage.—Report as an average percent by volume for the exposure or layer.

• Thickness.—Report as an average or range of thickness.

• Composition.—Provide a brief description of mineralogy and texture (e.g., leached, vuggy). Fracture density may be reported here if significant.

123 FIELD MANUAL

Healing.—Small veinlets which are components of a uniform shear zone and which actually form a bond between fragments tend to increase the strength of the shear zone (see following section). Healing should be determined by attempting to separate fragments manually or using a rock or pick. If fragments are bonded by some healing or cementing agent, the shear zone is described as partly healed (less than 50 percent of fragments bonded), mostly healed (more than 50 percent of fragments bonded), and totally healed (all fragments bonded by vein material).

Zone Strength.—When possible, the strength of the entire shear zone exposed in outcrops, tunnels, and exploratory trenches should be reported by the ease of which the sheared material can be dug from the exposure. The following guide is to be used: can be dug from wall, floor, or outcrop with light, moderate, or heavy finger pressure or hammer blow. Strength should be reported for each significant layer of a shear zone.

Direction of Movement.—If determinable, the amount, direction, and type of displacement are reported. Type and direction of displacement (dip-slip, strike-slip, oblique-slip, normal, reverse, right-lateral) may be directly observable as shown by drag, tension fractures, striations, offset "marker units" (such as beds, dikes, veins, or other structural units). The amount of both horizontal and vertical separation and, if possible, a net- slip solution should be included. Regional stress fields may be used to postulate displacement in the absence of site observations.

124 DISCONTINUITIES

Example Descriptions for Shears and Shear Zones

The following are example descriptions for both a uniform and a structured shear zone; actual descriptions may depend on the type of observation.

A description, using metric units, of a uniform shear in an angle hole could be:

“21.30 to 22.31: Shear. 210 mm thick, upper contact inclined 40E, lower contact inclined 61E from core axis, averages 51E, parallel to bedding. Composed of approx. 15%, blackish- green, moist, soft, chloritic clay and 85% 2 to 10 mm thick platy and lens-shaped, subrounded, polished, intensely weathered (W7) metasandstone fragments. Fragments break with light hand pressure. Fragments partly healed by 1 mm thick quartz-calcite veinlets.”

A structured shear zone in a vertical drill hole core could be reported in English units as:

“118.6 to 121.9': Shear zone. 2.3 ft thick, upper and lower contacts dip 40 to 45E, subparallel to foliation. Zone 1, upper 0.3 ft; consists of 45% green, moist, soft, chloritic clay gouge and 55% 0.05 to 0.1 ft subrounded, blocky, polished, fresh dike fragments; fragments break with moderate hammer blow. Zone 2 is 1.1 ft thick; consists of very intensely fractured, fresh dike which is partly healed by 0.01 to 0.3 ft-thick calcite veinlets and a 0.l ft-thick, vuggy quartz-calcite vein at base of dike. Zone 3 is 0.5 ft of No Recovery. Zone 4, the lower 0.3 ft; consists of 70% gray, moist, firm, silty gouge, and 15% 0.01 to 0.03 ft-thick, wedge-shaped, fresh, striated

125 FIELD MANUAL

horn-blende schist fragments, and 15% 0.02 ft-thick, angular, blocky, fresh quartz fragments. Fragments break with light hammer blow.”

Description of Shear-Disturbed Zones

Fractures, fracture zones, drag zones, mineralized bedrock, and dikes or large veins along which one contact is sheared but are not themselves sheared or enclosed within a zone, are not included in the thickness of a shear or shear zone. The associated zone should be identified to adequately describe geologic conditions of engineering significance. For example, the shear- disturbed zone and an adjacent dike might be described as:

“. . . The shear is bounded by a 1.5- to 4-ft wide shear-disturbed zone of very intensely to intensely fractured chloritized dike (FD8). This zone averages 3 ft wide along the upper contact and 2 ft wide in the associated chloritized dike adjacent to the lower contact. Hydrothermal alteration consisting of epidote, chlorite, pyrite, and quartz extends irregularly outward 2 to 7 ft normal to the shear boundaries.”

BIBLIOGRAPHY

[1] International Journal of Rock Mechanics Mining Science and Geomechanics Abstracts, v. 15, pp. 319- 368, 1978.

[2] The Glossary of Geology, 4th edition, American Geologic Institute, Alexandria, Virginia, 1997.

[3] Deere, D.U., and D.W. Deere, “RQD After Twenty Years,” U.S. Army Corps of Engineers, 1989.

126 DISCONTINUITIES

[4] Davis, George H., Structural Geology of Rocks and Regions, John Wiley & Sons, 1984.

[5] Earth Manual, Part II, Third Edition, Bureau of Reclamation, U.S. Department of the Interior, 1990.

127 Chapter 6

GEOLOGIC MAPPING AND DOCUMENTATION

Geologic mapping is defined as the examination of natural and manmade exposures of rock or unconsolidated materials, the systematic recording of geologic data from these exposures, and the analysis and interpretation of these data in two- or three-dimensional format (maps, cross sections, and perspective [block] diagrams). The maps and cross sections generated from these data: (1) serve as a record of the location of factual data; (2) present a graphic picture of the conceptual model of the study area based on the available factual data; and (3) serve as tools for solving three-dimensional problems related to the design, construction, and/or maintenance of engineered structures or site characterization. This chapter presents guidelines for the collection and documentation of surface and subsurface geologic field data for use in the design, specifications, construc-tion, or maintenance of engineered structures and site characterization studies.

Responsibilities of the Engineering Geologist

An engineering geologist defines, evaluates, and documents site-specific geologic conditions relating to the design, construction, maintenance, and remediation of engineered structures or other sites. This responsibility also may include more regionally based geologic studies, such as materials investigations or regional reconnaissance mapping. An engineering geologist engaged in geologic mapping is responsible for:

• Recognizing the key geologic conditions in a study area that will or could significantly affect hazardous and toxic waste sites or a proposed or existing structure; FIELD MANUAL

• Integrating all the available, pertinent geologic data into a rational, interpretive, three-dimensional conceptual model of the study area and presenting this conceptual model to design and construction engineers, other geologists, hydrologists, site managers, and contractors in a form that can be understood.

The process and responsibilities of engineering geology mapping are illustrated in figure 6-1.

The engineering geologist needs to realize that geologic mapping for site characterization is a dynamic process of gathering, evaluating, and revising geologic data and that the significance of these data, both to the structure and to further exploration, must be continually assessed. The initial exploration program for a structure is always based on incomplete data and must be modified continuously as the site geology becomes better understood. The key to understanding the site geology is through interpretive geologic drawings such as geologic maps, cross sections, isopachs, and contour maps of surfaces. These working drawings, periodically revised and re-interpreted as new data become available, are continuously used to assess the effects of the site geology and to delineate areas where additional exploration is needed. These drawings are used in designs, specifica-tions, and modeling and maintained in the technical record of the project.

Development of a Study Plan

Prior to mapping any project, a study plan must be developed. Depending on the complexity of the site geology, the nature of the engineered structure, and the level of

130 MAPPING Figure 6-1.—Process of engineering geology mapping.

131 FIELD MANUAL previous studies, the study plan may be preliminary or comprehensive. Although elements of the plan may be modified, expanded, or deleted as geologic data become available, the primary purpose of the study plan— coordination among all geologists and engineers working on the project—should be retained. Early study plan development and agreement to this plan by those involved in the project are necessary to prevent the collection of unneeded, possibly costly data and ensure needed data are available at the correct time in the analysis, design, and construction process.

Scope of Study

The purpose and scope of the mapping project are strongly influenced by the primary engineering and geologic considerations, the level of previous studies, and overall job schedules. The purpose and scope are formulated jointly by the geologists and engineers on the project. Time of year and critical dates for needed information also will have a great impact on the pace of data collection and the personnel needed to handle a mapping project. Discussion of these factors prior to initiating the mapping program is essential so that only necessary data are obtained and the work can be completed on schedule. Items to consider when defining the scope of a mapping program are:

1. Study limits.—Set general regional and site study limits based on engineering and geologic needs.

2. Critical features and properties.—Determine the critical geologic features and physical properties of site materials that will need to be defined and discuss the difficulties in collecting data on these features.

132 MAPPING

3. Schedules.—Determine schedules under which the work will be performed and define key data due dates. Prioritize work to be done. The time of year the mapping is to be performed, the type of mapping required, available personnel and their skills, the availability of support personnel such as drill crews and surveyors, and budget constraints will influence the work schedule and must be carefully evaluated.

4. Extent of previous studies.—Collect and study all available geologic literature for the study area. The extent and adequacy of previous studies helps to define the types of mapping required and how data will be collected, i.e., based on analyses, design, or construction needs.

5. Photography.—Aerial and terrestrial photography should be considered for any project. As a minimum, aerial photographs of the site should be reviewed. Aerial photographs reveal features that are difficult to recognize from the ground or at small scales. Extensive use of terrestrial or aerial photography will require a different approach to the mapping program. Define areas where terrestrial photogrammetry could aid mapping progress. Terrestrial photography of various types is an integral part of the final study record.

Specific Mapping Requirements

This section provides the basic considerations an engineering geologist should evaluate prior to starting any mapping project or portion of a mapping project.

Map Type

Define the types of mapping required and how data are to be collected, including special equipment needed for

133 FIELD MANUAL

data collection. The types of mapping required depend on the study purpose or the type of structure or site that is to be built or rehabilitated, structure size, the phase of study (planning through operation and maintenance), and the specific design needs.

Scales and Controls

Define the required scales for design or construction needs. Although finished maps can be enlarged or reduced photographically or by Computer-Aided Drafting Design (CADD)-generated drawings to any desired scale, in most cases map text and symbols will have to be redone for legibility. Selection of an adequate map scale at the beginning of a mapping project will save time and energy as well as help ensure that the types of data needed can be portrayed adequately on the final drawings. Suggested map scales for various types of investigations are listed under specific mapping techniques.

The horizontal and vertical accuracy and precision of locations on a map depend on the spatial control of the base map. General base map controls are listed in decreasing significance: (1) Survey Control or Controlled Terrestrial Photogrammetry—geology mapped from survey controlled observation points or by plane table or stadia; (2) Existing Topographic Maps—control for these maps vary with scale. The most accurate are large-scale photogrammetric topographic maps generated from aerial photographs for specific site studies; (3) Uncontrolled Aerial/Terrestrial Photogrammetry—Camera lens distor-tion is the chief source of error; (4) Brunton Compass/ Tape Surveys—can be reasonably accurate if measure-ments are taken with care; and (5) Sketch Mapping— Practice is needed to make reasonably accurate sketch

134 MAPPING maps. The Global Positioning System can provide adequate position locations depending on the required accuracy or precision.

Global Positioning System

The Global Positioning System (GPS) is a system of satellites that provides positioning data to receivers on earth. The receiver uses the positioning data to calculate the location of the receiver on earth. Accuracy and type of data output depends on many factors that must be evaluated before using the system. The factors that must be evaluated are: (1) the needs of the project, (2) the capabilities of the GPS equipment, and (3) the parameters necessary for collecting the data in an appropriate form.

Project Requirements

The location accuracy or precision needed by the project is a controlling factor whether GPS is appropriate for the project. The actual needs of the project should be determined, being careful to differentiate with “what would be nice.” Costs should be compared between traditional surveying and GPS.

GPS Equipment

Different GPS receiver/systems have different accuracies. Accuracies can range from 300 ft to inches (100 m to cm) depending on the GPS system. Costs increase exponen-tially with the increase in accuracy. A realistic evalua-tion of the typical accuracy of the equipment to be used is necessary, and a realistic evaluation of the needed, not “what would be nice,” accuracy is important. Possible accuracy and typical accuracy are often not the same.

135 FIELD MANUAL

Datums

The datum or theoretical reference surface to be used for the project must be determined at the start. U.S. Geologi-cal Survey (USGS) topographic maps commonly use North American Datum (NAD) 27, but most new surveys use NAD 83. Changing from one datum to another can result in apparent location differences of several hundred feet or meters if not done properly.

Map Projections

The map projection is the projection used to depict the round shape of the earth on a flat plane or map. The most common projections used in the United States are the Transverse Mercator and the Lambert Conformal Conic. State plane coordinate systems almost exclusively use one or the other. To use these state plane projections, location and definition parameters are necessary. Table 6-1 has the types of projections and the projection parameters for each state in the United States. A discussion of map projections and coordinate systems is in Map Projections - A Working Manual, USGS Profes-sional Paper 1395[1].

Transverse Mercator.—The Transverse Mercator projection requires a central meridian, scale reduction, and origin for each state or state zone.

Lambert Conformal Conic.—The Lambert Conformal Conic projection requires two standard parallels and an origin for each state or state zone.

Coordinate System.—The coordinate system is the grid system that is to be used on the project. The state plane

136 MAPPING

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (T indicates Transverse Mercator: L. Lambert Conformal Conic: H. Hotine Oblique Mercator. Modified slightly and updated from Mitchell and Simmons, 1945, p. 45-47)

Projec- Projec- Area tion Zones Area tion Zones

Alabama ______T 2 Nevada ______T 3 Alaska ______T 8 New L 1 Hampshire __ T 1 H 1 New Jersey ___ T 1 Arizona ______T 3 New Mexico ___ T 3 Arkansas ______L 2 New York _____ T 3 California _____ L 7 L 1 Colorado ______L 3 North Connecticut ____ L 1 Carolina L 1 Deleware ______T 1 North Dakota _ L 2 Florida ______T 2 Ohio ______L 2 L 1 Oklahoma _____ L 2 Georgia ______T 2 Oregon ______L 2 Hawaii ______T 5 Pennsylvania __ L 2 Idaho ______T 3 Puerto Rico & Illinois ______T 2 Virgin Indiana ______T 2 Islands _____ L 2 Iowa ______L 2 Rhode Island __ T 1 Kansas ______L 2 Samoa ______L 1 Kentucky ______L 2 South Louisiana _____ L 3 Carolina ____ L 2 Maine ______T 2 South Dakota _ L 2 Maryland _____ L 1 Tennessee ____ L 1 Massachusetts _ L 2 Texas ______L 5 Michigan1 Utah ______L 3 obsolete _____ T 3 Vermont ______T 1 current _____ L 3 Virginia ______L 2 Minnesota _____ L 3 Washington ___ L 2 Mississippi ____ T 2 West Virginia _ L 2 Missouri ______T 3 Wisconsin ____ L 3 Montana ______L 3 Wyoming _____ T 4 Nebraska _____ L 2

137 FIELD MANUAL

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (continued) Transverse Mercator Projection Central Scale Origin3 Zone meridian reduction2 (latitude) Alabama East ______85E 50' W. 1:25,000 30E 30' N. West ______87 30 1:15,000 30 00 Alaska4 2 ______142 00 1:10,000 54 00 3 ______146 00 1:10,000 54 00 4 ______150 00 1:10,000 54 00 5 ______154 00 1:10,000 54 00 6 ______158 00 1:10,000 54 00 7 ______162 00 1:10,000 54 00 8 ______166 00 1:10,000 54 00 9 ______170 00 1:10,000 54 00 Arizona East ______110 10 1:10,000 31 00 Central ______111 55 1:10,000 31 00 West ______113 45 1:15,000 31 00 Delaware ______75 25 1:200,000 38 00 Florida4 East ______81 00 1:17,000 24 20 West ______82 00 1:17,000 24 20 Georgia East ______82 10 1:10,000 30 00 West ______84 10 1:10,000 30 00 Hawaii 1 ______155 30 1:30,000 18 50 2 ______156 40 1:30,000 20 20 3 ______158 00 1:100,000 21 10 4 ______159 30 1:100,000 21 50 5 ______160 10 0 21 40 Idaho East ______112 10 1:19,000 41 40 Central ______114 00 1:19,000 41 40 West ______115 45 1:15,000 41 40 Illinois East ______88 20 1:40,000 36 40 West ______90 10 1:17,000 36 40 Indiana East ______85 40 1:30,000 37 30 West ______87 05 1:30,000 37 30

138 MAPPING

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (continued)

Transverse Mercator Projection

Central Scale Origin3 Zone meridian reduction2 (latitude) Maine East ______68E 30' W. 1:10,000 43E 50' N. West ______70 10 1:30,000 42 50 Michigan (old)4 East ______83 40 1:17,500 41 30 Central ______85 45 1:11,000 41 30 West ______88 45 1:11,000 41 30 Mississippi East ______88 50 1:25,000 29 40 West ______90 20 1:17,000 30 30 Missouri East ______90 30 1:15,000 35 50 Central ______92 30 1:15,000 35 50 West ______94 30 1:17,000 36 10 Nevada East ______115 35 1:10,000 34 45 Central ______116 40 1:10,000 34 45 West ______118 35 1:10,000 34 45 New Hampshire ______71 40 1:30,000 42 30 New Jersey ______74 40 1:40,000 38 50 New Mexico East ______104 20 1:11,000 31 00 Central ______106 15 1:10,000 31 00 West ______107 50 1:12,000 31 00 New York4 East ______74 20 1:30,000 40 00 Central ______76 35 1:16,000 40 00 West ______78 35 1:16,000 40 00 Rhode Island ______71 30 1:160,000 41 05 Vermont ______72 30 1:28,000 42 30 Wyoming East ______105 10 1:17,000 40 40 East Central 107 20 1:17,000 40 40 West Central 108 45 1:17,000 40 40 West ______110 05 1:17,000 40 40

139 FIELD MANUAL

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (continued)

Lambert Conformal Conic projection Origin5 Standard Zone parallels Longitude Latitude Alaska4 10 ______51E50' N. 53E 50' N. 176E00' W.5a 51E 00' N. Arkansas North ______34 56 36 14 92 00 34 20 South ______33 18 34 46 92 00 32 40 California I ______40 00 41 40 122 00 39 20 II ______38 20 39 50 122 00 37 40 III ______37 04 38 26 120 30 36 30 IV ______36 00 37 15 119 00 35 20 V ______34 02 35 28 118 00 33 30 VI ______32 47 33 53 116 15 32 10 VII ______33 52 34 25 118 20 34 085b Colorado North ______39 43 40 47 105 30 39 20 Central ______38 27 39 45 105 30 37 50 South ______37 14 38 26 105 30 36 40 Connecticut ____ 41 12 41 52 72 45 40 505d Florida4 North ______29 35 30 45 84 30 29 00 Iowa North ______42 04 43 16 93 30 41 30 South ______40 37 41 47 93 30 40 00 Kansas North ______38 43 39 47 98 00 38 20 South ______37 16 38 34 98 30 36 40 Kentucky North ______37 58 38 58 84 15 37 30 South ______36 44 37 56 85 45 36 20 Louisiana North ______31 10 32 40 92 30 30 40 South ______29 18 30 42 91 20 28 40 Offshore _____ 26 10 27 50 91 20 25 40 Maryland ______38 18 39 27 77 00 37 505c Massachusetts Mainland ____ 41 43 42 41 71 30 41 005d Island ______41 17 41 29 70 30 41 005c

140 MAPPING

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (continued) Lambert Conformal Conic projection (continued)

5 Standard Origin Zone parallels Longitude Latitude Michigan (current)4 North ______45E29' N. 47E 05' N. 87E00' W. 44E 47' N. Central ______44 11 45 42 84 20 43 19 South ______42 06 43 40 84 20 41 30 Minnesota North ______47 02 48 38 93 06 46 30 Central ______45 37 47 03 94 15 45 00 South ______43 47 45 13 94 00 43 00 Montana North ______47 51 48 43 109 30 47 00 Central ______46 27 47 53 109 30 45 50 South ______44 52 46 24 109 30 44 00 Nebraska North ______41 51 42 49 100 00 41 20 South ______40 17 41 43 99 30 39 40 New York4 Long Island __ 40 40 41 02 74 00 40 305f North Carolina ______34 20 36 10 79 00 33 45 North Dakota North ______47 26 48 44 100 30 47 00 South ______46 11 47 29 100 30 45 40 Ohio North ______40 26 41 42 82 30 39 40 South ______38 44 40 02 82 30 38 00 Oklahoma North ______35 34 36 46 98 00 35 00 South ______33 56 35 14 98 00 33 20 Oregon North ______44 20 46 00 120 30 43 40 South ______42 20 44 00 120 30 41 40 Pennsylvania North ______40 53 41 57 77 45 40 10 South ______39 56 40 58 77 45 39 20 Puerto Rico and Virgin Islands 1 ______18E 02' N. 18E 26' N. 66E 26' W. 17E 50' N.5g 2 (St. Croix) __ 18 02 18 26 66 26 17 505f, g

141 FIELD MANUAL

Table 6-1.—U.S. State plane coordinate systems – 1927 datum (continued)

Lambert Conformal Conic projection (continued) Origin5 Standard Zone parallels Longitude Latitude Samoa ______14E16' S. (single) 170 005h — — South Carolina North ______33E46' N. 34 58 81 00 33 00 South ______32 20 33 40 81 00 31 50 South Dakota North ______44 25 45 41 100 00 43 50 South ______42 50 44 24 100 20 42 20 Tennessee ______35 15 36 25 86 00 34 405f

Note: All these systems are based on the Clarke 1866 ellipsoid and are based on the 1927 datum. Origin refers to rectangular coordinates. 1 The major and minor axes of the ellipsoid are taken at exactly 1.0000382 times those of the Clarke 1866, for Michigan only. This incorporates an average elevation throughout the State of about 800 ft, with limited variation. 2 Along the central meridian. 3 At origin, x = 500,000 ft, y = 0 ft, except for Alaska zone 7, x = 700,000 ft; Alaska zone 9, x = 600,000 ft; and New Jersey, x = 2,000,000 ft. 4 Additional zones listed in this table under other projection(s). 5 At origin, x = 2,000,000 ft, 7 = 0 ft, except (a) x = 3,000,000 ft, (b) x = 4,186,692.58, y = 4,160,926.74 ft, (c) x = 800,000 ft, (d) x = 600,000 ft, (e) x = 200,000 ft, (f) y = 100,000 ft, (g) x = 500,000 ft, (h) x = 500,000 ft, y = 0, but radius to latitude of origin = -82,000,000 ft. system is used by most projects, but latitude/longitude, universal transverse mercator, or a local coordinate system may be used.

State Plane Coordinate Systems-changes for 1983 datum.—This listing indicates changes for the NAD 1983 datum from projections, parameters, and origins of zones for the NAD 1927 datum. State plane coordinates based on the 1927 datum cannot be correctly converted to coordinates on the 1983 datum merely by using inverse formulas to convert from 1927 rectangular coordinates to latitude and longitude, and then using

142 MAPPING forward formulas with this latitude and longitude to convert to 1983 rectangular coordinates. Due to readjustment of the survey control networks and to the change of ellipsoid, the latitude and longitude also change slightly from one datum to the other.

These changes are given in the same order as the entries in the 1927 table, except that only the changes are shown. All parameters not listed remain as before, except for the different ellipsoid and datum. Because all coordinates at the origin have been changed, and because they vary considerably, the coordinates are presented in the body of the table rather than as footnotes. Somoa is not being changed to the new datum.

Table 6-2.—U.S. State plane coordinate systems – 1983 datum [L indicates Lambert Conformal Conic] Area Projection Zones California L 6 Montana L 1 Nebraska L 1 Puerto Rico and Virgin Islands L 1 South Carolina L 1 Wyoming Unresolved Transverse Mercator projection Coordinates of origin (meters) Zone x y Other Changes Alabama East 200,000 0 West 600,000 0 Alaska, 2-9 500,000 0 Arizona, all 213,360 0 Origin in Intl. feet1

143 FIELD MANUAL

Table 6-2.—U.S. State plane coordinate systems – 1983 datum (continued) Transverse Mercator projection (continued) Coordinates of origin (meters) Zone x y Other Changes Delaware 200,000 0 Florida East, West 200,000 0 Georgia East 200,000 0 West 700,000 0 Hawaii, all 500,000 0 Idaho East 200,000 0 Central 500,000 0 West 800,000 0 Illinois East 300,000 0 West 700,000 0 Indiana East 100,000 250,000 West 900,000 250,000 Maine Lat. of origin 43E40' N. East 300,000 0 West 900,000 0 Mississippi East 300,000 0 Scale reduction 1:20,000, Lat. of origin 29E30' N. West 700,000 0 Scale reduction 1:20,000, Lat. of origin 29E30' N. Missouri East 250,000 0 Central 500,000 0 West 850,000 0 Nevada East 200,000 8,000,000 Central 500,000 6,000,000 West 800,000 4,000,000 New Hampshire 300,000 0

144 MAPPING

Table 6-2.—U.S. State plane coordinate systems – 1983 datum (continued) Transverse Mercator projection (continued) Coordinates of origin (meters) Zone x y Other Changes New Jersey 150,000 0 Central meridian 74E30'W. Scale reduction 1:10,000. New Mexico East 165,000 0 Central 500,000 0 West 830,000 0 New York East All parameters identical with above New Jersey zone. Central 250,000 0 West 350,000 0 Rhode Island 100,000 0 Vermont 500,000 0 Wyoming Unresolved

Lambert Conformal Conic projection

Coordinates of origin (meters) Zone x y Other Changes Alaska, 10 1,000,000 0 Arkansas North 400,000 0 South 400,000 400,000 California Zone 7 deleted. 1-6 2,000,000 500,000 Colorado, all 914,401.8289 304,800.6096 Connecticut 304,800.6096 152,400.3048 Florida, North 600,000 0 Iowa North 1,500,000 1,000,000 South 500,000 0 Kansas North 400,000 0 South 400,000 400,000 Kentucky North 500,000 0 South 500,000 500,000

145 FIELD MANUAL

Table 6-2.—U.S. State plane coordinate systems – 1983 datum (continued) Lambert Conformal Conic projection (continued) Coordinates of origin (meters) Zone x y Other Changes Kansas North 400,000 0 South 400,000 400,000 Kentucky North 500,000 0 South 500,000 500,000 Louisiana North 1,000,000 0 Lat. of origin 30E30' N. South 1,000,000 0 Lat. of origin 28E30' N. Offshore 1,000,000 0 Lat of origin 25E30' N. Maryland 400,000 0 Lat. of origin 37E40' N. Massachusetts Mainland 200,000 750,000 Island 500,000 0 GRS 80 ellipsoid used Michigan without alteration. North 8,000,000 0 Central 6,000,000 0 Long. of origin 84E22'W. South 4,000,000 0 Long. of origin 84E22'W. Minnesota, all 800,000 100,000 Montana 600,000 0 Standard parallels, 45E00' (single zone) and 49E00' N. Long. of origin 109E30' W. Lat. of origin 44E15' N. Nebraska 500,000 0 Standard parallels, 40E00' (single zone) and 43E00' N. Long. of origin 100E00' W. Lat. of origin 39E50' N. New York Long Island 300,000 0 Lat. of origin 40E10' N. North Carolina 609,621.22 0 North Dakota, all 600,000 0 Ohio, all 600,000 0

146 MAPPING

Table 6-2.—U.S. State plane coordinate systems – 1983 datum (continued) Lambert Conformal Conic projection (continued) Coordinates of origin (meters) Zone x y Other Changes Oklahoma, all 600,000 0 Oregon North 2,500,000 0 South 1,500,000 0 Pennsylvania, all 600,000 0 Puerto Rico and 200,000 200,000 (Two previous zones Virgin Islands identical except for x and y or origin.) South Carolina 609,600 0 Standard parallels, 32E30' (single zone) and 34E50' N. Long. of origin 81E00' W. Lat. of origin 31E50' N. South Dakota, all 600,000 0 Tennessee 600,000 0 Lat. of origin 34E20' N. Texas North 200,000 1,000,000 North Central 600,000 2,000,000 Central meridian 98E30' W. Central 700,000 3,000,000 South Central 600,000 4,000,000 South 300,000 5,000,000 Utah North 500,000 1,000,000 Central 500,000 2,000,000 South 500,000 3,000,000 Virginia North 3,500,000 2,000,000 South 3,500,000 1,000,000 Washington, all 500,000 0 West Virginia, all 600,000 0 Wisconsin, all 600,000 0 NOTE: All these systems are based on the GRS 80 ellipsoid. 1 For the International foot, 1 in = 2.54 cm, or 1 ft = 30.48 cm.

147 FIELD MANUAL

Units

English or metric units should be selected as early in the project as possible. Conversions are possible, but convert-ing a large 1-foot contour map to meters is no trivial matter.

Remember that when using several sources of location data, the reference datum must be known. Systematic differences in location data are generally due to mixing datums.

Specific Nomenclature and Definitions

Establish a uniform nomenclature system with written definitions for rock types, map units, and map symbols used. The American Geologic Institute Glossary of Geology [2] is the standard for geologic terms except where Reclamation has established definitions for its own needs. These definitions and nomenclature are discussed in chapters 2 through 5.

Field Equipment and Techniques

General geologic mapping equipment and techniques are discussed in field geology manuals such as Lahee (1961) [3] and Compton (1985) [4]. Refer to these texts for discussions of suggested field equipment and general geologic mapping techniques.

Use of Computers

Computers are used during a mapping program in four basic ways: (1) to process and analyze voluminous numerical data (e.g., joint data), (2) as a tool in the analysis of basic geologic data (e.g., construction of preliminary or final plan and section views which

148 MAPPING incorporate previously entered geologic data), (3) Computer Aided Drafting and Design (CADD) of section and plan views, and (4) in modeling geologic conditions. How computers will be used in the reduction, analysis, and drafting of the geologic data generated during a mapping program needs to be decided early because records of field data will depend on whether data are to be stored in digital format and restructuring these data at a later date is costly, time consuming, and introduces transcription errors.

Right-of-Way

Right-of-way is needed for any mapping of non- Reclamation land and should be obtained early to prevent work delays. Although "walk on" permission usually is obtained easily, permission for trenching and drilling may take several months, especially if archeological or environmental assessment is necessary.

Records

Systematic methods of recording field observations, traverse data, outcrop data, and trench logs are important. Suggested sample field book formats are shown under each section below dealing with specific mapping procedures, but any format should allow clear representation of the field data.

Geologic Considerations

The following are some key items that should be evaluated during a mapping project. The degree of importance varies with the project but the factors are common to most.

149 FIELD MANUAL

Lithology.—Differentiation between the various geologic deposits and lithologies in a study area is basic to geologic mapping. However, an engineering geologist is more concerned with the engineering characteristics of the unit than with its geologic definition, and these characteristics should be the controlling factor in how geologic units are subdivided. For some engineering geologic purposes, it may be reasonable to consolidate geologic units with similar engineering properties into a single engineering geologic map unit. Depending on the needs of the project, lithologic subunits may be defined jointly between the engineers and the geologists working on the job.

After the basic geologic subdivisions for a mapping job have been agreed upon, detailed descriptions of each subunit should be compiled and mapping symbols selected. Map unit definitions usually will apply specifically to the job or project area and normally will be modified as additional data are collected. Map symbols fall into several categories. American Geological Institute data sheets have a comprehensive tabulation of symbols.

Geologic contacts.—Two different line types normally are used on geologic maps to denote the precision and accuracy of geologic contacts. These are solid and broken (dashed or dotted) lines. Solid lines usually are used where exposures are excellent, such as a cleaned foundation or an area with nearly continuous outcrops. Solid lines indicate that the contacts are located with a prescribed degree of accuracy. Broken contacts are used when unsure of the accurate location of the contact, i.e., when the contact is covered by thin slopewash deposits (dashed line) or where the contact is buried by deep surficial deposits (dotted line). Confidence levels, expressed in feet or meters, for both types of contacts should be stated clearly in the definition of the contact

150 MAPPING line. The mapper should keep in mind the type of geologic data being compiled and use the appropriate line.

Discontinuities.—Discontinuities separate geological materials into discrete blocks that can control the stability and bearing capacity of a foundation or slope. Intersecting discontinuities in cut slopes can form unstable wedges. Because of the destabilizing or weakening effects, mapping and adequately describing discontinuities is critical in engineering geology studies. The various types of discontinuities and the terminology for describing their engineering properties are discussed in chapter 5.

Weathering and alteration.—The mechanical and chemical alteration of geological materials can significantly affect stability and bearing strengths. Adequately determining weathering depths, extent of altered materials and the engineering properties of these weathered and altered materials is critical in engineering geologic mapping. Refer to chapter 4 for definitions of weathering and alteration descriptors.

Water.—The location and amount of groundwater to be expected in an excavation and how it can be controlled is critical to the overall success of a project.

Geomorphology.—Study of landforms is often the key to interpreting the geologic history, structure, lithology, and materials at a site. Exploration programs can be better designed and implemented using landforms as a basis. The geomorphic history is important in determining the relative age of faults.

Vegetation indicators.—Differences in vegetation types and patterns can provide indirect data on lithologies, dis-continuities, weathering, groundwater,

151 FIELD MANUAL and mineralization. The water holding capacity of soil developed on one rock (e.g., shale) may differ considerably from the water holding capacity of soil developed on another type of rock (e.g., sandstone); consequently, the types of vegetation that grow in these soils can vary considerably. Minerals present in the parent rock may affect soil chemistry and may limit vegetation to types tolerant of highly acidic or alkaline soils or high concentrations of trace elements. Vegetation seeking groundwater moving up major joints and faults will form vegetation lineations that are highly visible on aerial photographs, particularly color infrared photo-graphs. In most locations, local conditions have to be assessed to use vegetative indicators effectively.

Cultural features (manmade).—Cultural features, such as water, gas or oil wells, road cuts or foundation excavations, can provide surface and subsurface data and should be reviewed early in the mapping project. When data collection through trenching and core drilling programs is considered, buried utility lines (water, gas, electrical, sewage, or specialized lines) can be hazardous or embarrassing when broken. Usually the utility or owners will locate their lines.

Field checking.—Field checking by both mapper and independent reviewer is a critical part of the mapping process. Field checking after a map is complete allows the mapper to check the interpretations at a given location with the geologic concepts developed on the map as a whole. Field checking by the independent reviewer ensures that the basic field data are correct and conform to project standards. Periodic field checking of previously mapped areas can be useful as the mapper's concept of the site geology changes with the addition of new surface and subsurface data.

152 MAPPING

Site Mapping

Engineering geologic mapping has two phases—mapping prior to construction and mapping during construction. In general, the following guidelines are for: (1) general mapping requirements, (2) suggested equipment, (3) specific preparations needed for the job, (4) type of documentation needed, and (5) special considerations that the mapping may require.

General

Detailed site geologic mapping studies generally are done for most structures or sites. Site mapping requirements are controlled by numerous factors, the most important of which are the type and size of structure to be built or rehabilitated or site to be remediated, the phase of study (planning through operation and maintenance), and the specific design needs.

Site mapping studies for major engineering features should be performed within an approximate 5-mile (8- km) radius of the feature, with smaller areas mapped for less critical structures. These studies consist of detailed mapping and a study of the immediate site, with more generalized studies of the surrounding area. This approach allows an integration of the detailed site geology with the regional geology. The overall process of site mapping is a progression from preliminary, highly interpretive concepts based on limited data to final concepts based on detailed, reasonably well-defined data and interpretation. This progression builds on each previous step using more detailed methods of data collection to acquire better defined geologic information. Typically, site mapping is performed in two phases: (1) preliminary surface geologic mapping and (2) detailed surface geologic mapping. All site mapping studies begin

153 FIELD MANUAL with preparation of a preliminary surface geologic map which delineates surficial deposits and existing bedrock exposures. The preliminary surface geologic map is then used to select sites for dozer trenches, backhoe trenches, and drill holes. Surface geologic maps are then re- interpreted based on the detailed surface and subsurface data. If required, detailed subsurface geologic data are also obtained from exploratory shafts and adits.

Suggested Equipment

The following list of basic equipment should meet most needs. Not all listed equipment is necessary for every project, but a Brunton Compass, geologist’s pick, (2- pound hammer may be necessary for rock sampling), maps, map board, aerial photographs, notebook, scale, tape measure, protractor, knife, hand lens, various pens and pencils, and a GPS should meet most needs.

Preparation

Whether a site mapping program is completed in one field season or over several years, the overall project schedule and budget are critical. A critical assessment should be made of the time available for the mapping program, the skills and availability of personnel to accomplish the work, weather conditions, and budget constraints.

Documentation

Site data are documented on drawings (and associated notes) generated during the study. The drawings fall into two general categories—working drawings and final drawings. Working drawings serve as tools to evaluate and analyze data as it is collected and to define areas where additional data are needed. Analysis of data in a three-dimensional format is the only way the geologist

154 MAPPING can understand the site geology. Drawings should be generated early in the study and continuously updated as the work progresses. These drawings are used for pre-liminary data transmittals. Scales used for working drawings may permit more detailed descriptions and collection of data that are not as significant to the final drawings. Final drawings are generated late in the mapping program, after the basic geology is well understood. Many times new maps and cross sections are generated to illustrate specific data that were not available or well understood when the working drawings were made. Final drawings serve as a record of the investigations for special studies, specifications, or technical record reports.

Preliminary Surface Geologic Mapping.—The purpose of preliminary surface geologic mapping is to define the major geologic units and structures in the site area and the general engineering properties of the units. Suggested basic geologic maps are a regional reconnaissance map at scales between 1 inch = 2,000 feet and 1 inch = 5,280 feet (1:24,000 to 1:62,500), and a site geology map at scales between 1 inch = 20 feet and 1 inch = 1,000 feet (1:250 to 1:12,000). Scale selection depends on the size of the engineered structure and the complexity of the geology. Maps of smaller areas may be generated at scales larger than the base map to illustrate critical conditions. Cross sections should be made at a natural scale (equal horizontal and vertical) as the base maps unless specific data are better illustrated at an exaggerated scale. Exaggerated scale cross sections are generally not suited for geologic analysis because the distortion makes projection and interpretation of geologic data difficult.

Initial studies generally are a reconnaissance-level effort, and the time available to do the work usually is limited.

155 FIELD MANUAL

Initially, previous geologic studies in the general site area are used. These studies should be reviewed and field checked for adequacy and new data added. Initial base maps usually are generated from existing topographic maps, but because most readily available topography is unsuitable for detailed studies, site topography at a suitable scale should be obtained if possible. Existing aerial photographs can be used as temporary base maps if topographic maps are not available. Sketch maps and Brunton/tape surveys or GPS location of surface geologic data can be done if survey accuracy or control is not available or necessary. Good notes and records of outcrop locations and data are important to minimize re-examination of previously mapped areas. Aerial photo-graphy is useful at this stage in the investigation, as photos can be studied in the office for additional data. Only after reasonably accurate surface geology maps have been compiled can other investigative techniques, such as trenching and core drilling, be used to full advantage. For some levels of study, this phase may be all that is required.

Detailed Surface Geologic Mapping.— The purpose of detailed surface geologic mapping is to define the regional geology and site geology in sufficient detail so geologic questions critical to the structure can be answered and addressed. Specific geologic features critical to this assessment are identified and studied, and detailed descriptions of the engineering properties of the site geologic units are compiled. Project nomenclature should be systematized and standard definitions used. Suggested basic geologic maps are similar to those for preliminary studies, although drawing scales may be changed based on the results of the initial mapping program. Maps of smaller areas may be generated to illustrate critical data at scales larger than the base map.

156 MAPPING

The preliminary surface geology maps are used to select sites for dozer trenches, backhoe trenches, and drill core holes. As the surface geology is better defined, drill hole locations can be selected to help clarify multiple geologic problems. Detailed topography of the study site should be obtained, if not obtained during the initial investigations. Data collected during the preliminary investigations should be transferred to the new base maps, if possible, to save drafting time. Field mapping control is provided primarily by the detailed topographic maps and/or GPS, supplemented by survey control if available or Brunton/ tape survey. If not, large scale aerial photographs of a site area flown to obtain detailed topography are useful in geologic mapping.

Dozer Trench Mapping

General

Dozer trenches are cut to expose rock or unconsolidated materials below the surface and major surface creep. Walls normally should be excavated vertically, free of narrow benches and loose debris. Upon completion of excavation, floors must be cleaned below any depth of ripping, loose rubble should be removed, and a new surface exposed. Structures such as contacts and shear zones must be traceable from wall into floor for optimum determination of their nature and attitude. The geologist is responsible to ensure the dozer operator produces a safe finished trench that meets Reclamation and Occupational Safety and Health Administration (OSHA) safety standards. If livestock are present, fencing of the trench with four strands of barbed wire may be required. After trench logging is completed, decide whether to leave the trench open or to backfill. At sites with complex geology, it is desirable to leave the

157 FIELD MANUAL trench open for reinterpretation of the trench in light of newly acquired data. Backfilling of the dozer trench may be necessary where an open trench would be a safety hazard. Generally, all trenches should be backfilled and com-pacted prior to abandonment.

Suggested Equipment

Additional equipment needed may include hard hat, scraper or putty knife, square-nosed shovel, plastic flagging, nails, wooden stakes, surveyors chain or tape measure (feet or meters) and log book. Use putty knife, shovel, and whisk broom for cleaning trench exposures and a Brunton tripod for more accurate trench bearings.

Preparation

Prior to working in a dozer trench, the geologist should inspect the excavation trench walls for failure planes (obvious or incipient) or loose materials. These should be removed before mapping starts. An examination of the whole trench should be made at the start of each work period. A baseline should be laid out along the toe of the trench wall or at the top of the excavation. Because dozer trenches often are not straight, the trench should be divided into a series of straight segments with stations established at each point where the trench changes direction. Each station should be marked by a stake, tied with flagging, and marked with the trench number and station letter (e.g., DT-12A). Flagging strips should be nailed to the wall approximately 6 feet (2 meters [m]) vertically above or below the station for another reference point in case minor sloughing buries or dislodges the stake.

158 MAPPING

Documentation

The scale and format selected for logging a backhoe trench depends on the type of data needed and the amount of detail to be illustrated. Typical dozer trench log scales are between 1 inch (in) = 5 feet (ft) (1:100) and 1 in = 10 ft (1 : 200), but scales of 1 in = 1 ft (1: 50) may be required in critical areas to adequately show structural and stratigraphic details. If trench geology is not complex, record trench logs, along with names of the field party and date in a field book. Determine and record the bearing, slope distance, and slope angle between each station. Survey the coordinates and elevations of each station. Orient the log book so the sketch and description may be viewed together (see figure 6-2). Sketch the walls and floors across the top page of the open log book. Mark the baseline at 5-foot (1.5-m) intervals and draw a single "hinge line”; wall above, floor below. Determine the vertical heights of the trench walls at each station and between stations, if the profile or thickness of surficial materials changes between stations.

Sketches should be accurate and illustrate the field relationship of soil and geologic units and structures. Use nails and flagging strips to mark obscure contacts or other features for ready reference during logging. Designate geologic units by name and symbol. Accurately plot the attitude of contacts, bedding, foliation or cleavage, faults, shear zones, and joints where they are determined using standard symbols, and write a description. If attitudes are determined from the wall, they may be projected along strike into the floor, if no change is apparent in the floor. Note and show the bedding or foliation wherever relationships are complex and differ from the recorded attitude (i.e., where surface creep, drag folds, or disturbed zones are exposed in the wall). Record unit attitudes that may have been affected

159 FIELD MANUAL Figure 6-2.—Sample trench log.

160 MAPPING by surface creep or slumping. Written descriptions of soil and rock units and structural zones should be restricted to the page below the sketch and should not be written over the sketch. Main heading for written descriptions are restricted to mappable geologic units. Intervals are noted where the contacts intersect the baseline. Indent subheadings within text to describe lithologic or structural variations within the mappable unit. An example of heading order is as follows:

DT-58, Sta. B-C, Distance - 27.5', Bearing - S. 45E W., Slope + 2 22.5-50.0': Metasediments (description) 39.9-41.0': Chlorite Schist B (description) 47.5-49.0': Talc Schist (description) 48.2-48.4': Shear Zone (description)

Stratigraphic units should be colored to complete the log. Photograph the trench to complement the log or to record specific details within the trench.

Backhoe Trench Mapping

General

Backhoe trenches are excavated to expose rock or unconsolidated materials below surficial deposits and major surface creep. Generally, backhoe trenches are excavated at sites which must be returned to near- original conditions and where dozer trenching would produce unacceptable damage. Backhoe trenches often are excavated in the floor of an existing dozer trench to deepen the excavation. Walls should be excavated vertically and free of narrow benches and loose debris. In most cases, the trench should be about 3 to 3-1/2 feet wide (1 m) (width of standard backhoe bucket), 10 to 12

161 FIELD MANUAL feet (3 to 3.6 m) deep, and slope at one end for easy access. Upon excavation completion, hydraulic trench shores are placed and pressurized or wooden shores constructed to support the trench walls. Shore construction and spacing must meet OSHA standards and standards outlined in Reclamation's Construction Safety and Health Standards manual. At no time should personnel enter unshored portions of the trench over 5 feet deep. The geologist who oversees the excavation of the backhoe trench is respon-sible for the construction of a safe, stable trench.

After trench logging is completed, decide whether to leave the trench open or to backfill. At sites with complex geology, leave the trench open, if possible, as this allows reinterpretation of the trench in light of newly acquired data. However, backhoe trenches are prone to sloughing with time, even when supported, and backfilling of the trench may be necessary for safety reasons. The coordi-nates and elevation of each end of the backhoe trench should be surveyed prior to backfilling.

Suggested Equipment

Standard field equipment is used during backhoe trench mapping. Additional equipment may include a hard hat, large knife, flat-blade pick or army trenching tool to clean off trench walls, putty knife, whisk broom, nails, flagging, twine, small string level, 100-foot (30-m) long surveyor's chain or tape, and map board or log book. The type of backhoe needed depends on how consolidated or cemented the material is, site accessibility, and depth to be excavated. Most of the larger, rubber-tired backhoes are suitable for excavation of typical trenches, but well consolidated or cemented material, steep site terrain, or trench depths over about 12 feet (3.6 m) may require a larger track-mounted hydraulic excavator.

162 MAPPING

Preparation

Each day prior to working in a backhoe trench, the trench along both sides and the trench walls should be examined for incipient fractures or loose materials, particularly within the surficial materials. These loose materials should be removed before work starts. Hydraulic trench shores should be checked visually for leakage and for loss of pressure by pushing on them with a foot. Re-pressure any loose shores and replace leaking shores. The stability of each shore should be checked before the mapper's weight is put on it, particularly if the shore is to be used to examine the upper trench wall or to climb out of the trench.

A backhoe trench must be cleaned prior to logging. During excavation, the backhoe bucket may smear clay and silt along the walls, obscuring structural and stratigraphic relationships. This smeared zone may be anywhere from a fraction of an inch thick to several inches thick, depending on the amount of fines and moisture in the material excavated. The smeared material can be removed by chipping or scraping with a large knife, flat- bladed pick, or army trenching tool. If the trench is excavated in reasonably consolidated material and the trench is free draining, a high pressure water and/or air jet will remove this material. Both walls should be spot cleaned and examined prior to major cleaning to determine which wall exposes the best geologic data. Usually only one wall is completely cleaned; the other wall is spot cleaned during trench logging to expose another view of critical features or relationships. After a wall is cleaned, a horizontal base line is established. The baseline is run at about eye level and constructed by stringing twine between nails driven into the cleaned trench wall. The twine can be leveled using a small string level (available in most hardware stores) prior to driving nails. When the baseline becomes either too high or too low for

163 FIELD MANUAL comfort-able measurements, a vertical offset of the string line is made and the baseline continued at the new horizon. In complex, critical areas where accurately located contacts are needed, a string grid with horizontal and vertical elements can be constructed off the baseline to assist in mapping.

Documentation

The scale and format selected for logging a backhoe trench depends on the type of data needed and the amount of detail to be illustrated. Typical backhoe trench log scales are between 1 in = 5 ft (1:100) and 1 in = 10 ft (1 : 200), but scales of 1 in = 1 ft (1 : 50) may be required in critical areas to adequately show structural and stratigraphic details. If trench geology is not complex, a notebook is suggested. The log book should be oriented so the sketch and description may be viewed together. The names of the field party, date, trench number, location, and other pertinent data should be recorded. If trench geology is complex and a larger scale is desired, cut sheets of grid paper attached to a map board may be used. These sheets are usually redrafted after trench logging is completed. If the backhoe trench is wet or wall material is sloughing down onto the map board, a blank grid sheet can be taped to the map board and overlain by sheets of mylar. Trench data sketched onto the mylar will not be smeared as easily, and the sheets can be erased without tearing. Prints of the sheets can be made for use in preliminary data transmittal or as check prints for field checking. Figure 6-3 shows a completed trench log.

Because the log sheets are separated easily, each sheet should be marked with the names of the field party, date, trench number, location, and other pertinent data.

164 MAPPING Figure 6-3.—Sample completed trench log.

165 FIELD MANUAL

Begin trench logging by recording the trench bearing. Begin at one end of the trench; place a surveyors chain or tape along the horizontal base line string. Vertical distance of the trench wall above and below the base line should be measured every 10 feet (3 m) or so and the trench outlines sketched. Sketches must be as accurate as possible to illustrate the field relationships of soil, geologic units, and structures. Use flagging to mark obscure contacts or other features for easier logging.

Intervals for the various geologic units and features are to be noted where the contacts intersect the baseline. Contacts above and below the baseline are located by two measurements—the vertical distance from the baseline and baseline distance—and sketched onto the log. Geologic units should be designated by name or symbol. Symbols to illustrate the attitude of contacts, bedding, fol-iation or cleavage, faults, shear zones, and joints should be drawn at the point where determined and also re-corded in the written description. Bedding or foliation should be depicted and noted wherever relationships are complex and differ from the recorded attitude (i.e., where surface creep, drag folds, or disturbed zones are exposed in the wall). Attitudes on units that may have been affected by surface creep or slumping should also be so noted.

Written descriptions of soil and rock units and structural zones should be restricted to the area below the sketch. Main headings for written descriptions are restricted to mappable geologic units. Description format is similar to that discussed for dozer trench mapping. After trench logging is completed, geologic units should be colored to complete the log and the trench field checked. Photo- graph the trench to complement the trench log or to record specific details within the trench. The limited space and poor lighting conditions in a backhoe trench

166 MAPPING many times make it difficult to obtain satisfactory photos. Generally, cameras capable of closeup focusing and loaded with fast film work best. Photographs taken while standing at the top of the trench generally are marginal because of poor lighting and perspective. The ends of the trench should be located by GPS or survey.

Construction Geologic Mapping

Geologic mapping during construction is to: (1) identify and delineate potential or actual construction-related needs and problems; (2) verify and better define geologic interpretations made during design studies, particularly for critical geologic features and properties; (3) determine if the geologic conditions are as interpreted during the design phase and ensure that the actual conditions revealed are as interpreted. If those conditions are not as interpreted, design modifications may be required; and (4) provide a record of as-built conditions in the event of litigation or operational problems.

To obtain meaningful data for mapping during construction, cooperation and coordination between the Contractor and the construction staff is required. The field geologist prioritizes mapping; and when the specific area is ready for mapping and approval, the staff and surveyors (if required) should accomplish the work as quickly as possible. Photographs should be taken using appropriate photographic equipment. All photographs should be captioned and dated.

Possible safety hazards that might occur during mapping should be evaluated, and appropriate precautions should be taken.

167 FIELD MANUAL

Large Excavation Mapping

General

Construction considerations prepared before construction begins should contain guidelines for the mapping of specific features. The scope and detail of mapping required at each portion of the site should be determined and suitable mapping scales determined. Suggested scales for detailed foundation mapping are 1 in = 5 ft to 1 in = 50 ft (1:50 to 1: 600), generalized foundation invert map scale 1 in = 20 ft to 1 in = 100 ft (1:20 to 1:1,000). Detailed, as-built foundation geology maps are used in final design modification, as a final record, and for use in possible future operation and maintenance problems. Mapping can be done on detailed topographic base maps generated from survey control, GPS, or plane table. Preferably, geology points are flagged and surveyed by a survey crew. Terrestrial photography, photogrammetry, and GPS can also be used to supplement mapping. Detailed photo-graphy of the entire foundation is important for inclusion in the final construction geology report and as a part of the construction record. Use standard nomenclature and symbols both on maps and photographs, but be consistent with those used in earlier studies and specifications. Use a systematic method of collecting mapping data, then compile these data into a useful and accurate geologic map.

Detailed, as-built geology maps of cutslopes are required in delineating and solving major slope stability problems and in selecting general slope support systems. Recom- mended scale selection for detailed cut-slope geology maps are 1 inch = 10 feet to 1 inch = 50 feet (1:100 to 1:600), generalized cutslope geology maps use a scale 1 inch = 20 feet to 1 inch = 100 feet (1:200 to 1:1,000). Generally, maps are on detailed topographic base maps

168 MAPPING generated from survey control. Geologic points may be flagged for survey by survey crews. Detailed photographs of the slopes are important.

Steep Slope Mapping

General

Define the purpose and goal for mapping and research the stratigraphy and structural geology prior to starting. Select scaling and safety equipment for specific areas.

Preparation

Special training is required for scaling. While scaling and mapping, a pocket tape recorder and camera are useful for documentation.

Suggested Equipment

Use the appropriate scaling equipment and systems. Standard mapping equipment needs to be reviewed and modified for scaling operations.

Documentation

Establish ground control for mapping including terrestrial photo mapping. Data collected while scaling should be based on the purpose of mapping and detail required. Establish general map controls such as grid controls.

Special Considerations

Select specific portions of an exposure to be mapped.

169 FIELD MANUAL

Canal and Pipeline Mapping

General

In reconnaissance investigations, surface geologic mapping is used to determine the most feasible alignment, which may be representative of the geologic conditions to be encountered, the lining requirements, and construction materials available. Design data investigations along canal alignments must be detailed enough to determine the final alignment and all associated requirements for specifications and construction.

Preconstruction investigations for canals and pipelines are less detailed because of the long distances involved. Consequently, geologic construction mapping is necessary to verify preconstruction assumptions, document changes from original assumptions, and provide data for potential design changes or claim analyses.

Preparation

General field mapping requirements.

Documentation

Pertinent geologic data that should be shown on the base maps include: soil and geologic units, all natural and manmade exposures, geologic structures, springs and seepage, surface channels, and potentially unstable areas. Where appropriate, photographs with overlays or detailed site-specific drawings should be used to show surface conditions in relation to the canal prism or associated canal structures. Base maps should be plan strip topo-graphy or orthophotography with scales of 1 in = 20 ft (1:400) to 1 in = 100 ft (1:2,000) with associated topographic profiles.

170 MAPPING

Underground Geologic Mapping

General

This is a general guide for recording tunnel geology and describes mapping requirements and procedures. This guide and the field geologist's judgement and experience should permit development of geologic data which adequately document geologic factors that are significant to design, construction, and stability of tunnels and shafts. Some of the necessary data may be obtained from other project personnel such as engineers, surveyors, and inspectors. The following items are of primary impor-tance during the construction or exploration for a wide range of tunnel and shaft types, excavation problems, geologic conditions, and contract administration require-ments. The data recorded and the emphasis given each item should be determined for each specific tunnel. (Note: references to tunnels apply equally to shafts)

Three principal objectives are to:

• Acquire progressive, timely mapping of all significant geologic features as exposed during the advance of the tunnel or shaft. These initial features are important for subsequent identification of changes which may take place, such as water flow, rock slaking, or support behavior, as the heading progresses and before lining or other completion measures are undertaken.

• Facilitate periodic transmittal of these data in preliminary form to the office so that conditions being encountered and their effect on the excavation can be used in immediate evaluation of current construction activities and anticipation of future excavation conditions.

171 FIELD MANUAL

• Assure that a systematic, clear, record of geologic conditions is compiled for design reviews and use by the project and contractor. These data should be included in the final construction geology report. These records may prove invaluable during subsequent operation and maintenance and in the planning and design of future tunnels and shafts. If geologically related problems occur, these data will be essential in evaluating the conditions.

Accuracy is essential, and consistency of data shown on tunnel maps is vital. If the maps are used in contract claim negotiations or in litigation, even a few errors or inconsistencies may compromise the entire map.

The preparation of an adequate tunnel or shaft geologic map requires a careful study of geologic structure, lithology, mineralogy, groundwater, and their effects on rock quality and behavior, tunneling methods, stability, and support. The preparation of a tunnel or shaft geologic map is a geologic mapping process; geologic data should be recorded directly on the map while making the observations and not described in notes for subsequent drafting in the office. An appropriately scaled tunnel or shaft mapping form, prepared prior to starting the mapping, is essential to systematic data collection. One- matte-sided mylar tunnel forms should be used in wet excavations and are recommended as a standard for all tunnel and shaft mapping. Figures 6-4 and 6-5 are examples of field mapping forms. The use of mylars in all tunnels facili-tates copying and immediate use. The extent or amount of mapping detail for a specific tunnel or shaft will depend on the driving method, geologic conditions, and design considerations. For example, tunnel face (head-ing) maps can be obtained under most conditions when conventional excavation (drill/blast) methods are used but are difficult to obtain in tunnels excavated by tunnel

172 MAPPING Figure 6-4.—Tunnel mapping form with key alphanumeric descriptors and data.

173 FIELD MANUAL Figure 6-5.—Tunnel mapping form with blocks for title and geologic data.

174 MAPPING boring machine (TBM). TBM excavated tunnels may be more difficult to map than conventionally excavated tunnels, depending on the level of detail required, machine configuration, and the support method. However, the key rock characteristics relative to tunnel stability must be mapped. In tunnels where shotcrete or precast segments are used for support, detailed mapping may be impossible; this does not cancel the requirement for mapping and recording of important data on the geologic conditions. The geologist must obtain required data with the available resources and under the specific conditions. These guidelines apply to all tunnel or shaft excavations regardless of whether the mapping is performed during project planning, design data acquisition, or construction.

Safety

Underground construction activities are inherently more hazardous than surface construction. Before working underground, the specific safety requirements for the particular tunnel should be determined. Self-rescuer training commonly is required, and the safety requirements as described in the Reclamation Safety and Health Standards [5] should be reviewed. Additional training or additional requirements may exist under special circumstances such as gassy conditions. Before beginning work, a familiarization tour of the work site (including the underground workings) should be made with project personnel, such as an inspector, intimately familiar with the job. Also, assume that every piece of equipment and worker is out to get you; you should always maintain an awareness of what the workers and equipment are doing around you.

175 FIELD MANUAL

General Preparation

Tunnel construction is essentially a linear activity. All access, equipment haulage, and work activities take place in a line. The mapping process should be planned such that a minimum number of trips to the heading are required and a minimum amount of time is spent at the heading. Geologic mapping can usually be integrated into an optimum part of the construction cycle. Unnecessarily spending time at the heading is not only inefficient but can interfere with the construction process by adding to an already congested situation.

Available geologic data should be reviewed and established nomenclature used as appropriate. Geologic features described in the available literature should be specifically investigated while mapping, especially those described in specifications documents. Forms should be designed to expedite the work as much as possible (figures 6-4 and 6-5), required mapping equipment must be available, and the construction cycle should be analyzed to determine the best and safest time to map. Tunnel map sheets should be a convenient size such as 8.5 x 11 inches (A4) or 11 x 18 inches (A3). This permits 100 feet (30 m) of tunnel on a scale of 1 inch = 10 feet (1:200) with sufficient space for concise explanations and a title block. The geology should be mapped in the tunnel directly on the matt side of mylar film. This map, developed in the tunnel, can be edited and copied for quick transmittal to the office. The value of current data cannot be overemphasized. Except under very special conditions, the recording of geologic data in a notebook without mapping for subsequent preparation of a graphic tunnel map is unacceptable. Without a graphic represen-tation during data acquisition, the interrelationships of geologic data cannot be properly evaluated, and data are missed or errors are introduced. Some items listed above will not apply to every tunnel,

176 MAPPING and some items may be shown more appropriately in a summary tunnel map (figure 6-6). This map presents a summary of essential engineering and geologic relationships. Plotting engi-neering and geologic data as a time line permits direct comparison of geologic conditions, supports installed, overbreak, excavation rate, etc., for correlation. Sum-mary sheet scales may range from 1 inch = 10 to 100 feet (1:100 to 1:1,000) depending on amount of data and complexity of the geology. Ongoing maintenance of these data avoids excessive compilation time after construction is completed. A summary tunnel map is required on tunnels for construction records.

When several individuals are mapping and/or contract requirements hinge on geologic data, e.g., payment based on ground classification, a project or specific mapping manual may be necessary. A manual provides an easy reference for data requirements and format, reduces inconsistency between geologists, and sets a specific mapping standard.

Excavation Configuration

Conventionally excavated tunnels are usually a modified horseshoe shape. Departures from this shape are usually for a special configuration or when ground conditions dictate a circular shape for optimizing support effectiveness. Machine-excavated tunnels are round if bored unless a road-header type machine is used. Road-header excavated tunnels are usually horseshoe shaped for construction convenience. Shafts are almost always round for optimizing support effectiveness and because most are drilled or bored either from the surface or raise-bored from the bottom. Exploratory shafts may be sunk conven-tionally if shallow. Whatever the shape, the map format should be designed to minimize the amount of projection

177 FIELD MANUAL and interpretation required. Whenever possible, the full periphery mapping method should be employed.

Data Requirements

The relationship of the geology to the engineering aspects of the tunnel or shaft is of primary importance. If geologi-cally related problems occur, the recorded data will be valuable to the geologist and engineer in evaluating the conditions, the cause(s), and in devising remedial measures. In most cases, geologic discontinuities, such as joints, faults, bedding, etc., are the most important factors affecting excavation stability; and these data are of primary importance. Also, the rock strength is important in high cover tunnels, and water is important in many situations. The following data are most important:

1. Rock Classification.— Lithology and related features such as foliation, schistosity, and flow structure. Rock descriptions should be concise; use standard descriptors.

• Formation boundaries — describe bedding thick-ness and attitude, areas of soft, or unstable rock. Give dip and strike unless otherwise noted. Dips of planes (not necessarily true dip) into tunnel are desirable in cases where they may influence excavation stability.

• Physical properties of the rock — determine hardness by comparison with common or familiar materials, brittleness, reaction to pick or knife, and color.

• Alteration — describe degree, type, extent, and effects on construction. Differentiate between weathering, other alteration, and cementation.

178 MAPPING Figure 6-6.—As-built summary geology tunnel map.

179 FIELD MANUAL

180 MAPPING

• Features — describe the size, form (tabular, irregular), contacts (sharp, gradational, sheared), and mineralization, if any.

2. Conditions Which Affect Stability of the Rock.—

• Joints or joint systems — describe spacing, conti-nuity, length, whether open or tight, slickensides, planarity, waviness, cementation, fillings, dip and strike, and water.

• Shear zones — describe severity of shearing and physical condition of rock in and adjacent to the zone, whether material is crushed or composed of breccia, gouge, or mylonite; describe gouge thickness, physi-cal properties, mineralogy and alteration; dip and strike, and water.

• Faults — give dimensions of fault breccia and/or gouge and adjacent disturbed or fractured zones, amount of displacement, if determinable, and the fault's effect on stability of rock.

3. Effects of Tunneling on Rock.— Comment on: the condition of rock after excavation, rate of air slaking or other deterioration of rock where appropriate, rock bursts, fallouts, development of squeezing or heavy ground, and time interval between first exposure and the beginning of these effects. Include the evidence used in evaluation, and the reaction of different rock types to conventional blasting or mechanical excavation method.

Periodic re-examination of the tunnel and comparison of originally mapped conditions with those existing later is recommended.

181 FIELD MANUAL

4. Tunnel Excavation Methods.—

Blast pattern — Give example of typical blast round pattern, type of explosive and quantity per yard (powder factor) of rock blasted, size of rock fragments, ease or difficulty of rock breakage and condition of the walls of the tunnel such as whether half-rounds (half of peripheral shot holes) are visible. Some of this infor-mation should be obtainable from the inspectors.

Overbreak — Overbreak and fallout should be measured as a peripheral average from "B" line (excavation pay line), where practical, and maximum at specific stations. Plot average overbreak on the section along tunnel alignment. Relate this to geologic conditions and construction methods, particularly blasting procedure.

Ground behavior — Blockiness, caving, swelling, and/ or squeezing should be described with evidence and effects.

Supports — Give size and spacing of ribs, size and types of struts, and behavior of supports in reaches of bad ground. Where supports show distress or have failed, give reason for failure, time after installation for load to develop, the remedial measures undertaken, and size and spacing of replaced supports or jump sets. If a ground classification system is being used, relate to geologic conditions and support used. Incorporate some reference to the actual need for support versus that installed. Use the proper terminology when describing supports. A good reference for tunnel supports (and conventional tunneling) is Rock Tunneling with Steel Supports [6].

182 MAPPING

Indicate where special supports such as mats, spiling, or breast boards are required and geologic reason. Where rock bolts (or split sets) are used, give spacing, size, length, type, anchor type, torque loading values, and quantities used. Note retorquing, if performed. Locations of rock bolts should be plotted on the geologic maps.

Machine excavation — In machine-type excavations (in addition to appropriate items above) give: rate of advance, pressures used, and description of cuttings or rock breakage. Describe the effect of cutters and grippers on rock walls, or other geologically related problems such as abrasive rock wearing cutters.

5. Hydrogeology .—Water flows should be mapped and quantities estimated. Daily heading and portal measurements should be recorded. The location of all significant flows should be plotted on the tunnel map and changes in rate or duration of flow recorded. If the water is highly mineralized, obtain chemical analyses of water for pos-sible effect on concrete or steel linings or contamination of water being discharged or to be conveyed by the tunnel.

6. Gas.—The following should be done:

• Determine type, quantity, occurrence, geologic asso- ciations, and points of discharge should be mapped.

• Samples should be taken. This is usually done by safety personnel.

• Record actions taken.

7. Instrumentation, Special Tests, Grout, and Feeler Holes.—Locations and logs (if available) should be shown on the tunnel maps.

183 FIELD MANUAL

8. Miscellaneous Excavations.—Geologic maps and sections of related excavations such as surge tanks, gate shafts, inlet and outlet portal open cuts are necessary.

Tunnel maps should include brief comments on the geologic conditions being encountered and their possible effects.

9. Sampling.—A systematic sampling program of the tunnel rock is essential to adequately record tunnel geology. These samples may be 2 in x 3 in (5 cm x 8 cm) or larger and should be secured in a labeled sample bag showing station, date, and wall position with an appropriate description. Rock that easily deteriorates should be protected with wax or plastic. Sampling at irregular (and locally close) intervals may be required to ensure that all important rock, geologic, and physical conditions are adequately represented. A representative stratigraphic series of samples should be collected. The judgement of the geologist who is familiar with the geology is the best guide in determining the most appropriate sampling interval.

Thorough photographic coverage provides a visual record of construction and geologic conditions. Postconstruction evaluations use construction photographs extensively and are an important part of the construction record. A camera should be part of the mapping equipment and routinely used. Photographs that show typical, as well as atypical, geologic conditions should be taken routinely. Identify photographs of significant features by number on the appropriate map sheet.

184 MAPPING

Underground Geologic Mapping Methods

Full Periphery Mapping

The full periphery (or developed surface) mapping method is widely used in engineering practice and involves creating a map of the surface of the underground excavation regardless of shape. The method produces a map which is virtually free from distortion and interpretation present in other methods where geologic features are projected onto a plane or section. The method has been used successfully in various types and shapes of excavations (Hatheway, 1982 [7]; U.S. Army Corps of Engineers, 1970 [8]; Proctor, 1971 [9]) and on numerous Reclamation projects.

The method uses a developed surface created by "unrolling" or "flattening out" the circumference of the tunnel or shaft to form a "plan" of the entire wall surface (figure 6-7). The geologic features are plotted on this plan. The method is especially effective in that geologic features of all types can be plotted directly onto the map regardless of orientation or location with no projection required. The method is useful for plotting curving or irregular discontinuities which are difficult to project to a flat plane as in other methods.

Procedure.—Full periphery mapping generally requires the assembly of field sheets prior to the actual start of mapping. This is done for drifts and tunnels by first drawing in the crown centerline of the plan (figure 6-7). The bases of the walls or the invert are then plotted at a circumferential distance from the crown centerline on the plan. For instance, if the tunnel is 10 feet (3.048 m) in excavated diameter, the invert centerline will be plotted 15.71 feet (4.79 m) (in scale) from the crown centerline. Plot springline at the appropriate circumferential

185 186 MAPPING distance from the crown centerline. This process is done for both walls and produces a plan which represents the actual wall surface of the excavation. The map layout is designed to be viewed from above the tunnel. Shaft data are plotted as viewed from inside the excavation. The tunnel invert is not mapped because rock surfaces usually are covered with muck or invert segments. Plot scales on either side of the plan to provide distance control while mapping. A longitudinal section view of the excavation may be added alongside the plan to provide a space to record types and locations of support, overbreak, etc. Plot geologic features on the field sheets (figures 6-4 and 6-5) by noting where the features intercept known lines, such as where a particular joint intercepts the crown centerline, the spring line on both walls, or the base of either wall. The trace of the joint is sketched to scale between these known points. The strike and dip of the discontinuity are recorded directly on the field sheet adjacent to the trace. The locations of samples, photographs, water seeps, and flows are plotted on the map (figure 6-8).

The Brunton compass is used to measure dips on the various discontinuities; but due to the presence of support steel, rock bolts, utilities, and any natural magnetism of the wall rock, a Brunton may not be reliable for deter-mining the strike of the feature. In this case, the strike may be determined by one of several methods. The first method is to align the map parallel to the tunnel where the feature is exposed in the wall and plot the strike by eye on the sheet parallel to the strike of the feature in the wall. The second method is to observe the strike of the feature on the map where it intersects the crown centerline. At this point, the crown is essentially hori-zontal, and the trace of the feature at this point represents the strike. The third method is slightly more complex but is the most accurate method of the three.

187 FIELD MANUAL Figure 6-8.—Full periphery geologic map example.

188 MAPPING

This method requires locating where the feature intersects springline on each wall of the full periphery map. These points are projected to the corrected springline. A line drawn between the projected points represents the strike of the feature. Note that these methods assume that the tunnel or drift is relatively horizontal. In some cases, if the excavation is inclined, the apparent strike can be corrected for the amount of inclination. A fourth method is to use a gyroscopic compass.

Other Applications.—With minor variations in the method described above, the full periphery method can be used equally well in vertical or inclined shafts, horseshoe shaped drifts and tunnels, and other regular shaped excavations.

Advantages.—The full periphery method:

• Involves plotting the actual traces of geologic features as they are exposed in the tunnel. This eliminates the distortion and interpretation introduced by other methods where the traces are projected back to a plane tangent to the tunnel.

• Allows the geologist to observe and plot irregularities in geologic features and make accurate three- dimensional interpretations of the features.

• Allows rapid and easy plotting of the locations of samples and photographs.

• Allows easy and rapid recording of the locations of rock bolts and other types of rock reinforcement.

189 FIELD MANUAL

Disadvantages.—

• Since the surface of the excavation is generally a curved surface, the trace of planar features, such as fractures, faults, and bedding planes, produce curves when plotted on the map.

• The full periphery method requires that the points at which features intersect springline be projected to the original tunnel diameter in order to compute the true strike of the discontinuity (figure 6-7).

Plan and Section

The plan and section method has been used in engineering practice but has generally been replaced by the full periphery mapping method. The plan and section method is still used where data interpretation is facilitated by the flat plan and sections. The method creates vertical sections commonly coincident with a wall or walls of a tunnel or shaft, through centerline, or is tangent to a curving surface commonly at springline or an edge of a shaft (figure 6-9). Geologic features are projected to the sections and plotted as they are mapped.

The method produces a map which is a combination of direct trace and projection or a projection of the walls except where the map is tangent to the excavation (figure 6-10). The plan through tunnel springline and centerline or shaft centerline is a projection of the geologic features exposed in the excavation.

Procedure.—The plan and section method generally requires the assembly of field sheets prior to the actual start of mapping. This is done for drifts and tunnels by drawing vertical sections the height of the excavation.

190 MAPPING

Figure 6-9.—Map layout of a tunnel for geologic mapping.

191 FIELD MANUAL

Figure 6-10.—Relationship of planar feature trace to map projections.

192 MAPPING

The bases of the walls or the invert form the base of the section with springline plotted and the crown forming the top of the section. For instance, if the tunnel is 20 feet (6 m) high, the crown will be 20 feet (6 m) from the invert. Springline is plotted the appropriate vertical distance from the crown or invert (figure 6-10). This process may be done for one or both walls, producing one or two vertical representations of the wall/arch exposure. Shafts are similar, but the section corresponds to the wall of a rectangular shaft or is tangent to the shaft wall at a point, and the map is a projection of the shaft of one diameter.

A section through tunnel springlines produces a plan projection of the arch except at the plan intersection with the wall at springline. The corresponding section through a shaft produces a vertical projection of the wall(s) through a shaft or along a diameter. The map represents the actual wall surface of the excavation only where the projection intersects the wall.

Scales are added on either side of the sections to provide distance control while plotting. An additional longitudinal section view of the excavation may be added to provide a space to record types and locations of support or overbreak. Geologic features are then plotted on the field sheets by noting where the features intercept known lines, such as where a particular joint intercepts the crown centerline, the spring line on both walls, or the base of either wall. The trace of the joint is then projected to the section between these known points. The attitudes of features are recorded on the field sheet adjacent to the trace. The location of samples, photographs, water seeps, and flows can be recorded by finding their location on the wall and projecting that location to the map.

193 FIELD MANUAL

Advantages.—The plan and section method:

• Produces two-dimensional sections and plans that do not require conversion. The sections and plans can be integrated directly with other plans and sections. The sections and plans are easily understood by individuals not familiar with full periphery mapping or individuals who have difficulty visualizing structural features in three-dimensions.

• Permits direct determination of strikes by springline intersections.

Disadvantages.—Since the surface of the excavation is generally a curved surface, the trace of planar features, such as fractures, faults, and bedding planes, are projections to a plane. The only objective data is where the map is coincident or tangent to the excavation surface.

The plan and section method requires:

• Plotting and observing geologic features and making accurate three-dimensional interpretations of the features by projecting locations to a plane.

• Plotting locations of samples and photographs by projection.

• Recording locations of rock bolts and other types of rock reinforcement by projection.

• Plotting is done after data collection and re- examination of the site is difficult or not practical.

194 MAPPING

Face Maps

The geology exposed in an excavation face is plotted directly on a map. The purpose of the face map is to provide a quick appraisal of rock conditions and provide data for special detailed studies. The combination of wall and face maps will usually give an adequate and clear permanent record of any complex tunnel geology. Natural scales such as 1 inch = 1 to 2 feet (1:50) are the most satisfactory. All significant geologic features which may affect the stability of the tunnel must be mapped.

Photogrammetric Mapping

Photogrammetric geologic mapping is a specialized method consisting of the interpretation of close-range stereophotography of excavation walls. Photogrammetric control is provided by surveyed targets or by a gnomon or scale in the photographs. The stereophotos are interpreted using photogrammetric software or an analytical plotter. Feature location accuracy can vary from a few inches (cm) to one-eighth of an inch (3mm) depending on equipment and survey control accuracy. The photogrammetric mapping can be combined with detail line surveys for small-scale data collection and control.

Exploration Mapping Method Selection

The geologic mapping format for exploratory drifts and shafts should be determined by data uses. Direct integra-tion of excavation maps into composite maps of a dam foundation is much easier if undistorted sections are available. The maps can be treated in the same manner as drill hole logs. The disadvantages of plan and section mapping may be offset by the advantages of easy inter-pretation and integration into other data bases.

195 FIELD MANUAL

Construction Mapping.—Full periphery geologic mapping should be used for routine construction activities. The advantages of increased speed and accuracy in production mapping and the reduction of interpretation offsets the disadvantages.

Summary

This guide to tunnel geologic mapping during construction has been developed for general use and serves to standardize procedures and data collection. Items of primary significance are included, but some are not adaptable to all tunnels or methods of tunnel excavation. The judgment of an experienced geologist is the best guide to the specific items and amount of detail required to provide pertinent, informative data. To ensure reliable and useful tunnel geologic studies, all important geology and related engineering construction data which may be significant to tunnel construction as well as in the planning, designing, and constructing of future tunnels should be considered for inclusion in the tunnel map and report.

Photogeologic Mapping

General

Aerial photographs generally are used in reconnaissance geologic mapping, geologic field mapping, and in generation of photo-interpretive geologic maps. Various scales of airphotos are valuable for regional and site studies, for both detection and mapping of a wide variety of geologic features important to engineering geology.

196 MAPPING

Types of Aerial Photographs

Panchromatic (Black and White).—Panchromatic photography records images essentially across the entire visible spectrum, and with proper film and filters also can record into the near-infrared. In aerial photography, blue is generally filtered out to reduce the effects of atmospheric haze.

Natural Color.—Images are recorded in the natural colors seen by the human eye in the visible portion of the spectrum.

False-Color Infrared.—Images are recorded using part of the visible spectrum and part of the near-infrared, but the colors in the resultant photographs are not natural (false-color). Infrared film is commonly used and is less affected by haze than other types. False-color photography is not the same as thermal-infrared imaging which uses the thermal part of the infrared spectrum.

Multispectral.—Photographs acquired by multiple cameras simultaneously recording different portions of the spectrum can aid interpretation.

Photogrammetry and Equipment

Use stereoscopes to view aerial photographs for maximum utility and ease of interpretation. Pocket stereoscopes are useful in the field or office. Large mirror stereoscopes are useful for viewing large quantities of photos or photos in rolls. Know the photo scale, resolution, and exaggeration. Be aware of the types of distortions inherent in airphotos.

197 FIELD MANUAL

Compilation of Photogeologic Map Data

Mapping should be done on transparent one-side-matte mylar overlays and not on the photographs. Any lines, even if erased, can confuse later interpretations using the photos. The mapping is then transferred to base maps minimizing the effects of distortions in photos due to the camera optics. Orthophoto quadrangles can help reduce this distortion.

Analysis of Aerial Photographs

General Interpretive Factors

Analysis of aerial photographs involves interpreting indirect data. In most cases, several factors are used to interpret geologic conditions. Interpretive factors usually used in the analysis of aerial photographs are:

Sun Angle.—High or low illumination angles may be desired, depending on the nature of the features to be detected.

Photographic Tone.—Variations in color, intensity, shade and shadows.

Texture.—Frequency of change in tone, evident as roughness, smoothness.

Color.—True and false-color imagery may be easier to interpret than panchromatic photographs, depending on features being observed. For some applications (e.g., low sun angle photography), panchromatic photography is better.

198 MAPPING

Geomorphic Shape and Pattern.—Geologic conditions can be identified by mapping various types of geomorphic features related to drainage, bedding, and structure.

Vegetation.—Some types of vegetation and vegetal patterns can assist in interpreting geology. Vegetation may indicate depth of soil, type of soil, available moisture, and type of bedrock.

Photoanalysis for Reconnaissance Geologic Mapping

Photo-reconnaissance geologic mapping can be done to produce a preliminary geologic map of the study area prior to going into the field to check and verify the interpreted geologic data or to produce a finished geologic map with little or no field checking. These maps are called photo-reconnaissance geologic maps and photo-interpretive geologic maps, respectively.

Photo-Reconnaissance Geologic Mapping

Photo-analysis prior to field work allows the mapper to form a preliminary concept of the geology of the study area and to select areas for detailed examination. Prior photo-analysis is critical if available field time is limited, especially when a large area is involved, as in regional studies, reservoir area mapping, and pipeline or canal alignment studies.

Photo-Interpretive Geologic Mapping

Geologic maps produced solely from aerial photographs with little or no field checking are useful when time, funds, or access are limited or when adverse weather prevents a more detailed field mapping program. The

199 FIELD MANUAL limitations of this form of geologic map are dependent on outcrop density and degree of exposure, amount of vegetative cover, contrast of the geologic units, and the skills of the photogeologic mapper. This type of map is useful for preliminary or reconnaissance level evaluations but should never be used for design level work.

Photoanalysis During Geologic Field Mapping

The location and verification of geologic features in the field can usually be expedited by using aerial photographs. Photographs often reveal landforms that are difficult to see or interpret from the ground, such as land-slides. Photographs can be used to clarify and speed up field mapping by allowing a comprehensive view of the study site and the relationships of the various geologic features exposed. Alternately viewing photos and exam-ining outcrops can greatly facilitate mapping.

Availability of Imagery

Aerial photography is available, commonly in a variety of scales and types, for essentially the entire conterminous United States. The principal repositories of publicly owned airphotos is the EROS Data Center, operated by the U.S. Geological Survey and the Agricultural Stabilization and Conservation Service (ASCS) of the U.S. Department of Agriculture. The USGS has several regional offices of the Earth Science Information Center (ESIC). The ESIC operates the Aerial Photography Summary Record System (APSRS), which is a standard reference data base for users of aerial photographs. The APSRS lists aerial photography available from a large number of government agencies and commercial companies. The lists are comprehensive and categorized by state and by latitude and longitude. APSRS data are

200 MAPPING available on request from ESIC. ESIC also provides information about cartographic products other than imagery.

Some important addresses and telephone numbers are: USDA-ASCS (801) 524-5856 Aerial Photography Field Office Customer Services 2222 West 2300 South P.O. Box 30010 Salt Lake City, UT 84130-0010 USGS (605) 594-6151 EROS Data Center Sioux Falls, SD 57198 USGS (303) 202-4200 ESIC Denver Federal Center Denver, CO 80225

USGS (650) 329-4309 ESIC 345 Middlefield Road Menlo Park, CA 94025

Aerial Photography Flight Planning

If air photos are not available at the right scale, or of the right type for an area, specific flights can be made. Successful airphoto mission planning requires consideration of several factors, including film type, scale, time of day (sun-angle), time of year, and the size of the area to be covered. Mission planning should not be done by someone unfamiliar with the process without assistance. Specifications should be written to ensure that the result-ing photographs will be appropriate for the

201 FIELD MANUAL intended purpose. Information critical to mission planning is available from the references listed below.

Time and Cost Estimating

The cost of data acquisition is relatively easy to estimate. The cost of interpretation is much harder to estimate, being a function of the time required, which is related to the size and complexity of the study area and the skill of the interpreter. The cost of a single drill hole will pay for a lot of aerial photography and interpretation.

References

A classic text on the use of airphotos in geology was reprinted in 1985 and should be readily available. Some of the equipment described is obsolete and it is essentially limited to discussion of panchromatic photography. The publication contains numerous stereopairs with geologic descriptions and is one of the best works on airphoto interpretation for geologists:

Ray, R.G., Aerial photographs in geologic interpretation and mapping, USGS Professional Paper 373, 230 p., 1960.

Other useful references are:

Lattman, L.H., and Ray, R.G., Aerial photographs in field geology, Holt, Rinehart and Winston, New York, NY 221 p., 1965.

Miller, V.C., Photogeology, McGraw-Hill, New York, NY, 248 p., 1961.

202 MAPPING

A reference containing no general discussion of principles, but with excellent examples of stereopairs of geologic features, associated topographic maps, and geologic annotations is:

Scovel, J.L., et al., Atlas of Landforms, Wiley & Sons, New York, NY, 164 p., 1965.

A broad and lengthy reference covering remote sensing in general, including much information about aerial photography of all types, is:

Colwell, R.N., editor, Manual of remote sensing, 2nd edition, American Society of Photogrammetry, Falls Church, VA, 272 p., 1983.

BIBLIOGRAPHY

[1] U.S. Geological Survey, Map Projections - A Working Manual, U.S. Geological Survey Professional Paper 1395, 1987.

[2 ] Jackson, Julia A., editor, The Glossary of Geology, 4th edition, American Geologic Institute, Alexandria, VA, 1997.

[3] Lahee, Frederic H., Field Geology, 6th edition, McGraw-Hill, Inc., New York, NY, 1961.

[4] Compton, Robert R., Geology in the Field, John Wiley and Sons, New York, NY, 1985.

[5] Bureau of Reclamation, Division of Safety, Safety and Health Standards, Denver Office, Denver, CO.

203 FIELD MANUAL

[6] Proctor, M.E., and White, T.L., Rock Tunneling with Steel Supports, Commercial Shearing, Inc., Youngs- town, OH, 1977.

[7] Hatheway, A.W., “Trench, Shaft, and Tunnel Map- ping,” Bulletin of the Association of Engineering Geologists, v. XIX, 1982.

[8] U.S. Army Corps of Engineers, “Engineering and Design, Geologic Mapping of Tunnels and Shafts by the Full Periphery Method,” Engineer Technical Letter No. 1110-1-37, Washington, DC, 1970.

[9] Proctor, R.J., “Mapping Geological Conditions in Tunnels,” Bulletin of the Association of Engineering Geologists, v. VIII, 1971.

204 Chapter 7

DISCONTINUITY SURVEYS

General

Physical properties of discontinuities generally control the engineering characteristics of a rock mass. Accurate and thorough description of discontinuities is an integral part of geological mapping conducted for design and construction of civil structures. It is improbable that any survey will provide complete information on all the discontinuities at a site. However, properly conducted surveys will furnish data with a high probability of accurately representing the site discontinuities. This chapter discusses discontinuity recording methodology. These recording methods can be applied to outcrops, drill holes, open excavations, and the perimeters of underground openings. The evaluation of discontinuity data is well described in the literature. For example, plotting discontinuity data on stereograms, contouring to determine prominent orientations, and subsequent wedge analyses are described in Rock Slope Engineering [1] and Methods of Geological Engineering in Discontinuous Rock and Introduction to Rock Mechanics [2,3]. “Chapter 5, Terminology and Descriptions for Discontinuities,” lists data that are typically recorded in discontinuity surveys.

It is extremely important that the actual discontinuity descriptors and measurement units be selected to support the anticipated rock mass classification system(s). Acquiring incomplete or excessive data may limit data usefulness in subsequent analyses, and result in excessive costs due to repeating surveys or from collecting more data than needed. FIELD MANUAL

Empirical Methods for Rock Mass Classification

A number of empirical methods have been developed to predict the stability of rock slopes and underground openings in rock and to determine the support requirements of such features. A method for estimating steel-arch support requirements in tunnels was one of the first [4], and various methods which address open-cut excavations and existing rock slopes have been used since. The Geomechanical Classification (Rock Mass Rating [RMR]) [5,6] and the Norwegian Geotechnical Institute (NGI) (Q-system Classification [Q]) [7] are commonly used. Both of these methods incorporate Rock Quality Designation (RQD) [8]. Since both the RMR and Q-system are based on actual case histories, both systems can be somewhat dynamic, and refinements based on new data are widely suggested. Additional information on RQD, RMR, and the Q-system is provided in chapter 2.

Other predictive methods include the Rock Structure Rating (RSR) [9] and the Unified Rock Classification System (URCS) [10]. “Keyblock” analysis [11,12] is a means of determining the most critical or “key” blocks of rock formed by an excavation in jointed, competent rock. An excellent single source of information on the various classification systems is in American Society for Testing Materials Special Technical Publication 984, Rock Classification Systems for Engineering Purposes.

Data Collection

Discontinuity data can be collected using areal or detail line survey methods. The areal method, which consists of the spot recording of discontinuities in outcrops within an area of interest, is of limited use in geotechnical analyses. Areal surveys should be applied only for preliminary scoping of a site or in cases where the lateral

206 DISCONTINUITY SURVEYS extent of exposed rock is inadequate to perform detail line surveys. The detail line survey (DLS) method (DLS or line mapping) provides spacial control necessary to accurately portray and analyze site discontinuities. DLS mapping was originally a method of mapping road cuts and open pit excavations. DLS use has been expanded both in scope and types of exposures mapped. Each geologic feature that intercepts a usually linear traverse is recorded. The traverse can be a 100-ft (30 m) tape placed across an outcrop, the wall of a tunnel, a shaft wall at a fixed elevation, or an oriented drill core. In all cases, the alignment of the traverse and the location of both ends of the traverse should be determined. The mapper moves along the line and records everything, as noted in chapter 5, or as needed to support analyses. Feature locations are projected along strike to the tape, and the distance is recorded. Regardless of the survey method, the mapper must obtain a statistically significant number of observations. A minimum of 60 discontinuity measurements per rock type is suggested for confidence in subsequent analyses [14].

The orientation of a discontinuity can be recorded either as a strike azimuth and dip magnitude, preferably using the right-hand rule, or as a dip azimuth and magnitude (eliminating the need for dip direction and alpha characters required by the quadrant system). According to the right-hand rule, the strike azimuth is always to the left of the dip direction. When the thumb of the right hand is pointed in the strike direction, the fingers point in the dip direction. The selected recording method should be used consistently throughout the survey.

Data acquired in a single straight-line survey are inherently biased. The more nearly the strike of a discontinuity parallels the path of a line survey, the less frequently discontinuities with that strike will be

207 FIELD MANUAL recorded in the survey. This is called line bias. The number of intersecting discontinuities is proportional to the sine of the angle of intersection. In order to compensate for line bias, a sufficient number of line surveys at a sufficient variety of orientations should be conducted to ensure that discontinuities of any orientation are intersected by at least one survey at an angle of at least 30 degrees. Common practice is to perform two surveys at nearly right angles or three surveys at radial angles of 120 degrees. True discontinuity (set) spacing and trace lengths can be obtained by correcting the bias produced by line surveys [15, 16].

All discontinuities should be recorded regardless of subtlety, continuity, or other property until determined otherwise. Data collection should be as systematic as practicable, and accessible or easily measurable discontinuities should not be preferentially measured. Con- sistency and completeness of descriptions are also important. Consistency and completeness are best maintained if all measurements are taken by the same mapper and data are recorded on a form that prompts the mapper for the necessary descriptors. A form minimizes the probability of descriptor omission and facilitates plotting on an equal area projection, commonly the Schmidt net (figure 7-1), or entering data for subsequent analysis. Computer programs are available that plot discontinuities in a variety of projections and perform a variety of analyses. Whether the plot format is the equal area projection (Schmidt net) or equal angle projection (Wulff net), evaluation of the plotted data requires an understanding of the method of data collection, form of presentation, and any data bias corrections. References 2 and 3 in the bibliography are good sources of data analysis background information.

208 DISCONTINUITY SURVEYS

Figure 7-1.—Equatorial equal area net (Schmidt net).

Different rock types in the same structural terrain can have different discontinuity properties and patterns, and the host rock for each discontinuity should be recorded. This could be an important factor for understanding subsequent evaluations of tunneling conditions, rock slopes, or the inplace stress field in underground openings.

Figure 7-2 is a form that can be used to record the data in an abbreviated or coded format. Recording these data will provide the necessary information for determining RMR and Q. These codes are derived from the descriptors for discontinuities presented in chapter 5.

209 FIELD MANUAL Figure 7-2.—Discontinuity log field sheet.

210 DISCONTINUITY SURVEYS

BIBLIOGRAPHY

[1] Hoek, E., and J. Bray, Rock Slope Engineering, revised 3rd edition, The Institute of Mining, London, 1981.

[2] Goodman, R.L., Methods of Geological Engineering in Discontinuous Rock, 1976.

[3] Goodman, R.L., Introduction to Rock Mechanics, 1980.

[4] Terzaghi, K., “Rock defects and loads on tunnel support,”Rock Tunneling with Steel Supports, Commercial Shearing, Inc., Youngstown, OH, 1946.

[5] Bieniawski, Z.T., Engineering Rock Mass Classifica- tions, 1989.

[6] Bieniawski, Z.T.,and C.M. Orr, “Rapid site appraisal for dam foundations by the geomechanics classification,” Proceedings 12th Congress Large Dams, ICOLD, Mexico City, pp. 483-501, 1976.

[7] Barton, N., F. Lien, and J. Lunde, “Engineering classification of rock masses for the design of tunnel support,” Rock Mechanics, v. 6, No. 4, pp. 189-236, 1974.

[8] Deere, D.U., A.J. Hendron, F.D. Patton, and E.J. Cord- ing, “Design of surface and near surface construction in rock,” Proceedings 8th U.S. Symposium Rock Mechanics, AIME, New York, pp. 237-302, 1967.

[9] Wickham, G.E., and H.R. Tiedemann, “Ground support prediction model—RSR concept,” Proceedings Rapid Excavation Tunneling Conference, AIME, New York, pp. 691-707, 1974.

211 FIELD MANUAL

[10] Williamson, D.A., “Unified rock classification system,” Bulletin of the Association of Engineering Geologists, v. XXI, No. 3, pp. 345-354, 1984.

[11] Goodman, R.E., and Gen-Hua Shi, “Geology and rock slope stability—application of a “keyblock” concept for rock slopes,” Proceedings 3rd International Conference on Stability in Open Pit Mining, Vancouver, June 1981.

[12] Goodman, R.E., and Gen-Hua Shi, Block Theory and Its Application to Rock Engineering, 1985.

[13] Piteau, D., “Geological factors significant to the stability of the slopes cut in rock,” Proceedings of the Open Pit Mining Symposium, South African Institute of Mining and Metallurgy, September 1970.

[14] Savely, J., “Orientation and Engineering Properties of Joints in Sierrita Pit, Arizona,” MS thesis, University of Arizona, 1972.

[15] Priest, S.D., and J.A. Hudson., “Estimation of discontinuity spacing and trace length using scanline surveys,” International Journal of Rock Mechanics-Mining Sciences and Geomechanics Abstracts, v. 18, No. 3, pp. 183-197, 1981.

[16] Terzaghi, R.D., “Sources of error in joint surveys,” Geotechnique, v. 15, No. 3, pp. 287-304, 1965.

212 Chapter 8

EXPLORATION DRILLING PROGRAMS

Introduction

This chapter is a guide for developing effective and efficient exploration drilling programs. Drilling programs that involve extensive soil sampling, rock coring, instrumentation installations, or in-place testing commonly have excessive cost overruns and late completion times. The effort put into developing a well organized drilling program that explicitly defines drilling and sampling requirements can lower exploration costs significantly by eliminating unnecessary or redundant work and meeting schedules. Good references on drilling methods and equipment are Groundwater and Wells, second edition, by Fletcher G. Driscoll, published by Johnson Division, St. Paul, Minnesota 55112, and Drilling: The Manual of Methods, Applications, and Management, CRC Lewis Publishers, Boca Raton, Florida, 1996.

Planning the Exploration Drilling Program

Developing an exploration program requires a thorough knowledge of the design requirements, site conditions, drilling equipment requirements and capabilities, and soil or rock core testing. It is extremely important that exploration needs be identified to avoid overdesign of a program by too many “it would be nice” requests.

A complete and detailed description of the drill site location, accessibility, work requirements, geology, and other pertinent information should be made available to either the drilling contractor or in-house drilling staff. This information is necessary for an effective and efficient drilling operation that will accomplish the program objectives. A major objective is to obtain the most information and samples possible from each hole by FIELD MANUAL optimizing location, drilling and sampling methods, depth, and completion. For example, a drill hole on the intersection of dam and outlet works centerlines drilled to the depth of the deepest data requirement and sampled for both structures provides data for both structures.

Most exploration is done in phases, with subsequent exploration designed to refine the understanding of a site. Drill holes should be logged as the holes are drilled, so hole depths and subsequent hole locations can be changed as exploration progresses. Because an exploration program evolves as data are acquired, information should be reviewed and added to maps and sections as the data become available.

Site Inspection

An onsite inspection of the drilling location should be made by the geologist, designers, and other essential members of the exploration team. The purpose of the onsite inspection is to determine the exploration needed to provide the data required for design. Data are required for several design disciplines with different needs. Having knowledgeable representatives see the site is important when formulating an exploration program. Changes and additions to exploration programs during or after exploration are expected but can be minimized with careful planning.

During the site inspection, the geologist and designers should discuss in detail all the design concerns that can only be solved by analyzing the subsurface geology. The team should be explicit as to the size, quantity, type, and quality of soil or rock samples that are necessary to develop an accurate evaluation of geologic conditions. The geologist can recommend the type of equipment and

214 DRILLING PROGRAMS drilling procedures needed, based on the drilling and sampling requirements, and to address design concerns as well as to provide samples needed for laboratory testing.

The onsite inspection should provide other pertinent information which is critical to the selection of specific equipment. The following factors should be addressed when preparing the exploration plan.

Topography-drill site accessibility.—The type of drilling equipment most suitable for the work needs to be determined. Truck-mounted, all-terrain, skid- mounted, or a combination of several types may be appropriate. Heavy excavation and hauling equipment may be required to construct access roads, drill pads, stream crossings, temporary bridges, or pipe culverts for river crossings. Explosives and track drills may be required to prepare drill pads or remove unsafe rock overhangs from drill sites, and roadbase or rockfill may have to be to be placed over soft mud or swamp. Helicopter support may be needed for fly-in rigs and heavy timber clearing. A source of water for drilling needs to be identified. Other considerations are whether there is a relatively close and level area that may be used as a temporary drill yard/staging area and how close equipment can be safely driven into the drill area.

Right-of-way, access permits, drilling permits, construction or clearing permits.—The drilling locations, whether on public or private land, may require access permits. Several different types of permits may be needed, including archeological and environmental permits. These permits may take considerable time to obtain and should be acquired as soon as possible. The limitations of the permits should be determined. Construction or clearing permits may be needed. Most

215 FIELD MANUAL states require special licenses or permits for drill operators who perform water-well drilling and installation.

Protection of the Environment

Environmental, archeological, and biological factors may place restrictions or conditions on a site. Disposal of the cleared material should be arranged. The use of drilling mud requires planning and implementation prior to drilling. If the drill mud circulation pits can be excavated, the mud pits may have to be enclosed with fencing to keep out animals. Drill mud and cuttings as well as fuel and oil spills or oil change residue will require disposal. Some drill mud, cuttings, and water should be stored because the material is considered a hazardous waste. These materials may have to be disposed of at approved sites. Crossing shallow streams can create contamination or turbidity problems. Drill hole completion and site restoration should be formulated. Dust abatement may be necessary for travel over the access roads. Routes through planted fields should be arranged before travel.

Drilling

Many factors should be considered during the development of the exploration plan as listed below:

• Are the drill sites on rock

• Can downhole hammers be used to set collar casing

• Are surficial materials suitable for hollow-stem auger use

• If the drill hole is to be water-pressure tested, may drilling mud or air foam be used

216 DRILLING PROGRAMS

• Are soil samples required

• Can casing or hollow-stem augers be advanced through the surficial deposits so that rock coring can be performed

• Can the drill hole be used to combine geophysical and in-place testing

• Will geophysical testing be required in the drill hole

• Are angle holes required

• Will the holes require directional drilling control and then be verified by survey

• Will polyvinyl chloride (PVC) casing have to be installed for survey confirmation

• Will water pressure tests or permeability tests be required as the hole is drilled or can the testing be performed after the hole is completed

• Will the permeability tests require packers and pressure testing or gravity head pressure

• Will the holes require instrumentation installation

• What are the requirements for the backfill in the instrumentation drill hole and how is it to be placed

• Will the outside annulus of the casing require grouting

• What are the hole completion requirements

217 FIELD MANUAL

Equipment

• Are the requirements for soil sample and/or rock core sizes compatible with existing commercially available equipment

• Will the samples or cores have to be transmitted to the testing laboratories in sealed liners, split tube liners, thin-wall steel tubes, or cheesecloth and wax seals in core boxes

• Are there special concerns for the samples and their delivery

• Will those concerns require them to be transported in vibration-free containers

• Should the samples be protected from freezing

• Should the samples be weighed in the field and the density and moisture content determined before delivery to the laboratories

• What is the minimum drill equipment that should be specified considering the total hole depth, size of core or soil sample requirements, borehole diameter, and rod size

• What is the minimum mud pump or air compressor rating that should be specified

• Where is the water source; will water have to be hauled or can it be pumped to the drill site

• How much water line will have to be laid

218 DRILLING PROGRAMS

Traffic Control and Safety

• Will the drill locations require traffic control, detours, barricades, flag personnel, etc., for safety and public protection

• Will road or highway travel require rerouting during the drilling program

• Has permission been obtained from local, county, or state officials to close roads

• Will drilling be performed in high visibility areas

• Will equipment security and vandalism be enough of a problem to warrant nighttime security personnel or fencing

Special Considerations

• Will the drilling require excavating or constructing ramps and drill pads on the slope face of an earth embankment • Will the embankment slope face drilling have to be done with skid-rigs on timber cribbing platforms or with specialized drills that are capable of traversing and drilling into embankment slope faces without excavating ramps or benches • Will underground drilling be required • Establish and include all underground safety requirements in the drilling specifications • Size the underground drilling equipment so it will be suitable for the height and width of the tunnel or drift

219 FIELD MANUAL

• Is there potential for large water inflows • Is there potential to intercept reservoir water during underground drilling operations • Will the drilling program require drill setups on scaffolds or hanging platforms • Are qualified personnel available to review the design of any scaffold or hanging platform drill setup, and will they have the authority to accept or reject the construction • Will the drilling program require operation from a floating plant (barge) or a jack-up platform • Obtain data for fluctuating river rises or falls, flow rate, and depth of water under normal flow conditions • Will drilling be required in the vicinity of overhead transmission lines, transformer boxes, or underground buried utilities • Have all underground utilities been located and flagged • Will the program require helicopter service for fly- in rigs • Have fly-in hazards been identified prior to start, such as transmission lines, heavy timber, turbulent winds, and rough terrain • Are artesian pressures anticipated • Are circulation loss zones anticipated • Have contingency plans been prepared to seal and contain artesian water flow or large volume water flow that may be encountered during any drilling operations

220 DRILLING PROGRAMS

• Has it been determined how the drill holes are to be completed, i.e., capped and locked collar casing, collar casing guard fixtures, or install piezometers or other monitoring instrumentation, or backfilled and grouted

Drilling in Dam Embankments

The Bureau of Reclamation's (Reclamation) embankment design practice minimizes development of stress patterns within an embankment. Stress patterns could lead to hydraulic fracturing by drill fluids during drilling. Certain embankment locations and conditions have a higher potential for hydraulic fracturing than others, and improper drilling procedures or methods will increase the potential for hydraulic fracturing. Site locations and conditions where hydraulic fracturing by drilling media are more likely to occur and adversely affect a structure's performance include the following:

1. In impervious cores with slopes steeper than 0.5H:1V, cut-off trenches, and upstream-inclined cores.

2. Near abutments steeper than 0.5H:1V, where abrupt changes in slopes occur, and above boundaries in the foundation which sharply separate areas of contrasting compressibility.

3. Near structures within embankments.

4. In impervious zones consisting of silt or mixtures of fine sand and silt.

Recommended procedures for developing exploration and instrumentation programs and for drilling in the impervious portion of embankment dams are as follows:

221 FIELD MANUAL

1. The embankment design should indicate whether a hydraulic fracturing potential exists.

2. If a high potential for hydrofracturing exists, the type of equipment and the method and technique to be used for drilling must have the approval of the exploration team. Once drilling has commenced, drilling personnel are responsible for controlling and monitoring drill media pressure, drill media circulation loss, and penetration rate to assure that the drilling operation minimizes the possibility for hydraulic fracturing.

3. If a sudden loss of drill fluid occurs during any embankment drilling within the dam core, drilling should be stopped immediately. Action should be taken to stop the loss of drill fluid. The reason for loss should be determined, and if hydraulic fracturing may have been the reason for the fluid loss, the geologist and designer should be notified.

With the exception of augering, any drilling method has the potential to hydraulically fracture an embankment if care is not taken and attention is not paid to detail. Augering is the preferred method of drilling in the core of embankment dams. Augering does not pressurize the embankment, and no potential for hydrofracturing exists. Use of a hollow-stem auger permits sampling in the embankment and allows sampling/testing of the founda-tion through the auger’s hollow stem, which acts as casing.

Drilling methods which may be approved for drilling in embankment dams if augering is not practical (i.e., cobbly fill) are as follows:

222 DRILLING PROGRAMS

1. Cable tool

2. Direct rotary with mud (bentonite or biodegradable)

3. Direct rotary with water

4. Direct rotary with air-foam

5. Down-hole hammer with reverse circulation

Selection of any one of the above methods should be based on site-specific conditions, hole utilization, economic considerations, and availability of equipment and trained personnel.

Any drilling into the impervious core of an embankment dam should be performed by experienced drill crews that employ methods and procedures that minimize the potential for hydraulic fracturing. It is essential that drillers be well trained and aware of the causes of and the problems resulting from hydraulic fracturing.

Safety

Drilling safety requirements and safety requirements in general are available in Reclamation Safety and Health Standards, Bureau of Reclamation, United States Department of Interior, 1993.

Preparation of Drilling Specifications and Format

The work requirements should be compiled in a clear and concise manner for use by the personnel who will

223 FIELD MANUAL perform and inspect the work. The following is a suggested specifications format for drilling contracts. a. General Description of Exploration Program

(1) Available Geologic Data

(2) Identification of Design Concerns

(3) Generalized Exploration Drilling, Coring, Testing, Instrumentation Requirements b. Location of Work

(1) Area Identification

(2) Nearest Community

(3) Emergency Facilities

(4) Nearest Living Quarters/Crew Camp Area

(5) Freight Facilities

(6) Fuel and Supply Business Locations

(7) Travel Routes/Road Restrictions

(8) Public/Private Land Access Routes/Restrictions

(9) Right-of-Way Permits c. Site Location

(1) Hole Locations

(2) Topography/Accessibility

224 DRILLING PROGRAMS

(3) Protection of the Environment

(4) Water Source

(5) Waste Disposal Area/Acceptable Waste Disposal Method

(6) Drill Yard Storage Area—Restrictions d. Work Requirements

(1) Site Preparation

(2) Collaring Holes—Boring Size—Angle

(3) Casing Requirements

(4) Sample Requirements (Disturbed/Undisturbed)

(5) Sample Sizes and Intervals

(6) Care and Transportation of Samples

(7) Core Sizes and Intervals

(8) Care and Preservation of Rock Core

(9) In-Place Testing Requirements

(10) Instrumentation Requirements

(11) Hole Backfill and Completion

(12) Site Cleanup

225 FIELD MANUAL e. Equipment Requirements

(1) Drill Rig Capabilities

(2) Pump/Air Compressor Capabilities

(3) Drilling Media

(4) Sampling/Coring Equipment

(5) In Situ Testing Equipment

(6) Instrumentation Equipment

(7) Core Boxes/Sample Containers f. Special Drilling Concerns g. Potential for Program Change, Modification, or Extension h. Safety Program/Safety Requirements/Safety Contingency Plans i. Exploration Drilling Reports and Logs j. Labor Checks/Equipment Checks/Cost Accounting

226 Chapter 9

GROUNDWATER DATA ACQUISITION METHODS

Introduction

This chapter provides information that will help select, install, and operate appropriate groundwater instrumentation and to collect, establish, maintain, and present the groundwater data. Most types of engineering geology investigations require acquisition and use of groundwater data. The data required may vary from simple monthly verification of the water level elevations along a canal-axis profile to hourly monitoring of piezometric conditions in multiple zones within a landslide or embankment. Successful implementation of a groundwater instrumen-tation program depends on knowledge of subsurface conditions, preliminary identification of all probable future uses of the data, and careful planning of an instrumentation system and data acquisition program to meet these data requirements. This chapter will provide the user with:

• A detailed description of methods employed in designing and installing groundwater monitoring systems.

• A detailed description of available manual and automated methods and techniques used in monitoring ground and surface water.

• A discussion of data base management and data presentation.

• A listing of more detailed and specific source material on groundwater data acquisition methods. FIELD MANUAL

General

The importance of fully evaluating and understanding geologic factors controlling groundwater flow—including porosity, storativity, permeability, transmissivity, velocity, recharge, and discharge—cannot be overemphasized. This evaluation needs to be made at the onset of the exploration program and continually repeated throughout the investigations. These factors will ultimately control the type of groundwater acquisition methods required.

Geologic Controls on Groundwater

Geologic controls on groundwater flow impact the design of observation systems and must be identified in the preliminary planning of the instrumentation program. For example:

1. Permeable materials, such as clastic sediments, karstic limestone, and fractured rock, control the type and size of well point, well screen, or piezometer to be used and must be accounted for in designing instrumentation for the program.

2. Relatively impermeable materials, such as clays, silts, shales, siltstones, and massive rock present special problems which must be accounted for in selecting the type and size of piezometer to be installed. Generally these materials require use of the smallest size piezometer practical because changes in water level and volume in the hole are small and require long periods of time to react. Pore pressure measurements in this type of geologic environment should be considered, particularly if short-term periodic—daily or weekly—changes in groundwater conditions are needed.

228 GROUNDWATER

3. Layering, attitude of layers, boundaries, weathering and alteration, and environment of deposition all influence selection of instrumentation.

Design and Installation of Observation Wells and Piezometers

Analysis of the Geologic Environment

The presence of variations in the geologic environment must be anticipated. Perched water tables, artesian aquifers, sources of recharge and discharge, known boundaries and barriers, and structural controls such as fractures, joints, faults, shears, slides, folds, and stratigraphic contacts should be considered when selecting instrument types and sizes. The preliminary instrumentation design should be advanced enough to allow procurement of needed equipment, but flexible enough to adapt to changes in the environment.

Different types of groundwater observation instruments provide different data types. Observation wells and piezometers are selected in accordance with the data required and the aquifer material and type. To be useful, reliable, and accurate, the well or piezometer design must be tailored to the subsurface conditions. Single or unconfined aquifer zones can be monitored by using a screened or perforated standpipe or porous tube piezometer, or by a pore-pressure transducer. Multiple zones may be monitored using multiple drill holes, multiple piezometers in a single drill hole, or multiple piezometer ports in a single standpipe.

229 FIELD MANUAL

Design

The most important aspect in the design of a groundwater monitoring well is the purpose and use of the well; whether for taking water samples, measuring water levels, geophysical investigations, or a combination of uses.

The hydrogeologic environment and the type of down- hole instruments that may be used in the well will influence the choice of well diameter, casing type, screen to be used, and the interval to be monitored.

Components of a typical well include a screened interval surrounded by filter/gravel-pack material isolated by a bentonite and/or cement grout seal, blank casing to the surface, and a protective well cover.

PVC is the most widely used material for standpipes (casing and screens) in monitoring wells. It is relatively inexpensive and presents few chemical interferences in water quality sampling. Many other materials are available for specific uses, including galvanized and stainless steel, Teflon©, and other plastics.

The diameter of the well depends on the instrumentation to be installed and the intended use. If the well is to be sampled, by either pump or bailer, a 3-inch (75-mm) diameter hole is the preferred size for accuracy and for complete development of the hole, but smaller sizes can be used with small bailers and peristaltic pumps. Wells used for measuring water levels only may be smaller diameter or may have multiple small diameter standpipes within a 4-inch (100-mm) to 8-inch (200-mm) diameter hole. A standpipe designed to accommodate an M-scope water level sensor can be ¾ inch (19 mm) diameter. However, if the standpipe is to be

230 GROUNDWATER instrumented with a pneumatic or vibrating wire piezometer or if a recorder and electric probe will be used to monitor the water level, then the diameter of the standpipe depends on the size of the instrument or transducer to be installed. Lengths of well screen and casing (PVC perforated and solid standpipe) must have uniform inner and outer casing diameters. Inconsistent inner diameters cause problems when instruments with tight clearance are lowered into the well. The pipe may need to be reamed to remove the beads and burrs. A filter pack is generally composed of washed sand and gravel and is placed within the screened interval. The interval may extend above the screen depending on the zone thickness. The pack is designed primarily to allow water to enter the standpipe while preventing the movement of fines into the pipe through the slots, and to allow water to leave the standpipe when water levels drop. If the well is to be used for sampling, the pack material should be sterilized to prevent possible contamination before placement into the well. The gravel pack should be tremied through a pipe to prevent bridging. The top of the pack may be checked using a small diameter tamping tool, or a properly weighted surveyor’s tape.

A seal is installed to create an impermeable boundary between the standpipe and the casing or drill hole wall. The seal should be placed in a zone of low permeability, such as a clay bed above the zone to be monitored. This ensures that water will not travel vertically along the casing or drill hole.

Cement grout can shrink due to temperature changes during curing and may crack. This causes a poor bond between the grout and the standpipe. A 1-foot (0.3-m) bentonite seal should be placed preferably as pellets or by tremieing a bentonite slurry immediately below and

231 FIELD MANUAL above the cement grout seal. This helps ensure a reliable plug. Any seal material (optional with bentonite pellets) should be tremied into place. This prevents bridging or caking along the hole wall. The seal must be reliable so that the screened interval monitors only the desired groundwater zone.

A drill hole containing multiple standpipes, each monitoring a zone or distinct water bearing strata, may have several isolating seals. To test the integrity of the seals, a gravity head test may be performed by adding water to the shallowest standpipe and continuously measuring the water level in the next lower piezometer to detect any leakage through or around the seals. If the water leaks into the lower interval, the piezometric head will rise in the lower standpipe.

A protective cover helps prevent damage to the standpipe and reduces surface water drainage into the backfilled hole. The casing should extend 5 to 10 feet (1.5 to 3 m) below ground and be grouted into place. Upon completion of the monitoring well, standpipe should be bailed or blown dry and the water level allowed to recover to a static level. A completion log should be prepared using the drillers' records, geologic log, and measurements. The log should include the actual depths and thicknesses of each component of the well; the standpipe's total depth; the screened interval, the isolated interval; the type of filter pack; the depth, thickness, and type of isolating seals; and a reference point from which all measurements were taken, such as top of casing or ground surface. Many excellent references are available to design and install groundwater monitoring wells for various purposes. Refer to these at the end of this chapter for more detailed instructions.

232 GROUNDWATER

Construction Materials

Construction materials for observation wells and piezometers are dictated by the projected use of the instrument and the permeability of the aquifer. The diameter of the standpipe, the type of standpipe used (metal versus plastic), screen slot size/porous tube type, and gravel pack material are all variables dictated by aquifer characteristics.

In a relatively permeable material, the diameter of a standpipe is not critical; sand or gravel pack around the well tip may not be required, but the screen slot size may be critical to the success of the installation. Too small screen or slot size may restrict instrument reaction to changes in water levels.

In a relatively impermeable material, pipe diameter may be critical, a pack material of select sand or fabric wrap usually is required, and a well point or screen assembly usually is needed, (0.010-0.020-inch [0.0250.05 centimeter (cm)] slot size). Generally, the smallest diameter pipe practical should be used in this sort of monitoring application, keeping in mind that the standpipe diameter must be large enough to install a means of measuring water levels. If the volume of the hole is too large, too much water must move in and out of the hole to accurately reflect the water level. If rapid reaction to water level or changes is needed, a pressure transducer may be more appropriate than an open-tube piezometer or standpipe.

A variety of materials can be used as the standpipe. Polyvinyl chloride (PVC) plastic pipe is economical and easy to install. Plastic pipe is fairly fragile, deformable, and can be destroyed accidentally during installation. Metal pipe is more durable for installation but generally

233 FIELD MANUAL costs more than plastic, rusts or corrodes, and is subject to iron bacterial action. Generally, if grout plugs are used to isolate zones, black pipe is preferred because the zinc in galvanized pipe can react with the plug and destroy the seal. The inside diameter (I.D.) of the pipe depends on the permeability of the aquifer material and can vary from as small as ½ inch (13 millimeters [mm]) to 2 inches (50 mm) or larger. The diameter of the riser is critical to instrumentation of the observation well or piezometer. Generally, ¾-inch (19 mm) pipe is the smallest practical size that can be used in automated applications. Reaming of the pipe prior to installation to remove burrs, weld seams, and blebs of galvanizing material is a necessary precaution to ensure that the standpipe will be usable if the pipe I.D. and measuring device outside diameter (O.D.) are close.

The screen assembly selected for an observation well or piezometer can be a well point, well screen, porous tube, or perforated pipe (commercially manufactured or field fabricated). Screen should be PVC or corrosion-resistant metal. Slot-size is determined by filter material size and aquifer material.

The gravel-pack material selected is determined by the particle sizes of the aquifer material and the size of the well screen. Concrete sand or reasonably well-graded sand to pea gravel can be used.

Plug material used to isolate the interval to be monitored can be tremied cement grout, bentonite pellets, or a combination of the two. A bentonite slurry also may be used in some instances but must be tremied in place. Bentonite pellets are preferred if only one isolation method is used.

234 GROUNDWATER

Methods Used to Measure Groundwater Levels

General

Groundwater measurements (and any instrumentation readings) should be interpreted concurrently with reading. Erroneous readings and faulty equipment need to be detected as encountered, and timely interpretation is a reliable method of bad reading detection. The person(s) taking the readings must understand the equipment and gather reliable data from the instruments. If bad read-ings or faulty equipment are not detected by concurrent interpretation, months of irretrievable data can be lost, and erroneous interpretations or data impossible to inter-pret can result.

Manual Methods Used to Measure Groundwater Levels

Chalk and Surveyors' Chain.—Probably the oldest and one of the most reliable methods for measuring wells is the surveyors' chain and chalk method. This method is not recommended where water level depths exceed several hundred feet (300 m+).

A lead weight may (but not necessary) be attached to a steel measuring tape (surveyors' chain). The lower 5 feet (1.5 m) of the tape is wiped dry and covered with solid carpenter's chalk if the water level is roughly known. The tape is lowered into the well, and one of the foot marks is held exactly at the top of the casing. The tape is pulled up. The line can be read to a hundredth of a foot (0.003 m) on the chalked section. This reading is sub-tracted from the mark held at the measuring point, and the difference is the depth to water.

235 FIELD MANUAL

The disadvantage to this method is that the approximate water depth must be known so that a portion of the chalked section will be submerged to produce a wetted line. Deep holes require a long surveyor’s chain which can be difficult to handle. M-Scope (Electric Sounder).—An M-scope is an electric sounder or electrical depth gauge consisting of an electrode suspended by a pair of insulated wires and a milliammeter that indicates a closed circuit and flow of current when the electrode touches the water surface. Usually, AA flashlight batteries supply the current. The insulated wire usually is marked off in 1-foot to 5-foot (0.3- to 1.5-m) intervals. The best devices have the measuring marks embedded directly into the line. Markers that are attached to the line slip, making it necessary to calibrate the instrument frequently.

With the reel and indicator wire in one hand and the other hand palm up with the index finger over the casing or piezometer pipe, the wire is lowered slowly over the finger into the piezometer pipe or well casing. By sliding the wire over the finger, the wire is not cut or damaged by the sharp casing or piezometer pipe. Several readings can be taken to eliminate any errors from kinks or bends in the wire. The water level depth can be measured from the top of casing using the mark-tags on the insulated wire and a tape measure marked in tenths and hundredths of a foot. The advantage of this method is that water level depths in holes several hundred feet deep can be measured fairly quickly and accurately. The disadvantage to this method is that malfunctioning or mechanical problems develop in the instrument giving er-roneous water level readings. Before going into the field, the instrument must be checked for low batteries, tears, scrapes on the insulated wires, and iron-calcium buildup on the part of the electrode touching the water surface.

236 GROUNDWATER

Airline and Gauge.—This method uses a small diameter pipe or tube inserted into the top of the well casing down to several feet below the lowest anticipated water level. The exact length of airline is measured as the line is placed in the well. The airline must be air tight and should be checked. The airline must hang vertically and be free from twists and spirals inside the casing. Quarter-inch (6.3 mm) copper or brass tubing can be used. The upper end of the airline is fitted with suitable connections and a Schraeder valve so that an ordinary tire pump can be used to pump air into the tube. A tee is placed in the line so that air pressure can be measured on a pressure gauge.

This device works on the principle that the air pressure required to push all the water out of the submerged portion of the tube equals the water pressure of a column of water of that height. A reference point (e.g., top of casing or pipe) and the depth to the lower end of the airline must be known. Air is pumped into the airline until the pressure on the gauge increases to a maximum point where all the water has been forced out of the airline. At this point, the air pressure in the tube just balances the water pressure. The gauge reading shows the pressure necessary to support a column of water of a height equal to the distance from the water level in the well to the bottom of the tube.

If the gauge reads the direct head of water, the submerged length of airline is read directly. The total length of airline to the reference point, minus the submerged length gives the depth to water below the measuring point. If the gauge reads in pounds per square inch, multiply the reading by 2.31 to convert to feet of water. An accurate, calibrated gauge and a straight, air-tight airline are important.

237 FIELD MANUAL

Popper.—A simple and reliable method of measuring water levels is with a popper. A tape with a popper attached to the bottom is lowered into the well or casing until the water is reached, as indicated by a pop. The popper is raised above and lowered to the water surface several times to accurately determine the distance. A popper consists of a small cylinder closed at the top and open at the bottom. The open bottom causes a popping sound when the water surface is hit. A 1-inch (in) or 1½-in (25- or 40-mm) pipe nipple 2 to 3 in (50 to 75 mm) long with a cap on top works satisfactorily.

Pressure Gauge for Monitoring Artesian Wells.— Additional standpipe or casing can theoretically be extended to eventually equal the head of the water. A simple method to determine the artesian head is to attach a pressure gauge to the casing or the piezometer pipe. The gauge selected may be read directly or in feet (meters) of water. Install a tee on the standpipe or on the casing so that a pressure gauge and valve can be attached to the tee. The valve may be used to bleed the pressure gauge to see if the gauge is working and can be used to measure the flow on the artesian well. When a pressure reading is taken, a flow measurement should also be taken. During the winter months, the valve should be cracked open to allow the well to flow slightly to prevent the riser pipe from freezing and breaking. The line to the gauge should be bled of water. If the pressure gauge used is in lbs/in2, multiply the gauge reading by 2.31 to obtain the head of water above the valve.

Continuous Recorders

Stevens Recorder.—The Stevens Recorder (produced by Stevens Water Resources Products) provides a reliable and economical way to obtain continuous water

238 GROUNDWATER level data. The recorder is a float type consisting of a 3- to 6-inch (76- to 152-mm) float connected to a pulley which turns a calibrated gear-driven drum. A power source, such as a spring clock or small motor, rotates the drum at a known rate giving a constant indication of elapsed time. Gearing between the float pulley and the chart drum provide a changeable ratio of water movement to pen movement on the chart. A time scale is available on the chart, and continuous recordings may be maintained for up to several months. When a Stevens recorder is used in a well, the minimum diameter of the well casing is 4 inches (100 cm). An advantage of the Stevens recorder is versatility. Hydrographs can be created with scales of 1:1 to 1:20. Most recorders can be set from 4 hours to several months. Johnson-Keck has a water level sensing instrument that can continuously record water levels in ½-inch (13-mm) pipe and larger. Transistorized circuitry is used to control a battery powered motorized reel. The sensing float is attached to one end of the control wire, and the other end of the wire is connected to the reel. The instrument is connected to a Stevens type F or Stevens type A recorder. The control wire passes around the recorder pulley, and the sensing device is placed in the casing. The sensing device seeks the water surface; and once the water surface is found, the circuitry keeps the sensing device at the water surface.

Many float recorders can be attached to digital recorders for continuous records. Data from this type of instrument can be used and easily interfaced with a computer system.

Bristol Recorders.—Recorders for monitoring continuous artesian pressures are produced by Bristol Instru- ment Systems. The Bristol and Stevens recorders are similar in that pressure and time are recorded on a

239 FIELD MANUAL chart. The instrument usually contains diaphragms that can be adjusted to varying pressure conditions. The spring-driven clock usually is calibrated for 30 days. The Bristol recorder is very useful for observing pressure changes in artesian wells but is limited by freezing conditions in northern climates. A pressure gauge installed in the line between the artesian water and the pressure recorder is very useful. This gauge provides a good indication of the working condition of the instrument.

Gas Bubbler Transducer.—Pneumatic or gas bubble transducers are manufactured by many companies. The transducers vary from a single readout box to a complicated array of instruments that will measure several wells at once. A gas is forced through a tube at a constant rate past a diaphragm. When the pressure of the gas on the diaphragm and the water pressure on the other side of the diaphragm are equal, a constant reading is obtained. This reading equals the amount of water over the diaphragm. This number multiplied by 2.31 will give the amount of water head over the instrument. These instruments may be used as a single unit or connected into an electronic data acquisition system.

Maintenance.—A good maintenance program is necessary to ensure reliable performance of mechanically actuated recorders. The instruments and data collected are only as good as the preventive maintenance. A routine preventive maintenance program should be scheduled for all the instruments. In some cases, daily inspection of recorders is required; however, if the instrument is working properly, weekly inspections may be sufficient. Preventive maintenance can often be accomplished when the charts are changed.

240 GROUNDWATER

Methods and Techniques Used to Estimate Flows from Seeps, Springs, and Small Drainages

A thorough and detailed discussion of weirs, flumes, stilling wells, and other techniques is presented in Reclamation’s Water Measurement Manual [1]. Small seeps, springs, and intermittent drainages are often encountered in field investigations. These features can provide key information during design and construction and may be key indicators of structure performance or environmental impacts that may affect the project. The location of drainage features, the rate of flow, and the time of year of the observation are important information. Flow can be estimated accurately using the methods described below:

Estimate the rate of flow in an open channel using Q=VA, where:

Q = rate of flow V = velocity A = cross sectional area of channel

The cross-sectional area is determined by direct measurements where possible. Where impractical, the cross- sectional area may be estimated or scaled from a topographic map.

Velocity is determined using a float, a measuring tape, and a stop watch by timing how long a floating object takes to travel a given distance. This provides a crude but reasonably accurate estimate of flow. Other methods may include a pitot tube or flow meter.

Substitute the values obtained into the Q=VA equation to obtain the volume of flow.

241 FIELD MANUAL

Measure flow from small springs and seeps directly by diverting the flow, or in some manner channel the flow to a point for collection in a container, such as a bucket. Determine the rate of flow by timing how long it takes to fill the container. Select points along a drainage where abrupt dropoffs occur and use this method. It is better to measure, however crudely; but if not possible, estimate the flow. Many more sophisticated methods can be used to obtain more accurate flow measurements, if necessary. Determination of the most appropriate method can be made if preliminary data are available.

Computer-Based Monitoring Systems

General

Water level monitoring may be automated. Monitoring landslides can require a great number of points and frequent readings. A variety of data types may be required, which may include measurements of not only water levels and pore pressure changes, but deformation and movement as well. Systems required to collect, store, format, and present these data are available allowing realtime analysis of a wide variety of data types.

Components of a Computer-Based Monitoring System

1. Many types of instruments including inclinometers, pressure transducers, strain gauges, water level gauges, and flowmeters can be used in a monitoring system. Electronic instruments are available in many sizes and shapes; preliminary selection of the instrument type

242 GROUNDWATER should be made during the initial design of the system. The inside diameter of the well must be sized to accept the transducer.

2. Acquired data is sent from the instrument at the well to the data logger or processor. This is done by hardwire from the instrument, line-of-sight radio, satellite radio, or phone lines.

Data from the monitoring points may be preprocessed in the field prior to transmittal to the central computer. A number of microprocessor data scanners that collect and reduce data can be installed at various field locations. The central computer queries the field scanners to obtain periodic updates. The remote scanners can be interro- gated as frequently as desired. This may include a continuous data scan mode.

3. Data scanners reduce the instrument output to usable data. Data scanners can be the end destination for more simple systems or can be part of a more elaborate system. Generally, two types of signals are generated by instruments used in geotechnical monitoring: (a) digital and (b) analog current or voltages. Data scanners which accept and reduce data from both types of signals are available.

Many manufacturers offer complete packages of automated instrumentation systems, including computer hardware and software. If the initial observation well program is designed for automation, most of these systems will provide the high quality data required.

Special Applications

Many types of instrumentation can be used in a single drill hole. A multiple use casing collects groundwater

243 FIELD MANUAL data from a large number of horizons within a single drill hole. Casing is available specifically for pore- pressure observations, or grooved casing can be used so that the well can be completed for both pressure and inclinometer measurements. Isolation between horizons can be accom-plished either by installing a bentonite seal or by using a packer assembly designed as an integral part of a monitoring system. Use of a monitoring system greatly reduces drilling costs, provides detailed monitoring of critical drill holes, and provides a greater flexibility than systems previously available. Small diameter drill holes can be used to obtain a large number of isolated water level intervals and, depending on the application, can be very cost effective.

Data Base Management and Data Presentation

Standard forms are available to record field data, although standard data sheets often must be modified for specific applications. Data sheets must include remarks and information that include the monitoring well num-ber, location, elevation reference points, type and size of well, dates and times the well was read, depth to water, and the elevation of the water surface. Periodic readings of these observation wells over long periods of time generate numerous data sheets. Computerization of the data base very rapidly can become a necessity if data are to be readily available and easily analyzed.

Data entry and storage in digital format allows electronic transfer of data and greater flexibility in developing, analyzing, and presenting data. Data may be tabulated or presented as time-depth/elevation plots and interpre-tive drawings such as contours and other three dimensional plots. Tremendous volumes of data

244 GROUNDWATER can be reduced quickly to a usable format. Use of a commer-cially available data base allows data use and manipu-lation without specialized software or training.

Definitions

Aquifer—A body of soil or rock that is sufficiently permeable to conduct groundwater and to yield economically significant quantities of water to wells and springs.

• Confined aquifer—An aquifer bounded above by impermeable beds, or beds of distinctly lower permeability than that of the aquifer itself. An aquifer containing confined groundwater.

• Unconfined aquifer—An aquifer having a water table. An aquifer containing unconfined ground-water.

Artesian—An adjective referring to groundwater confined under hydrostatic pressure.

Artesian aquifer—An aquifer containing water under artesian pressure.

Aquitard—A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. An aquitard does not readily yield water to wells or springs but may serve as a storage unit for groundwater.

Aquiclude—A body of relatively impermeable rock or soil that is capable of absorbing water slowly but functions as an upper or lower boundary of an aquifer and does not transmit significant groundwater.

245 FIELD MANUAL

Water table or water level—The surface between the zone of saturation and the zone of aeration; the surface of a body of unconfined groundwater at which the pressure is equal to atmospheric pressure.

Zone of aeration or Vadose zone—Subsurface zone containing water under pressure less than atmospheric, including water held by capillarity, and containing air or gases generally under atmospheric pressure. This zone is limited above by the land surface and below by the surface of the zone of saturation or water table.

Saturation—The maximum possible content of water in the pore space of rock or soil.

Zone of saturation—A subsurface zone in which all of the interstices are filled with groundwater under pressure greater than atmospheric. The zone is still considered saturated even though the zone may contain gas-filled interstices or interstices filled with fluid other than water. This zone is separated from the zone of aeration by the water table.

References

American Geological Institute, Glossary of Geology, 4th edition, Alexandria, VI, 1997.

Bureau of Reclamation, Embankment Dam Instrumentation Manual, U.S. Department of the Interior, United States Government Printing Office, Washington, DC, 1987.

Bureau of Reclamation, Ground Water Manual, 2nd edition, A Water Resources Technical Publication,

246 GROUNDWATER

U.S. Department of the Interior, United States Government Printing Office, Washington, DC, 1995.

Driscoll, Fletcher G., Groundwater and Wells, 2nd edition, published by Johnson Division, St. Paul, MN 55112, 1987.

Leupold and Stevens Inc., Stevens Water Resources Data Book, 3rd edition, P.O. Box 688, Beaverton, OR 97005.

Morrison, Robert D., “Equipment, and Application,” Ground Water Monitoring Technology Procedures, Timco Manufacturing Inc., Prairie du Sac, WI, 1983.

BIBLIOGRAPHY

[1] Bureau of Reclamation, Water Measurement Manual, 3rd edition, A Water Resources Technical Publication, U.S. Department of the Interior, United States Government Printing Office, Washing-ton, DC, 1997.

247 Chapter 10

GUIDELINES FOR CORE LOGGING

These guidelines incorporate procedures and methods used by many field offices and are appropriate for "standard" engineering geology/geotechnical log forms, computerized log forms, and many of the modified log forms used by various Bureau of Reclamation (Reclamation) offices.

General

Introduction

This chapter describes the basic methods for engineering geology core logging and provides examples and instructions pertaining to format, descriptive data, and techniques; procedures for working with drillers to obtain the best data; caring for recovered core; and water testing in drill holes. The chapter also provides a reference for experienced loggers to improve their techniques and train others. Most of the discussions and examples shown pertain to logging rock core, but many discussions apply to soil core logging, standard penetration resistance logs, and drive tube sample logging.

Purpose, Use, and Importance of Quality Core Logging

The ability of a foundation to accommodate structure loads depends primarily on the deformability, strength, and groundwater conditions of the foundation materials. The remediation of a hazardous waste site can be formulated only by proper characterization of the site. Clear and accurate portrayal of geologic design and evaluation data and analytical procedures is paramount. Data reported in geologic logs not only must be accurate, FIELD MANUAL

consistently recorded, and concise, but also must provide quantitative and qualitative descriptions.

Logs provide fundamental data on which conclusions regarding a site are based. Additional exploration or testing, final design criteria, treatment design, methods of construction, and eventually the evaluation of structure performance may depend on core logs. A log may present important data for immediate interpretations or use, or may provide data that are used over a period of years. The log may be used to delineate existing foundation conditions, changes over time to the foundation or structure, serve as part of contract documents, and may be used as evidence in negotiations and/or in court to resolve contract or possible responsible party (PRP) disputes.

For engineering geology purposes, the basic objectives of logging core are to provide a factual, accurate, and concise record of the important geological and physical characteristics of engineering significance. Characteristics which influence deformability, strength, and water conditions must be recorded appropriately for future interpretations and analyses. Reclamation has adopted recognized indexes, nomenclature, standard descriptors and descriptive criteria, and alphanumeric descriptors for physical properties to ensure that these data are recorded uniformly, consistently, and accurately. Use of alphanumeric descriptors and indexes permits analysis of data by computer. These descriptors, descriptive criteria, examples, and supporting discussions are provided in chapters 3, 4, and 5.

Exploration should be logged or, as a minimum, reviewed by an experienced engineering geologist. The logger should be aware of the multiple uses of the log and the needs and interests of technically diverse users. The

250 CORE LOGGING

experienced logger concentrates on the primary purposes of the individual drill hole as well as any subordinate purposes, keeping in mind the interests of others with varied geological backgrounds including geotechnical engineers, contract drillers, construction personnel, and contract lawyers. An experienced logger tailors the log to meet these needs, describing some seemingly minor features or conditions which have engineering significance, and excluding petrologic features or geologic conditions having only minor or academic interest. Less experienced loggers may have a tendency to concentrate on unnecessary garnishment, use irrelevant technical terms, or produce an enormously detailed log which ignores the engineering geology considerations and perhaps the purpose for completing the drill hole. Adequate descriptions of recovered cores and samples can be prepared solely through visual or hand specimen examination of the core with the aid of simple field tests. Detailed microscopic or laboratory testing to define rock type or mineralogy generally are necessary only in special cases.

Empirical design methods, such as the Rock Mass Rating System Geomechanics Classification (RMR) and Q-system Classification (Q), are commonly used for design of underground structures and are coming into common use for other structures as well. If these methods are used, the necessary data must be collected during core logging.

If hazardous waste site characterization is the primary purpose of the drilling, the log should concentrate on providing data for that type of investigation.

Drilling and logging are to determine the in-place condition of the soil or rock mass. Any core condition, core loss, or damage due to the type of bit, barrel, or other equipment used, or due to improper techniques used in

251 FIELD MANUAL

the drilling and handling processes should be described. Such factors may have a marked effect on the amount and condition of the core recovered, particularly in soft, friable, weathered, intensely fractured materials or zones of shearing. Geologic logs require the adequate description of materials; a detailed summary of drilling equipment, methods, samplers, and significant engineering conditions; and geologic interpretations. Complete geologic logs of drill holes require adequate descriptions of recovered surficial deposits and bedrock, a detailed summary of drilling methods and conditions, and appropriate physical characteristics and indexes to ensure that adequate engineering data are available for geologic interpretation and analysis.

Format and Required Data for the Final Geologic Log

Organization of the Log

The log forms are divided into five basic sections: a heading block; a left-hand column for notes; a center column for indexes, additional notes, water tests and graphics; a right-hand column for classification and physical conditions; and a comments/explanation block at the bottom. Data required for each column are described in the following discussion and the referenced example logs. Log DH-123, figure 10-1, and log B-102, figure 10-2, are the most complete and preferred examples; other variations are presented but in some cases are not complete.

Heading

The heading block at the top of the form provides spaces for supplying project identifying information, feature,

252 CORE LOGGING

Figure 10-1.—Drill hole log, DH-123, sheet 1 of 2.

253 FIELD MANUAL

Figure 10-1.—Drill hole log, DH-123, sheet 2 of 2.

254 CORE LOGGING

Figure 10-2.—Drill hole log, B-102, for Standard Penetration Test, sheet 1 of 3.

255 FIELD MANUAL

Figure 10-2.—Drill hole log, B-102, for Standard Penetration Test, sheet 2 of 3.

256 CORE LOGGING

Figure 10-2.—Drill hole log, B-102, for Standard Penetration Test, sheet 3 of 3.

257 FIELD MANUAL hole number, location, coordinates, elevation, bearing and plunge of hole, dates started and completed, and the name(s) of the person(s) responsible for logging and review. Locations should preferably be in coordinates unless station and offset are all that is available.

Provide both coordinates and station and offset if available. The dip or plunge of the hole can be the angle from horizontal or from vertical, but the reference point should be noted on the log. Spaces for depth to bedrock and water levels are also provided. All this information is important and should not be omitted. Below the heading, the body of the log form is divided into a series of columns covering the various kinds of information required according to the type of exploratory hole.

Data Required for the "Drilling Notes" Column

Data for the left-hand column of all drill hole logs are similar whether for large-diameter sampling, Standard Penetration Tests, rock core, or push-tube sampling logs. These data are field observations and information provided by the driller on the Daily Drill Reports. Examples are provided for some of these data headings; a suggested guideline and preferred order is presented in the following paragraphs but may differ depending on the purpose and type of exploration. Headers for data can indicate whether depths are in feet (ft) or meters (m), eliminating the need to repeat "ft" or "m" for each interval entry. An example of the Drilling Notes column is provided on figures 10-1 through 10-4.

General Information.—This includes headers and data for the hole purpose, the setup or site conditions, drillers, and drilling and testing equipment used.

258 CORE LOGGING

Figure 10-3.—Drill hole log, DH-SP-2, sheet 1 of 2.

259 FIELD MANUAL

Figure 10-3.—Drill hole log, DH-SP-2, sheet 2 of 2.

260 CORE LOGGING

Figure 10-4.—Drill hole log, SPT-107-2, sheet 1 of 3.

261 FIELD MANUAL

Figure 10-4.—Drill hole log, SPT-107-2, sheet 2 of 3.

262 CORE LOGGING

Figure 10-4.—Drill hole log, SPT-107-2, sheet 3 of 3.

263 FIELD MANUAL

1. Purpose of hole — Includes reason for drilling the hole, such as foundation investigation, materials investigation, instrumentation, sampling, or testing.

2. Drill site or setup — Includes general physical description of the location of the drill hole. Information on unusual setups, such as adjacent to a stream, or drilled from a barge, gallery, or adit, may help understand the unusual conditions.

3. Drillers — Names of drillers may be significant for reference or for evaluating or interpreting core losses, drilling rates, and other drilling conditions.

4. Drilling equipment —

• Drill rig (make and model)

• Core barrel(s), tube(s), special samplers (type and size)

• Bits (type and size)

• Drill rods (type and size)

• Collar (type)

• Water test equipment (rod or pipe size, hose size, pump type and capacity, and relative position and elevation of pressure gauges or transducers), packers (type—mechanical or pneumatic)

Example: Skid-mounted Sprague and Henwood Model 250. NWD3 bottom discharge bit with a 5-ft (1.5-m), split-tube inner barrel. 5-ft (1.5-m) NW rods. Water tested with NX pneumatic

264 CORE LOGGING

packer No. 12 with 1-1/4-inch (in) (32-millimeter [mm]) pipe, Bean pump with 35-gallons per minute (gal/min) (159 liters per minute) maximum volume, and 1-in (25-mm) water meter. (Water testing equipment can be a separate heading if desired.)

Drilling Procedures and Conditions.—These headers and data should include methods, conditions, driller's comments, and records for water losses, caving, or casing.

1. Drilling methods — Synopsis of drilling, sampling, and testing procedures, including procedures and pressures for drive or push tubes used through the various intervals of the hole.

2. Drilling conditions and driller's comments — Note by interval the relative penetration rate and the action of the drill during this process (i.e., 105.6- 107.9: drilled slowly, moderate blocking off, hole advancing 15 minutes per foot [.3 meter]). Unusual drilling conditions should be summarized. Changes in drilling conditions may indicate differences in lithology, weathering, or fracture density. The geologist needs to account for variations in driller's descriptions; each driller may describe similar conditions with different adjectives or percentage estimates. Any other comments relative to ease or difficulty of advancing or maintaining the hole should be noted by depth intervals. Drillers' comments need to adequately describe conditions encountered while advancing the hole. Statements such as "normal drilling" or "no problems encountered" are not useful.

Differences in drilling speeds, pressures, and penetration rates may be related to the relative

265 FIELD MANUAL

hardness and density of materials. Abrupt changes in drilling time may identify lithologic changes or breaks and also may pinpoint soft or hard interbeds within larger units. Often, these may be correlated with geophysical logs. If the driller provides useful and accurate records of drilling conditions and procedures, an accurate determination of the top and bottom of key marker horizons can be made even without core.

Drilling progress should be recorded while drilling; recovery can be improved by relating recovery to optimum pressures and speeds, as well as providing data for interpretation. For each run, the driller should record the time when starting to drill and when stopping to come out of the hole. Most of these drilling progress data are qualitative rather than quantitative values. Controlling factors are not only the type of materials encountered but also may be mechanical or driller variables. These variables may include type and condition of the bit, rotation speed, drilling fluid pressure, etc. THE PURPOSE OF THE BORING IS TO OBTAIN THE HIGHEST QUALITY CORE AND MOST COMPLETE RECOVERY AND INFORMATION, NOT JUST FEET PER HOUR OR SHIFT.

3. Drilling fluid — Type and where used (including drilling fluid additives). This may be combined with or discussed under the heading, drilling methods.

4. Drilling fluid return — Include interval/percent return. Drilling fluid return may be combined with color.

5. Drill fluid color — Include interval/color.

266 CORE LOGGING

6. Caving conditions — Intervals of cave with appropriate remarks about the relative amount of caving are to be noted. When possible, report the actual caving interval rather than the depth of the hole.

7. Casing record — Casing depth is the depth of casing at the start of the drilled interval (see the example below).

8. Advancement (push-tube or Standard Penetration Test (SPT) applications) — Include depth/ interval sampled.

9. Cementing record — Note all intervals cemented and if intervals were cemented more than once. This information may be combined with the casing record, as shown below:

Example of casing and cementing record:

Interval drilled Size Casing depth (feet) (inch) (feet) 0.0-2.3 6 Cs 0.0 2.3-4.5 6 Cs 2.0 4.5-9.2 6 Cs 4.0 9.2-15.3 NxCs 8.0 15.3-18.7 NxCs 15.0 18.7-33.2 Cmt 12.1-18.7 Cmt

Hole Completion and Monitoring Data.—Data shown in this section of the left-hand column include hole completion, surveys, water levels, drilling rates or time, and reason for hole termination.

267 FIELD MANUAL

1. Borehole survey data — Include if obtained.

Example of survey data:

Depth Bearing Plunge

59 90E1 79 S 72EW 90E 99 S 75E W 89E 119 S 72E W 89E Average S 72E W 89E

1 E = degrees.

2. Water level data — Note depths and/or elevations, water quantities, and pressures from artesian flows. Water levels or flows should be recorded during hole advancement, between shifts, or at the beginning or end of a shift, but definitely should be recorded at completion of the hole and periodically thereafter. It may be advantageous to leave space or provide a note to refer the user to additional readings provided elsewhere on the log for subsequent measurements. Computer generated logs allow convenient updating of water levels long after the hole is completed.

Examples of drill hole logs illustrate optional format and subsequent readings. Examples of how to record data are:

268 CORE LOGGING

Depth to Date Hole depth water 1981 (feet) (feet) 11-02 25.0 6.0 Bailed 100 gal: Level before 6.0 Level after 21.0 or: Depth to Hole depth water Date (feet) (feet) 11-03-81 25.0 15.0 11-04-81 40.0 29.0 01-05-82 95.2 7.0 01-15-82 95.2 Flowing 25 gal/min 02-03-82 95.2 Flowing 5 gal/min at 5 pounds per square inch (lb/in2)

3. Hole completion — Indicate how hole was completed or backfilled; if jetting, washing, or bailing was employed; depth of casing left in hole or that casing was pulled; location and type of piezometers; location, sizes, and types of slotted pipes (including size and spacing of slots) or piezometer risers; type and depth of backfill or depths of concrete and/or bentonite plugs; location of isolated intervals; and elevation at top of riser(s). Hole completion can be shown graphically (see figure 10-5).

269 FIELD MANUAL

Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 1 of 3.

270 CORE LOGGING

Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 2 of 3.

271 FIELD MANUAL

Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 3 of 3.

272 CORE LOGGING

4. Reason for hole termination — State whether the hole reached the planned depth or reason why the hole was stopped short.

5. Drilling time — Total time, setup time, drilling time, and downtime should be recorded on drillers' daily sheets and should also be recorded on the drill log. These records are essential for determining exploration program costs.

Center Columns of the Drill Log

Computer Logs.—Computer-generated logs offer several options for the content and format of the log such as permeability, penetration resistance, or rock properties which have some differences in format. Examples of each are shown in figures 10-2 through 10-5.

Standard Geologic Log Form.—The following discussion pertains to the center columns for the standard Reclamation log (form 7-1337). The columns shown on all figures are self-explanatory. The columns can be modified or new columns added to the existing log form for recording appropriate indexes or special conditions.

The percolation tests (water-pressure tests) column should record the general information of the tests. Additional data may be recorded on "water testing" log forms or drillers' reports.

Type and size of hole, elevation, and depth columns are self-explanatory.

Core recovery should be recorded in percent of recovery by run. Although desirable, core recovery does not necessarily require a visual graph. Core recovery should be noted carefully by the driller for each run on the daily

273 FIELD MANUAL drill reports; however, this column should be the record of those measurements determined by the geologist during logging. Measuring the core while in the split tube or sampler, if possible, will produce the most accurate recovery records.

A hole completion column may be added which graphically portrays how the hole was completed. If used, an explanation of the graphic symbols should be provided on the log form.

Rock quality designation (RQD) should be reported by core run. RQD should be included on the log in graph or tabular form regardless of the type project. RQD is used in almost any engineering application of the hole data. Most contractors are interested in RQD as an index of blasting performance, rippability, and stability. RQD is described and explained in chapter 5.

A lithologic log or graphic column is helpful to quickly visualize the geologic conditions. Appropriate symbols may be used for correlation of units, shear zones, water levels, weathering, and fracturing (see figure 10-1).

The samples and testing column should include locations of samples obtained for testing and can later have actual sample results inserted in the column, if the column is enlarged.

Modifications to Standard Log Form.—Modifications or adaptations of the center columns are permissible and, in some instances, encouraged. Examples are:

1. The use of a continuation sheet for longer drill logs saves time and is easier to type. The sheets may have only one column to continue the right-hand narrative, or may be divided into two or more

274 CORE LOGGING

columns. See sheets 2 and 3 for drill hole SPT-107-2, figure 10-4, for an example; also see sheet 3 of 3 for drill hole DH-DN/P-60-1, figure 10-5.

2. The center column may be modified to portray additional data such as hole completion, various indexes, alphanumeric descriptors, or laboratory test data.

Standard penetration test hole SPT-107-2, figure 10-4, is a modified penetration resistance log which shows laboratory test results; a percent gravel/percent sand/ percent fines column; liquid limit/plasticity index (LL/PI) column, a field moisture column, and other modifications. Drill hole DH-SP-2, figure 10-3, has columns for reporting field density test results, moisture, porosity, percent saturation, percent fines/percent sand, LL/PI, and laboratory classification.

3. Another modification, shown on DH-SP-2, figure 10-3, is a drawing showing the location of the hole in relation to the structure being explored. Diagrams or graphs, such as water levels, may illustrate data better than a column of figures.

Required Data and Descriptions for the Right- Hand "Classification and Physical Condition" Column

General.—An accurate description of recovered core and a technically sound interpretation of nonrecovered core are the primary reasons for core logging. The logger needs to remember that any interpretation, such as a shear, must be based on observed factual data. The interpreted reason for the core loss is given, but usually

275 FIELD MANUAL it is best to define the area of core loss as the interval heading. For example:

99.4. to 101.6: No Recovery. Interpreted to be intensely fractured zone. Drillers reported blocking off, core probably ground up during drilling.

103.4 to 103.7: Open Joint?. Drillers reported 0.3-ft drop of drill rods during drilling and loss of all water. Joint surfaces in core do not match.

0.7 to 11.6: Silty Sand. Poor recovery, only 6.2 ft recovered from interval. Classification based on recovered material and wash samples.

0.9 to 3.2: Rockbitted. No samples recovered. (Usually this would be subheaded under a previous description, inferring the materials are the same as the last recovered).

Descriptions of Surficial Deposits.—Surficial deposits such as slope wash, alluvium, colluvium, and residual soil that are recovered from drill holes are described using USBR 5000 and 5005. If samples cannot be obtained, then description of the cuttings, percent return and color of drilling fluid, drilling characteristics, and correlation to surface exposures is employed. Always indicate what is being described—undisturbed samples, SPT or wash samples, cuttings, or cores. Descriptors and descriptive criteria for the physical characteristics of soils must conform to the established standards. Chapter 11 provides guidelines for soil and surficial deposit descriptions.

Extensive surficial deposits usually are described using geologic and soil classifications. Where surficial deposits are very shallow and not pertinent to engineering applications for design or remediation or where geologic

276 CORE LOGGING classification such as landslides or talus is preferable, units may be given genetic or stratigraphic terms only. For example, Quaternary basin fill, recent stream channel deposit, Quaternary colluvium, zone 3 embankment, and random fill may be described generally; or these may be unit headings with group name subheadings. The format is:

Geologic and group name. i.e., Alluvium, (sandy silt). Field classification in parentheses if classified, refer to chapters 3 and 11 for exceptions.

Classification descriptions. Additional descriptors (particle sizes, strength, consistency, compactness, etc., from the USBR 5000 and 5005 standards descriptive criteria).

Moisture. (dry to wet).

Color.

If cores or disturbed samples are not available, describe as many of the above items as can be determined from cuttings, drill water color, drilling characteristics, correlation to surface exposures, etc. Remember that for rockbitted, no recovery, or poor recovery intervals, a classification and group name should be assigned as a primary identification.

Description of Rock.—Description of rock includes a rock unit name based on general lithologic characteristics followed by data on structural features and physical conditions. Bedrock or lithologic units are to be delineated and identified, not only by general rock types but by any special geological, mineralogical features with engineering significance, or those pertinent to interpretation of the subsurface conditions.

277 FIELD MANUAL

Any information which is characteristic of all of the rock units encountered normally is included under the main heading, producing more concise logs. Differences can be described in various subheadings. Rock core is to be described in accordance with descriptors and descriptive criteria presented in chapters 4 and 5. A suggested format is:

1. Rock name — A simple descriptive name, sufficient to provide others with possible engineering properties of the rock type; may include geological age and/or stratigraphic unit name.

2. Lithology (composition/grain sizes/texture/ color) — Give a brief mineralogical description. Describe grain shape and size or sizes and texture using textural adjectives such as vesicular, porphyritic, schistose. (Do not use petrographic terms such as hypidiomorphic, subidioblastic). Other pertinent descriptions could include porosity, absorption, physical characteristics that assist in correlation studies, and other typical and/or unusual properties. Provide the wet color of fresh and weathered surfaces.

Contacts should be described here also. If the contacts are fractured, sheared, open, or have other significant properties, the contacts should be identified and described under separate subheadings.

3. Bedding/foliation/flow texture — Provide a description of thickness of bedding, banding, or foliation including the dip or inclination of these features.

4. Weathering/alteration — Use established descriptors which apply to most of the core or use individual subheadings. For alteration other than

278 CORE LOGGING weathering, use appropriate descriptors. These may or may not be separate from weathering depending upon rock type and type of alteration. Also, include slaking properties if the material air or water slakes. (Weathering may be used as first or second order headings for some logs.)

5. Hardness — Use established descriptors.

6. Discontinuities — These include shears, joints, fractures, and contacts. Discontinuities control or significantly influence the behavior of rock masses and must be described in detail. Detailed discussions of indexes and of descriptive criteria, descriptors, and terminology for describing fractures and shears are provided in chapter 5 and 7.

Fractures or joints should be categorized into sets if possible, based on similar orientations, and each set should be described. When possible, each set should be assigned letter and/or number designations and variations in their physical properties noted by depth intervals. Significant individual joints also may be identified and described. Physical measurements such as spacing and orientation (dip or inclination from core axis), information such as composition, thickness, and hardness of fillings or coatings; character of surfaces (smooth or rough); and, when possible, fracture openness should be recorded. In drill core, the average length between fractures is measured along the centerline of the core for reporting any of the fracture indexes. However, when a set can be distinguished (parallel or subparallel joints), true spacing is measured normal to the fracture surfaces.

279 FIELD MANUAL

Description of Shears and Shear Zones.—Shears and shear zones should be described in detail, including data such as the percentage of the various components (gouge, rock fragments, and associated features such as dikes and veins) and the relationship of these components to each other. Gouge color, moisture, consistency and composition, and fragment or breccia sizes, shape, surface features, lithology, and strengths are recorded. The depths, dip or inclination, and true thickness, measured normal to the shear or fault contacts, also must be determined, if possible, along with healing, strength, and other associated features. A thorough discussion of shears and shear zones is contained in chapter 5.

Description of Core Loss.—The significance of core loss is often more important than recovered core. Lost core may represent the worst conditions for design concepts, or it may be insignificant, resulting from improper drilling techniques or equipment. Core losses, their intervals, and the interpreted reason for the loss should be recorded on the log.

Written Description Form.—The written description for physical conditions consists of main headings, indented subheadings, and text which describes the important features of the core. Headings and indented subheadings divide the core into readily distinguishable intervals which are pertinent to an engineering geology study. Assigned unit names should correlate with those unit names used for surface mapping. These headings may describe portions of the core or the entire core, depending on how well the headings encompass overall characteristics. Items characteristic of the entire core in one hole may be stated under the major heading; however, in other holes, this same information may have to be broken out into various subheadings because it is not applicable to the entire core. In this discussion,

280 CORE LOGGING several logs are referenced as examples. These logs do not necessarily reflect the established standards, and each may be deficient in some format or context; they are existing logs which are included as examples of different situations which may be encountered. A discussion of headings follows:

1. Main headings — The main heading usually divides surficial deposits from bedrock. However, other methods are also acceptable, for example, the summary log in figure 10-5.

2. First order heading — The first order headings may be based on weathering or lithology. When the initial rock type exhibits more than one weathering break or the lithologic properties are most significant, lithology would be the first order heading. Weathering may be used as first order headings where significant. If a weathering break coincides with a lithologic break, or only one weathering break is present, they may both be included in the main heading. Depending on lithologies present, for example, if there is only one rock type, the first order headings may be based on fracturing. Lithology, weathering, or fracturing can also be the subject of the first order heading. In certain circumstances, a shear or shear zone or other feature could be given a first order or any lower order heading in order to emphasize a feature’s presence or importance. The arrangement which will result in the simplest log is usually the best and should be used. The following examples illustrate the use of first, second, and third order headings. These examples are not intended to represent examples of complete logs.

An example in which weathering is preferred as the first order heading is:

281 FIELD MANUAL

0.0-5.0: SLOPE WASH (main heading).—General description could include the total description of the unit.

5.0-200.0: PALEOZOIC CALAVERAS GROUP (main heading).

5.0-100.3: Moderately Weathered (first order heading based on weathering; descriptions of weathering applicable to all lithologies could be presented here).

5.0-10.9: Basalt 10.9-20.1: Limestone 20.1-50.3: Shale 50.3-100.3: Sandstone

100.3-150.0: Slightly Weathered 100.3-120.2: Sandstone 120.2-150.0: Shale

150.0-200.6: Fresh Shale

An example in which lithology is preferred as the first-order subheading is:

0.0-5.0: SLOPE WASH (main heading).—General description, could include the total description of the unit.

5.0-200.6: PALEOZOIC CALAVERAS GROUP (main heading).—General description applicable to all lithologies.

5.0-100.3: Sandstone (first order heading based on lithology)

5.0-10.2: Intensely weathered

282 CORE LOGGING

10.2-40.1: Moderately weathered

40.1-80.2: Slightly weathered

80.2-100.3: Fresh

100.3-150.1: Fresh Shale (first order heading which combines weathering and lithology)

150.1-200.6: Fresh Diabase

3. Second order heading — The second order heading and the associated description contain the char-acteristics of the rock that are unique to an interval that is not described in the main and first order headings. The second order heading usually is based on weathering if the first order heading is based on lithology. If the first order heading is based on weathering, the second order heading would usually be based on lithology. Fracture data can be described here if similar throughout the interval; if not, divide fracture data into third order headings.

4. Third order heading — The third order heading is usually based on fracture data, subordinate features, variations in lithology, etc. This includes variations of rock quality within a certain lithology due to shears, joints, bedding or foliation joints, or other discontinuities. Core recovery lengths are an indicator of fracturing and should be described under this heading, as in the interval from 87.2 to 101.2 in DH-123 figure 10-1. If the fractures are mainly prominent joint sets or other discontinuities, the spacing and orientation of individual sets, along with the overall fracture characteristics, should be noted.

283 FIELD MANUAL

5. Additional indentations — Additional indentations usually are used to describe important addi-tional subordinate features, such as veins or veinlets, variations in lithology, shears, and zones of non- or poor recovery.

In summary, any information consistent throughout a higher order heading, but usually included in a lower one, should be described in the higher order heading to prevent repetition.

Data Required for the Comments/Explanation Block

The comments/explanation block at the bottom of the log form is used for additional information. This may include abbreviations used, gauge height for packer tests, and notes. The hole start and completion date should be in the heading, as well as the date logged. Revision dates of the log should be noted to ensure that the most recent version of the log can be identified. (Date logged and any subsequent revision dates should be entered in this block). The computer log file name can be recorded in this block.

Method of Reporting Orientation of Planar Discontinuities and Structural Features

True dips can be measured directly in vertical holes. The dips of planar features in vertical holes are recorded as "dips 60E”or "60E dip" (see drawing 40-D-6499, figure 5-9). True dip usually is not known in angle holes; and, orientation is measured from the core axis and called inclination, i.e., "Joints are inclined 45E from the core axis" (figure 5-9). If dips are known from oriented core or other surveys, dips may be recorded instead of inclination

284 CORE LOGGING in angle holes. Figure 5-9 demonstrates how misinter- pretations can occur; the inclination of a joint in the core from a 45E inclined angle hole can be interpreted as a horizontal joint or as a vertical joint by rotating the core.

Core Recovery and Core Losses

Descriptions of core in the Classification and Physical Condition column should describe the recovered core, not only by physical measurements (maximum, minimum, and mostly range or average), but should identify and include the interpretation for any core losses, especially if the losses are thought to represent conditions different from the core recovered. Designers and other users of the completed log can incorporate into their design all the factual data that are seen and recorded. What is not seen or reported (core losses) is more difficult to incorporate into the design and may well be the most significant information. Also, core losses and interpretations of the reasons for their loss are significant engineering data that may correlate open joints, soft zones, or shears from boring to boring or from surface features to the subsurface explorations.

Core losses can result from three generalized conditions: inaccurate measurements by the drillers; poor drilling techniques, equipment, and handling; or geologic conditions. The geologist, using the depth of hole, recovered core, observations of the core, and drillers observations, is the individual to make interpretations of the core loss. All core should be measured by the logger. If using a split-tube barrel, the core should be measured while in the barrel and always after core segments are fitted together (using the midpoint of core ends). Unac- countable losses should be reconciled, and the location of the loss determined.

285 FIELD MANUAL

Tape checks or rod checks are the most reliable and preferred methods for knowing the exact location of geologic conditions (top of each run is known with certainty) and where losses occur. All core runs should be measured and recorded; gains and losses can be transferred to adjacent runs and cancel out each other during the process of determining where the core loss is located. Inaccurate drillers’ measurements, or locations where portions of the previously drilled interval was left in the hole (pulled off, or fell back in and redrilled), can be determined by examining and matching the end and beginning of each core run to see if they fit together or show signs of being redrilled. Gains may be attributed to pulling out the bottom of the hole, mismeasurement, recovering core left in the hole from the previous run, or recovery of expansive, slaking, or stress relieving materials.

Where unaccountable losses occur, the examination of core to determine the reason for that loss is critical. Poor drilling methods (excessive pressure, speed, excessive water discharge from the drill bit, not stopping when fluid return plugs), inaccurate measurements, or geologic conditions responsible for core losses should be determined. Core may have spun in the barrel after blocking; an intensely fractured zone may have been ground up; or a shear zone, open joint(s), solution cavity, or joint fillings may have been washed away. Geologic interpretation of the core loss is based on examining recovered core and the fractures present in the core. Drill water losses and color or changes in the drilling conditions noted by the driller may suggest an interpretation of the core loss. Where losses occur near a recovered clay "seam," clay coats fracture surfaces, slickensides and/or breccia and gouge are present, the core loss may be interpreted as a shear or shear zone. The description should include all the factual information—discontinuity surface orientations, slickensides, coatings, gouge and/or fractures; and the

286 CORE LOGGING interpretation that the loss occurred in a shear. Depending on the confidence in the interpretation based on the observed conditions, the description can be given as "shear," or "shear?," or "probable shear zone." When a portion of a shear zone has been lost during drilling, the no recovery zone should be described as part of the shear and the loss or part of the loss included in the shear's thickness.

Samples

If the geologist selects representative or special samples for laboratory testing, an appropriate space should be left in the core box to ensure that when logs are reviewed or photographs are taken, core recovery is not misleading. Either filler blocks or a spacer which indicates the top and bottom depths of the sample and a sample number can be used to fill the sample space. For N-size cores, a length of 2- by 2-inch (50- by 50-mm) block or other spacers that fill the tray work well. These blocks also should be used to separate core runs. The lettering on the blocks should be easily readable at a distance. Spray painting the blocks white or yellow and lettering them with black waterproof pens enhances visibility and legibility. The sample interval, and sample number if desired, must be recorded in the Samples for Testing column on the log. Portions of the core may be preserved as representative samples or to protect samples from slaking or other deterioration.

287 FIELD MANUAL

Core Photography

General Photographic Methods

Transmittal of core photographs with the final logs is recommended. The photos may be included in the data package or as an appendix to the data report. Cores should be photographed while fresh. Before and after photographs of materials that slake or stress-relieve are recommended. The importance of photographing the core before it has been disturbed in transit and before its moisture content has changed cannot be overemphasized. If proper precautions during transport are followed, and the core is logged in a timely manner, reasonably good photographs can be obtained away from the drilling site. This permits the labeling of core features, if desired.

If possible, cores should be photographed in both color and black and white at 8- by 10-inch (200- by 250-mm) size. Black and white photographs do not degrade over time like color photographs. Core photographs should be submitted with the final logs in the geology data report; color photographs are best for data analysis.

Many methods are employed for photographing core. Each box of core can be photographed separately as the box is first filled or three or more boxes can be photographed at a time. There are advantages to both procedures:

• Greater detail and photographs depicting fresher conditions are the major advantages of photographing each box individually.

• When photographing several boxes at a time, transitional features, changes in weathering or fracturing, or large shear zones can be seen in one photograph.

288 CORE LOGGING

The best method is a combination of the two. Pictures of individual boxes at the drill site and later pictures of the entire hole are the best of two worlds.

Individual Box Photography

Any portion of core that is in danger of altering or disaggregating because of slaking or "discing" due to stress relief, expansion, or shrinkage due to changes in moisture or confinement because of down time, ends of shifts, or weekends must be boxed and photographed. Under these circumstances, the core should be photographed while at or near the material natural condition (even if a box is only partially filled).

Each photograph should be taken from approximately the same distance so that the scale of each photograph is identical. The box should fill the frame of the camera, thereby obtaining the highest quality resolution or core detail, and the camera should be held as close to normal to the core as possible. A tripod should be used if possible. Tilting the core box and, if necessary, standing in a pickup bed or other vantage point may be helpful. Most core boxes can be tilted about 70 to 80E before any core is in danger of spilling out, so very little additional height is required. A simple 2- by 4-foot (0.6- by 1.2-m) wood frame may be constructed, or the core box may be leaned against a tool box, pickup tailgate, or other stable object. A Brunton compass can be used to ensure that the box and the camera are placed at a consistent, uniform angle. Shadows should be eliminated as much as possible.

All core should be photographed both wet and dry. In hot or dry weather, the unphotographed boxed core should be covered by moist cloth. When ready to photograph, any dry zones should be touched up using a wet cloth or

289 FIELD MANUAL paintbrush. In extremely hot weather, the boxed core can be sprayed or sprinkled with water. A water hose, garden sprayer, or spray bottle works well for this operation. Wait for the water to be absorbed so that there is no objectionable sheen or glare-producing film of water on the core at the instant of film exposure.

A labeled lid, letter board, or another frame which shows feature, drill hole number, photograph, or core box number, and depths of the top and bottom of the cored interval should be included in the photograph. A scale in feet and/or tenths of a foot or meters is helpful.

Photographing Multiple Boxes

As soon as possible after the core is removed from the barrel and boxed, the core should be photographed. To facilitate the photography, construct a frame capable of supporting three or more boxes at a time for use at the drill yard or core storage yard. Photograph the core dry then spray with water to bring back the natural moisture color. The same precautions about glare referred to previously should be followed.

A frame which shows the project, feature, hole number, box __ of __boxes, and from—to, as a minimum, should be used for the photograph. Other optional but recommended entries may include date photographed, and a scale.

Special Circumstances

Special photography such as closeups of shear zones or other special features may be worthwhile. When these photographs are taken, a common object or scale should be included to provide the viewer with relative or actual dimensions.

290 CORE LOGGING

When cores are coated with drill mud, a brush, wet rag, or pocket knife should be used to wash or scrape off the mud so that materials are their natural color and features of the core are not obscured. This step obviously must be taken prior to logging the material.

Photograph Overlays

Acetate or mylar overlays on photographs of core can help interpretation of exposed features. Details shown may include labels for shears, weathering, lithologies, or items of special interest. Other items that may be shown on overlays are joint sets, and they may be coded by an alpha or numeric character or by colored ink.

Equipment Necessary for Preparing Field Logs

The following equipment or supplies are necessary for adequately preparing geologic logs: Core recovery sheets and rough log forms or computer data sheets.—For recording core recovery and maintaining accurate depth measurements for determining core loss intervals.

Drillers' reports.—Daily drill reports (figure 10-6) to check measurements for core recovery, identifying changes in condition or contacts in intervals of poor recovery, determining reasons for core loss, and evaluating openness of fractures.

Knife.—Core hardness/strength characteristics; cleaning or scraping drill mud from core to allow logging and measurement of core recovery.

Hammer.—Core hardness/strength characteristics.

291 FIELD MANUAL Figure 10-6.—Daily drill report.

292 CORE LOGGING

Tape measure or folding ruler (engineering scale with hundredths of feet or metric as appropriate).— Recovery measurements, thickness of units, shears and fillings, and spacing of fractures.

Protractor.—Measuring orientation of contacts, bedding and foliation, and fracture orientation.

Hydrochloric acid.—Mineral or cementing agent identification (3:1 distilled water to acid).

Hand lens.—Mineral or rock identification, minimum 10X.

Marking pen.—Waterproof ink for marking core for mechanical breaks, depth marks on core, sample marking.

Paintbrush and/or scrub brush, and water.—For cleaning core and for identifying wet color and incipient fractures.

Color identification charts (Munsel Color System or American Geological Institute Rock Color Chart).

Filler block (spacer) material.—For identifying non- recovery intervals and location of samples and for recording drill depths.

Sample preparation materials.—Wax, heater, container, brush, cheese cloth, etc.

Rock testing equipment.—Schmidt hammer, point load apparatus, pocket penetrometer or torvane.

293 FIELD MANUAL

Instruction to Drillers, Daily Drill Reports, and General Drilling Procedures

Communication between the geologist and driller is extremely important. Establishment of lines of communication, both orally and in writing, is key to a successful exploration program.

The role of the geologist in the drilling program is as an equal partner with the driller at the drill site. Establishment of this partnership at the beginning of the drilling program will result in better data. Failure to establish a good working relationship with the drill crew often results in unanswered questions and a poor quality end product. One way to establish good working rapport is to keep the drillers informed and to plan with them.

Drill Hole Plan

A suggested method for ensuring that a clear understanding of what the drilling requirements and expectations are from the drill hole is the preparation of a drill hole plan. The plan is prepared prior to starting the hole and after the geologist has used available interpretive data and has determined whether special testing and procedures or deviations in standard practice are required. This document provides the driller with information about safety, special site conditions, purpose of the hole, procedures to be followed, water testing requirements, materials expected to be recovered, any special sampling or geophysical testing required, and hole completion requirements.

Guidelines for Drillers

The following guidelines provide a framework for preparing written instructions for drill crews or for

294 CORE LOGGING

contract drill specifications. Also, the guidelines serve to help geologists correct poor drilling procedures, collect additional data, or improve core handling and logging.

Drill Setup.—To ensure that drill holes are completed at the desired location and along the correct bearing and plunge, the use of aiming stakes and a suitable device for measuring angles should be provided by the geologist and used by the drill crews. Drillers should use aiming stakes set by the geologist or survey crew for the specified bearing of the drill hole. The rig must be anchored properly so that it will not shift. If stakes have been removed or knocked over, they should be replaced by the geologist. Also, drillers must ensure the hole is drilled at the designated angle. The geologist should check the plunge angle with Brunton compass, and/or the drillers should use an appropriate measuring device.

Daily Drill Reports Preparation.—The drillers should prepare duplicate daily drill reports using carbon paper (additional copies of each report may be required on contract rigs). All copies must be legible and preferably printed. One copy should be provided to the geologist for monitoring progress and for preparation of the geologic log. The drill report has a space opposite each run for each item of information required; each of these spaces need to be filled out completely. Data should be added to the report or recorded in a notebook after each run. Drillers should record data as it occurs. See drawing 40-D-6484 (figure 10-6) as an example for reporting daily drill activities. Many field offices have local forms on which these data can be recorded. Comments regarding specific items to be recorded on the daily reports are contained in the following paragraphs.

1. Recording depths and core loss — Check for agreement on depths for intervals drilled by

295 FIELD MANUAL

consecutive shifts. Depths should be recorded in feet and tenths of feet or to the nearest centimeter, as appropriate. Tape checks or rod checks may be required at change of shift or more frequently when requested by the geologist. The section entitled “Core Recovery and Core Losses” contains instructions for proper use of core measurements, filler blocks (spacers), and tape checks. The driller is responsible for knowing the depth of the barrel and the hole at all times. Discrepancies between intervals drilled and recovery need to be resolved. Only standard length drill rods should be used. Core should be measured while it is still in the inner barrel and after it is placed in the core box. Record the most correct measurement of the two in the report. In the event core is left in the hole, the next run should be shortened accordingly; the left amount and proper hole entry and startup procedures should be followed to facilitate recovery.

2. Recording drilling conditions — Make sure drilling conditions, such as fast or slow, hard or soft, rough or smooth, even or erratic, moderately fast or very slow, bit blocks off, etc., are indicated for each run. Record time in minutes per foot (meter) of penetration. Any changes in the drilling rate within a run also should be noted along with intervals of caving or raveling. If the bit becomes plugged or blocking off is suspected, the driller should stop drilling and pull the core barrel. Also, when drill circulation is lost, the driller should pull and examine the core.

3. Drilling fluid return and color — The type, color, and estimated percent of drilling fluids returned should be recorded for each core run. The depth of changes in fluid loss or color is particularly

296 CORE LOGGING important. If drilling mud is used, indicate number of sacks used per shift. In case of total loss of drilling fluid, it may be necessary to pressure test the interval.

4. Description of core — Drillers need to describe the core in general terms; i.e., moderately hard, very hard, soft, clay seams, broken, color, etc. If familiar with the rock types, drillers may report more than just general terminology.

5. Water-pressure testing — Holes in rock are typically water tested in 10-foot (3-m) intervals at pressures of approximately ½ lb/in2 (3.5 kilopascals [kPa]) to 1 lb/in2 (6.90 kPa) per foot (1/3 m) of cover up to 100 lb/in2 (690 kPa). NOTE: Pressures may be modified for each site. Factors such as density of materials, "overburden pressure" or "cover," bedding, purpose of testing, distances from free faces, water levels, and artesian pressures all must be taken into account so that pressure testing does not unintentionally hydrofracture the foundation or jack foundation materials. Pressures should be determined by the geologist. If a range of pressures is used, and disproportionately high water losses are obtained at the higher pressures, the pressures should be stepped down and water losses at the lower pressures recorded. Water test pressures should be stepped up 3 to 5 times and then stepped down. Flow versus pressure should be plotted; and if the relationship is not linear or smoothly curved, hydrofracturing or jacking may be occurring. If the decreasing pressure curve does not follow the increasing pressure curve, washing, plugging, or hydrofracturing or jacking may be occurring without the foundation materials returning to the prewater test state. Intentionally increasing the pressure until the foundation is fractured or jacked is a good

297 FIELD MANUAL

way to determine appro-priate grout pressures. Gravity tests, overlapping pressure tests, and variations in the length of the interval tested may be used to ensure complete test data. For example, a packer interval of 8 feet (2.4 m) may be used if the hole is caving too badly to get 10 feet (3 m) of open hole. Also, if a packer will not seat at 10 feet (3 m) above the bottom of the hole and there is good rock at 12 feet (3.66 m), a 12-foot test interval may be used. If losses are above 15 gal/min (1.146 liters per second [L/sec]), exceed pump or system capacity, or water is known to be bypassing the packer, reduce the length of the packer interval and retest.

Losses should be recorded in gallons and tenths of gal/min (L/sec). The driller should record the water meter reading at 1-minute intervals, and the test should be run for a full 5 minutes at each pressure increment after the flow has stabilized. The driller should report the average flow in gal/min (L/sec) for the 5-minute test. Each driller should keep his own record of the packer data in case questions arise concerning the testing. A suggested form for recording data is shown in figure 10-7.

6. Casing or cementing depths — The depth of the casing or the cemented interval should be shown for each core run. Do not cement any more of the hole than is necessary to repair a caving or raveling interval. The use of additives such as calcium chloride or aluminum powder, if permitted, will reduce the set time. These materials should be added to the water and not to the cement.

7. Recording unusual conditions — All unusual conditions or events should be noted in the "Notes"

298 CORE LOGGING Figure 10-7.—Water testing record.

299 FIELD MANUAL

column of the report. This includes such items as sudden changes in drilling speed, loss of circulation, drop of drill string (open joints or cavities), casing and cementing procedures, caving, squeezing, packer failures, and gas.

8. Recording setups, drilling, and downtime — Time must be noted on reverse side of report. Type, number, and size of bit is indicated here also.

9. Recording water level measurements — Measurement should be recorded at the start of each day shift and shown on the day shift report. Holes should be jetted or bailed prior to completion of the hole to obtain reliable water level data. Immediately after jetting or bailing, the depth to water should be recorded.

10. Care of core and core boxes — Split-tube (triple tube) core barrels should be used. If not used, the core should not be damaged when extracted from the core barrel. Do not beat on the barrel with a metal hammer; use a rubber mallet/hammer or a piece of wood. The best way to remove core from a solid barrel is by using a pump to pressurize the inside of the barrel and extrude the core (stand back!). The mud pump will work satisfactorily for this. Core should be extracted from the inner tube and carefully placed into core boxes by hand. The use of cardboard or plastic halfrounds is recommended (see figure 10-8. Core pieces should be fitted into the core box and fragments should be arranged to save space. Long pieces may be broken for better fit in the core box, but a line should be drawn across the core to denote mechanical breaks. If 5-foot (1.5-m) core

300 CORE LOGGING

Figure 10-8.—Use of half-round to protect core.

301 FIELD MANUAL

boxes are used, mechanical breaks to fit 5-foot runs in boxes are reduced. Figure 10-9 shows a typical core box for N-size core.

Core should be placed in the core box from left to right, with the top to the left, bottom to the right, starting at the top of the box so the core reads like a book. The ends and top of the box should be marked with black enamel paint or indelible felt pen. Core blocks, which mark the depths, are placed between each run and the depth marked. Data on the outside of the left end of the box should include the project, feature, drill hole number, box number, and depth interval in the box.

Filler blocks (spacers) are necessary to properly record information and minimize disturbance to the core during handling. Blocks should be placed with a planed side marked with either black enamel paint or indelible felt-tip pen; 2- by 2-inch (50- by 50-mm) blocks work well for N-size core. All core runs must be separated with blocks properly labeled at the top and bottom of the run. Sample intervals should be marked in the boxes using wooden blocks of lengths equal to the missing core so that the sample may be returned to the box. Gaps for core losses should not be left in the core box. Core left in the hole and recovered on the next run may be added to the previous run. Filler blocks inserted where unaccountable core losses occur should show the length of loss in tenths of feet, as follows: LC (lost core) 0.3 foot, or NR (no recovery) 0.3 foot. The core loss block indicates that a certain length of core was unaccountably lost within a run, and the block should be placed at the depth of the core loss. If the point of core loss cannot be determined, the block can be placed in the core box at the bottom of

302 CORE LOGGING Figure 10-9.—Standard N-size core

303 FIELD MANUAL

304 CORE LOGGING

the run, preceding the bottom of run block. Cavities may be marked on the block. All spacer, sample, and core loss blocks should be nailed to the bottom or sides of the box to prevent movement of the core.

At the drill site, core boxes should be lined up, preferably on boards or planks, in order from top to bottom, with labels and up side to left, in a safe area and kept covered with lids. While in the field, do not place boxes where sliding or caving of slopes is likely to occur and keep out of the way of vehicles and equipment. Core boxes, especially those containing soft, slaking, or intensely fractured core material, should be covered immediately to prevent damage by rain or drying. Tray partitions in boxes should be nailed so that nails do not protrude from bottom of boxes.

When the core is moved, be careful to prevent disturbance, breakage, or spilling. Damage to the core during transportation can be minimized by using nailed-down spacers and a 3/4- to 1-inch thick (19-25-mm) foam-rubber pad placed between the top of the core and the secured core box lid.

Hole Completion.—Completion of the drill hole should meet the requirements established by the exploration program and at the direction of the field geologist. Drill holes usually will be completed either with sufficient casing or plastic pipe to assure that the hole will stay open for later water level observations. In areas where vandalism may occur or when long-term monitoring is contemplated, a standpipe and suitable cap with lock should be installed. Completion information should be indicated on the driller's report. The drill hole number should be stamped or welded into the casing. If groundwater observation riser pipes have been installed,

305 FIELD MANUAL install a minimum 3-foot (1-m) length of surface casing with a locking cap as a standpipe to mark the drill hole and protect the riser pipe. Grouted in place, this standpipe can also serve to protect the observation well from infiltration by surface runoff.

Concrete Core Logging

Concrete structures are commonly cored to assess the quality of concrete or as part of foundation investigations on existing features. An early macroscopic assessment of concrete core is warranted for the following reasons:

• Concrete physical condition may suggest changes in the drilling program or sampling techniques that would be difficult to modify after drilling is complete. A different approach in drilling or sampling techniques may be necessary to determine the cause of distress or failure.

• Shipping, handling, and sample preparation may modify the concrete core by inducing, modifying, or masking fractures or causing core disintegration.

• Core could be lost or destroyed before reaching the laboratory.

• Macroscopic examination may provide the required information eliminating the need for a petrographic examination.

This section is based on American Society for Testing Materials Designations (ASTM) C 823-83 and C 856-83.

Purposes of Examination.—Investigations of in- service concrete conditions are usually done to: (a) determine the ability of the concrete to perform

306 CORE LOGGING satisfactorily under anticipated conditions for future service; (b) identify the processes or materials causing distress or failure; (c) discover conditions in the concrete that caused or contributed to satisfactory performance or failure; (d) establish methods for repair or replacement without recurrence of the problem; (e) determine conformance to construction specification requirements; (f) evaluate the performance of the components in the concrete; and (g) develop data for fixing financial and legal responsibility.

In addition to the usual drill log information, the following should be provided, if available:

• Reason for and objectives of the coring program.

• Location and original orientation of each core.

• Conditions of operation and service exposure.

• Age of the structure.

• Results of field tests, such as velocity and rebound or Schmidt hammer data.

Figure 10-10 is an example of a drill hole log showing the types of information that can be shown and a format for a log showing both rock and concrete core.

Examination.—Concrete core is commonly marked in the field showing the top and bottom depths at the appropriate ends and at any of the following features. Below are listed the major items to examine and record:

Fractures — Cracks or fractures in core are best seen on smooth surfaces and can be accented by wetting and partial drying of the surface. Old crack surfaces are often different colors than fresh fracture

307 CORE LOGGING

Figure 10-10.—Log of concrete and rock core.

307 CORE LOGGING surfaces. Old fracture surfaces often have reaction products or alteration of the surfaces. Fractures often follow structural weaknesses.

Reacted particles — Rims on gravel or sand are often caused by weathering processes unless other factors indicate chemical reactions with the cement paste. Crushed aggregate with rims probably is due to chemical reaction with the cement paste.

Reaction products — Crushed aggregate with rims usually indicates alteration in the concrete, such as alkali-silica reaction or alkali-carbonate reaction. Rims in paste bordering coarse aggregate and light colored areas in the paste may be gel-soaked or highly carbonated paste adjoining carbonate aggregate that has undergone an alkali-carbonate reaction. White areas of fairly hard, dry material or soft, wet material that has fractured and penetrated the concrete and aggregate or fills air voids should be recorded. Alkali aggregate reaction products can be differentiated from calcium carbonate deposits by using hydrocloric acid. The reaction products do not fizz.

Changes in size or type of fine and coarse aggregate — Sizes, shapes, and types of aggregate can vary in a structure due to changes in mixes, placement procedure, or sources and should be logged.

Voids — Voids (honeycomb, popcorn) are indicators of trapped air, inadequate vibration, or insufficient mortar to effectively fill the spaces among coarse aggregate particles. Voids should be described and the volume percent estimated.

309 FIELD MANUAL

Segregation of components — Concrete components can become segregated or concentrated during placement. Large aggregate sizes can separate from fine aggregate, and paste can separate from the aggregate, especially near forms or finished surfaces.

Cold joints or lift lines — Weak joints or zones can form in concrete due to long periods between buckets or mixer loads. Poor vibration or poor or improper preparation of previous lift surfaces can form zones of weakness or actual planes similar to joints in rock. These surfaces, called lift lines, should be described and any material on the surfaces described. Lift lines can be very subtle and difficult to locate. Design or construction data often provide clues as to where to look for lift lines and construction joints. The core should be examined wet. Clues to lift line locations are: (1) aligned aggregate along the surfaces each side of a line, (2) coarser aggregate above the lift line than is below the line, (3) different shape, gradation, or composition of aggregate above and below the lift line, (4) a thin line of paste on the lift line, and (5) no aggregate crosses the lift line.

Steel or other imbedded items — Reinforcing steel and orientations should be described as well as other materials encountered such as timber, steel lagging, dirt, or cooling pipes.

Changes in color of the cement — Changes in paste color can indicate reaction products or changes in cement type or cement sources and should be logged.

Aggregate-paste bond — The bond between the aggregate and cement should be described. A good bond is characterized by concrete breaking through

310 CORE LOGGING the aggregate and not around the particles. A fair bond is characterized by concrete breaking through and around the aggregate. A poor bond has concrete breaking around the aggregate.

Aggregate rock type — The aggregate rock type can be important in determining the causes of concrete problems. For example, limestone often has chert inclusions suggesting an aggregate reaction, whereas an igneous rock such as granite probably will not react with cement. Both the coarse and fine aggregate should be examined.

Aggregate shape — Aggregate shape is usually unique to each source. Rounded or subrounded aggregate is probably natural. Angular (sharp) aggregate is probably crushed.

Mechanical breaks — Mechanical breaks in the core and whether the break is around or through the aggregate should be noted.

311 Chapter 11

INSTRUCTIONS FOR LOGGING SOILS

General

All subsurface investigations of soils for construction materials and for most engineering purposes using test pits, trenches, auger holes, drill holes, or other exploratory methods should be logged and described using the standards in USBR 5000 [1] and 5005 [1] (Unified Soil Classification System [USCS]) in accordance with the established descriptive criteria and descriptors presented in chapter 3 and the guidelines presented in this section.

All investigations associated with land classification for irrigation suitability, as well as data collection and analyses of soil and materials related to drainage investigations, should be logged and described using the U.S. Department of Agriculture terminology outlined in appendix I to Agriculture Handbook No. 436 (Soil Taxonomy), dated December 1975 [2].

Test pits and auger holes may be logged on a form (figure 11-1), or logs may be computer generated. For metric design studies and specifications, information is to be in metric units. For specifications using English units, the written soil description should use metric units for the description of soil particle sizes (millimeters instead of inches). Example word descriptions are shown in figures 11-2 through 11-11. FIELD MANUAL

Figure 11-1.—Log of test pit or auger hole.

314 LOGGING SOILS

Figure 11-2.—Clean coarse-grained soils.

315 FIELD MANUAL

Figure 11-3.—Fine-grained soils.

316 LOGGING SOILS

Figure 11-4.—Soil classifications based on laboratory test data.

317 FIELD MANUAL

Figure 11-5.—Auger hole with samples taken.

318 LOGGING SOILS

Figure 11-6.—Reporting laboratory classification in addition to visual classification.

319 FIELD MANUAL

Figure 11-7.—Undisturbed soils.

320 LOGGING SOILS

Figure 11-8.—Coarse-grained soils with fines.

321 FIELD MANUAL

Figure 11-9.—Coarse-grained soils with dual symbols.

322 LOGGING SOILS

Figure 11-10.—Reporting in-place density tests and percent compaction.

323 FIELD MANUAL

Figure 11-11.—Soil with measured percentages of cobbles and boulders.

324 LOGGING SOILS Formats for Test Pits and Auger Hole Logs

General Instructions

The following subsection provides general instructions for log format and descriptions. Refer to chapter 3 for descriptive criteria, classification, and group names and symbols. • Capitalize the group name. If cobbles and boulders are present, include them in the typical name.

• Describe plasticity of fines as: “approximately 30 percent (%) fines with high plasticity” “approximately 60% fines with low to medium plasticity” “approximately 10% nonplastic fines”

• Give results of hand tests when performed.

• Use “reaction with hydrochloric acid (HCl).”

• Do not give unnecessary information such as “no odor,” “no gravel,” and “no fines.”

However, the negative result of a hand test is positive information and should be reported as “no dilatancy,” “nonplastic,” “no dry strength,” or “no reaction with HCl.”

For reporting maximum particle size, use the following: Fine sand Medium sand Coarse sand 5-millimeter (mm) increments from 5 mm to 75 mm 25-mm increments from 75 mm to 300 mm 100-mm increments over 300 mm

325 FIELD MANUAL For example, “maximum particle size 35 mm” or “maximum particle size 400 mm” are the correct format and size increment.

Table 11-1 is a checklist for log descriptors. Format for descriptions, results, and other information are in the following subsections.

Table 11-1.—Checklist for the description of soils in test pit and auger hole logs

1. Group symbol. - Capitalized and shown in the left- hand column. 2. Depth. - Depths of interval classified, shown in either meters or feet and tenths of units in second column from the left. 3. Identification of sample. - Type and size of sample and origin of sample, shown in third column from the left. 4. Classification and description column. - a. First paragraph. - (1) Depth of interval classified (2) Group name capitalized (3) Percent of fines sand and gravel by weight (include trace amounts but not added to percentage which must equal 100 percent) (4) Description of particles (a) Particle size range: describe as either gravel - fine or coarse, or sand—fine, medium, or coarse (b) Hardness of particles (coarse sand and larger) (c) Particle angularity (angular, subangular, sub-rounded, or rounded) (d) Particle shape (flat, elongated, or flat and elongated) (e) Maximum particle size or dimension

326 LOGGING SOILS (5) Description of fines (a) Plasticity (nonplastic, low, medium, or high) (b) Dilatancy (none, slow, or rapid) (c) Dry strength (none, low, medium, high, or very high) (d) Toughness (low, medium, or high) (6) Moisture condition (dry, moist, or wet) (7) Color (moist color) (8) Odor (mention only if organic or unusual) (9) Reaction with HCl (none, weak, or strong) b. TOTAL SAMPLE (BY VOLUME): second paragraph, if applicable - i.e., more than 50 percent plus 75-mm material (1) Percent of cobbles and percent of boulders (2) Same information as item 4.a (4) c. IN-PLACE CONDITION: third paragraph (second paragraph if less than 50 percent oversize) (1) Consistency; fine-grained soils only (very soft, soft, firm, hard, or very hard) (2) Structure (stratified, lensed, slickensided, blocky, fissured, homogeneous) (3) Cementation (weak, moderate, strong) (4) Moisture (if an in-place condition paragraph is included, moisture is not described in the first paragraph) (5) Color (if an in-place condition paragraph is included, color is not described in the first paragraph) (6) Result of in-place density and/or moisture tests d. GEOLOGIC INTERPRETATION: (fourth paragraph) geologic description including genetic name, stratigraphic name if known, and any local name.

327 FIELD MANUAL 5. Remarks block. - Provide additional description or remarks such as root holes, other debris found, caving, degree of difficulty to auger or excavate, reason for refusal or reached predetermined depth, and water level information or hole completion.

Figure 11-12 is a field form for logging soils.

Reporting by Method of Classification

Preparation of Logs Based on Visual Classifica- tion.—List fines, sand, and gravel in descending order of percent (must add up to 100 percent). For visual classification, estimate percentages to the closest 5 percent. Precede the estimated percentages with “approx.,” not “about.” If a component is present but is less than 5 percent of the total, use “trace.” “Trace” is not included in the 100 percent.

Preparation of Logs Based on Laboratory Classifi- cation.—When logs are prepared using laboratory classifications (based on laboratory tests), the information must be presented on the log as shown in figure 11-4. The difference between a laboratory and a visual classification is depicted in figure 11-6.

The visual classification should not be changed, nor should the estimated percentages, plasticity description, or the results of the hand tests (dry strength, dilatancy, and toughness) be changed to reflect laboratory tests results. The visual classification is based on the total material observed; whereas, the laboratory classification is based on a representative sample of the material.

328 LOGGING SOILS FIELD FORM—SOIL LOGGING HOLE NO. ____

DATE ______PROJECT ______FEATURE ______AREA ______DRILLER ______LOGGED BY ______

SAMPLE INTERVAL AND TYPE: Type Moisture Sample Sample Interval ______Sample Weight (Lbs) ______Interval______

Typical Name ______Group Symbol ______

SIZE DISTRIBUTION, CHARACTERISTICS: (5-mm increments from 5 to 75 mm, 255-mm increments from 75 to 300 mm, 100mm increments over 300 mm)

Boulders (>300 mm) __% (vol.) Max. size (mm) __ Hardness __ Angularity _____

Cobbles (75-300 mm) __% (vol.) Max. size (mm) ___ Hardness ___ Angularity ____

Gravel __% Coarse (20-75 mm) __ Fine (5-20 mm) ___ Hardness ___ Angularity __

Sand ___% Coarse ___ Medium ___ Fine ___ Hardness ___ Angularity _____

Fines _____% Plasticity: Nonplastic _____ Low _____ Medium _____ High _____ Dilatancy: No _____ Slow _____ Rapid _____ Dry Strength: No ____ Low ____ Medium ____ High ____ Very High ____ Toughness: Low _____ Medium _____ High _____

Maximum Size: Fine Sand ____ Medium Sand ____ Coarse Sand ______mm

Moisture: Dry _____ Moist _____ Wet _____

Color ______Odor ______Organic Debris and Type ______

Reaction with HCl: None _____ Weak _____ Strong _____

EXCAVATING/AUGERING/DRILLING CONDITIONS:

Hardness: Very Soft _____ Soft _____ Hard _____ Very Hard _____

Penetration Action: Smooth ___ Mod. Smooth ___ Mod. Rough ___ Rough ____

Penetration Rate: Very Fast ____ Fast _____ Slow _____ Very Slow _____

PAGE ___ OF ___

Figure 11-12.—Field form - soil logging.

329 FIELD MANUAL The specimens for testing are to be samples that represent the entire interval being described (see USBR 7000 and 7010 [1]). The material collected must be split or quartered to obtain the specimen that is to be tested in the laboratory.

Coefficients of uniformity and curvature (Cu and Cc) are to be calculated and reported on the logs for coarse- grained materials containing 12 percent or less fines.

Laboratory gradation percentages and Atterberg limits are to be reported to the nearest whole number.

Procedures for Reporting Laboratory Data in Addi- tion to Visual Classification and Description.—In some instances, gradation analyses and Atterberg limit tests are performed on soil samples in conjunction with preparation of logs of test pits or auger holes. These data should be shown on the logs and clearly identified as laboratory test data.

Specimens for testing are to be from samples that represent the entire interval being described. If this is not possible, the location of the sample should be given as part of the word description. The sample taken should be split or quartered to get the specimen size required for testing (figure 11-5, interval 0.0 to 9.8 feet (ft).

Laboratory test data are to be presented in a separate paragraph. If the test results indicate a different classification, and therefore different group symbol and/or group name than the visual classification, give the laboratory classification symbol and name in this paragraph (figure 11-6).

330 LOGGING SOILS Note: For logs which incorporate the test results, the statement “Classification by laboratory” should be placed in the “Remarks” portion of the log.

Coefficients of uniformity and curvature (Cu and Cc) are to be calculated and reported on the logs for coarse- grained materials containing 12 percent or less fines.

All laboratory gradation percentages and Atterberg limits are to be reported to the nearest whole number.

Reporting Undisturbed (In-Place) Conditions

List in-place conditions on logs of test pits in a separate paragraph (figure 11-7). Do not give in-place soil conditions (consistency, compactness) on auger hole logs (unless the holes are large enough to inspect). Instead, describe difficulty of augering (figure 11-8). Also describe caving or any other unusual occurrences during drilling of the auger hole.

In-place density tests are often performed in test pits or trenches. When a large quantity of logs are reviewed, density information on the log can save time, even though additional time is required for preparation of the log.

Results of in-place density tests that are performed in test pits or trenches are to be included on the log in the descriptive paragraph on in-place conditions, as illustrated in figure 11-10.

Results of any laboratory compaction tests (Proctor, minimum and maximum density) performed on the material from the in-place density tests or from the pit or trench are to be included on the log.

331 FIELD MANUAL For pipeline investigations, the percent of the maximum dry density or the percent relative density should be in parentheses on the logs (figure 11-10).

Densities are reported to the nearest 0.1 pound per cubic foot (lb/ft3) or 1 kilogram per cubic meter (kg/m3). Moisture content is reported to the nearest 0.1 percent. Percent of laboratory maximum dry density or relative density is reported to the nearest whole number.

Geologic Interpretations

Geologic interpretations should be made by or under the supervision of a geologist. Give geologic interpretation in a separate paragraph (figure 11-7). Interpretation should also be included in the narrative section of the materials portion of the design data submittals.

Description Formats on Test Pit and Auger Hole Logs for Soils with Cobbles and Boulders

If the soil has less than 50 percent cobbles and boulders (by volume), give the group name of the minus 75-mm portion and include cobbles and/or boulders in the group name (figure 11-11). Use two paragraphs to describe soil. Refer to chapter 3 for a more complete discussion of classification and classification group names and symbols.

• Describe the minus 75-mm fraction in the first paragraph. These component percentages are estimated by weight.

• Describe the total sample in a second paragraph. These percentages are estimated by volume. Even if the percentage of cobbles and boulders is determined by measurement, use “approx.” in the word description.

332 LOGGING SOILS If the soil has more than 50 percent cobbles and boulders (by volume), list cobbles and boulders first in the name (figure 11-13). Do not give a group symbol or group name.

• Describe the total sample in the first paragraph. Percentages are estimated by volume.

• Describe the minus 75-mm fraction in a second paragraph. Percentages are estimated by weight.

Angular particles larger than 75 mm are described as cobbles and boulders, not as rock fragments. A description of their shape should be provided in the word description.

Description of Materials Other than Natural Soils

Materials which are not natural soils are not described or classified in the same manner as natural soils. The section titled “Use of Soil Classification as Secondary Identification Methods for Materials other than Natural Soils”, chapter 3, outlines the criteria to be followed and provides example descriptions for test pit and auger hole logs. Refer to appropriate sections in chapter 3 for example format and descriptions. Figures 11-14 through 11-17 show a variety of logs of test pits and auger holes reflecting miscellaneous conditions.

Format of Word Descriptions for Drill Hole Logs

The descriptions of surficial deposits and soil-like materials in geologic logs of exploration holes should use similar descriptive criteria and format established for test pits and auger holes except as noted in the following paragraphs.

333 FIELD MANUAL

Figure 11-13.—Soil with more than 50 percent cobbles and boulders.

334 LOGGING SOILS

Figure 11-14.—Borderline soils.

335 FIELD MANUAL

Figure 11-15.—Test pit with samples taken.

336 LOGGING SOILS

Figure 11-16.—Disturbed samples.

337 FIELD MANUAL

Figure 11-17.—Two descriptions from the same horizon. (Top) Undisturbed soil containing estimated percent of boulders. (Bottom) Disturbed soil containing trace of cobbles.

338 LOGGING SOILS Exceptions to Test Pit and Auger Hole Format and Descriptions for Drill Hole Logs

Unlike test pit logs where geologic interpretations may be provided at the bottom of the log form, geologic interpretations are required on drill hole logs. The geologic classification (e.g., Quaternary Alluvium, Quaternary Glacial Outwash, Quaternary Landslide, Tertiary Basin Fill Deposits) should be provided as main headings on the geological drill hole log.

Group names are capitalized in all test pit and auger hole logs. Where capitalization of the group name would conflict with main headings on drill hole logs, capitalize only the first letter of each word of the group name and the group symbol. If the first letter of each word is not capitalized, the group name is considered informal usage only and not a classification.

Classification and word description format for drill hole logs is similar to those used for test pit logs. Also, materials recovered from drill holes are generally considered to represent in-place conditions. These criteria do not apply when samples are not recovered or when poor recovery precludes classification (figure 11-18).

Samples Recovered from Wash Borings or as Cuttings

When drill holes are advanced with a rock bit, water jet, or other nonsampling methods, a group symbol and name or classification of the recovered materials should not be assigned, nor should in-place descriptions, such as consistency, be used. However, descriptive criteria, such as particle size, dry strength, and reaction with HCl, should be provided using the same terminology and format used for auger holes.

339 FIELD MANUAL Figure 11-18.—Drill hole advanced by tri-cone rock bit.

340 LOGGING SOILS Descriptions should be preceded by “Recovered cuttings as . . .” or “Recovered wash samples as. . .” (figure 11-18, interval 0.0-11.7 ft.

Poor or Partial Recovery

Where poor or partial recovery precludes accurate classification, a primary classification should not be assigned, but as much descriptive information as possible should be provided. Recovered materials, together with drilling conditions, cuttings, and drilling fluid color or losses, may be used to interpret reasons for losses and types of materials lost. However, an appropriate subheading (i.e., “Poor Recovery”) should be used (figure 11-19, 2.1 to 3.9 ft.

Materials Other Than Soils and Special Cases

As discussed in chapter 3, “Use of Soil Classification as Secondary Identification Methods for Materials Other Than Natural Soils,” exceptions to the test pit and hole classification and format are also applicable to hole logs. These special cases include processed or manmade materials, shells, partially lithified or poorly cemented materials and decomposed bedrock, and shallow surficial deposits or soils. Other special categories of soil-like materials should be classified by USBR 5000 or USBR 5005[1]. These are soil-like slide-failure zones or planes; shear or fault zones; bedrock units which are recovered as soil-like material or consist of soil-like material; and landslides and talus (figures 11-20, 11-21, and 11-22).

Format and classification for these exceptions are described below.

341 FIELD MANUAL Figure 11-19.—Log showing poor recovery.

342 LOGGING SOILS Figure 11-20.—Log of landslide material (a).

343 FIELD MANUAL Figure 11-21.—Log of landslide material (b).

344 LOGGING SOILS Figure 11-22.—Log of bedrock.

345 FIELD MANUAL Processed or Manmade Materials.—Surficial deposits such as tailings, crushed rock, shells, or slag are assigned a genetic name such as filter, bedding, drain material, shells, tailings, or road base, and a classification group name and symbol are assigned in quotation marks, for example: Filter material, “poorly graded sand (SP-SM).” Soil descriptors are then used to describe the materials.

Where drill holes penetrate embankment materials, main headings on the drill hole logs should be a classification of the type of embankment, such as “Zone 3 Miscellaneous Embankment.” The materials recovered in each interval are classified, and group names and symbols are provided as subheadings. See 1.0- to 3.9-ft and 3.9- to 15.4-ft intervals shown in figure 11-19.

Partially Lithified or Poorly Cemented Materials and Decomposed Rock.—Descriptions of partially lithified or poorly cemented materials such as siltstone, claystone, sandstone, and shale or decomposed rock which are broken down during drilling or field classification testing should be classified by an appropriate rock unit name or by geologic formation name, if known, of the in- place materials. The materials are then described using descriptors for rock (chapter 4). A soil classification for the broken down materials should be reported in quotation marks on the drill logs and all figures, tables, drawings, or narrative descriptions. The disaggregating mechanism (e.g., drilling or testing) should be specified (figure 11-22, interval 17.3 to 67.9 ft).

Shallow Surficial Deposits.—Surficial deposits such as drill pad or dozer trench fill for drill setups, shallow slope wash, or topsoil materials which will not be used in, or influence, design or construction may be classified by genetic classification (e.g., “fill,” “slopewash,” or “topsoil”). Complete classification descriptions are not required on drill hole logs; however, a classification name and/or

346 LOGGING SOILS symbol may be assigned and is often desirable. Although a complete description is not required on each log, an adequate description of these materials should be provided in a general legend or explanation drawing and in the narrative of the report, if not completely described in drill hole logs.

Slide Failure Zones or Planes, Shear or Fault Zones, and Interbeds Recovered as Soil-like Materials.—These features should be described using geologic names as well as behavior and soil classifications.

Landslides and Talus.—Surficial deposits such as landslides and talus should be assigned their genetic geologic name in the main headings of the drill hole log. Landslide debris composed primarily of soils is classified as landslides in the main heading. Soil-like materials should be classified and group names and symbols provided in the headings. The materials are then described using the descriptive criteria for drill hole logs. Where materials are predominantly rock fragments such as talus and block slides, the materials should be logged similar to the method used in figure 11-22.

Equipment Necessary for Preparing the Field Log

The following is a list of equipment for field testing and describing materials.

Required equipment: • Small supply of water (squirt bottle)—for performing field tests • Pocket knife or small spatula • Materials for taking or preserving samples—sacks, jars, labels, cloth, wax, heater, etc.

347 FIELD MANUAL • Hammer—for hardness descriptors • Tape measure and/or rule (engineer's scale and metric scale) • Petrie dish for washing specimens • Small bottle of dilute hydrochloric acid [one part HCl (10 N) to three parts distilled water. When preparing the dilute HCl solution, slowly add acid into the water following necessary safety precautions. Handle with caution and store safely. If solution comes in contact with skin, rinse thoroughly with water.] • Rags for cleaning hands • Log forms

Optional apparatus:

• Small test tube and stopper or jar with lid • Plastic bags for “calibration samples” • Hand lens • Color identification charts • Paint brush and/or scrub brush and water for cleaning samples • Marking pens • Protractor • Drillers' reports for drill holes • Comparison samples (in jars): fine gravel—3/4 inch to No. 4 sieve; medium sand—No. 4 to No. 10 sieve; and coarse sand—No. 10 to No. 40 sieve • Small No. 4 and 200 sieves

348 LOGGING SOILS Example Descriptions and Format

The examples which follow illustrate the preferred format, description, and organization, and some of the more significant exceptions to typical standards.

Laboratory Classifications in Addition to Visual Classifications

In some instances, laboratory classifications may be determined in addition to the field visual classification. This may be done to confirm the visual classification, particularly when starting work in a new location or because the classification may be critical.

The laboratory data used must be reported in a separate paragraph at the end of the work description, as shown in the examples in figure 11-23. If the laboratory classification is different from the visual classification, as in the upper example, give the group symbol in the left- hand column and the group name in the paragraph on the laboratory data.

DO NOT CHANGE THE VISUAL CLASSIFICATION OR DESCRIPTION. The visual classification is based on a widely observed area in the excavation, whereas the laboratory classification is based on a sample of the material.

If the visual classification was the best judgment of an experienced classifier, both are correct in what they represent.

349 FIELD MANUAL

Figure 11-23.—Geologic interpretation in test pit (sheet 1).

350 LOGGING SOILS Word Descriptions for Various Soil Classifications

Figures 11-6 to 11-17 illustrate some typical word descriptions based on the soil classifications.

Logs are generally typed and single spaced. The examples in this manual are presented double spaced for legibility.

Samples Taken

In addition to the brief description of the samples taken under the “classification group symbol” column, a more complete description of any samples taken from each depth interval is included in the word descriptions. The description should include the size of the sample, the location represented by the sample, and how the sample was obtained (e.g., quartering and splitting).

Examples of how to report the sample information for a pit or trench are shown in figures 11-24 through 11-33.

Some examples use the abbreviated method of indicating the group name with the group symbol. This abbreviated method is described in appendix X5 in USBR 5000, “Determining Unified Soil Classification (Laboratory Method)” [1] and chapter 3.

Reporting Laboratory Data

Classifications Based on Laboratory Data

If the soil classification reported on the logs is based on laboratory data and not a visual classification, this should be clearly and distinctly reflected on the log.

351 FIELD MANUAL

Figure 11-24.—Geologic interpretation in test pit (sheet 2).

352 LOGGING SOILS using a geologic profile (1). Figure 11-25.—Geologic interpretation in test pit

353 FIELD MANUAL

Figure 11-26.—Geologic interpretation in test pit (sheet 3).

354 LOGGING SOILS

Figure 11-27.—Geologic interpretation in test pit (sheet 4).

355 FIELD MANUAL using a geologic profile (2). Figure 11-28.—Geologic interpretation in test pit

356 LOGGING SOILS

Figure 11-29.—Geologic interpretation in test pit (sheet 5).

357 FIELD MANUAL

Figure 11-30.—Geologic interpretation in test pit (sheet 6).

358 LOGGING SOILS

Figure 11-31.—Geologic interpretation in test pit (sheet 7).

359 FIELD MANUAL

Figure 11-32.—Geologic interpretation in test pit (sheet 8).

360 LOGGING SOILS

Figure 11-33.—Geologic interpretation in test pit using a geologic profile (3).

361 FIELD MANUAL The laboratory data should be reported on the log form as shown in the examples in figure 11-4.

The location of the sample and any laboratory tests performed need to be clearly described.

The coefficients of uniformity and curvature (Cu, Cc) are to be calculated and reported for coarse-grained soils containing 12 percent fines or less.

Gradation percentages and Atterberg limits are to be reported to the nearest whole number.

The fact that the classification is a laboratory classification needs to be indicated in the “classification group symbol” column.

The words “about” or “approximately” are not used in the word description.

Soils with More Than 50 Percent Cobbles and Boulders

If the soil contains more than 50 percent (by volume) cobbles and/or boulders:

1. The first paragraph describes the total sample and includes the information on the cobbles and boulders. The information in the paragraph is the same as described previously for cobbles and boulders. 2. The words “COBBLES” or “COBBLES AND BOULDERS” are listed first in the classification group name:

362 LOGGING SOILS COBBLES WITH POORLY GRADED GRAVEL COBBLES AND BOULDERS WITH SILTY GRAVEL 3. A classification symbol is not given. Where a report or form requires a classification symbol, use the words “cobbles” or “cobbles and boulders” instead. An example of a word description for a soil with more than 50 percent cobbles and boulders is shown in figure 11-13.

Special Cases for USCS Classification

Some materials that require a classification and description according to USCS should not have a heading that is a classification group name. When these materials will be used in, or have influence on, design and construction, they should be described according to the criteria for logs of tests pits and auger holes, and the classification symbol and group name should be in quotation marks. The heading should be as follows:

TOPSOIL DRILL PAD GRAVEL ROAD SURFACING MINE TAILINGS UNCOMPACTED FILL FILL

For example:

Classification symbol Description

TOPSOIL 0.0 to 1.6-ft TOPSOIL—would be classified as “ORGANIC SOIL (OL/OH).” About 90%

363 FIELD MANUAL fines with low plasticity, slow dilatancy, low dry strength, and low toughness; about 10% fine to medium sand; soft, wet, dark brown, organic odor; roots present throughout strata; weak reaction with HCl.

Reporting In-Place Density Tests

In-place density tests are sometimes performed in test pits in borrow areas so that in-place densities can be compared with the expected compacted densities for the embankment. The required volume of material needed from the borrow area can also be calculated. The in-place density is also used to evaluate the expansion or collapse potential for certain soils.

The density should be reported in the paragraph on in-place condition. Examples of the format are shown in figure 11-10. The upper example is used when only the density is determined. The lower example is used when a laboratory compaction test is also performed to calculate the percent compaction (or D value if rapid method is used) (USBR 7240, [1]). For cohesionless soils, similar information is reported for the maximum index density, the minimum index density, and the percent relative density.

If the in-place density test hole spans two (or more) depth intervals of classification, the data and comments for the test should be placed in the interval description corresponding to the top of the test hole. At the end of the information reported, the comment (in all capital letters) must be added: “NOTE: TEST EXTENDED INTO UNDERLYING INTERVAL.” An in-place density test should not span different materials or layers.

364 LOGGING SOILS Because the laboratory compaction test is generally performed on the material removed from the test hole, note that the data are for a mixture of intervals by adding, “NOTE: COMPACTION TEST PERFORMED ON MATERIAL MIXED FROM TWO DIFFERENT INTERVALS.”

The density units are lb/ft3 or kilonewtons per cubic meter (kN/m3).

Samples Taken

In addition to the brief description of the samples taken under the “Classification Group Symbol” column, a more complete description of any samples taken from each depth interval is included in the word description. The description should include the size of the sample, the location represented by the sample, and for each sample, how the sample was obtained (e.g., quartering and splitting).

An example of how to report the sample information for an auger hole is shown in figure 11-17. An example of how to report the sample information for a test pit or trench is shown in the section on word descriptions of undisturbed samples.

The approximate weight of samples should be stated.

Measured Percentages of Cobbles and Boulders

If the percentages of the plus 3-inch particles are measured, not estimated, the percentages are reported to the nearest 1 percent. In the word description for the plus 3-inch particles, do not use the term “about” before the percentages.

365 FIELD MANUAL The procedure for measuring the percent by volume of cobbles and boulders is given in the test procedure, USBR 7000, “Performing Disturbed Soil Sampling in Test Pits”[1]. This method is rarely used; percentages are usually estimated. It is not recommended that the percentages be measured for auger holes, since the mass of material recovered is generally insufficient to obtain a reliable gradation of plus 3-inch particles.

Figures 11-23 through 11-33 show a variety of logs of test pits using both the USCS and the geologic interpretation of the parent material. Note that USCS indicates that bedrock has been altered or weathered to a soil-like material. For engineering considerations, use the USCS but present the rock conditions as well.

BIBLIOGRAPHY

[1] Bureau of Reclamation, U.S. Department of the Interior Earth Manual, Part 2, third edition, 1990.

[2] U.S. Department of Agriculture, Agriculture Handbook No. 436, Appendix I (Soil Taxonomy), December 1975.

366 Chapter 12

HAZARDOUS WASTE SITE INVESTIGATIONS

General

Hazardous waste site investigations are geologic by nature. Site geology affects how the contaminants enter and migrate through the environment, controls the severity of the contamination problem, and determines if and how the contamination is remediated. An accurate characterization of site geology is critical for the successful removal and/or remediation of hazardous waste.

Investigations at hazardous waste sites use the same basic tenets of geology commonly applied in other areas of engineering geologic exploration. Even though these engineering geologic investigation techniques are universal, certain specialized criteria and regulations are required at hazardous waste sites which differ from traditional geologic work. This chapter assumes that accepted geologic procedures and equipment are used at hazardous waste sites and only discusses the variations in the planning, implementation, and documentation of geologic field work required at such sites. Documentation at hazardous waste sites plays a very prominent role and involves much more effort than other geologic investigations.

This chapter provides a general overview of documents, terminology, processes, requirements, and site specific factors for an investigation. This information can be used to better prepare or conduct a field program. Much information provided here is extracted from numerous Environmental Protection Agency (EPA) guidance documents. Hazardous waste investigations involve a FIELD MANUAL myriad of documents and processes, mostly referred to by acronyms. See the appendix for an explanation of the more common acronyms.

In hazardous waste investigations, understanding the contaminant’s physical and chemical properties is very important. These properties are useful for predicting pathways that allow contaminant migration through complex subsurface conditions. The understanding of subsurface conditions permits a program designed to better investigate and sample potentially contaminated soil, rock, and water.

Common Terminology and Processes

The "typical" hazardous waste site remediation process involves several investigation phases. Each phase usually has a different emphasis and a different level of detail.

In general, there are two sets of regulations involved in hazardous waste site remediation: Resource Conserva- tion Recovery Act (RCRA) and Comprehensive Environ- mental Response, Compensation, and Liability Act (CERCLA). RCRA regulations are largely confined to operators and generators of existing facilities, whereas CERCLA regulations are confined to the investigation of abandoned sites (Superfund). Although most Bureau of Reclamation (Reclamation) activities involve CERCLA investigations, wastes generated during the investigation may fall under RCRA regulations.

According to EPA guidelines (Guidance for Performing Preliminary Assessments Under CERCLA, EPA/540/G- 91/013), EPA uses a structured program to determine appropriate response for Superfund sites. The CERCLA/

368 HAZARDOUS WASTE

Superfund Amendments and Reauthorization Act of 1986 (SARA) process ideally evolves through the following phases: (1) discovery, (2) preliminary assessment, (3) site inspection, (4) hazard ranking, (5) remedial investigation, (6) feasibility study, (7) record of decision, (8) remedial design, (9) remedial action, and (10) operation and maintenance. Removal actions may occur at any stage.

Documentation

Proper documentation at jobs involving hazardous waste is more important than at more "traditional" geologic investigation sites. The alleged low concentration values for risks to human health and the associated costs for contaminant testing are primary reasons for good documentation. Soil contaminants are typically reported in parts per million (ppm) (milligram per kilogram [mg/Kg]) and water contaminants are typically reported in parts per billion (ppb) (microgram per liter [µg/L]). Since relatively low concentration levels may influence a decision for an expensive cleanup, the prevention of cross contamination and proper testing procedures is a necessity. Also, proper documentation is necessary for legally defensible data.

EPA has established documentation requirements for investigations. This chapter discusses the various documents needed by EPA under the Superfund program with an emphasis on the Sampling and Analysis Plan (SAP). Other documents such as the Health and Safety Plan (HASP), Spill Prevention Plan, and Community Relation Plan are often pertinent to the field operation.

The SAP will assist in preparing the required documents necessary before actual site work begins. Specific requirements for individual programs vary greatly, and

369 FIELD MANUAL common sense and regulatory concurrence dictate the level of detail needed. The EPA report Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, Interim Final, October 1988 (EPA/540/G-89/004) provides additional details regarding EPA-required documentation.

Work Plan (WP)

The WP includes a review of the existing data (background and study rationale), documents the decisions to be made during the evaluation process, and presents anticipated future tasks. The WP also designates responsibilities and sets the project schedule and cost. The primary use of the WP is to provide an agreed procedure to accomplish the work. The WP also provides other interested agencies (such as local government agencies) the opportunity to review proposed work. The WP is placed in the Administrative Record.

The WP may include an analysis and summary of the site background and physical setting, an analysis and summary of previous studies and response actions, a presentation of the conceptual site model (including the nature and extent of contamination), a preliminary assessment of human health and environmental impacts, additional data needs to conduct a baseline risk assessment, the preliminary identification of general response actions and alternatives, and the data needs for the evaluation of alternatives.

Sampling and Analysis Plan (SAP)

The SAP provides the "nuts and bolts" of the procedures to be used at a site and must be site specific. The SAP should consist of three parts:

370 HAZARDOUS WASTE

(1) A Field Sampling Plan (FSP) that provides guidance for all field work by defining in detail the sampling and data-gathering methods to be used on a project.

(2) An Analysis Plan (AP) that describes analysis of the collected data, such as the contaminant chemical data, the groundwater quality, and the geologic setting.

(3) A Quality Assurance Project Plan (QAPP) that describes the quality assurance and quality control protocols necessary to achieve Data Qaulity Objectives (DQOs). Data Quality Objectives are qualitative and quantitative statements that clarify the study objective, define the type of data to collect, determine the appropriate collection conditions, and specify tolerable decision error limits on the quality and quantity of data needed to support a decision.

The level of detail contained within the SAP varies. Depending on the WP, the testing, analysis, and quality control may be delegated to a differing lead agency or contractor. Whether the SAP contains individual FSP, AP, and/or QAPP, the SAP indicates the field personnel roles and responsibilities, the acquired data goals, the analytical methods, and how these methods meet the DQOs. Guidance for the selection and definition of field methods, sampling procedures, and custody can be obtained from the EPA report Compendium of Superfund Field Operations Methods, December 1987 (EPA/540/P-87/001 or National Technical Information Service [NTIS] publication PB88-181557). This report is a compilation of demonstrated field techniques that have been used during remedial response activities at hazardous waste sites.

371 FIELD MANUAL

The FSP specifies the actual data collection activities to be performed. The AP provides the details if changes in sampling methods or number of samples need to be made. If the AP is a separate document, the FSP should spell out in detail exactly how and why samples will be collected in the field.

Included with the SAP (sometimes as an appendix to the FSP) are the standard operating procedures (SOPs) to be used during the investigations. The SOPs describe, in item-by-item detail, the exact steps to be followed for each sampling procedure. Included in the SOPs are calibration and maintenance requirements for equipment to be used. Manufacturer's recommendations and usage manuals can serve as part of the individual SOPs. Further details regarding standardized tasks are given in the EPA Quality Assurance Technical Information Bulletin Creating SOP Documents.

The QAPP is a companion document typically written when the FSP is final. The QAPP ensures that data and the subsequent analyses are of sufficient quantity and quality to accurately represent the conditions at the site. The QAPP often describes policy, organization, and functional activities not addressed within the work plan.

The following is a suggested SAP format.

Example Sampling and Analysis Plan

FSP 1. Site Background 2. Sampling Objectives 3. Sample Location and Frequency 4. Sample Designation 5. Sampling Equipment and Procedures 6. Sample Handling and Analysis

372 HAZARDOUS WASTE

AP 1. Objective(s) of the Data Collection 2. Analytical Methods and Software 3. Parameters Available and Required 4. Analytical Assumptions (Boundaries, Estimated Data) 5. Data Management and Manipulation 6. Evaluation of Accuracy (Model Calibration and/or Sensitivity Analysis)

QAPP 1. Project Organization and Responsibilities 2. QA Objectives for Measurement 3. Sample Custody 4. Calibration Procedures 5. Data Reduction, Validation, and Reporting 6. Internal Quality Control 7. Performance and System Audits 8. Preventative Maintenance 9. Data Assessment Procedures 10. Corrective Actions 11. Quality Assurance Reports

Health and Safety Plan (HASP)

Each field activity will vary as to amount of planning, special training, supervision, and protective equipment needed. The HASP, prepared to support the field effort, must conform to the Reclamation “Safety and Health Standards.” The site-specific HASP should be prepared concurrently with the SAP to identify potential problems early in the planning stage, such as availability of trained personnel and equipment. The HASP preparer should review site historical information along with proposed activities to identify potentially hazardous operations or exposures and to require appropriate protective measures. Appendix B of the Occupational Safety and

373 FIELD MANUAL

Health Guidance Manual for Hazardous Waste Site Activities (National Institute for Occupational Safety and Health/Occupational Safety and Health Administration/U.S. Coast Guard/U.S. Environmental Protection Agency, 1985) provides an example of a generic format for an HASP. Commercial computer programs that allow preparers to "fill in the blanks" to produce rudimentary HASPs are also available.

A HASP should include, as appropriate, the following elements: 1. Name of site health and safety officer and names of key personnel and alternates responsible for site safety and health. 2. Listing of the potential contaminants at the site and associated risk(s). 3. A health and safety risk analysis for existing site conditions and for each site task and operation. 4. Employee training assignments. 5. A description of personal protective equipment to be used by employees for each of the site tasks and operations being conducted. 6. Medical surveillance requirements. 7. A description of the frequency and types of air monitoring, personnel monitoring, and environmental sampling techniques and instrumentation to be used. 8. Site control measures. 9. Decontamination procedures. 10. Standard operating procedures for the site.

374 HAZARDOUS WASTE

11. A contingency plan that meets the requirements of 29 CFR 1910.120(l)(1) and (l)(2). 12. Entry procedures for confined spaces. 13. Local emergency numbers, notification procedures, and a clear map (and written instructions) showing the route to the nearest medical facility capable of handling emergencies arising from a hazardous waste site.

Spill Prevention Plan (SPP)

All samples, equipment, cuttings, and other materials that have been exposed to potential contaminants must be decontaminated and/or tested and treated according to Applicable or Relevant and Appropriate Requirement (ARAR). Contingencies must be made for accidentally releasing and spreading contaminants into the environment during field activities at hazardous waste sites. Contaminants may originate from substances brought onto the site for specialized testing (e.g., standards for chemical testing), from accumulations of "free" contaminants, or from contaminated natural water which is released during sampling or investigations. Sufficient equipment (e.g., drums, absorbents, etc.) must be onsite to effectively control spills. In addition, key personnel should be identified for the control of spills. Paramount to such planning are spill prevention measures. Spill prevention plans may be incorporated into appropriate sections of a SAP or HASP, if desired.

Contaminant Characteristics and Migration

A primary difference between conventional engineering geology investigations and hazardous waste investigations is that drilling methods may impact the contaminant sampling results and increase migration

375 FIELD MANUAL paths. Lubricants, fuels, and equipment may mask specific chemical testing or react with the contaminant of concern (COC). All samples, waste discharges, and equipment used in the investigations require evaluation in relation to the potential contaminant(s). The following unique site factors are also important.

Contaminant Properties

Some contaminants are inherently mobile, for example, volatile organic compounds (VOCs). When released, VOCs can migrate rapidly through air, soil, and groundwater. Other contaminants, such as heavy metal solids, are less mobile. Heavy metals tend to accumulate on the surface of the ground. Although heavy metals may not readily migrate into and through the subsurface, heavy metals may still migrate through the air as airborne particles. Understanding the behavior of COCs is very important because behavior will significantly influence the ultimate design of the exploration program. For example, investigations to find gasoline, a light nonaqueous phase liquid (LNAPL), should concentrate on the water table surface. Dense, nonaqueous phase liquid (DNAPL) investigations should concentrate towards the bottom of the aquifer(s) or water table. Note that some contaminants react with investigation materials; e.g., TCE in high concentrations reacts with polyvinyl chloride (PVC) pipe.

When possible, the typical contaminant investigation will estimate the source type and location. The source type may be barrels, storage tanks, pipelines, injection wells, landfills, or holding ponds. In investigations that involve groundwater contamination, the investigation must address collecting samples of material that may be moving or have moved off site.

376 HAZARDOUS WASTE

Identifying the contaminant and its behavior within the hydrogeologic environment must be kept foremost in mind while developing the program. Hydrochemical parameters such as density, diffusivity, solubility, soil sorption coefficient, volatilization (vapor pressure), and viscosity may impact the specific contaminant movement. Biological activities or meteoric waters may impact various COCs in the subsurface. Some contaminants degrade over time and under some environmental conditions. In some instances, the degradation product (TCE to vinyl chloride) is worse than the original product.

A general introductory geological hazardous waste investigation reference is the Standard Handbook for Solid and Hazardous Waste Facility Assessments, by Sara, 1994. A general introductory reference for environmental chemistry is Fundamentals of Environmental Chemistry, by Manahan, 1993. A reference on DNAPL materials is DNAPL - Site Evaluation by Cohen and Mercer, 1993. A reference for groundwater chemical and physical properties is Groundwater Chemicals - Desk Reference, by Montgomery, 1996. Toxicological Profile Series published by the U.S. Department of Health and Human Resources describes physical, chemical, and biological processes which effect contaminant fate and transport.

Geologic Factors

The migration of contaminants is dependent on the subsurface materials and water. The arrangement of the geologic materials impacts the direction and flow rate of the contaminants and groundwater. Geologic factors such as stratigraphy, structure, and lithology control the occurrence and movement of water.

Various geologic factors to consider include: depth of soil, depth to bedrock, depth to the water table, seasonal

377 FIELD MANUAL variations in water table, water quality characteristics of site aquifers, mineralogic compositions of soil and rock, gradation, consolidation, and fracturing. Contaminant characteristics, such as property differences between solid or liquid materials, differences in liquid viscosity, or differences in liquid density relative to water, may influence how the contaminants interact with geologic factors and how the contamination plumes will behave.

Hydrologic Factors

Groundwater flow is a function of precipitation, runoff, and infiltration (figure 12-1).

Groundwater flow occurs through two zones: the unsaturated (vadose or aeration) zone and the saturated zone. Each zone can be either soil or rock. Groundwater movement is affected by the characteristics of the material pore spaces (porosity) and the interconnectivity of the pore spaces (permeability). Water movement occurs under a hydraulic gradient.

Other terms often used in groundwater are transmissivity and storativity. Both terms are bulk terms used to describe the water over the entire hydrologic unit. Trans- missivity is directly related to permeability. Storativity is a dimensionless value often incorrectly equated with specific yield. For a more detailed description, see the Bureau of Reclamation Water Resource Technical Publi- cation, Ground Water Manual, second edition, 1995 or Groundwater, by Freeze and Cherry, 1979.

An unconfined aquifer, often referred to as a "water table" aquifer, has no overlying confining layer. Water infiltrat- ing into the ground percolates downward through air- filled interstices of the vadose zone to the saturated zone. The water table, or surface of the saturated groundwater

378 HAZARDOUS WASTE Figure 12-1.—Aquifer types.

379 FIELD MANUAL body, is in contact with the atmosphere through the open pores of the material above and is in balance with atmospheric pressure.

A confined, or artesian, aquifer has an overlying, confining layer of lower permeability than the aquifer. Water in an artesian aquifer is under pressure, and when the confining layer is penetrated, the water will rise above the bottom of the confining bed to an elevation controlled by the aquifer pressure. If the confining layer transmits some water into adjacent layers, the aquifer is said to be a "leaky aquifer." A perched aquifer is created by beds of clay or silt, unfractured rock, or other material with relatively lower permeability impeding the downward percolation of water. An unsaturated zone is present between the bottom of the perching bed and the regional aquifer. Such an aquifer may be permanent or may be seasonal.

Aquifers are typically anisotropic; i.e., flow conditions vary with direction. In granular materials, the particle shapes, orientation, and the deposition process usually result in vertical permeability being less than horizontal permeability. The primary cause of anisotropy on a microscopic scale is the orientation of platy minerals. In some rock, the size, shape, orientation, and spacing of discontinuities and other voids may result in anisotropy. These factors should always be considered when modeling contaminant migration from hazardous waste sites.

After the natural flow conditions at a site are characterized, the presence of artificial conditions which may modify the flow direction or velocity of groundwater is determined. Such items as surface water impoundments and drainages may influence overall groundwater flow models. Also, if existing water wells are present in the area, pumping may be drawing the contaminants toward the wells. All possible influences affecting the

380 HAZARDOUS WASTE groundwater flow must be identified to model contaminant plume migration rates and paths.

Classification and Handling of Materials

Classification of soils for engineering properties is described in chapter 3. “ Instructions for Logging Soils and Surficial Deposits” (chapter 11) describes logging procedures, but there are two significant differences for hazardous waste investigations.

(1) Logging of the soil is often limited to visual inspection of cuttings. The sampling protocol may prohibit the handling or poking of samples. Often the samples are sealed for chemical testing, and time for classification is restricted to the period when the sample is being packaged. Size of samples is kept to a minimum to reduce the amount of investigation- derived waste.

(2) All material recovered or generated during an investigation (samples, cuttings, water, etc.) should be considered hazardous waste unless proven otherwise. Material removed should not be considered “normal” waste unless tested and permitted.

The RCRA “statutory” definition for hazardous waste is broad and qualitative and does not have clear bounds. Hazardous waste is defined as material meeting the regulatory definition contained in 40 CFR 261.3. However, the definitions of solid and hazardous waste contained in 40 CFR 261 are relevant only in identifying the waste. Material may still be considered solid or hazardous waste for purposes of other sections of RCRA. Some waste defined under the present regulatory statutes could become hazardous waste in the future.

381 FIELD MANUAL

From the RCRA document, the definition of hazardous waste is any

. . .solid waste or combination of solid wastes which because of its quantity, concentration, or physical, chemical, or infectious characteristics may: (A) cause, or significantly contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or (B) pose a substantial present or potential hazard to humans or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.

The level of contamination acceptable within the subsurface is based on a complex formula that involves the risk of exposure; toxicity, mobility, and volume of contaminants; and the cost of remediation. Soil and rock removed from a site cannot be returned to a site after the investigation has been completed.

Investigation waste water must be tested and handled under a different set of rules. If the water is mixed with cuttings, the material is considered a combination of solid wastes. If the water is discharged on a site, the water typically must meet drinking water standards. EPA currently requires that sole source aquifers have special project review criteria for Federal actions possibly affecting designated aquifers. Water withdrawn for public drinking water supplies currently falls under the Safe Drinking Water Act (SDWA) (Public Law 93-523) regulations, as amended and reauthorized (1974). (See 40 CFR 141 G for applicable water supply systems. See 40 CFR 143 for applicable water supply systems.) Note that the number of regulated constituents and their respective maximum contaminant levels (MCLs) are frequently updated.

382 HAZARDOUS WASTE

Identifying and classifying hazardous waste is described in Hazardous Waste, by Wagner, 1990. Procedures for site evaluation are contained in EPA Guidance for Conducting Remedial Investigation and Feasibility Studies Under CERCLA, 1988.

Field Sampling Protocol

One of the most difficult parts of any investigation is collecting representative samples. A sampling strategy must be efficiently and logically planned which delineates site location, number of samples collected, types of samples collected, testing methods to be used, and the duration and frequency of sampling. The difficulties of drilling in the “right” location and the problems associated with collecting representative samples is similar to traditional investigations. However, for hazardous waste investigation, the COC must be considered in both time and space. Statistical considerations should be part of the sampling program. The following are references for sampling statistical considerations:

• Harvey, R.P. “Statistical Aspects of Air Sampling Strategies.” In: Detection and Measurement of Hazardous Gases; edited by C.F. Cullis and J.G. Firth. Heineman Educational Books, London, 1981.

• Mason, B.J. Protocol for Soil Sampling: Tech- niques and Strategies. EPA Environmental Systems Laboratory, Contract No. CR808529-01-2. March 30, 1982. EPA-600/54-83-0020.

• Smith, R., and G.V. James. The Sampling of Bulk Materials. The Royal Society of Chemistry, London. 1981.

383 FIELD MANUAL

• Environmental Protection Agency. Handbook for Sampling and Sample Preservation of Water and Wastewater. September 1982. EPA 600/4-82-029.

Sampling Strategies

Investigators must determine the correct number and types of samples to be collected, the proper chemical testing methods (analytical procedures), and the proper sampling equipment before field activities begin. Sample containers, preservatives, sample quantities, and proper holding times are also dictated by the chosen methods.

Table 12-1 is a list of recommended sampling containers and holding times for various classes of contaminants in soils.

Several sampling strategies are available, each with advantages and disadvantages. Random sampling uses the theory of random chance probabilities to choose representative sample locations. This is appropriate when little information exists concerning the material, locations, etc. Random sampling is most effective when the number of sampling locations is large enough to lend statistical validity to the random selection.

Systematic random sampling involves the collection of randomly selected samples at predetermined, regular intervals (i.e., a grid). The method is a common sampling scheme, but care must be exercised to avoid over- sampling of one material or population type over others.

Stratified sampling is useful if data are available from previous investigations and/or the investigator has experience with similar situations. This scheme reduces the number of samples needed to attain a specified precision. Stratified sampling involves the division of the

384 HAZARDOUS WASTE

Table 12-1.—EPA recommended sampling containers, preservation requirements, and holding times for soil samples

Container1 Holding Contaminant Preservation2 time3 Acidity P, G 14 days Alkalinity P, G 14 days Ammonia P, G 28 days Sulfate P, G 28 days Sulfide P, G 28 days Sulfite P, G 48 hours Nitrate P, G 48 hours Nitrate-Nitrite P, G 28 days Nitrite P, G 48 hours Oil and grease G 28 days Organic carbon P, G 28 days Metals Chromium VI P, G 48 hours Mercury P, G 28 days Other metals P, G 6 months Cyanide P, G 28 days Organic compounds Extractables Including: Phthalates, nitro- G, Teflon®- 7 days until samines, organic pesticides, lined cap extraction PCBs, nitroaromatics, iso- phorone, polynuclear aroma- 30 days tics hydrocarbons, haloethers, after chlorinated hydrocarbons, and extraction tetrachlorodibenzo-p-dioxin (TCDD)

Footnotes at end of table.

385 FIELD MANUAL

Table 12-1.—EPA recommended sampling containers, preservation requirements, and holding times for soil samples (continued)

Container1 Holding Contaminant Preservation2 time3 Purgeables Halocarbons and G, Teflon®-lined 14 days aromatics septum Acrolein and acrylonitrate G, Teflon®-lined 3 days septum Orthophosphate P, G 48 hours Pesticides G, Teflon®-lined 7 days until cap extraction

30 days after extraction Phenols G 28 days Phosphorus G 48 hours Phosphorus, total P, G 28 days Chlorinated organic G, Teflon®-lined 7 days compounds cap

1 P = polyethylene, G = glass. 2 All samples are cooled to 4 EC. Preservation is performed immediately upon collection. For composites, each aliquot preserved at collection. When impossible to preserve each aliquot, samples may be preserved by maintaining 4 EC until compositing and sample splitting is completed. 3 Samples are analyzed as soon as possible. Times listed are maximum holding if analysis is to be valid.

Source: Description and Sampling of Contaminated Soils, EPA/625/11-91/002 (1991).

386 HAZARDOUS WASTE sample population into groups based on sample characteristics. The procedure involves handling each group or division separately with a simple random sampling scheme.

Judgement sampling introduces a certain amount of judgment into the sampling approach and should be avoided if a true random sample is desired. Judgment sampling allows investigator bias to influence decisions, which can lead to poor quality data or improper conclusions. If the local geology is fairly well understood, judgement sampling may provide the most efficient and cost-effective sampling scheme; however, regulatory concurrence, rationale, and proper documentation will be necessary.

Hybrid sampling is a combination of the types previously described. For example, an initial investigation of drums might be based on preliminary information concerning contents (judgement, stratified) and then random sampling of the drums within specific population groups (random). Hybrid schemes are usually the method of choice for sampling a diverse population, reducing the variance, and improving precision within each subgroup.

After the appropriate sampling scheme has been chosen, the specific type of samples necessary for characterization must be identified. The unique characteristics of the site COCs will play an important role in determining which media will be sampled. Some sampling devices are described in this manual or the Earth Manual, parts 1 and 2, USBR, 1990 and 1999. A summary of sampling devices is shown in table 12-2.

387 FIELD MANUAL

Table 12-2.—Summary of soil sampling devices

Sampling device Applications Limitations Hand-held samplers Spoons and Surface soil samples Limited to relatively scoops or the sides of pits or shallow depths; trenches disturbed samples Shovels and A wide variety of soil Limited to relatively picks conditions shallow depths Augers1 Screw auger Cohesive, soft, or hard Will not retain dry, soils or residue cohesionless, or granular material Standard General soil or May not retain dry, bucket auger residue cohesionless, or granular material Sand bucket Bit designed to retain Difficult to advance auger dry, cohesionless, or boring in cohesive granular material soils (silt, sand, and gravel) Mud bucket Bit and bucket de- Will not retain dry, auger signed for wet silt and cohesionless, or clay soil or residue granular material

Dutch auger Designed specifically for wet, fibrous, or rooted soils (marshes)

1 Suitable for soils with limited coarse fragments; only the stoney soil auger will work well in very gravelly soil.

388 HAZARDOUS WASTE

Table 12-2.—Summary of soil sampling devices (continued)

Sampling device Applications Limitations Augers1 In situ soil Collection of soil sam- Similar to standard recovery ples in reusable liners; bucket auger auger closed top reduces contamination from caving sidewalls Eijkelcamp Stoney soils and stoney soil asphalt auger Planer auger Clean out and flatten the bottom of predrilled holes Tube samplers2 Soil probe Cohesive, soft soils or Sampling depth residue; representative generally limited to samples in soft to less than 1 meter medium cohesive soils and silts Thin-walled Cohesive, soft soils or Similar to tubes residue; special tips for Veihmeyer tube wet or dry soils available Soil recovery Similar to thin-walled Similar to probe tube; cores are Veihmeyer tube collected in reusable liners, minimizing contact with the air

1 Suitable for soils with limited coarse fragments; only the stoney soil auger will work well in very gravelly soil. 2 Not suitable for soils with coarse fragments.

389 FIELD MANUAL

Table 12-2.—Summary of soil sampling devices (continued)

Sampling device Applications Limitations Tube samplers1 (continued) Veihmeyer Cohesive soils or Difficult to drive into tube residue to depth of dense or hard mate- 10 feet (3 meters [m]) rial; will not retain dry, cohesionless, or granular material; may be difficult to pull from ground Peat sampler Wet, fibrous, organic soils Power-driven samplers Split spoon Disturbed samples Ineffective in cohe- sampler from cohesive soils sionless sands; not suitable for collection of samples for laboratory tests requiring undisturbed soil Thin-walled samplers Fixed piston Undisturbed samples Ineffective in sampler in cohesive soils, silt, cohesionless sands and sand above or below water table Hydraulic Similar to fixed-piston Not possible to limit piston sampler the length of push or sampler to determine amount (Osterberg) of partial sampler penetration during push

1 Not suitable for soils with coarse fragments.

390 HAZARDOUS WASTE

Table 12-2.—Summary of soil sampling devices (continued)

Sampling device Applications Limitations Thin-walled samplers (continued) Free piston Similar to stationary Not suitable for sampler piston sampler cohesionless soils Open drive Similar to stationary Not suitable for sampler piston sampler cohesionless soils Pitcher Undisturbed samples Frequently sampler in hard, brittle, cohe- ineffective in sive soils and ce- cohesionless soils mented sands; representative samples in soft to medium cohesive soils, silts, and some sands; variable success with cohesionless soils Denison Undisturbed samples Not suitable for sampler in stiff to hard cohe- undisturbed sive soils, cemented sampling of sands, and soft rocks; cohesionless soils or variable success with soft cohesive soils cohesionless materials Vicksburg Similar to Denison sampler sampler except takes wider diameter samples

In addition, the following references may be consulted for sample collection methods: • Environmental Protection Agency. Characterization of Hazardous Waste Sites - A Methods Manual, Volume I - Site Investigations. April 1985. EPA 600/4-84-075.

391 FIELD MANUAL

• Environmental Protection Agency. Characterization of Hazardous Waste Sites - A Methods Manual: Volume II. Available Sampling Methods. September 1983. EPA 600/4-83-040, PB84-126929.

• Environmental Protection Agency. A Compendium of Superfund Field Operation Methods. December 1987. EPA 540/P-87-001, PB88-181557.

Samples can be either grab or composite samples. Grab samples are collected at a discrete point, representing one location and/or time interval. Composite samples are collected from several sources which are then accumulated to represent a broader area of interest. The requirements for testing will often dictate which sampling method is used. For example, composite samples of soil cannot be used for volatile compounds because portions of the contaminants may easily volatilize during collection.

Many soil samples are collected as grab samples. Soil samples should be collected from areas where dumping, spills, or leaks are apparent. Soil samples should be collected from areas upstream and downstream from suspected contaminant entry and in areas where sediment deposition is significant. Samples can be collected readily from the first 18 inches (450 mm) (depending upon the soil type) by using relatively simple tools, such as spades, scoops, and dredge scoops. If scoops are used for collecting surface soil samples, purchase enough scoops to use a new scoop for each sample rather than decontaminating scoops between samples. Not only is time saved, but cross contamination is kept to a minimum. The COC must also be considered. If sampling for heavy metals, metal scoops should not be used, or if sampling for semivolatiles, plastic scoops should be avoided. Samples from greater depths usually require more elaborate methods or equipment, such as test pits, hand augers, thin-wall tube samplers, hand or

392 HAZARDOUS WASTE power corers, bucket augers, cutting or wash samples, direct-push tools, etc. The nature of the geologic material to be sampled will influence significantly the methods to use, but every effort should be made to reduce the amount of investigation-derived waste generated from the sampling method. Direct-push sampling (such as the Geoprobe®) is preferable in that drill cuttings and drilling fluids are not generated.

A useful field pocket guide is available from EPA: Description and Sampling of Contaminated Soils, EPA/625/12-9/002, November 1991. This guide addresses soil characterization, description, sampling, and sample handling. Within this guide are general protocols for soil sample handling and preparation. The following are procedures from the guide:

Soil Sample Collection Procedures for Volatiles.—

1. Tube samples are preferred when collecting for volatiles. Augers should be used only if soil conditions make collection of undisturbed cores impossible. Soil recovery probes and augers with dedicated or reusable liners will minimize contact of the sample with the atmosphere.

2. Place the first adequate grab sample, maintaining and handling the sample in as undisturbed a state as possible, in 40-milliliter (mL) septum vials or in a 1-liter (L) glass wide mouth bottle with a Teflon®-lined cap. Do not mix or sieve soil samples.

3. Ensure the 40-mL containers are filled to the top to minimize volatile loss. Secure the cap tightly, but do not overtighten.

393 FIELD MANUAL

4. Examine the hole from which the sample was taken with an organic vapor instrument after each sample increment. Record instrument readings.

5. Label and tag sample containers, and record appropriate data on soil sample data sheets (depth, location, etc.).

6. Place glass sample containers in sealable plastic bags, if required, and place containers in iced shipping container. Samples should be cooled to 4 degrees Centigrade (EC) as soon as possible.

7. Complete chain of custody forms and ship as soon as possible to minimize sample holding time. Scheduled arrival time at the analytical laboratory should give as much holding time as possible for scheduling of sample analyses.

8. Follow required decontamination and disposal procedures.

Soil Sample Collection and Mixing Procedures for Semivolatiles and Metals.—

1. Collect samples.

2. If required, composite the grab samples or use discrete grab samples.

3. If possible, screen the soils in the field through a precleaned O-mesh (No. 10, 2-millimeter [mm]) stainless steel screen for semivolatiles, or Teflon®- lined screen for metals.

4. Mix the sample in a stainless steel, aluminum (not suitable when testing for aluminum), or glass mixing container using appropriate tool (stainless steel spoon, trowel, or pestle).

394 HAZARDOUS WASTE

5. After thorough mixing, place the sample in the middle of a relatively inexpensive 1-meter (m) square piece of suitable plastic, canvas, or rubber sheeting.

6. Roll the sample backward and forward on the sheet while alternately lifting and releasing opposite sides or corners of the sheet.

7. After thorough mixing, spread the soil out evenly on the sheet with a stainless steel spoon, trowel, spatula, or large knife.

8. Take sample container and check that a Teflon® liner is present in the cap, if required.

9. Divide the sample into quarters, and take samples from each quarter in a consecutive manner until appropriate sampling volume is collected for each required container. Separate sample containers would be required for semivolatiles, metals, duplicate samples, triplicate samples (split), and spiked samples.

10. Secure the cap tightly. The chemical preservation of solids is generally not recommended.

11. Label and tag sample containers, and record appropriate data on soil sample data sheets (depth, location, etc.).

12. Place glass sample containers in sealable plastic bags, if required, and place containers in iced shipping container. Samples should be cooled to 4 EC as soon as possible.

13. Complete chain of custody forms and ship as soon as possible to minimize sample holding time. Scheduled arrival time at the analytical laboratory

395 FIELD MANUAL

should give as much holding time as possible for scheduling of sample analyses.

14. Follow required decontamination and disposal procedures.

Water Quality Sample Collection Methods

Surface Water Collection.—Surface water on or adjacent to a suspected hazardous waste site can yield significant information with minimal sampling effort. Surface water can reveal the presence of contamination from several pathway mechanisms. If only a knowledge of the presence or absence of contamination in the water is needed, the collection of grab samples will usually suffice. If the water source is a stream, samples also should be collected upstream and downstream from the area of concern. Additional monitoring of surface water is required of seeps, spills, surface leachates, etc. If the site has National Pollutant Discharge Elimination System (NPDES) outfalls, the discharges should be sampled.

Water quality samples are often the most important material collected at a site. Determining the appropriate number of samples and appropriate test method is critical to a successful program. A good guidance document to develop a water quality sampling program and provide the reasoning for collecting appropriate water samples is EPA’s Handbook, Ground Water, volumes I and II, EPA/625/6-90/016. There are several factors to consider in the selection of appropriate sampling devices. Time and money are obvious factors; however, the data use, formation permeability, water depth, and contamination type are considerations. Water monitoring goals and objectives should be addressed, such as:

396 HAZARDOUS WASTE

• Is the investigation to determine source(s)? • Are the investigations included for a time critical removal action? • Have the potential contaminants been identified? • Will there be a follow up risk assessment and/or remediation? • Are there potential responsible parties (PRPs) involved?

Water samples can be routinely analyzed for current EPA listed priority pollutants. Alkalinity, acidity, total organic halogens, and chemical oxygen demand are often indicators of contamination. Routine tests can be used as screening techniques before implementing more costly priority pollutant analyses. Bioassessment samples, if needed, are described in Rapid Bioassessment Protocols for Use in Streams and Rivers, EPA/444/4-89-001. If technical impracticability (Guidance for Evaluating the Technical Impracticability, EPA Directive 9234.2-25, or natural attenuation are potential remediation options, additional water quality parameters may need testing consideration.

Groundwater Collection.—Groundwater contamination is usually difficult and costly to assess, control, and remove. Monitoring wells sample a small part of an aquifer, depending on screen size, length, placement depth, pumping rates, and other factors. The use of wells and piezometers can introduce additional problems due to material contamination, inadequate construction, and uncertainties of the water zone sampled. Guarding against cross contamination of multiple aquifers is important. Proper well construction requires significant skill. General guidelines for design and construction of monitoring wells can be found in American Society for Testing Materials (ASTM)

397 FIELD MANUAL

D5092-90, and guidelines for sampling can be found in RCRA Groundwater Monitoring Draft Technical Guidance, EPA/530-R-93-001. For general details on groundwater quality monitoring well construction, see figure 12-2. The location of the screen and designing and development of the screen and sand pack is extremely important in hazardous waste wells. Meeting the turbidity requirement of less than five nephelometric turbidity units (NTUs) is difficult to achieve in the best circumstances. Drilling exploration and monitoring wells in sequence from least to most contaminated areas is good practice because this minimizes the possibility of introducing contaminants into cleaner aquifers or areas.

Although the Compendium of ERT Groundwater Sampling Procedures, EPA/540/P-91/007, provides standard operating procedures for emergency response teams, the recommended water quality sampling procedures for groundwater should be in accordance with EPA’s Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures, EPA/540/S-95/504. The Minimal Drawdown (MD) method requires using a submersible pump placed within a riser and not operated until the well has stabilized. The use of bailers and hand pumps, including automated hand pump systems for water quality sampling, is discouraged under the MD method.

Limiting water column disturbance is a primary reason for installing a dedicated submersible pump. Lowering a temporary sampling device into the water column creates a mini-slug test. The surge of water may induce sediments into the monitoring well. As a result, the water may not meet the five NTU limit that is part of the requirement for water quality monitoring wells. Sediments can significantly impact testing. If sediment

398 HAZARDOUS WASTE

Figure 12-2.—Typical monitoring well construction for water quality sampling.

399 FIELD MANUAL content is great, additional tests, such as comparing total versus dissolved solids, should be considered.

Some sampling devices may induce volatilization. Peristaltic pumps, bailers, or hand pumps in low-flow conditions can impact the test results for semi-volatile and volatile compounds. Peristaltic pumps may induce volatilization if the samples are lifted from depths greater than about 25 feet.

The MD method is the preferred sampling collection method because the method uses a low pumping rate (as low as 0.1 liter per minute) and attempts to limit drawdown to less than 0.3 foot. If the extraction rate exceeds the ability of the formation to yield water for low permeability wells, turbulent conditions can be induced within the borehole. Water may trickle and fall down the casing. This may potentially increase air exposure and can entrain air in the water.

Although preferred water quality sampling uses the MD method, other methods may be acceptable to EPA or other regulatory agencies. Devices such as bailers or peristaltic and hand pumps are routinely used at some sites. However, if these devices are used and surge the well, water sampling protocols often require that the well be purged of at least three well volumes of water prior to collecting a sample.

Whatever sample device is selected, stabilization of typical water quality parameters, such as pH, redox potential, conductivity, dissolved oxygen, and turbidity, are usually required. Which water quality parameters are specified may be dependent on the site conditions and regulatory requirements. The water extraction devices and procedures should be specified in the FSP and

400 HAZARDOUS WASTE correlated to match the site conditions, contaminants, and the regulatory agency requirements.

Vadose Zone.—In addition to sampling aquifers at hazardous waste sites, significant information can be obtained by vadose zone sampling. Leachates from COCs migrate through the vadose zone toward the water table. Samples collected from this zone can indicate the types of contaminants present and can aid in assessing the potential threat to the aquifer below. The various types of vadose zone monitors can be used to collect water samples or interstitial pore space vapors for chemical analyses and to determine directional flow of COCs. The main advantage is that such sampling is relatively inexpensive, simple to do, and can begin supplying information before aquifer monitoring is started. The types of vadose zone monitors, their applications, and their use in satisfying the requirements of RCRA are discussed in Vadose Zone Monitoring at Hazardous Waste Sites, EMSL-LV KT-82-018R, April 1983.

Geophysical Methods

Geophysical methods can be used effectively at hazardous waste sites to assist in defining the subsurface character of the site, to assist in the proper placement of monitoring wells, to identify buried containers and debris, and to decrease the safety risks associated with drilling into unknown buried materials. A good overview of the subject of geophysical methods for surveying hazardous waste sites is: Geophysical Techniques for Sensing Buried Wastes and Waste Migration, prepared for EPA by Technos, Inc., available from the National Water Well Association.

401 FIELD MANUAL

Miscellaneous Methods

Ambient concentrations of volatile and semivolatile organics, trace metals, and particulate matter in the air can provide important data on the atmospheric migration path and the populations at risk and can be used for source evaluations and personnel monitoring. Portable monitoring devices such as organic vapor analyzers, stain detector tubes, or other monitors can detect the presence of various atmospheric hazards. Other monitors commonly used at hazardous waste sites are explosi- meters, oxygen indicators, and personal sampling pumps.

Other specialized sampling techniques may be necessary at hazardous waste sites to sample media normally not found in the geologic environment. Wipe samples may be used to document the presence of toxic materials and to determine that site or equipment decontamination has been adequate. Wipe sampling consists of rubbing a moistened filter paper, such as Whatman 541 filter paper, over a measured area of 15 in2 (100 cm2) to 10 ft2 (1 m2). The paper is then sent to a laboratory for analysis.

Sample Analysis

Onsite laboratories and field analytical equipment, such as portable gas chromatographs (GCs) and immunoassay kits, can be very beneficial for rapid analyses. Rapid- analysis equipment, such as GCs, immunoassay, and colorometric kits, are a cost-effective alternative for providing qualitative and semi-quantitative chemical data and for screening large numbers of samples prior to submittals for laboratory testing. Another beneficial use of field screening techniques is to provide general contaminant level data for samples to be tested in the laboratory. If a sample has a very high contaminant

402 HAZARDOUS WASTE concentration, the sample may have to be diluted before being analyzed to protect the laboratory instruments from costly contaminant saturation problems.

There are many standardized testing procedures and methods for hazardous waste evaluation. Table 12-3 lists some common method series. Each series contains numerous individual methods. There are over 25 series- 500 (determination of organic compounds in drinking water) methods. Method 502.1 is for halogenated volatile organics (purgeable halocarbons) by GC (48 compounds); Method 502.2 is for nonhalogenated volatile organics by GC (6 compounds); Method 503.1 is for aromatic and unsaturated volatile organics (purgeable aromatics) by GC (28 compounds); Method 507 is for nitrogen and phosphorus containing pesticides by GC (66 substances).

The following references discuss some of the common methods:

• Methods for the Determination of Organic Compounds in Drinking Water. EPA-600/4- 88/039, December 1988 (500 Series).

• Guidelines Establishing Test Procedures for the Analysis of Pollutants Under the Clean Water Act. 40 CFR Part 136, October 26, 1984 (600 Series, for effluent - wastewater discharged to a sewer or body of water).

• Test Methods for Evaluating Solid Waste. SW-846, 2nd Edition, Revised, 1985 (8000 Series for groundwater, soil, liquid, and solid wastes).

• Methods for Chemical Analysis of Water and Wastes. EPA-600/4-79-020, March 1983.

403 FIELD MANUAL

Table 12-3.—Common laboratory testing methods1

Method testing series Analytes

100 - EPA method Physical properties - water 200 - EPA method Metals - water 300 - EPA method Inorganic, non-metallics - water (i.e., alkalinity) 400 - EPA method Organics - water (i.e., chemical oxygen demand, total recoverable petroleum hydrocarbons [TRPH]) 500 - EPA method Organic compounds in drinking water 600 - EPA method Organic compounds in effluent 900 - EPA method Biologic - water (i.e., coliform, fecal streptococcal) 1000 - SW-846 method Ignitability, toxicity characteristic leaching procedure (TCLP), extractions, cleanup, headspace - solids 3000 - SW-846 method Acid digestion, extractions, cleanup, headspace - solids 4010 - SW-846 method Screening for pentachlorophenol by immunoassay - solids 5000 - SW-846 method Organic (purge and trap, gas chromatograph/mass spectrometer [GC/MS], sorbent cartridges) 6000 - SW-846 method Inductively coupled plasma (spectrometry) 7000 - SW-846 method Metals - solid waste 8000 - SW-846 method Organic compounds in solid waste 9000 - SW-846 method Inorganics, coliform, oil and grease extractions - solids

1 This list is not inclusive. Significant overlap and exceptions are present. Methods listed are basic guides to provide the investigator with the general structure of the testing method scheme. Numerous individual methods exist within each series.

404 HAZARDOUS WASTE

• Standard Methods for the Examination of Water and Wastewater, 19th edition, Greenberg; American Public Health Association, Washington, DC, 1995.

Reference guides are also available from several sources, such as the Trace Analysis Laboratory Reference Guides from Trace Analysis Laboratory, Inc., 3423 Investment Boulevard, No. 8, Hayward, California 94545, telephone (415) 783-6960.

An important consideration in planning any field investigation program is scheduling the anticipated activities. Sufficient time must be allowed for the peculiarities of hazardous waste work. Several factors must be considered: (1) time for establishing work zones and erecting physical barriers, (2) time for establishing equipment, personnel, and vehicle decontamination stations, (3) time needed to decontaminate equipment and personnel, ( 4) loss of worker efficiency due to safety monitoring, safety meetings, and the use of protective clothing, (5) documentation requirements and sample- handling procedures, and (6) inventory and procurement of specialized sample containers, preservative preparation, and reference standards, and equipment calibrations.

Safety at Hazardous Waste Sites

A major factor during hazardous waste site investigations is the safety of both the general public and the site investigators. The following references may be of assistance:

405 FIELD MANUAL

• Interim Standard Operation Safety Guides. Revised September 1982, U.S. EPA, Office of Emergency and Remedial Response (OERR).

• Guidance Manual for Protection of Health and Safety at Uncontrolled Hazardous Substances Sites. EPA, Center for Environmental Research Information (ORD) (in draft, January 1983).

• Reclamation Safety and Health Standards. U.S. Department of the Interior, Bureau of Reclamation, Denver, Colorado, 1993.

• Chemical Substance Hazard Assessment and Protection Guide. OWENS/URIE Enterprises, Inc., Henehan, Urie, & Farlern, Wheat Ridge, Colorado, 1994.

Sample Quality Assurance and Quality Control

Sample QA procedures confirm the quality of the data by documenting that integrity is present throughout the sample history. Several sample types are used. Field blanks are samples of a "pure" substance, either water, solid, or air, which are collected in the field using the same procedures as are used for actual environmental samples. The purpose of the field blank is to ensure that outside influences are not contaminating the true samples (i.e., vehicular exhaust) during sampling. If "hits" are discovered in the field blank, the question arises whether contamination not associated with the site is affecting the true samples.

Trip blanks are samples of a "pure" substance (analyte- free deionized water which accompanies samples with volatile contaminants) prepared in a laboratory or other

406 HAZARDOUS WASTE controlled area and placed in a shipping container with environmental samples. The purpose of the trip blank is to ensure that samples were not cross contaminated during shipment and storage. "Hits" in a trip blank indicate that COCs were present in a container to a degree sufficient to infiltrate into the trip blank sample jar and, hence, possibly into true samples.

Equipment blanks are used when sampling equipment is cleaned and re-used for subsequent sample collection. The blanks verify the effectiveness of field cleaning procedures. The final rinse for the sampling equipment is often made with analyte-free deionized water. The rinse water is run on or through the sampling equipment, collected in appropriate containers and preserved. These samples are usually collected on a schedule, such as once every 10 episodes.

Duplicates are samples collected at the same time, in the same way, and contained, preserved, and transported in the same manner as a corresponding duplicate. Duplicates are used to determine the precision of the laboratory method and integrity of the sample from collection through testing. Duplicates are typically collected once every 10 samples.

Matrix spikes provide the best overall assessment of accuracy for the entire measurement system. For water investigation episodes, a laboratory usually prepares the spike samples, sends them to the site, and the spike sample(s) are included in the sample handling and shipping process. The samples are analyzed blind by the off-site laboratory. Matrix spikes can also be made from certified mixtures of a contaminant and clean soil in the field.

407 FIELD MANUAL

All types of blanks and duplicates must be prepared in the same sample containers as actual samples including labeling and identification schemes so that the laboratory analyzes the sample without knowing that the samples are quality control (QC) samples (blind testing).

In addition to field QC samples, the analytical laboratory also uses QC samples. Method blanks are organic-free or deionized water carried through the analytical scheme like a sample. Method blanks measure contamination associated with laboratory activities. Calibration blanks are prepared with standards to create a calibration curve. Internal standards are measured amounts of certain compounds added after preparation or extraction of a sample. Surrogates are measured amounts of certain compounds added before preparation or extraction of a sample to determine systematic extraction problems. Duplicates and duplicate spikes are aliquots of samples subjected to the same preparation and analytical scheme as the original sample. Laboratory control standards (LCSs) are aliquots of organic-free or deionized water to which known amounts of analyte have been added. LCSs are subjected to the sample preparation or extraction procedure and analyzed as samples.

Field, laboratory, data validation, and report presentation documents must be meticulously maintained during hazardous waste site investigations. All field activities should be recorded in bound, consecutively numbered log books. Each entry should be made with indelible ink, and all strike outs should be made by a single line which allows the original error to be legible and initialed and dated by the person making the correction. Entries should include date, weather conditions, personnel involved with the activity, the type of activity being performed, unusual circumstances or variations made to the SOPs, and data appropriate to the activity being

408 HAZARDOUS WASTE performed. This is a diary of all activities on a site. The investigator responsible for the activity is responsible for maintaining the field log book. An important purpose of the field log book is to document any changes made to SOPs. If such changes may affect data quality, concurrence with managers or regulatory personnel is required in writing. All records must be under control at all times. Unique project numbers should be assigned to all log books, documents, and reports. All records must be maintained and custody documented so that unauthorized changes or tampering are eliminated. Log book entries should be photocopied on a regular schedule to ensure that field data are not lost if the original book is lost or destroyed.

Activities during an investigation must be reviewed to ensure that all procedures are followed. System audits should consist of inspections of training status, records, QC data, calibrations, and conformance to SOPs. System audits are performed periodically on field, laboratory, and office operations. Each major investigation type should be subject to at least one system audit as early as practicable. Performance audits include evaluation and analysis of check samples, usually from laboratory activities. Readiness reviews occur immediately prior to beginning each type of field activity to assess the readiness of the team to begin work. A checklist of prerequisite issues, such as necessary equipment, controlled documents, training, assignments, spare parts, field arrangements, etc., are discussed and documented.

If any weaknesses or deficiencies are identified, the investigator must resolve them before field activities proceed.

409 FIELD MANUAL

Sample Management

There must be control and documentation of all samples after the environmental samples are collected in the field. The proper quantity of a sample must be collected to have sufficient volume for the subsequent analysis. The proper sample container and preservative must be used so that sample integrity is not compromised. Many types of samples (e.g., volatiles) must be cooled, usually to 4 EC, throughout their history after collection. The proper analytical methods must be identified to obtain the desired result. The laboratory must handle and track the received samples in a timely and accurate manner to ensure that the results are correct.

Sample Custody

Sample custody is a prime consideration in the proper management of samples. Sample custody is designed to create an accurate, written, and verified record that can be used to trace the possession and handling of the samples from collection through data analyses and reporting. Adequate sample custody is achieved by means of QA-approved field and analytical documentation. A sample is considered in custody if the sample is (1) in one's actual physical possession, (2) is in one's view after being in one's physical possession, (3) is in one's physical possession and then locked up or otherwise sealed so that tampering will be evident, or (4) is kept in a secure area restricted to authorized personnel only. Personnel who collect samples are personally responsible for the care and integrity of these collected samples until the samples are properly transferred or dispatched. To document that samples are properly transferred or dispatched, sample identification

410 HAZARDOUS WASTE and chain of custody procedures must be followed. Sample custody in the field and in transit involves the steps described below.

Sample Identification.—The sample must first be properly and uniquely identified. Sample identification entails establishing a scheme which ensures that each sample is identified in such a way that one sample cannot be mistaken for another. Examples of sample labels are shown in figure 12-3. Labels must be filled out immediately after the sample is collected to ensure that containers are not later misidentified. Indelible ink must be used on all labels, and the writing must be legible. For samples which require preservation, the sample labels must have a space on the label reserved for noting the preservative added, or other treatments, such as filtering, compositing, etc. Labels can be removed from a sample jar during shipment, especially if the accompanying ice melts and saturates the shipping labels. Double-label samples such as sacked soil whenever possible or completely wrap the label over the sample bottle with wide, water-proof tape. Also record the collection of each sample in the field log book and chain of custody records.

Chain of Custody.—Once all samples for a specific sampling task have been collected, the sampler(s) will complete the chain of custody record (figure 12-4). Specific procedures for completing this form should be included in the work plan documents specific to the project. This record accompanies the samples to their destination. All samples typically are transferred from the sample transport container (e.g., cooler) and kept in the exclusion zone until transferred to a noncontaminated sample transport container in the contamination reduction zone. The samples, with accompanying documentation, are

411 FIELD MANUAL

Figure 12-3.—Soil and water sample identification labels.

412 HAZARDOUS WASTE Figure 12-4.—Chain of custody record.

413 FIELD MANUAL then prepared for either distribution to the onsite laboratory or shipment to an analytical laboratory in the support zone.

When transferring the possession of samples, the individuals relinquishing and receiving the samples will sign, date, and note the time on the chain of custody record. This record documents sample custody transfer from the sampler to the analyst. Note that some commercial shippers (such as Federal Express) do not sign chain of custody records but do prepare separate shipping documents which indicate receipt of the cooler(s). When samples are passed among field personnel while still onsite, chain of custody records do not need to be signed, as long as physical possession is retained by identified, responsible personnel during transit of the container(s).

Packaging

Samples must be packaged properly for shipment and dispatched to the appropriate laboratory for analysis; a separate record accompanies each shipment. Samples within shipping containers will be sealed for shipment to the laboratory by using custody seals (figure 12-5). Seals are made of paper, with adhesive backing, so that they will tear easily to indicate possible tampering. There are two methods of using custody seals. One method is to place several sample containers in individual plastic bags (or boxes) within the shipping container and then place the custody seal along the only opening of each bag. An advantage of this scheme is that the seal is not exposed to outside influences; but the disadvantages are that the bags are very pliable, and shifting may cause the seal to break, and the seal may become immersed in water if ice melts around the bags. The second method is to place the custody seal on the outside of the cooler, along a seam of

414 HAZARDOUS WASTE Figure 12-5—Custody seal.

415 FIELD MANUAL the lid. The advantage of this method is that the seal is stuck to the solid body of the cooler. The main disadvantage is that the seal is exposed to handling by the shipping company and other personnel from the field to the laboratory. The seal must not be broken accidentally because a broken seal will place all the samples represented by the seal in jeopardy of disqualification due to tampering. An option may be to place clear tape over the seal as added protection.

The samples within a container must be packed to avoid rattling and breakage. Styrofoam "popcorn" or bubble pack sheeting are acceptable packing materials. Organic packing materials, including sawdust, should be avoided due to the possibility of becoming wet from melting ice. Each sample jar should be wrapped such that jar-to-jar contact is avoided. Also, it is usually desirable to place ice at the bottom of the container, and place the samples above the ice, with a water-proof barrier between the ice and samples. This way, if the ice melts, there is a lessened probability of the samples becoming immersed. If time is available, ice should be double-wrapped, using several "ice packages" to lessen spillage potential. Chemical ice packs and dry ice should be avoided, if possible, to lessen the chance of chemical contamination. The chain of custody record must accompany each container and list only the samples contained within the specified cooler. The original chain of custody record should be sealed in a "zip-lock" plastic bag and taped to the inside top of the cooler lid. When the laboratory opens a cooler, the number and identification of each sample contained within the cooler must exactly match the corresponding chain of custody record. A copy of the chain of custody record is to be retained by the investigator or site manager, and a copy is also retained by the laboratory. A three-carbon copy type chain of custody record is best.

416 HAZARDOUS WASTE

The water drain at the lower edge of the cooler must be sealed so there is no possibility of the drain opening. If any leakage occurs from a cooler containing environmental samples, the shipping company will cease shipment and delay the arrival of the samples, possibly exceeding the holding times of the contained samples. A shipping company may have unique requirements; but as a general rule, the weight of a cooler should not exceed 50 to 70 pounds. If sent by mail, the package must be receipt requested. If sent by common carrier, a government bill of lading can be used. Proper shipment tracking methods must be in place. Copies of all receipts, etc., must be retained as part of the permanent documentation.

Upon arrival at the laboratory, the containers will be opened, the custody seals inspected and documented, and any problems with chain of custody, temperature, or sample integrity noted. The laboratory custodian will then sign and date the chain of custody record and enter the sample identification numbers into a bound, paginated log book, possibly assigning and cross- referencing a unique laboratory number to each sample received. The laboratory then controls the samples according to the SOPs specified in their work plan documents.

Decontamination

Decontamination consists of removing contaminants and/or changing their chemical nature to innocuous substances. How extensive decontamination must be depends on a number of factors, the most important being the type of contaminants involved. The more harmful the contaminant, the more extensive and thorough decontamination must be. Less harmful contaminants may

417 FIELD MANUAL require less decontamination. Only general guidance can be given on methods and techniques for decontamination. The exact procedure to use must be determined after evaluating a number of factors specific to the site.

When planning site operations, methods should be developed to prevent the contamination of people and equipment. For example, using remote sampling techniques, using disposable sampling equipment, watering down dusty areas, and not walking through areas of obvious contamination would reduce the probability of becoming contaminated and require a less elaborate decontamination procedure.

The initial decontamination plan is usually based on a worst-case situation. During the investigations, specific conditions are evaluated including: type of contaminant, the amount of contamination, the levels of protection required, and the type of protective clothing needed. The initial decontamination system may be modified by adapting it to actual site conditions.

418 Chapter 13

SURFACE GEOPHYSICAL INVESTIGATIONS

Introduction

Surface geophysical surveys have been applied to mineral and petroleum exploration for many years. A magnetic compass was used in Sweden in the mid-1600s to find iron ore deposits. The lateral extent of the Comstock ore body was mapped using self-potential methods in the 1880s. A very crude type of seismic survey measured the energy resulting from blasting operations in Ireland in the late 1800s. The idea that energy travels through a material with a certain velocity came from this survey. During World War I, geophysical techniques were used to locate artillery pieces. Anti-submarine warfare in World War II led to magnetic and sonar surveys.

The main emphasis of geophysical surveys in the formative years was petroleum exploration. Technology developed for oil and gas surveys led to the use of geophysical surveys in many important facets of geotechnical investigations. Geophysical surveys have been applied to civil engineering investigations since the late 1920s, when seismic and electrical resistivity surveys were used for dam siting studies. A seismic survey was performed in the 1950s in St. Peter’s Basilica to locate buried catacombs prior to a renovation project. From the late 1950s until the present time, geophysical techniques have had an increasing role in both groundwater exploration and in geotechnical investigations. Geophysical surveys are now used routinely as part of geological investigations and to provide information on site parameters (i.e., in place dynamic properties, cathodic protection, depth to bedrock) that in some instances are not obtainable by other methods. Values derived from seismic geophysical surveys are obtained at strain levels different from some site parameters obtained by other means. FIELD MANUAL

All geophysical techniques are based on the detection of contrasts in different physical properties of materials. If contrasts do not exist, geophysical methods will not work. Reflection and refraction seismic methods contrast compressional or shear wave velocities of different materials. Electrical methods depend on the contrasts in electrical resistivities. Contrasts in the densities of different materials permit gravity surveys to be used in certain types of investigations. Contrasts in magnetic suscepti- bilities of materials permit magnetic surveying to be used in some investigations. Contrasts in the magnitude of the naturally existing electric current within the earth can be detected by self-potential (SP) surveys.

Seismic refraction surveys are used to map the depth to bedrock and to provide information on the compressional and shear wave velocities of the various units overlying bedrock. Velocity information also can be used to calculate in place small-strain dynamic properties of these units. Electrical resistivity surveys are used to provide information on the depth to bedrock and information on the electrical properties of bedrock and the overlying units. Resistivity surveys have proven very useful in delineating areas of contamination within soils and rock and also in aquifer delineation. Gravity and magnetic surveys are not used to the extent of seismic and resistivity surveys in geotechnical investigations, but these surveys have been used to locate buried utilities. Self-potential surveys have been used to map leakage from dams and reservoirs.

Geophysical surveys provide indirect information. The objective of these surveys is to determine characteristics of subsurface materials without seeing them directly. Each type of geophysical survey has capabilities and limitations and these must be understood and considered when designing a geophysical investigations program.

2 SURFACE GEOPHYSICAL INVESTIGATIONS

Geophysical interpretations should be correlated with real “ground-truth”data such as drill hole logs. It is very important that the results of geophysical surveys be integrated with the results of other geologic investigations so that accurate interpretation of the geophysical surveys can be made.

The following sections provide the theory behind and guidelines for uses of geophysical surveys, particularly in geotechnical investigations. Although this chapter does not provide all the detail necessary, the theory and interpretation methods involved in geophysical surveying are included in references in the bibliography. The references should be used to supplement the materials presented in this chapter.

Seismic Surveys

Seismic Refraction Surveys

Purpose.—Seismic refraction surveys are used to determine the compressional wave velocities of materials from the ground surface to a specified depth within the earth. For most geotechnical investigations, the maximum depth of interest will be specified by the nature of the project. In many cases the objective of a seismic refraction survey is to determine the configuration of the bedrock surface and the compressional wave velocities of the underlying materials. Bedrock may be defined by compressional wave velocities. The information obtained from a seismic refraction survey is used to compute the depths to various subsurface layers and the configurations of these layers. The thickness of the layers and the velocity contrasts between the layers govern the effectiveness and the accuracy of the survey. Seismic refraction surveys do not provide all compressional wave velocities or delineate all

3 FIELD MANUAL subsurface layers. Seismic refraction interpretation assumes that layer velocities increase with depth.

Applications.—Seismic refraction surveys have been used in many types of exploration programs and geotechnical investigations. The initial application of these surveys was mapping of salt domes in the early days of oil exploration. Seismic refraction surveys are now routinely used in foundation studies for construction projects and siting studies, fault investigations, dam safety analyses, and tunnel alignment studies. Seismic refraction surveys are also used to estimate rippability (Appendix C). Figure 13-1 is a schematic of a seismic refraction test.

Figure 13-1.—Simplified diagram of a seismic refraction test.

Seismic Reflection Surveys

Purpose.—Seismic reflection surveys have been used successfully in petroleum and geothermal exploration projects and to investigate for shallow coal. The information obtained from seismic reflection surveys can be used to define the geometry of the different subsurface layers and structural features.

4 SURFACE GEOPHYSICAL INVESTIGATIONS

Applications.—High resolution seismic reflection surveys provide definitive information on the locations and types of faults, as well as the location of buried channels. Shallow, high resolution seismic reflection surveys are playing an increasingly important role in geotechnical investigations. When correctly used, seismic reflection surveys may provide data that seismic refraction surveys can not (e.g., velocity reversal information). However, compressional (P) wave velocity information derived from reflection surveys may not be as accurate as from refraction surveys. The compressional wave velocities are needed for the analysis of the reflection records themselves and for seismic refraction surveys, uphole velocity surveys, and sonic logs.

Shear Wave Surveys

Purpose.—Shear (S) waves travel through a medium at a slower velocity than compressional (P) waves and arrive after compressional waves. Other types of secondary arrivals also exist due to reflections, combinations of reflections and refractions, and surface waves. Field survey techniques are designed to suppress compressional and unwanted reflected or refracted wave arrivals. The field procedure optimizes shear wave generation as well as the polarity of the wave energy.

Applications.—For geotechnical investigations, shear wave velocities provide information on the low-strain dynamic properties of a given material. The relationships between compressional wave velocity, shear wave velocity, density, and in place dynamic properties of materials are shown in table 13-1. The compressional wave velocity can be determined from refraction surveys, the shear wave velocity from shear wave surveys, and the density from borehole geophysics or laboratory testing. The cross-hole seismic method is a common procedure used to determine

5 FIELD MANUAL

Table 13-1.—Determining moduli and ratios for typical velocities of earth materials from refraction surveys

Vp = Compressional wave velocity (ft/s) (m/s)

Vs = Shear wave velocity (ft/s) (m/s) E = Young's Modulus (lb/in2) (MPa) G = Shear Modulus (lb/in2) (MPa) K = Bulk Modulus (lb/in2) (MPa) µ = Poisson's Ratio D = Density (in situ) (lb/ft3) (kg/m3)

D 2 Shear Modulus: G = Vs Young's Modulus: E = 2G(1+F) D 2 Bulk Modulus: K = (Vp-4/3Vs )

Velocity Ratio: Vp/Vs 2 2 Poisson's Ratio: µ = (.05) [Vp/Vs] -2/[Vp/Vs] -1\

material dynamic properties. Compressional waves and shear waves are generated in one drill hole, and the seismic wave arrivals are received in companion drill hole(s). The seismic source(s) and receiver(s) are located at equal depths (elevations) for each recording. Drill hole deviation surveys are performed in each drill hole to accurately determine the distances between each of the drill holes at all recording intervals. For typical seismic velocities of earth materials, see table 13-2.

Surface Wave Surveys

Purpose.—Surface wave surveys produce and record surface waves and their characteristics. Surface waves have lower frequencies and higher amplitudes than other seismic waves. Surface waves result from the construc- tive and destructive interference of refracted and reflected seismic waves. Surface waves that travel along the boundaries of a body are called Stanley waves. Surface waves are the slowest type of seismic

6 SURFACE GEOPHYSICAL INVESTIGATIONS

Table 13-2.—Typical velocities of earth materials Velocity (meters per Material (feet per second) second) Dry silt, sand, loose gravel, 600-2,500 200-800 loam, loose rock, talus, and moist fine-grained topsoil Compact till, indurated 2,500-7,500 800-2,300 clays, gravel below water table*, compact clayey gravel, sand, and sand-clay Weathered, fractured, or 2,000-10,000 600-3,000 partly decomposed rock Sound shale 2,500-11,000 800-3,400 Sound sandstone 5,000-14,000 1,500-4,000 Sound limestone, chalk 6,000-20,000 2,000-6,100 Sound igneous rock 12,000-20,000 3,700-6,100 Sound metamorphic rock 10,000-16,000 3,100-4,900 *Water (saturated materials 4,700 1,400 should have velocities equal to or exceeding that of water)

wave, traveling along the boundaries between different materials. The characteristics must be determined in addition to recording the waves. Normally, surface waves are filtered out of seismic data or are ignored. The term. "ground roll," in the oil exploration industry denotes surface waves. Special care is taken in seismic reflection surveys to filter out surface waves because they can interfere with desired reflections. The different types of surface waves and their characteristic motions are shown in figure 13-2.

7 FIELD MANUAL

Figure 13-2.—Types of surface waves.

Applications.—The principal application of surface wave surveying for geotechnical investigations is to determine the type and characteristics of surface waves that can exist at a site. This information is used to determine preferred site frequencies and for earthquake design analysis.

8 SURFACE GEOPHYSICAL INVESTIGATIONS

Vibration Surveys

Purpose.—Vibration surveys measure the vibration levels produced by mechanical or explosive sources. Once these levels are determined, structures can be designed to reduce the possibility of vibration damage.

Applications.—Vibration surveys have been performed for quarrying and mining operations, excavations, measuring the effects of traffic on sensitive equipment, and measuring the effects of aircraft (sonic vibrations) on urban areas and historical buildings. Many manufacturing and research facilities contain extremely sensitive equipment with very small vibration tolerances. Vibra- tion surveys can be very useful in determining the exact levels of allowable vibration and in designing procedures to reduce vibration levels produced by construction and blasting activities. The same type of vibration survey can be used in quarrying and/or mining operations to reduce vibration levels while maintaining rock breakage and fragmentation.

Electrical Resistivity Surveys

The electrical resistivity of any material depends largely on its porosity and the salinity of the water in the pore spaces. Although the electrical resistivity of a material may not be diagnostic, certain materials have specific ranges of electrical resistivity. In all electrical resistivity surveying techniques, a known electrical current is passed through the ground between two (or more) electrodes. The potential (voltage) of the electrical field resulting from the application of the current is measured between two (or more) additional electrodes at various locations. Since the current is known, and the potential can be measured, an apparent resistivity can be calculated. The separation

9 FIELD MANUAL between the current electrodes depends on the type of surveying being performed and the required investigation depth.

For representatives values of resistivity, see table 13-3.

Table 13-3.—Representative values of resistivity

Material Resistivity (ohm-m)

Clay and saturated silt 1-100 Sandy clay and wet silty sand 100-250 Clayey sand and saturated sand 250-500 Sand 500-1,500 Gravel 1,500-5,000 Weathered rock 1,000-2,000 Sound rock 1,500-40,000

Electrical Resistivity Profiling Surveys

Electrical resistivity survey profiling is based on lateral changes in the electrical properties of subsurface materials.

Purpose.—Electrical resistivity profiling is used to detect lateral changes in the electrical properties of subsurface material, usually to a specified depth. Electrode spacing is held constant.

Applications.—Electrical resistivity has been used to map sand and gravel deposits, determine parameters for cathodic protection, map contamination plumes in hazardous waste studies, and used in fault studies.

10 SURFACE GEOPHYSICAL INVESTIGATIONS

Electrical Resistivity Sounding Surveys

Electrical resistivity sounding surveys measure vertical changes in the electrical properties of subsurface materials. The electrode spacing used for resistivity sounding is variable, with the center point of the electrode array remaining constant. The depth of investigation increases as the electrode spacing increases.

Purpose.—Resistivity soundings are used to investigate variations of resistivity with depth. Electrode spacing is varied.

Applications.—Electrical resistivity soundings are commonly used for aquifer and aquaclude delineation in groundwater investigations. The technique has been used for bedrock delineation studies where there is not a sufficient velocity contrast to permit seismic surveying. Vertical electrical soundings have been used for large scale mineral investigations, geothermal investigations, cathodic protection and toxic waste studies, and in conjunction with self-potential surveys for seepage investigations.

Electrical Resistivity Dipole-Dipole Surveys

Dipole-dipole surveying potential electrodes may have any position with respect to the pair of current electrodes. When the current and potential electrodes are positioned along the same line, the array is referred to as an axial dipole array (figure 13-3). The current electrodes are separated from the potential electrodes by an interval, n, which is some multiple of the current and potential electrodes separation, a. The separation of the current and potential electrodes is normally equal.

11 FIELD MANUAL Figure 13-3.—Dipole resistivity array. 13-3.—Dipole Figure

12 SURFACE GEOPHYSICAL INVESTIGATIONS

Purpose.—Dipole-dipole arrays are used to determine both the lateral and vertical changes in electrical properties of subsurface materials with one electrode array.

Applications.—The dipole-dipole array has limited applications in engineering and groundwater geophysics. This type of electrode array has been used primarily in mineral and geothermal exploration. The method has been used to delineate abandoned mines, mapping saltwater/fresh water interfaces, and mapping buried stream channels.

Electromagnetic Conductivity Surveys

Electromagnetic Conductivity Profiling Surveys

Electromagnetic (EM) surveying uses time-varying, low frequency, electromagnetic fields induced into the earth. A transmitter, receiver, and a buried conductor are coupled by electrical circuitry through electromagnetic induction. The characteristics of electromagnetic wave propagation and attenuation by a material can permit interpretation of the electrical conductivities of the subsurface materials.

Purpose.—Since electrical conductivity is the reciprocal of electrical resistivity, electromagnetic surveys are used to provide resistivity information on subsurface materials. Electromagnetic conductivity profiling surveys are specifically used to determine lateral changes in conductivity of the subsurface materials.

Applications.—Electromagnetic surveys have been used primarily for mineral exploration; and with the exception of magnetic surveys, EM surveys are the most commonly

13 FIELD MANUAL used geophysical surveys for minerals. EM surveys have been used in engineering and groundwater investigations. The method is found to be particularly useful in mapping contaminant plumes and buried metallic waste such as metal drums containing hazardous chemicals. EM surveys are suited to hazardous waste studies because the surveying procedure does not require equipment to touch potentially contaminated ground. The method has been used to locate buried pipes and cables and to locate landmines.

Electromagnetic Conductivity Sounding Surveys

Purpose.—Electromagnetic conductivity sounding surveys are used to determine vertical changes in conductivity of subsurface material.

Applications.—Electromagnetic sounding surveys can locate areas of permafrost, gravel deposits, map bedrock topography, and provide general geological information. EM sounding and profiling surveys have been applied to mapping areas of salt water intrusion, archaeological investigations, and fault studies.

Ground Penetrating Radar Surveys

Purpose

Ground penetrating radar (GPR) surveys have the same general characteristics as seismic surveys. The depth of investigation with GPR is extremely shallow when compared to seismic surveys. This disadvantage is partially offset by the much better resolution of GPR.

14 SURFACE GEOPHYSICAL INVESTIGATIONS

Applications

Ground penetrating radar surveys can be used for a variety of very shallow geotechnical investigations, including the locations of pipes or other buried manmade objects such as timbers, very high resolution mapping of near-surface geology, and detecting cavities, piping, and leakage in dams. The applications are limited by the very shallow penetration depth of the very high radar frequencies. Silts, clays, salts, saline water, the water table, and any other conductive materials in the subsurface severely restrict or stop penetration of radar.

Self-Potential Surveys

Purpose

Self-potential ([SP] spontaneous potential or natural potential) is the natural electrical potential existing within the earth due to many causes. These causes can be classified broadly into two groups (excluding manmade causes):

Mineralization Potential.—Mineralization potential is commonly the result of chemical concentration cells formed when conductive mineral deposits, such as graphite or sulfide, are intersected by the water table. Mineralization potentials are almost always negative and may have values up to several hundred millivolts. Back- ground potentials can be either positive or negative and usually have values of only a few tens of millivolts.

Background Potential.—Background potential is commonly the result of (a) two electrolytes of different concentration being in contact with one another, (b) electrolytes flowing through a capillary system or

15 FIELD MANUAL porous media, (c) an electrolyte in contact with a solid, and (d) electromagnetically induced telluric (large scale flow in the earth’s crust) currents.

The background potentials developed by electrolytes flowing through a capillary system or porous media (called electro-filtration or streaming potentials) are used to study seepage. Water flowing through a capillary system collects and transports positive ions from the surrounding materials. The positive ions accumulate at the exit point of the capillary, leaving a net positive charge. The untransported negative ions accumulate at the entry point of the capillary leaving a net negative charge. If the streaming potentials developed by this process are of sufficient magnitude to measure, the entry point and the exit point of zones of concentrated seepage may be determined from the negative and positive self potential anomalies.

Applications

Self-potential surveys have been used to map the lateral extent of mineral deposits and, in some instances, provide information of the configuration of the deposits. Another exploration application has been to map the depth to and configuration of certain geothermal areas. Normally, in geothermal applications, self-potential surveying is used in conjunction with other geophysical surveys (gravity, seismic, and electrical).

In geotechnical investigations, self-potential surveys have been used to map leakage paths from dams. Self- potential surveying has also been used to map leaks from canals and buried pipelines that transport liquids. Detachment walls and lateral limits of some landslide masses have been mapped with self-potential surveys.

16 SURFACE GEOPHYSICAL INVESTIGATIONS

Self-potential surveying may play an important role in hazardous waste investigations and in monitoring leakage from dams.

Magnetic Surveys

Purpose

Magnetic surveys measure anomalous conditions within the Earth’s magnetic field. The Earth’s magnetic field resembles the field of a bar magnet. The field is twice as strong in the polar regions than at the equator. The intensity of the field in the polar regions is approximately 60,000 gammas; while at the equator, the intensity is approximately 30,000 gammas. The Earth’s magnetic field is not symmetrical but contains many large per- turbations due to local variations in magnetic materials and larger magnetic features. Within the Earth’s field, anomalies on the order of one gamma to several thousand gammas are detected by magnetic surveys. The smaller anomalies can be detected with complex instruments, and the larger anomalies can be detected with simpler instruments and field techniques.

Applications

Magnetic surveys have their widest applications in petroleum and mineral exploration programs. For applications in petroleum exploration, the application is somewhat simpler because the sources of most magnetic anomalies lie within the basement complex and the overlying sediments are often "transparent" to magnetic surveys.

In geotechnical investigations, magnetic surveys have been used to detect buried barrels of contaminated

17 FIELD MANUAL materials and to detect and map buried pipelines. Magnetic surveys have also been used in archaeological investigations.

Gravity Surveys

Purpose

Gravity anomalies are the result of contrasts in densities of materials in the Earth. If all the materials within the Earth were layered horizontally and were of uniform density, there would be no density contrasts. Density contrasts of different materials are controlled by a number of different factors; the most important are the grain density of the particles forming the material, the porosity of the material, and the interstitial fluids within the material. Generally, soil and shale specific gravities range from 1.7 to 2.2. Massive limestone specific gravities average 2.7. While this range of values may appear to be fairly large, local contrasts will be only a fraction of this range. A common order of magnitude for local density contrasts is 0.25. Density contrasts can be determined by calculating the gravity effect of a known model and comparing that effect with the observed gravity determined from a gravity survey.

Applications

Gravity surveys provide an inexpensive determination of regional structures that may be associated with groundwater aquifers or petroleum traps. Gravity surveys have been one of the principal exploration tools in regional petroleum exploration surveys. Gravity surveys have somewhat limited applications in geotechnical investigations. Gravity surveys have been used to obtain information on bedrock depths and the top of rock

18 SURFACE GEOPHYSICAL INVESTIGATIONS configuration in areas where it has not been possible or practical to use other geophysical techniques. Micro- gravity (high-precision) surveys have been used in a few instances to obtain information on the success of grouting programs. In these cases, microgravity surveys are performed before and after grouting operations and density contrasts of the two surveys are compared. Microgravity surveys have been used for archaeological investigations.

Glossary

Accelerometer – Transducer with output proportional to acceleration. A moving coil geophone (type of transducer) with a response proportional to frequency may operate as an accelerometer.

Acoustic Logging – borehole log of any of several aspects of acoustic-wave propagation (e.g., a sonic, amplitude, character, or three-dimensional log).

Air Wave – Energy from a shot which travels in the air at the velocity of sound.

Amplitude – The size of a signal, either in the ground or after amplification. Usually measured from the zero or rest position to a maximum excursion. The amplitude of a signal has units based on the measurement of the signal (e.g., acceleration (inch per square second [in/sec2]), velocity (inches per second [in/sec]) or displacement (inches [in]).

Analog – (1) A continuous physical variable (such as voltage or rotation) that has a direct relationship to another variable (such as acceleration) with one

19 FIELD MANUAL

proportional to the other. (2) Continuous as opposed to discrete or digital.

Anomaly – A deviation from normal or the expected. For example, a travel time anomaly, Bouger anomaly, free-air anomaly.

Apparent Velocity – (1) The velocity that a wave-front registers on a line of geophones. (2) The inverse slope of a time-distance curve.

Automatic Gain Control (AGC) – The output amplitude controls the gain of a seismic amplifier, usually individual for each channel; but sometimes, multi-channel devices are used.

Basement (Complex) – (1) generally of igneous and metamorphic rocks overlain unconformably by sedimentary strata. (2) Crustal layer beneath a sedimentary layer and above the Mohorovicic discontinuity.

Bedrock – Any solid rock exposed at the surface of the earth or overlain by unconsolidated material.

Bit – A binary digit; either a 1 (one) or 0 (zero).

Body Waves – The only waves that travel through the interior of a body consisting of P-waves and S-waves.

Byte – Word.

Cable – The assembly of electrical conductors used to connect geophone groups or other instruments.

20 SURFACE GEOPHYSICAL INVESTIGATIONS

Casing – Tubing or pipe used to line drill holes or shot- holes to keep them from caving.

Cathodic Protection – Electrical corrosion protection for pile foundations, electrical grounding mats, buried pipelines, or any metal subject to corrosion.

Channel – (1) A single series of interconnected devices through which geophysical data can flow from source to recorder. (2) An elongated depression or geological feature. (3) An allocated portion of the radio frequency spectrum.

Channel Wave – An elastic wave propagated in a layer of lower velocity than layers on either side. Energy is largely prevented from escaping from the channel because of repeated total reflection at the channel boundaries or because rays that tend to escape are refracted back toward the channel.

Character. – (1) The recognizable aspect of a seismic event, usually displayed in the waveform that distinguishes the event from other events. Usually, a frequency or phasing effect, often not defined precisely and dependent upon subjective judgment.

Common Depth Point (CDP). – The same portion of subsurface that produces reflections at different offset distances on several profiles.

Compressional Wave – An elastic body wave with particle motion in the direction of propagation. Same as P-waves, longitudinal wave, dilatation wave, irrotational.

Converted Wave – A wave that is converted from longitudinal to transverse, or vice versa, upon reflection or refraction at oblique incidence from an interface.

21 FIELD MANUAL

2 Critical Angle – Angle of incidence, c, for which the refracted ray grazes the contact between two media

(of velocities V1 and V2): 2 sin c = V1/V2

Critical Distance – (1) The offset at which a refracted event becomes the first break; cross-over distance. (2) The offset at which the reflection time equals the refraction time (i.e., the offset at which the reflection occurs at the critical angle).

Crossfeed (Crosstalk) – Interference resulting from the unintentional pickup of information or noise from another channel.

Datum – (1) The arbitrary reference level to which measurements are corrected. (2) The surface from which seismic reflection times or depths are measured, corrections having been made for local topographic and/or weathering variations. (3) The reference level for elevation measurements, often sea level.

Delay Time – (l) In refraction work, the additional time taken for a wave to follow a trajectory to and along a buried marker over that which would have been taken to follow the same marker hypothetically at the ground surface or at a reference level. Normally, delay time exists separately under a source and under a detector and depends on the depth of the marker at wave incidence and emergence points. Shot delay time plus geophone delay time equals intercept time. (2) Delay produced by a filter. (3) Time lag introduced by a delay cap.

22 SURFACE GEOPHYSICAL INVESTIGATIONS

Diffraction – (1) Scattered energy which emanates from an abrupt irregularity, particularly common where faults cut reflecting interfaces. The diffracted energy shows greater curvature than a reflection (except in certain cases where there are buried foci), although not necessarily as much as the curve of maximum convexity. Diffraction frequently blends with a reflection and obscures the fault location or becomes confused with dip. (2) Interference produced by scattering at edges. (3) Causes energy to be transmitted laterally along a wave crest. When a portion of a wave train is interrupted by a barrier, diffraction allows waves to propagate into the region of the barrier's geometric shadow.

Digital – Representation of quantities in discrete units. An analog system represents data as a continuous signal.

Dipole – A pair of closely spaced current electrodes that approximates a dipole field from a distant pair of voltage detecting electrodes.

Elastic Constants –

(1) Bulk modulus, k. – The stress-strain ratio under hydrostatic pressure.

∆P k = ∆VV/

where )P = pressure change, V = volume, and )V = volume change.

23 FIELD MANUAL

(2) Shear modulus, :. – rigidity modulus, Lame's constant. The stress-strain ratio for simple shear.

µ = FAt / ∆LL/

where Ft = tangential force, A = cross-sectional area, L = distance between shear planes, and )L = shear displacement. Shear modulus can also be expressed in terms of other moduli as:

µ = E ()1+ σ

where E = Young's modulus, and F = Poisson's ratio.

(3) Young's modulus, E. – The stress-strain ratio when a rod is pulled or compressed.

∆FA/ E = ∆LL/

where )F/A = stress (force per unit area), L = original length, and )L = change in length.

(4) Lame' constant, 8. – a tube is stretched in the up-direction by a tensile stress, S, giving an upward strain, s, and S’ is the lateral tensile stress needed to prevent lateral contraction, then:

λ = S' s

This constant can also be expressed in terms of Young’s modulus, E, and Poisson’s ratio, F:

24 SURFACE GEOPHYSICAL INVESTIGATIONS σ λ = E ()()112+−σσ

Electromagnetic – Periodically varying field, such as light, radio waves, radar.

End Line – Shotpoints that are shot near the end of the spread.

Fan Shooting – An early use of the refraction seismograph to find salt domes within a thick, low- velocity section; detectors located in widely spaced fan-like arrays radiating from the shot locations.

Filter – (1) A device that discriminates against some of the input information. The discrimination is usually on the basis of frequency, although other bases such as wavelength or moveout (see velocity filter) may be used. The act of filtering is called convolution. (2) Filters may be characterized by their impulse response or, more usually, by their amplitude and phase response as a function of frequency. (3) Band- pass filters are often specified by successively listing their low-cutoff and high-cutoff points. (4) Notch filters reject sharply at a particular frequency. (5) Digital filters filter data numerically in the time domain. Digital filtering can be the exact equivalent of electrical filtering. Digital filtering is very versa- tile and permits easy filtering according to arbitrarily chosen characteristics.

First Break or First Arrival – The first recorded signal attributable to seismic wave travel from a source. First breaks on reflection records provide information about weathering. Refraction work is based

25 FIELD MANUAL

principally on the first breaks, although secondary (later) refraction arrivals are also used.

Frequency – The repeat rate of a periodic wave, measured in hertz. Angular frequency, measured in radians per second.

Galvanometer – A coil suspended in a constant magnetic field. The coil rotates through an angle proportional to the electrical current flowing through the coil. A small mirror on the coil reflects a light beam proportional to the galvanometer rotation.

Geophone (Seismometer, Jug) – Instrument used to convert seismic energy (vibration) into electrical energy.

Geophone Station – Location of a geophone on a spread.

Gravimeter. – An instrument for measuring variations in gravitational attraction.

Gravity Survey – A survey performed to measure the gravitational field strength, or derivatives, that are related to the density of different rock types.

Group Velocity – The velocity at which most of the energy in a wave train travels. In dispersive media where velocity varies with frequency, the wave train changes shape as it progresses so that individual wave crests appear to travel at velocities (the phase velocity) different from the overall energy as approximately enclosed by the envelope of the wave train. The velocity of the envelope is the group velocity. Same as dispersion.

26 SURFACE GEOPHYSICAL INVESTIGATIONS

Head Wave – See refraction wave.

Hidden Layer – A layer that cannot be detected by refraction methods; typically, a low velocity layer beneath a high velocity layer.

Hydrodynamic Wave – A seismic surface wave propagated along a free surface. The particle motion is elliptical and prograde (M2 type Rayleigh or Sezawa) (e.g., Rayleigh-type wave dependent upon layering).

Hydrophone (Pressure Detector) – A detector sensitive to variations in pressure, as compared to a geophone, which is sensitive to motion. Used when the detector can be placed below a few feet of water such as in marine or marsh applications or as a well seismometer. The frequency response of the hydrophone depends on the depth beneath the surface.

In-line Offset – Shot points that are in line, but offset to a spread.

Lead – An electrical conductor (wire cable) used to connect electrical devices. Geophones are connected to cables at the takeouts via leads on the geophones.

Love Wave – A surface seismic wave associated with layering. This wave is characterized by horizontal motion perpendicular to the direction of propagation, with no vertical motion.

27 FIELD MANUAL

Low-velocity Layer (LVL) – The surface layer that has low seismic velocity.

Magnetic Survey – A survey to measure the magnetic field or its components as a means of locating concentrations of magnetic materials or determining depth to basement.

Mis-tie – (1) The time difference obtained on carrying a reflection event or some other measured quantity around a loop; or the difference of the values at identical points on intersecting lines or loops. (2) In refraction shooting, the time difference from reversed profiles that gives erroneous depth and dip calculations.

Multiple – Seismic energy that has been reflected more than once (e.g., long-path multiple, short-path multiple, peg-leg multiple, and ghosts).

Noise – (1) Any undesired signal or disturbance that does not represent any part of a message from a specified source. (2) Sometimes restricted to random energy. (3) Seismic energy that is not resolvable as reflections. Noise can include microseisms, shot- generated noise, tape-modulation noise, and harmonic distortions. Sometimes divided into coherent noise (including non-reflection coherent events) and random noise (including wind noise, instrument noise, and all other energy which is non- coherent). (3) Random noise can be attenuated by compositing signals from independent measurements. (4) Sometimes restricted to seismic energy

28 SURFACE GEOPHYSICAL INVESTIGATIONS

not derived from the shot explosion. (5) Disturbances in observed data due to more or less random inhomo- geneities in surface and near-surface material.

Noise Analysis – A profile or set of profiles used to gather data for an analysis of coherent noise. Used to design geophone arrays in reflection surveys.

Noise Survey (Ground Noise Survey) – A survey of ambient, continuous seismic noise levels within a given frequency band. This technique is a useful tool for detecting some geothermal reservoirs because they are a source of short-period seismic energy.

On-line – Shot points that are not at any point on a spread other than at the ends.

Original Data – (1) Any element of data generated directly in the field in the investigation of a site. (2) A new element of data resulting from a direct manipulation or compilation of field data.

Oscillograph – A device that records oscillations as a continuous graph of corresponding variation in an electric current or voltage.

Oscilloscope – A device that visually displays an electrical wave on a screen (e.g., on a cathode ray tube).

29 FIELD MANUAL

Phase Velocity – The velocity of any given phase (such as a trough or a wave of single frequency); it may differ from group velocity because of dispersion.

Plant – The manner in which a geophone is placed or the coupling to the ground.

Primacord – An explosive rope that can be used to either connect explosive charges or to detonate separately as a primary energy source.

Profile – The series of measurements made from several shotpoints to a recording spread from which a seismic data cross section or profile can be constructed.

Radar – An exploration method where microwaves are transmitted into a medium and are reflected back by objects or layers. The reflected microwaves are received and processed to provide an image of the subsurface. May be used for shallow penetration surveys.

Rayleigh Wave – A seismic wave propagated along a free surface. The particle motion is elliptical and retrograde.

Ray Path – The path of a seismic wave. A line every- where perpendicular to wave-fronts (in isotropic media).

Reconnaissance – (1) A general examination of a region to determine its main features, usually preliminary to a more detailed survey. (2) A survey to determine

30 SURFACE GEOPHYSICAL INVESTIGATIONS

regional geological structures or to determine whether economically prospective features exist, rather than to map an individual structure.

Reflection Survey – A survey of geologic structure using measurements made of arrival times of seismic waves that have been reflected from acoustic impedance change interfaces.

Refraction Survey – A survey of geologic structure using compressional or head waves. Head waves involve energy that enters a high-velocity medium (refractor).

Refraction Wave (Headwave, Mintrop Wave, Conical Wave) – Wave travel from a point source obliquely downward to and along a relatively high velocity formation or marker and then obliquely upward. Snell's law is obeyed throughout the trajectory. Angles of incidence and of emergence at the marker are critical angles. Refracted waves typically following successively deeper markers appear as first arrivals with increasing range (shot to detector distance). Refracted waves following different markers may have different arrival times for any given range. Refracted waves cannot arise for angles of incidence less than the critical angle for any given marker. At the critical angle, the refracted wave path (and travel time) coincides with that of a wide angle reflection.

Refractor (Refraction Marker) – An extensive, relatively high-velocity layer underlying lower velocity layers that transmits a refraction wave nearly horizontally.

31 FIELD MANUAL

Resistivity – An electrical property of rock reflecting the conductivity of an electrical current. Resistivity is the ratio of electric field intensity to current density.

Resistivity Meter – A general term for an instrument used to measure the in place resistivity of soil and rock materials.

Resistivity Survey – A survey that measures electric fields and earth resistivity of a current induced into the ground.

Reverse Profile – A refraction seismic profile generated by shooting both ends of a spread.

Roll-along – A mechanical or electrical switch that connects different geophones (or geophone groups) to the recording instruments. The use of a roll-along switch permits common depth point reflection data to be easily acquired in the field.

Seismic Amplifier – An electronic device used to increase the electrical amplitude of a seismic signal.

Seismic Camera – A recording oscillograph used to make a seismic record.

Seismic Cap – A small explosive designed to be detonated by an electric current that detonates another explosive. These caps are designed to provide very accurate time control on the shot.

Seismic Velocity – The rate of propagation of seismic waves through a medium.

Seismogram – A seismic record.

32 SURFACE GEOPHYSICAL INVESTIGATIONS

Self-potential (Spontaneous Potential, Natural Potential, SP) – The direct current or slowly varying natural ground voltage between nearby non- polarizing electrodes.

Shear Wave – A body wave with the particle motion perpendicular to the direction of propagation. (Same as S-wave, equivoluminal, transverse wave.)

Shooter – The qualified, licensed individual (powderman) in charge of all shot point operations and explosives on a seismic crew.

Shot Depth – The distance from the surface down to the explosive charge. The shot depth is measured to the center or bottom of the charge with small charges. The distances to both the top and bottom of the column of explosives are measured with large charges.

Shot Instant (Time Break, TB, Zero Time) – The instant at which a shot is detonated.

Shot Point – Location of the energy source used in generating a particular seismogram.

Signal Enhancement – A process used in seismographs and resistivity systems to improve the signal-to- noise ratio by real-time adding (stacking) of successive waveforms from the same source point. Random noise tends to cancel out, and the coherent signal tends to add or stack.

Snell’s Law – When a wave crosses a boundary between two isotropic mediums, the wave changes direction such that the sine of the angle of incidence of the wave divided by the velocity of the wave in the first medium equals the sine of the angle of refraction of

33 FIELD MANUAL

the wave in the second medium divided by the velocity of the wave in the second medium (see critical angle).

Spread – The layout of geophone groups from which data from a single shot are simultaneously recorded.

Stanley Wave – A type of seismic surface wave propagated along an interface.

Surface Wave – Energy that travels along or near the surface (ground roll).

Takeout – The connections on a multiconductor cable for connecting geophones. May refer to the short cable leads from the geophones (pigtails).

Time Break – The mark on a seismic record that indicates the shot instant or the time the seismic wave was generated.

Trace – A record of one seismic channel. This channel may contain one or more geophones.

Vibration Monitor – A sensitive, calibrated recorder of ground and structural acceleration and velocity. Measurements are made to determine vibration amplitudes and modal frequencies of buildings, towers, etc., under ambient conditions, as well as to detect potentially damaging vibrations caused by blasting, pile driving, etc.

34 SURFACE GEOPHYSICAL INVESTIGATIONS

Vibroseis – A seismic energy source consisting of controlled frequency input into the earth by way of large truck mounted vibrators. Trademark of Continental Oil Company (Conoco).

Wave Length – The distance between successive similar points on two adjacent cycles of a wave measured perpendicular to the wavefront.

Wave Train – (1) The sum of a series of propagating wave fronts emanating from a single source. (2) The complex wave form observed in a seismogram obtained from an explosive source.

Weathering Spread – A short-spaced geophone interval refraction spread used to provide corrections to refraction data caused by delay times in near- surface, low-velocity materials.

WWV(B) – The National Institute of Standards and Tech- nology (NIST) radio stations that broadcast time and frequency standards.

For the definition of other geophysical terms used in this manual, refer to: Glossary of Terms Used in Geophysical Exploration, Society of Exploration Geophysicists, Tulsa, Oklahoma, 1984.

35 FIELD MANUAL

Bibliography

Mooney, H.M., Handbook of Engineering Geophysics, Volume 1: Seismic, Bison Instruments, Inc., Minneapolis, Minnesota, 1984.

Telford, W.M., et al., Applied Geophysics, Cambridge University Press, New York, New York, 1976.

U.S. Corps of Engineers, Geophysical Exploration for Engineering and Environmental Investigations, Engineering Manual EM 111-1-1802, 1995.

U.S. Geological Survey, Application of Surface Geophysics to Ground-Water Investigations, Chapter D1, Book 2, Techniques of Water-Resources Investigations of the United States Geological Survey, 1974.

Van Blaricom, R., compiler, Practical Geophysics II for the Exploration Geologist, Second Edition, Northwest Mining Association, Spokane, Washington, 1992.

Ward, S.H., editor, Geotechnical and Environmental Geophysics, Society of Exploration Geophysics, Tulsa, Oklahoma, 1990.

36 Chapter 14

BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Introduction

Wireline surveys determine physical properties in and beyond the wall of a borehole by devices attached to a cable, or wireline. Subsurface geologic conditions and engineering characteristics can be derived directly or indirectly from the wide variety of measurable properties available by wireline surveying. Wireline logging techniques commonly are classified by the kind of energy that is input (active systems) or received (passive systems), including electric, seismic or acoustic, nuclear, magnetic, gravity, or optical. Logging tools are also classified according to whether they are for use in open holes or cased holes. Data from several methods are often combined to evaluate a single geologic or engineering characteristic. This chapter describes the methods and discusses the application of borehole wireline surveying to geotechnical exploration and investigation.

Electric Logging Techniques

An electric log is a continuous record of the electrical properties of the fluids and geologic materials in and around a borehole. Electric logging is performed in the uncased portion of a borehole by passing electric current through electrodes in the logging device, or sonde, and out into the borehole and the geologic medium. Other electrodes located on the surface or in the borehole complete the circuit to the source and recording device. Electric logging surveys are efficient and cost effective because the process is automated and several electrical properties are measured simultaneously by combining several electrode configurations in the same tool. FIELD MANUAL

Electric logging techniques can be used in geotechnical investigations to assess the variation with depth of geologic materials and associated fluids. Electric logs from two or more boreholes are used to correlate and determine the continuity of geologic strata or zones that have similar electrical properties. Since the electrical properties depend on physical characteristics, the porosity, mineral composition, water content (saturation), water salinity, lithology, and continuity of the bedding can often be deduced. Borehole electric logs are also the best source of control for surface electrical surveys by providing subsurface layer resistivities. Electric log correlation of continuous layers from borehole to borehole is relatively simple. The interpretation of physical properties from electric logs can be ambiguous and complicated. Different combinations of water content, salinity, mineralogy, porosity, and borehole peculiarities can produce similar electric logs.

Spontaneous Potential (SP) Log

The spontaneous potential or SP logging device records the difference in potential in millivolts between a fixed electrode at the surface and an electrode in a borehole (figure 14-1). The measured potential difference changes as the electrical potential between the borehole fluid and the fluids in the various strata opposite the sonde changes. The spontaneous potential device commonly is incorporated into the multiple-electrode resistivity sonde so that resistivity and SP logs are acquired simultaneously. Figure 14-2 illustrates a typical SP resistivity log. The recording is a relative measurement of the voltage in the borehole. Readings opposite shales or clays are relatively constant and form the shale baseline, or "shale line." The SP curve typically deflects to the left or right opposite permeable formations depending on the salinity of the drilling mud. Sandstone and other porous

38 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Figure 14-1.—Spontaneous potential survey elements. and permeable strata allow the different fluids to mix and produce salinity of the pore fluid with respect to the borehole fluid and the clay content of the strata. The SP peaks are commonly displayed to the left of the shale line because negative potentials are more commonly encountered. In fresh water, SP anomalies are typically inverted (i.e., they appear to the right of the shale baseline).

SP logs are used in combination with resistivity logs to define strata boundaries for correlation and to infer the lithology of the strata as a function of permeability and resistivity. The shape of the SP curve depends on the drilling mud used and the geologic strata encountered. For example, the SP curve for a shale bed would indicate zero deflection (the shale line in figure 14-2), and the

39 FIELD MANUAL

Figure 14-2.—Electric log showing SP and resistivity in different beds.

40 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS resistivity curve would indicate low resistivity because of bound water in the clay and trapped water in the shale. Generally, the SP and resistivity curves converge opposite shale strata (A in figure 14-2) and diverge opposite permeable fresh water sands (B in figure 14-2). A limestone bed, which usually is highly resistive but develops little spontaneous potential, would produce a large resistivity deflection but a subdued SP peak (C in figure 14-2). A permeable sand bed with pore water of high salinity typically would produce little resistivity deflection but a large negative SP peak (D in figure 14-2). The determination of lithologies from SP logs should be done cautiously because many factors contribute to the magnitudes and directions of the curve deflections. The SP log is best used with resistivity and other logs to detect strata boundaries and to correlate strata between boreholes. The SP log is also used to determine formation water resistivities.

Single-Point Resistance Log

Single-point resistance loggers are the simplest electrical measuring devices. A current can flow between a single electrode placed in a borehole and another electrode at the ground surface (figure 14-3). The earth between the electrodes completes the circuit. Single-point resistance logs are not commonly used in modern logging operations but illustrate the principal of down-hole electric logging. The resistance, R, of the circuit (electrodes plus earth) can be calculated from Ohm’s Law, R = V/I, where V is the measured voltage drop and I is the current through the circuit. The resistance of a circuit is determined by the conductor’s size, shape, and resistivity, p, an intrinsic property of a material. Resistance of the conductor (the earth) is a convenient and useful property determined by pore fluid content, pore fluid composition, lithology, and continuity of strata. The resistivity of the measured

41 FIELD MANUAL

Figure 14-3.—Single-point resistivity array. section of earth is determined from p = KR, where K is a geometric factor which differs for different electrode configurations and R is the measured resistance V/I. A single point resistance log measures an apparent resistance of a section made up of borehole fluid and the various individual strata between the borehole and the ground surface electrode. The multiple electrode arrays discussed below are designed to narrow and better define the measured sections so that individual strata are represented more accurately by the logs.

Multiple Electrode Array Log

Wireline electrical systems using multiple electrode arrays in the borehole provide better resolution of

42 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS resistivity and associated properties of individual strata within the subsurface than can be achieved with the single-point array. Multiple electrode arrays include the short- and long-normal array, lateral array, and focused- current or guard logging systems. Current electrodes usually are designated A and B, and potential electrodes are designated M and N. "Normal" arrays place the in- hole current electrode far away, at effective infinity (figure 14-4A). "Lateral" devices place the two potential electrodes close together with respect to the in-hole current electrode (figure 14-4B). Conventional modern logging systems use a sonde made up of two normal devices and one lateral device to produce three resistivity logs and the SP log simultaneously.

The normal resistivity arrays (figure 14-4A) are called short normal or long normal depending on the spacing of the in-hole current (A and B) and potential (M and N) electrodes. The industry standard AM electrode spacing is 16 inches (in) for the short normal and 64 in for the long normal. The normal arrays measure the electrical potential at the in-hole electrode M. The greater the spacing between the current and measuring electrodes, the greater the effective penetration (effective penetration distance = ½ AM) of the device into the surrounding geologic medium.

The lateral resistivity array is shown in figure 14-4B. The actual positions of the electrodes may vary from the circuit shown, but the resistivity measurements are the same. The lateral array spacing is measured from the A current electrode to the center (0) of the potential electrode configuration and is called the AO spacing. The lateral array measures the potential difference, or gradient, between the two in-hole potential electrodes and is also called the gradient array. The influence of the

43 FIELD MANUAL

Figure 14-4.—Multiple-electrode resistivity arrays. (A and B are current electrodes. M and N are potential electrodes.) geologic medium away from the borehole (the effective penetration of the system) is greatest for the lateral array with an 18-foot 8-in spacing and least for a 16-in short normal array.

44 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

The focused-current, or guard, resistivity device is a modified single-electrode array in which "guard" current electrodes are placed above and below a central current electrode and two pairs of potential electrodes (figure 14-5). Current in the central and guard electrodes is adjusted so that zero potential exists between the potential electrodes and the current is thus forced or focused to flow out into the geologic medium in a narrow band. The device then measures the potential between the sonde electrodes and a reference electrode at the ground surface. Focusing the current into a band of predetermined thickness gives the focused array much greater thin bed and stratum boundary resolution than the other arrays.

Geotechnical applications for multiple-electrode resistivity arrays include apparent resistivity and an approximation of true resistivities of individual strata or zones. Resistivity data aid in the interpretation of surface electrical surveys, which generally are less expensive to conduct than down-hole surveys and can be applied over large areas. Since the depth of penetration of the measuring circuit into the geologic medium varies with the electrode spacing, logs of the various arrays (short- and long-normal and lateral) can be analyzed collectively to evaluate the effects of bed thickness, borehole fluids, drilling mudcake, variations in fluids, and permeabilities of strata at various distances from the borehole. The curve shapes of the logs for several boreholes permit correlation of strata and zones from borehole to borehole. Normal devices produce better boundary definition of thick strata than do lateral devices, but lateral logs are more effective in delineating thin strata and thin, highly resistive zones. The focused logs discriminate more sharply between different strata, define strata boundaries better, and give a better approximation of true stratum resistivity than do normal or lateral logs. Porosity and

45 FIELD MANUAL

Figure 14-5.— Focused current, or guard, resistivity array. water content of strata and salinity of pore fluids can be calculated from the logs if sufficient information is obtained.

Microlog

Special purpose electric logging devices are available to supplement or, in some cases, replace standard resistivity

46 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS logs. The microlog (also called contact log, microsurvey, and minilog) records variations in resistivity of a narrow, shallow zone near the borehole wall. The microlog sonde is equipped with three closely spaced electrodes placed on a rubber pad which is pressed against the borehole wall (figure 14-6). Microlog electrode spacings are about 1 to 2 in (2.5 to 5 centimeters [cm]). Depth of investigation for the microlog is about 3 in (7.5 cm) from the borehole wall. Normal, lateral, and guard arrays can be configured in the microlog survey. Porous permeable zones allow the mud cake to penetrate the strata, and the resulting microlog will indicate resistivities close to that of the mud.

Induction Log

Induction logging is performed in dry boreholes or boreholes containing nonconducting fluids. Induction logging can be done in holes cased with polyvinyl chloride (PVC) casing. The induction logger is housed in a sonde that uses an induction coil to induce a current in the geologic medium around a borehole. The induction logger is a focused device and produces good thin-bed resolution at greater distances from the borehole than can be achieved with normal spacing devices. A primary advantage over other devices is that the induction logger does not require a conductive fluid in the borehole.

Nuclear Radiation Logging Techniques

A nuclear radiation log is a continuous record of the natural or induced radiation emitted by geologic materials near the borehole. Nuclear radiation logging is performed by raising a sonde containing a radiation detector or a detector and a radioactive source up a borehole and recording electrical impulses produced by a radiation detector.

47 FIELD MANUAL

Figure 14-6.—Microlog resistivity logging device.

Nuclear radiation logging can be used in geotechnical investigations to correlate strata between boreholes, aid in determining lithology, and derive or measure directly many physical parameters of the subsurface materials,

48 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS including bulk density, porosity, water content, and relative clay content. Most nuclear radiation logging systems can be operated in cased boreholes, giving them an advantage over electrical wireline logging systems. Nuclear logs can also be run in old boreholes, which are more likely to be cased than recent boreholes. The logs are among the simplest to obtain and interpret, but the calibrations required for meaningful quantitative interpretations must be meticulously performed. Nuclear radiation logging tools should be calibrated in controlled calibration pits. Under favorable conditions, nuclear borehole measurements approach the precision of direct density tests of rock cores. The gamma-gamma density log and the neutron water content log require the use of isotopic sources of nuclear radiation. Potential radiation hazards necessitate thorough training of personnel working around the logging sources.

Three common wireline nuclear radiation systems are the gamma ray or natural gamma logger, the gamma-gamma or density logger, and the neutron logger. The gamma- gamma and neutron devices require the use of a radioactive source material. The gamma ray device is a passive system and does not use a radioactive source. All the systems employ an in-hole sonde containing the source and detector. Most devices require a borehole diameter of at least 2 in (5 cm) and investigate a zone extending 6 to 12 in (15 to 30 cm) from the borehole. Applications differ for the three systems and depend on the properties measured.

Gamma Ray (Natural Gamma) Log

The gamma ray or natural gamma radiation device provides a continuous record of the amount of natural gamma radiation emitted by geologic materials near the sonde. The gamma-ray detector converts incoming

49 FIELD MANUAL gamma radiation to electrical impulses proportional to the number of rays detected and sends the amplified electrical impulses to the surface. Gamma ray logs generally reveal the presence of shale or clay beds because clay minerals commonly contain the potassium isotope K40 ,which is the primary source of natural gamma radiation in most sediments. Shales and clays usually produce a high gamma ray count, or a peak on the log.

The relative density of a stratum is also indicated by natural gamma ray logs because gamma radiation is absorbed more by dense materials than by less dense materials. Gamma ray logging can be conducted in cased boreholes and is sometimes used in place of SP logging to define shale (clay) and non-shale (non-clay) strata. The natural gamma ray and neutron logs are usually run simultaneously from the same sonde and recorded side- by-side. The gamma ray log also infers the effective porosity in porous strata with the assumption that high gamma counts are caused by clay filling the pores of the strata. Gamma ray logs are used to correct gamma- gamma density logs. Gamma ray logs are standard in radiation logging systems.

Natural Gamma Spectral Log

Spectral logging permits the identification of the naturally occurring radioactive isotopes of potassium, uranium, and thorium which make up the radiation detected by the natural gamma ray detector. Spectral logging technology allows the detection and identification of radioactive isotopes that contaminate water resources, or are introduced as tracer elements in hydrologic studies.

50 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Density or Gamma-Gamma Log

The gamma-gamma or density logging device measures the response of the geologic medium to bombardment by gamma radiation from a source in the sonde. Electrons in the atoms of the geologic medium scatter and slow down the source gamma rays, impeding their paths to the detector. Figure 14-7 illustrates the operation of the gamma-gamma device. Since electron density is proportional to bulk density for most earth materials, strata with high bulk densities impede the source gamma rays more than low density strata and produce correspondingly lower counts at the detector. The primary use of the gamma-gamma log is determining bulk density. If bulk density and grain density are known from samples and if fluid density can be determined, the porosity can be calculated. Gamma-gamma logs can also be used for correlation of strata between boreholes.

Gamma-gamma logging is best conducted in uncased boreholes using decentralizing devices to keep the sonde

Figure 14-7.—Gamma-gamma logging sonde.

51 FIELD MANUAL against the borehole wall. The system is affected by borehole diameter and wall irregularities and must be carefully calibrated for the effects of hole diameter, decay of the strength of the radioactive source, natural gamma radiation in the geologic medium, and borehole fluid density. A caliper log is commonly run to permit calibration for hole diameter. Some logging systems simultaneously display the gamma ray count on one side of the log and bulk density on the other side, with the bulk density log automatically corrected for the effects of mud cake and wall irregularity.

Neutron Log

Neutron logging is an active system that measures the response of the geologic medium to emission of neutron radiation from a source located in the sonde. Neutrons emitted by the source are captured by certain atoms, especially hydrogen nuclei, in the strata near the sonde. Figure 14-8 illustrates the operation of the neutron logging device. Collision of neutrons with atoms of the geologic medium causes secondary emission of neutrons and gamma rays, a portion of which are picked up by the detector. A high concentration of hydrogen atoms near the source captures a greater number of neutrons and produces a smaller counting rate at the detector.

Neutron detectors may detect gamma (neutron-gamma) or neutron (neutron-neutron) radiation. Water and hydrocarbons contain high concentrations of hydrogen atoms. If the fluid in the strata is assumed to be water, the neutron log is an indicator of the amount of water present. Determination of volumetric water content (weight of water per unit volume measured) is a principal use of neutron logging. In saturated materials, the neutron log can be an indicator of porosity, the ratio of the volume of void space to the total volume. Bulk densities from gamma-gamma logs, grain densities from samples, caliper

52 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Figure 14-8.—Neutron logging sonde. log data, and natural gamma log information can be combined with the volumetric water contents from neutron logs to calculate the more commonly used geotechnical parameters of water content by weight, wet and dry density, void ratio, porosity, saturation, and lithology.

Neutron logs and natural gamma radioactive logs can be obtained through thick borehole casing and are usually run together. Figure 14-9 illustrates the format of the tandem logs and typical responses for several lithologies. The response of different lithologies to the natural gamma and neutron devices is controlled directly by the amount of radioactive material present (especially the clay content) and the fluid content and indirectly by the porosity and bulk density of the material. For example, the saturated sand of figure 14-9 absorbs neutron radiation, produces a correspondingly low neutron log count, and produces a low natural gamma count because of the lack of clay in its pores.

53 FIELD MANUAL

Figure 14-9.—Typical curve responses for nuclear radiation logs.

54 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Neutron activation or spectral logs provide spectral analyses of the geologic medium near the borehole to detect the presence of certain elements. The spectral logging sonde activates a neutron source in bursts of short duration and activates the gamma ray detector only during the source bursts. As a result, only certain radiation ("prompt" gamma rays) is detected. The system produces a plot of counts versus gamma ray energy. Peaks on the energy/count plot identify specific elements, for example carbon, silicon, magnesium, or chlorine. Spectral logs may have application to groundwater quality investigations.

Neutrino Log

Neutrino logs are not necessarily a borehole log, but the method can and often is performed in drill holes. Neutrino sources are located throughout the universe with the closest and most useful source being the sun. Using the sun as a neutrino source eliminates the need for a special source, and there are no handling and licensing problems that are often associated with other nuclear logs. Neutrinos penetrate the earth with little to no impediment, so neutrino logs can be run at any time of day or night. Logging tools generally consist of strings of widely spaced photomultiplier tubes (PMT) placed into the borehole. High-energy neutrinos passing through the rock will occasionally interact with the rock and create a muon. These muons emit Cherenkov light when passing through the array and are tracked by measuring the arrival times of these Cherenkov photons at the PMTs. Resolution is high because the source (Sun) only subtends half a degree at this distance (93 million miles from Earth). Neutrino logging is particularly useful in cased holes and when fluid in the hole is not a factor. New or old holes can be logged no matter what the hole contains. These logs are often used for tomography. Tomography is

55 FIELD MANUAL particularly useful and convenient because, as the Earth rotates, the source penetrates a full 360 degrees, similar to CAT scan or Magnetic Resonance Imaging. A drawback is that 24 hours is required to run a complete neutrino tomography log.

Acoustic/Seismic Logging Techniques

Wireline acoustic/seismic logging systems use medium- to high-frequency acoustic (sonic) energy emitted from a sonde to image the borehole wall or to obtain seismic velocities of the geologic material in the wall or in the formation away from the borehole. Acoustic systems use sonic energy generated and propagated in a fluid such as water. Seismic systems use sonic energy propagated through the ground in geologic materials. The three systems discussed in this section are the acoustic velocity logger, an acoustic and seismic energy system; a borehole imaging device, an acoustic system; and the cross-hole seismic technique, a seismic technique.

The borehole imaging and acoustic velocity systems are used in geotechnical investigations to evaluate geologic conditions including attitude and occurrence of discontinuities and solution cavities and in determining the effective porosity and elastic properties of rock. The down-hole systems also supply subsurface information for interpreting surface-applied geophysical surveys. The frequency of the energy pulse produced by the sonde’s transducer determines whether the energy penetrates the borehole wall for acoustic/seismic velocity surveys. Medium frequencies are used in acoustic/seismic velocity surveys. The energy is reflected from the wall for imaging surveys. High frequencies are used in acoustic/seismic velocity surveys. Borehole imaging velocity devices generate compressional (P-wave) energy. The acoustic

56 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS velocity device generates primarily compressional energy but also generates shear (S-wave) energy if the shear wave velocity exceeds the fluid velocity. The cross-hole seismic technique generates P- and S-wave energies and determines their velocities.

Acoustic Velocity Log

The continuous acoustic velocity (sonic) logger measures and records the velocity of acoustic energy (seismic waves) in the material adjacent to the borehole. A transmitter located at one end of the sonde generates an electro- mechanical pulse that is transmitted through the borehole fluid into the borehole wall and by refraction to a receiver located at the other end of the sonde (figure 14-10). The propagation velocities of the seismic waves can be calculated by travel times and distance traveled from transmitter to receiver. The devices must be operated in a fluid-filled borehole. Compressional wave oscillations set up by the sonde’s transmitter in the borehole fluid set up, in turn, oscillations in the borehole wall. Compressional, shear, and surface waves propagate in and along the wall and then, as compressional waves, back through the borehole fluid to the receiver. Compressional waves have the highest velocity and arrive first, followed by the shear waves and the surface waves. Devices with two receivers cancel the borehole fluid travel times so that only the refracted wave paths through the borehole wall are measured. Single-receiver devices require the borehole fluid acoustic velocity and borehole diameter for calculation of seismic velocities. The acoustic pulses generated at the transmitter are in the lower ultrasonic range around 20 kilohertz (kHz).

The simplest acoustic logging devices display a single graphical trace or waveform of the arrival of each pulse

57 FIELD MANUAL

Figure 14-10.—Elements of a simple wireline acoustic velocity device. and are called amplitude-modulated devices. Intensity- modulated acoustic logging devices record the entire continuous acoustic wave (see figure 14-11). Intensity- modulated, or three-dimensional (3-D), devices express wave frequency by the width of light and dark bands and

58 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS entations. The intensity The entations. band, amplitude by the shading intensity of the band. of the intensity shading by the amplitude band, Figure 14-11.—Acoustic log pres Figure 14-11.—Acoustic modulated waveform wave frequency by the width of the of the width by the wave frequency waveform modulated

59 FIELD MANUAL amplitude by the degree of light or dark shading (figures 14-11 and 14-12). The P-wave, S-wave, and surface wave arrivals can be discerned on the 3-D records. Strata or zones of different seismic velocity produce contrasting signatures on the 3-D log. The phyllite zones in figure 14-12 represent softer materials of lower seismic velocity than the metabasalts and produce correspondingly later arrival times. Fractures or other discontinuities can often be seen as disruptions in the bands.

Figure 14-12.—Sample of intensity modulated acoustic log. Lithologies from core samples.

In addition to determining seismic velocities to aid interpretation of seismic surveys, 3-D logs show lithologic contacts, geologic structure, and solution features. The P- and S-wave velocities can be used directly to calculate the dynamic elastic properties of rock, including Poisson’s ratio, Young’s modulus, and bulk and shear moduli. For example, Poisson’s ratio is calculated using:

12VV22− µ = ps 22− VVps

60 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

where Vp and Vs are the compressional and shear wave velocities, respectively. The effective porosity of the strata can also be evaluated.

Acoustic velocity devices require a borehole diameter of 3 in or greater. The in-place geologic materials must have compressional wave velocities higher than the velocity of the borehole fluid (approximately 4,800 feet per second [ft/sec] [1,450 meters per second (m/sec)] for water) for the waves to be refracted and detected. Soils generally do not have sufficiently high seismic velocities for acoustic velocity logging. The wave train (trace) type velocity loggers often are equipped with a radiation logging device and caliper on the same sonde for simultaneous acoustic and natural gamma ray logging and borehole diameter measurement.

Acoustic Borehole Imaging Log

The acoustic borehole imaging device uses high-frequency acoustic waves to produce a continuous 360-degree image of the borehole wall. Physical changes in the borehole wall are visible as changes in image intensity or contrast. Proprietary trade names for the acoustic borehole imaging device include "Televiewer" and "Seisviewer." Figure 14-13 illustrates the operation of an acoustic borehole imaging device. A piezoelectric transducer and direction indicating magnetometer are rotated by a motor inside the tool housing at approximately three revolutions per second (rps). The transducer emits pulses of acoustic energy toward the borehole wall at a rate of about 2,000 pulses per second at a frequency of about 2 megahertz (MHz). The high-frequency acoustic energy does not penetrate the borehole wall, and the acoustic beams are reflected from the borehole wall back to a transducer. The intensity of the reflected energy is a function of the physical condition of the borehole wall,

61 FIELD MANUAL

Figure 14-13.—Acoustic borehole imaging system. including texture (rough or smooth) and hardness (a function of the elasticity and density of the material). The image is oriented to magnetic north with every revolution of the transducer. Fractures, cavities, and other open discontinuities produce low-amplitude acoustic reflections and are readily discerned in their true orientation, width, and vertical extent on the image.

The acoustic borehole imaging device can detect discontinuities as small as 1/8 in (3 millimeters [mm]) wide and

62 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Figure 14-14.—Traces of planar discontinuities intercepting the borehole (left) as they appear on the acoustic borehole imaging record (right). can sometimes distinguish contrasting lithologies. Discontinuities, contacts, and other linear features intercepting the borehole at an angle other than 90 degrees produce a characteristic sinusoidal trace that can be used to determine the strikes and dips of the features. Figure 14-14 shows how planar discontinuities of different orientations appear on the acoustic imaging log. Vugs and solution cavities are displayed as black

63 FIELD MANUAL areas, and their traces can be analyzed to determine their size (in two dimensions) and percentage of the borehole. The device can also be used to inspect casing and well screens for defects. The acoustic imaging device must be operated in a fluid-filled borehole.

Cross-Hole Seismic Test

Cross-hole tests are conducted by generating a seismic wave in a borehole and recording the arrival of the seismic pulse with geophones placed at the same depth in another (receiver) borehole. Source and geophones are placed at several regular depth intervals in the boreholes to determine seismic wave velocities of each material. Compressional and shear wave velocities can be determined with the cross-hole test. Figure 14-15 illustrates the essential features of a cross-hole seismic test. The seismic source may be either an explosive or a mechanical device. A vertical hammer device, clamped to the borehole wall, is the typical source arrangement. Cross-hole geophones configured in triaxial arrays are used because directional detectors are necessary to identify the S-wave arrival. Two or more receiver holes are sometimes used.

The raw data of cross-hole tests are the times required for P- and S-waves to travel from the seismic source in one borehole to the detectors in the receiver hole or holes. The corresponding P- and S-wave arrival times can be used to calculate seismic velocities as the ratios of distance to travel time, assuming the arrivals are direct (non- refracted) arrivals. If refraction through a faster zone occurs, true velocities must be calculated, similar to surface refraction seismic calculations.

64 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Figure 14-15.—Cross-hole seismic test.

Borehole spacing (distance) is critical in cross-hole tests. Generally, spacing should be no greater than 50 feet (ft) (15 meters [m]) or less than 10 ft (3 m). Borehole deviation surveys should be conducted prior to testing to determine precise spacing between holes at each shotpoint depth.

Cross-hole tests have several applications in engineering geology. S-wave cross-hole tests provide data on material properties for static and dynamic stress analysis. In addition to providing true P- and S-wave velocities at different depths, cross-hole surveys can detect seismic anomalies such as zones of low velocity underlying a zone of higher

65 FIELD MANUAL velocity or a layer with insufficient thickness or velocity contrast to be detected by surface refraction tests.

Seismic Tomography

Tomography is a method of constructing an image of some physical property inside an object from energy sent through the object in many directions. Much like medical tomography (such as a CAT scan) is used to create images of features inside the human body; geophysical tomography is used to create images of features beneath the ground or within engineered structures. There are several types of geophysical tomography. Cross-hole seismic tomography is one of the most common types of geophysical tomography. Cross-hole seismic tomography involves sending seismic energy from one borehole to another. A transmitter is lowered into one borehole, and the transmitted seismic energy is recorded by a string of receivers located in the second borehole. The positions of the transmitter and receivers are varied so that the seismic energy is transmitted between the two boreholes over a large depth range and at many different angles. The arrival times of the transmitted seismic energy are used to construct an image of seismic P-wave velocity of the geologic materials between the two boreholes. In addition, the amplitudes of the transmitted signals may sometimes be used to construct an image of the apparent attenuation of the geologic materials. Attenuation is a measure of the amount of energy loss of the seismic signal and is related to such factors as material type, degree of compaction or cementation, porosity, saturation, and fracturing. Cross-hole seismic tomography may be used to image geologic features such as solution cavities, fracture zones, and lithologic contacts. Tomography may also be used to evaluate engineered structures such as concrete cut-off walls, grout curtains, and concrete dams.

66 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Borehole Optical Systems

Borehole optical logging systems include borehole film- recording cameras and borehole television cameras. Optical logging systems permit viewing and recording visible features in the walls of dry or water-filled boreholes, wells, casing, pipelines, and small tunnels.

Borehole cameras are an important supplement to geotechnical drilling and sampling programs because the cameras show geologic and construction features in place and in relatively undisturbed condition. The aperture (opening), true orientation (strike and dip), and frequency (number per foot of borehole) of discontinuities in the rock mass can be determined with optical logging systems. The effective or fracture porosity associated with open discontinuities can be derived also. The occurrence and size of solution cavities, the rock type from visual examination of rock and mineral textures and color of the borehole wall, and the location of stratigraphic contacts can be determined. Other geotechnical applications include inspecting contacts of rock or soil against concrete and of the interior of rock or concrete structures. Optical logging systems permit viewing soft or open zones in rock that may be overlooked in normal drilling and sampling operations. Zones of poor sample recovery or of drilling fluid loss can be investigated.

Borehole Television Camera.—Borehole television systems provide real-time viewing of the interior of a dry or water-filled borehole. The typical system (figure 14-16) consists of a down-hole probe and surface-mounted cable winch, control unit, power supply, television monitor, and video tape unit. The down-hole probe contains a television camera facing vertically downward toward a partially reflecting mirror inclined 45 degrees to the axis

67 FIELD MANUAL

Figure 14-16.—Borehole television logging system. of the probe. A compass/clinometer used to determine the orientation of features in the borehole wall and the inclination of the borehole can be viewed selectively through the mirror by varying the relative intensities of lamps located above and below the plane of the mirror. A motor within the probe rotates the camera and mirror assembly (or the mirror only) 380 degrees in a reciprocating fashion (clockwise, then counterclockwise) as the probe is lowered or raised within the hole. The

68 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS operator controls the motion and logging speed of the probe. A full image of the borehole wall is obtained with each rotation.

A viewing head can be attached to the probe to allow axial viewing of the hole directly ahead. The probe ascent or descent and camera rotation can be slowed or stopped for examination of borehole features. The entire viewing sequence is usually videotaped.

Borehole television systems are commonly used to inspect large concrete structures and rock for defects, determine the effectiveness of grouting operations, check the condition of concrete joints, estimate the volume of cavities within a rock or soil mass, and inspect the screens of water wells. Television images can be used to determine attitudes of discontinuities but are less effective for complete borehole mapping than the borehole film camera systems that portray the borehole walls as discrete, full- color, separate images more suitable for detailed study and measurement.

Borehole Film Camera.—The borehole film camera produces consecutive, over-lapping, 16-mm color still photographs of 360 degree, 1-in (25-mm) sections of the walls of NX or larger boreholes. The system consists of a down- hole probe and surface- mounted lowering device, metering units, and power supply. Figure 14-17 illustrates the down-hole probe. The probe consists of a 16-mm camera mounted in line with the probe axis and facing a truncated conical mirror, which is surrounded by a cylindrical quartz window. A film magazine and film drive mechanism are mounted above the camera in the probe housing. A ring-shaped strobe illuminates the borehole wall in synchronization with the camera’s film advance. Film advance, probe movement, and strobe lighting are synchronized to expose a frame every 3/4 in

69 FIELD MANUAL

Figure 14-17.—Borehole film camera.

70 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

(20 mm) along the hole, so that a photograph with 1/4-in (6-mm) overlap of every 360-degree, 1-in (25-mm) section is taken. The truncation of the conical mirror allows the camera simultaneously to photograph a compass/clinometer located directly beneath the mirror. Photographs produced by the camera are viewed individually (still frame) using a special projector. The image of the mirror face is projected onto a flat film plane. The outer ring of the image "doughnut" represents the base, and the inner ring is the top of the 1-in section of the borehole wall. Planar discontinuities intersecting the borehole wall produce a trace on the image like the shaded curve of figure 14-18 (top). In a vertical borehole, the outer and inner rings of the image "doughnut" are horizontal traces. Points of intersection of planar discontinuities with a ring thus define the strike of the feature in vertical boreholes. The compass area in the center of the image of figure 14-18 shows the bearing of intersecting planes. The dip of the feature can be determined graphically by counting the number of successive frames in which the feature appears. A steeply dipping plane intersects several frames, a gently dipping plane only a few frames, and a horizontal plane intersects one frame. The thickness or width of the discontinuity can also be measured directly from the image. Data from inclined boreholes must be corrected to true strike, dip, and width. The NX borehole film camera is a proven tool for supplying subsurface data in difficult drilling and sampling situations and for providing complete quantitative information on discontinuities and borehole anomalies. Strike can be measured accurately to about 1 degree, dip (or inclination) to about 5 degrees, and thickness or width of discontinuities to a hundredth of an inch (0.1 mm) or better.

71 FIELD MANUAL

Figure 14-18.—Projection of borehole wall image into the film plane from the conical mirror of the borehole film camera.

72 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

In operation, the borehole film camera probe is lowered to the bottom of the hole and raised by a hand-cranked winch at a logging speed of between 5 and 10 feet per minute (ft/min). A single load of film can photograph 75 to 90 ft of borehole. Since the camera has no shutter or light metering capability, the aperture must be preset to satisfy lighting requirements of hole diameter and reflectivity of the borehole wall. The lens aperture ranges from f 2.8 for dark rock to f 22 for light colored rock. The maximum range (depth of field) is about 12 in. Boreholes larger than NX require centering of the probe in the hole.

Borehole Image Processing System (BIPS)

The Borehole Image Processing System (BIPS) uses direct optical observation of the borehole wall in both air and clear-fluid filled holes. The BIPS tool has a small fluorescent light ring that illuminates the borehole wall. A conical mirror in a clear cylindrical window projects a 360-degree optical slice of borehole wall into the camera lens. The tool also contains a digital azimuth sensor that determines the orientation of the image. The optical images are digitized and stored.

The BIPS analysis provides color images of the borehole wall. In a two-dimensional (2-D) projection, planar features that intersect the borehole wall appear as sinusoids. Processing allows the borehole wall to be viewed like a core, regardless of whether core was actually recovered. Strike and dip of planar features intersecting the borehole wall are determined during processing.

Other Wireline Systems

This section discusses wireline devices that are available for supplementary or special purpose applications. These

73 FIELD MANUAL systems include the borehole caliper log, directional surveys, borehole temperature log, borehole gravity log, magnetic log, and flowmeter log.

Borehole Caliper Log

The borehole caliper log provides a continuous record of changes in borehole diameter determined by a probe equipped with tensioned mechanical arms or an acoustic transducer. Caliper or borehole diameter logs are one of the most useful and simple of all logs obtained in borehole geophysics. Caliper logs provide the physical size of a drill hole and should be run in all borings in which other geophysical logging is anticipated. Caliper logs provide indirect information on subsurface lithology and rock quality. Borehole diameter varies with the hardness, fracture frequency, and cementation of the various materials penetrated. Borehole caliper surveys can be used to accurately identify washouts or swelling or to help determine the accurate location of fractures or solution openings, particularly in borings with core loss. Caliper logs can also identify more porous zones in a boring by locating the intervals in which excessive mud filter cake has built up on the walls of the borehole. One of the major uses of borehole caliper logs is to correct for borehole diameter effects. Caliper logs also can be used to place water well screens, position packers for pressure testing in foundation investigations for dams or other large engineering structures, and help estimate grout volumes in solution or washout zones.

Mechanical calipers are standard logging service equipment available in one-, two-, three-, four-, or six-arm probe designs. Multiple-arm calipers convert the position of feelers or bow springs to electrical signals in the probe. The electrical signals are transmitted to the surface through an armored cable. Some caliper systems average

74 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS the movement of all the arms and record only the change in average diameter with depth, and others provide the movements of the individual arms as well as an average diameter. The shape or geometry of the borehole cross section can be determined with the individual caliper arm readings. A six-arm caliper capable of detecting diameter changes as small as 1/4 inch in 6-in to 30-in diameter boreholes produces a record like that shown on figure 14-19. The six arms are read as three pairs so that the diameter in three directions is recorded in addition to the average diameter.

Mechanical calipers are lowered to the bottom of the borehole in closed position, the arms are released, and the tool is raised. The calipers must be calibrated against a known minimum and maximum diameter before logging.

The acoustic caliper measures the distance from an acoustic transducer to the borehole wall. Individual diameter readings for each of four transducers mounted 90 degrees apart are obtained and also the average of the four readings. A special purpose acoustic caliper designed for large or cavernous holes (6 ft to 100 ft in diameter) uses a single rotating transducer to produce a continuous record of the hole diameter.

Directional Surveys

In some situations, borehole deviation must be accurately determined. Several methods of accomplishing this have been devised. Borehole survey instruments initially consisted of single or multiple picture (multishot) cameras that photographed a compass and plumb bob at selected locations in the borehole. Depths were based on the length of cable in the borehole. The camera was retrieved from the hole, and the film developed and interpreted.

75 FIELD MANUAL

Figure 14-19.—Log of six-arm mechanical caliper.

76 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

A fluxgate compass or gyroscope is commonly used today to measure azimuth and an inclinometer to measure deviation from vertical. The information is then electronically transmitted to the surface via a cable. This method provides a continuous survey of the hole and not just checks at intervals. Systems are also available that use accelerometers and gyroscopic sensors to survey boreholes and provide real time data via a cable or ultrasonically via the mud.

Borehole Fluid Temperature Log

The standard borehole fluid temperature logging device continuously records the temperature of the water or drilling fluid in an open or cased borehole as a sonde is raised or lowered in the borehole. The standard, or gradient device uses a single thermistor (thermal resistor) that responds to temperature variations in the fluid. A small change in temperature produces a large change in resistance, which is converted to a change in electrical current. A differential device is sometimes used to record differences in temperature between two positions in the borehole by the use of two thermistors or one thermistor and a memory unit within the control module. The log produced by the temperature device shows temperature as a function of depth.

Temperature logging is usually performed before standard geophysical logging operations to permit correction of other logs (e.g., the resistivity logs) for the effects of borehole fluid temperature. Temperature logs can also be used to locate the source and movement of fluids into or out of the borehole and identify zones of waste discharge or thermal pollution in groundwater. Grouted zones behind casing can be located by the cement heat of hydration.

77 FIELD MANUAL

The temperature probe must be calibrated against a test fluid of known temperature immediately before temperature logging. Borehole fluids must be allowed to reach a stable temperature after drilling operations before logging can be conducted. Open boreholes take longer to stabilize because of the differences in thermal conductivity of the various materials encountered.

Borehole Gravity Log

A borehole gravity meter (or gravimeter) detects and measures variations in the force of gravity. The device determines the bulk density of a large volume of soil or rock between a pair of measuring stations in the borehole (figure 14-20). The bulk density (D) is proportional to the measured difference in gravity (G) between the two stations and inversely proportional to the vertical distance (Z) between the stations: ∆G ∆GG=− G ρ = 12 ∆Z

The borehole gravity meter has been used primarily by the oil industry to determine the porosity (especially porosity because of fractures and vugs). Porosity is calculated using standard equations relating bulk density, fluid density, and specific gravity of solids (matrix density). Although density and porosity are also provided by the gamma-gamma density logger (see “Nuclear Radiation Logging Techniques”), because of the large volume and radius of investigation, gravity meter data are less affected by borehole effects such as mudcake and irregular hole diameter. Gravity meter density determinations are more representative of the geologic medium away from the borehole than are gamma-gamma

78 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS logs. The radius of investigation of the gravity meter is an estimated five times the difference in elevation between the measuring stations (see figure 14-20).

The borehole gravity meter is not a continuous recording instrument. The tool must be positioned at a preselected measurement station, allowed to stabilize, and then a

Figure 14-20.—Elements of borehole gravity logging.

79 FIELD MANUAL measurement taken. Instrument readings are converted to gravity values using a conversion table. Bulk density is then calculated using the difference in gravity values and depth between the two stations. Usually two or three traverses are made in the hole at repeated stations and the values averaged. The precision of the method increases with decreasing distance between measuring stations.

Surveys may be conducted in cased or uncased holes. Several corrections to the data are necessary, including corrections for earth-moon tides, instrument drift, borehole effects, subsurface structure, gravity anomalies, hole deviation from vertical, and the free-air vertical gravity gradient. The instrument should be calibrated to correct for drift and tides. The borehole gravity logger is available commercially but is not a standard log. An apparent advantage over other bulk density/porosity logging methods is the reduction of borehole effects and the greater sample volume.

Magnetic Log

The magnetic field in an uncased borehole is the result of the Earth’s magnetic field and any induced or remnant magnetism. These fields can be directly measured. Magnetic susceptibility is the degree that a material is effected by a magnetic field and is the basis for the logging technique. Susceptibility logs measure the change of inductance in a coil caused by the adjacent borehole wall. The magnetic susceptibility is proportional to the amount of iron-bearing minerals in the rock.

80 BOREHOLE GEOPHYSICAL AND WIRELINE SURVEYS

Flowmeter Log

A flowmeter measures fluid flow in boreholes. A flowmeter log provides information about locations where fluid enters or leaves the borehole through permeable material or fractures intersecting the borehole.

Conventional flowmeters employ a spinner or propellor driven by fluid moving through the borehole. High resolution flowmeters such as the heat pulse flowmeter can measure very low flow rates. Heat pulse flowmeters have a heating element that heats borehole fluid. The flow rate and direction of the heated fluid pulse is measured by detectors located above and below the heat element. Elec- tromagnetic flowmeters induce a voltage in electrically conductive borehole fluid moving at a right angle through a magnetic field. The induced voltage is proportional to the velocity of the conductive borehole fluid.

Bibliography

Hearst, J. R, and Nelson, P.H., Well Logging for Physical Properties, McGraw-Hill Book Co., New York, 1985.

Labo, J., A Practical Introduction to Borehole Geophysics, Society of Exploration Geophysicists, Tulsa, Oklahoma, 1987.

81 Chapter 15

REMOTE SENSING TECHNIQUES

Introduction

This chapter briefly summarizes the capabilities, limitations, and requirements of typical remote sensing techniques. Depending on the nature of the data and the objective of the study, geologic interpretation of remotely sensed data may be simple or complicated. Remote sensing is a tool that makes some tasks easier, makes possible some tasks that would otherwise be impossible, but is inappropriate for some tasks. Depending on the individual situation, remote sensing may be extremely valuable. Some remote sensing interpretations can stand on their own with confidence, but for most, establishing ground truth is essential.

Imaging Systems

There are three main types of imaging systems, two of which are widely used in terrestrial applications:

Photographic.—Cameras and film are used. Photography provides the best spatial resolution but less flexibility in spectral data collection and image enhancement. Spatial resolution is dependent on altitude, focal length of lenses, and the types of film used. Spectral resolution is limited to visible and near infrared wavelengths.

Electronic Spectral Sensors.— Detectors are used, usually scanners, that may have less spatial resolution than photographs but can gather spectral data over wide spectral ranges that enable a wide variety of imaging processing, mineral, and geologic identification. These remote sensing systems include satellites, such as Landsat, airborne sensors carried on aircraft, and FIELD MANUAL spectrometers carried on the ground. This type of remote sensing has several categories, including multispectral, hyperspectral, and imaging spectroscopy.

Vidicon. – A television-type system. Vidicon systems generally are inferior to other types both spatially and spectrally. They are used mostly on space probes because of operational constraints.

Resolution

Two types of resolution are important to remote sensing.

Spatial.— The sharpness of an image and the minimum size of objects that can be distinguished in the image are a function of spatial resolution.

Spectral.—The width or wavelength range of the part of the electromagnetic spectrum the sensor or film can record and the number of channels a sensor uses defines spectral resolution. The electromagnetic spectrum is an ordered array of electromagnetic radiation based on wavelength. Certain portions of the electromagnetic spectrum, including the visible, reflective infrared, thermal infrared, and microwave bands, are useful for remote sensing applications. Rocks, minerals, vegetation, and manmade materials have identifying spectral signatures and distinctive absorptive and reflective spectral characteristics. Given sufficient spectral data, digital image processing can generally identify unique spectral signatures. In practice, instrument limitations or cost limits on computer processing may preclude identification of some materials.

84 REMOTE SENSING TECHNIQUES

Photography

The uses of aerial photography in engineering geology are discussed in Volume 1, chapter 6. A brief description of types is presented below.

Panchromatic photography records images essentially across the entire visible spectrum and, with proper film and filters, also can record into the near-infrared spectrum. In aerial photography, blue generally is filtered out to reduce the effects of atmospheric haze.

Natural color images are recorded in the natural colors seen by the human eye in the visible portion of the spectrum.

False-color infrared images are recorded using part of the visible spectrum and part of the near-infrared, but the colors in the resultant photographs are arbitrary and not natural. Infrared film commonly is used and is less affected by haze than other types.

Multispectral photographs acquired by multiple cameras simultaneously recording different portions of the spectrum can facilitate interpretation.

Terrestrial photographs acquired on the ground or at low altitude with photogrammetric cameras can be used to map geologic features such as strike and dip of joints, faults, and geologic contacts. This type of geologic photogrammetry can also be done from historic construction photographs if enough survey control features can be located in the photographs and tied to present control or known points. Terrestrial photogrammetry has proven useful on several dam projects in which mapping of geologic features by standard methods was very difficult or impossible.

85 FIELD MANUAL

Thermal Infrared Imagery

Thermal infrared systems create images by scanning and recording radiant temperatures of surfaces. Some characteristics of thermal image data are generic to digital image data, and enable computer image processing. Other characteristics are unique to thermal infrared images and make thermal image data valuable interpretive tools.

Thermal infrared imagery can be interpreted using conventional photogeologic techniques in conjunction with the thermal properties of materials, instruments, and environmental factors that affect the data. Where thermal characteristics of a material are unique, thermal infrared imagery can be easy to interpret and can be a great help in geologic studies. Thermal characteristics of a material can vary with moisture content, differential solar heating, and topography making interpretation more difficult and ambiguous.

Multispectral Scanner Imagery

Multispectral scanner (MSS) images are a series of images of the same target acquired simultaneously in different parts of the electromagnetic spectrum. MSS images are an array of lines of sequentially scanned digital data. They may have unique distortions and may or may not have high resolution or information content. Scanner systems consist of scanning mechanisms, spectral separators, detectors, and data recorders.

A digital image is actually an array of numerical data and can be computer processed for a variety of purposes. Geometric distortions caused by sensor characteristics can be removed or distortions can be introduced.

86 REMOTE SENSING TECHNIQUES

Computer processing can be used to precisely register a digital image to a map or another image. Various types of data (e.g., thermal and visible imagery or a digital image and digitized gravity data) can be merged into a single image. Subtle information, difficult to interpret or even to detect, can sometimes be extracted from an image by digital processing.

Airborne Imaging Spectroscopy

The “image,” or data, consist of an array of reflected spectra collected in a two-dimensional array of pixels. Specific spectral features may be identified and pixels with the same spectral wavelength feature may be mapped in colors. Different colors are assigned to different reflectance spectra, and an image is generated from these classifications. A number of different airborne systems are becoming available with various spatial and spectral characteristics. A few commercially available systems are capable of recording 10 or more spectral bands simultaneously, ranging from ultraviolet to thermal infrared wavelengths. The key factor in spectral identification of materials, geologic features, or vegetation is the system’s spectral resolution or number of channels. Currently, the premier sensor for imaging spectroscopy is the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory airborne visible and infrared imaging spectrometer (AVIRIS). AVIRIS simultaneously collects data over a spectral range of 0.4 micron to 2.4 microns in 224 channels. The number of channels and very high quality of data allow discrimination of very small spectral absorption features and, therefore, the user can distinguish and map hundreds of types of minerals or vegetation. The AVIRIS instrument is operated by Jet Propulsion Laboratory (JPL) onboard a NASA ER-2

87 FIELD MANUAL

(modified U-2). Commonly operating at an altitude of 63,000 feet, the spatial resolution is approximately 20 meters. The AVIRIS instrument is also operated by JPL onboard a twin-engine aircraft at lower altitudes. The spatial resolution is approximately 1 meter. The size of data sets and the number of separate spectral bands on some airborne systems may require data consolidation or careful selection of data subsets for special processing. Because the Earth’s atmosphere introduces it’s own spectral absorption features along the light path from the ground to the sensor, removal of atmospheric spectral features is essential to proper analysis of spectroscopy or hyperspectral data. Ground calibration spectra using a field spectrometer operating over the same wavelength ranges and resolution collected at the same time as the overflight is generally required to achieve the highest quality mapping and discrimination of materials. Interpretation usually involves normal photogeologic techniques along with knowledge of spectral characteristics and the data manipulations applied. The spectral imaging data can be analyzed with specialized commercially available software, which relies primarily on statistical analyses and projection of a few spectral features in an image. Software being developed at the U.S. Geological Survey (USGS) Imaging Spectroscopy Laboratory is based on a comparison of laboratory spectral features of several hundred minerals and materials in a spectral library. This software, known as “Tetracorder,” rapidly identifies and maps all the key spectral features of known minerals or materials in each pixel of an AVIRIS or other hyperspectral image. The companion field spectrometer can also be used in its own right to collect both laboratory and field spectra of materials for identification. Applications may include distinguishing different types of clay minerals (e.g., expansive or not) as the geologist maps in the field in real time.

88 REMOTE SENSING TECHNIQUES

High resolution can be obtained and, with proper band selection and processing, complex geochemistry, mineralogy, vegetation, or other materials information can be mapped from the imagery. These technologies have been used very successfully in mapping large areas for several environmental/engineering geology related projects. Because of the complexity of the geology and the size of the area studied, the calibration and analysis of imaging spectroscopy data is not trivial. The volume of high quality data that can be collected using imaging spectroscopy over immense areas in one flight may provide an advantage over any other traditional method of mapping in certain applications.

Satellite Multispectral Scanner Imagery

Landsat is the NASA satellite for civilian remote sensing of the Earth’s land surface. The Landsat MSS records seven bands at 30-meter resolution. The MSS is useful for some geological applications, although it is oriented primarily toward agricultural uses. The Landsat 7 is equipped also with a thematic mapper (TM) that has increased spatial and spectral resolution compared to the MSS.

SPOT, a French satellite, provides panchromatic imagery with up to 10-meter spatial resolution. MSS imagery is capable at 20-meter resolution of stereo imaging. Other commercially available satellites designed for rapid and repeated imagery of customer-selected sites are also being put in orbit to produce imagery of any area. In addition, archives of once classified satellite imagery gathered by United States spy satellites have become available to the public and government agencies and may be a source of data and images.

89 FIELD MANUAL

Satellite imagery provides a synoptic view of a large area that is most valuable for regional studies. With increasing resolution and new sensors, site-specific geologic mapping with satellite images is also of value to engineering geology.

Radar Imagery

Radar is an active remote sensing method (as opposed to passive methods like photography and thermal infrared) and is independent of lighting conditions and cloudiness. Some satellite radar imagery is available, like Landsat, and coverage may be useful for regional geologic studies. Side-looking airborne radar (SLAR) produces a radar image of the terrain on one side of the airplane equivalent to low-oblique aerial photography. Radar interferometry is a quickly emerging field of radar remote sensing. Radar interferometry techniques will detect very small changes in topography, such as those caused by landslide movements, fault displacements, erosion, or accretion, and can be mapped remotely over large areas.

Radar imagery has some unusual distortions that require care in interpretation. Resolution is affected by several factors, and the reflectivity of target materials must be considered. The analysis and interpretation of radar imagery requires knowledge of the imaging system, the look direction, and the responses of the target materials.

Radar can penetrate clouds and darkness and, to some extent, vegetation or even soil. Distortions, image geometry, and resolution can complicate interpretation, as can a lack of multispectral information.

90 REMOTE SENSING TECHNIQUES

Side Scan Sonar

Side Scan Sonar (SSS) is used for underwater surveys and not remote sensing in the typical sense of using aerial or space platforms to image the Earth’s surface. SSS produces images underwater and may have useful applications to engineering geologic studies of reservoirs, dams, and other structures or surfaces hidden by water. SSS works by sending out acoustic energy and sensing the return of the acoustic signal. Materials on the bottom surface under water reflect the signal at different strengths depending on the material properties and the angles of incidence and reflection of the signal. The varying strength of signal return is then used to form an image. An image of the reflected signal that looks like a black and white aerial photograph is the output. The acoustic signal is generated by a torpedo-like instrument that is towed behind a boat by cable. Resolution of objects or features on the bottom of a reservoir varies with the frequency of the signal generated and the height of the torpedo above the bottom of the water body.

Single- and Multi-Beam Sonar

Other types of sonar devices that can be used to map the topographic surface of a reservoir bottom include single- beam and multi-beam sonar. These devices send a direct acoustic signal and measure the time of return. This is translated to a depth to the bottom or feature. By sending continuous signals along a line of survey, a profile of the bottom is developed. When multiple lines are tied together in criss-crossing patterns with Global Positioning System (GPS) positions being recorded simultaneously, a topographic map of the bottom can be generated. Multi-beam systems send out multiple beams

91 FIELD MANUAL at different angles simultaneously, thereby generating a topographic surface over much larger areas in greater detail than single-beam systems.

Applications to Engineering Geology

The most useful form of remote sensing for engineering geology applications is aerial photography because of its high resolution, high information content, and low cost. Various scales of aerial photography are available for regional and site studies, for both detecting and mapping a wide variety of geologic features.

Applications of other forms of remote sensing to engineering geology depend on the nature of the problem to be solved and the characteristics of the site geology. Some problems can best be solved using remote sensing; for others, remote sensing is of little value. In some cases, the only way to find out if remote sensing can do the job is to try it.

Appropriate remote sensing data are often not available for the area of interest, and the data must be acquired specifically for the project. Mission planning and time and cost estimating are critical to a remote sensing data collection program. Numerous factors make planning a remote sensing mission more complicated than planning a conventional aerial photographic mission. Remote sensing mission planning is best done in consultation with someone with experience in the field.

Estimating the cost of data acquisition is relatively easy. Estimating the cost of interpretation is a function of the time and image processing required and is much harder. Some forms of remote sensing are inexpensive to acquire and require little processing to be useful. Other forms

92 REMOTE SENSING TECHNIQUES may be expensive to acquire or may require much processing, perhaps needing experimentation to determine what will work in an untried situation. The cost must be weighed against the benefits.

Bibliography

Two excellent reference books on remote sensing and applications to geology are:

Sabins, F.F., Remote Sensing Principles and Interpreta- tion, 2nd edition: Freeman, New York, 449 p., 1987.

Siegal, B.S., and Gillespie, A. R., editors, Remote Sensing in Geology, Wiley & Sons, New York, 702 p., 1980.

For a thorough treatment of remote sensing ("more than you ever wanted to know about remote sensing"), including a 287-page chapter on geological applications with abundant color images, see:

Colwell, R N., editor, Manual of Remote Sensing, 2nd edition, Falls Church, Virginia, American Society of Photogrammetry, 2724 p., 1983.

93 Chapter 16

WATER TESTING FOR GROUTING

Introduction

Water testing is necessary for evaluating seepage potential and for determining whether grouting is necessary or practical. Water testing for designing a grout program is often secondary to the main purpose of the water testing program, which is to determine permeabilities for seepage evaluation or control. Design of an exploration program for water testing for grouting can be significantly different from permeability testing for the design of a dam or tunnel because of the desired results, the restricted area of a damsite, or the often high-cover linear tunnel site. Regardless of the main reason for the investigations, design of a program for water testing for grouting should consider:

(1) The type of structure to be built. Water testing for evaluating and grouting a dam foundation is significantly different than water testing for a tunnel. More drill holes are generally available for testing in dam foundations where seepage potential is the primary concern and grouting is secondary. Relatively few drill holes are available for evaluating tunnel alignments because of the great depths often necessary and the linear nature of a tunnel. A great deal of judgment is necessary in evaluating the data for tunnels because of the small sample size. Ground conditions are of primary interest, and permeability and groutability are secondary, especially if the tunnel will be lined.

(2) The geologic conditions at the site and the variations between areas or reaches. Generalizations based on other sites are usually inaccurate because geologic conditions depend on the FIELD MANUAL

interrelationship of the local depositional, tectonic, and erosional history that uniquely determine geologic conditions important to the permeability and groutability of a site. Damsite foundation permeabilities can vary over short distances because of lithology and fracture changes, faults, or stress relief in the abutments. Tunnel studies compound the difficulties because of the linear nature of the structure, the often high cover, and access problems. Proper evaluation of water test results requires that the values be correlated with geologic conditions. The permeability values should be noted and plotted on the drill logs along with the water takes and test pressures. The test interval should be drawn on the log so that the water test data can be related to fracture data.

(3) The level of seepage control desired. Seepage quantities beneath a dam in the arid West may be insignificant compared to those in an area with abundant rainfall. Infiltration into a tunnel may be insignificant in one area but, because of overlying cultural and environmental features, may be the controlling factor in a dewatering, excavation, or lining design. The economic value of the water may also be a significant factor.

(4) Groutability and permeability are not necessarily related. A highly fractured rock or a gravel may be very permeable but essentially ungroutable using standard cement grout. Water test data must be correlated with geologic data to properly assess groutability.

(5) Groutability depends on fracture openness and number. Connectivity is not necessarily important because of the relatively limited travel of grout.

96 WATER TESTING FOR GROUTING

(6) Permeability depends on fracture openness, number, and connectivity. Highly fractured rock with low connectivity will have low permeability, and a slightly fractured rock with high connectivity can have high permeability.

(7) Exploratory drill hole orientations introduce a significant bias into water test results. The orientation of the drill hole relative to the fractures has a direct effect on the number of fractures intercepted by the hole. Vertical boreholes intercept very few vertical fractures and can provide very misleading water test information on rock mass permeability and groutability. A vertical hole drilled in a material that has predominantly vertical fractures like flat-bedded sediments will not intercept the fractures that control the rock mass permeability. Drill holes should be oriented to cross as many fractures as possible not only for more meaningful permeability tests but also to get more meaningful rock mass design parameters. If a preferred hole orientation is not practical, the results may be adjusted for the orientation bias.

(8) Water test calculation results can be very misleading. Water test calculations based on a 10-foot (3-meter [m]) interval with one 1/4-inch (6-millimeter [mm]) fracture taking water can have a significantly different seepage and grout potential than a 10-foot (3 m) interval with dozens of relatively tight fractures taking the same amount of water. Each water test must be evaluated individually to determine what the data really mean.

(9) Different rock types, geologic structures, or in situ stresses have different jacking and

97 FIELD MANUAL

hydrofracture potential and, therefore, different maximum acceptable water testing and grouting pressures. Dam foundations are more sensitive to jacking and hydro-fracturing than tunnels. Dam foundations can be seriously damaged by jacking and hydrofracturing. A dam foundation in interbedded sedimentary rock with high horizontal in situ stresses is very sensitive to jacking. A dam foundation in hard, massive granite is almost unjackable and may have to be hydrofractured before any movement can take place. Tunnels are less susceptible to jacking because of overburden depth and may benefit from jacking open fractures to provide grout travel and closure of ungrouted fractures.

(10) Rock mass permeability or groutability cannot be determined by drill holes alone. Mapping and analysis of the fractures are necessary factors in determining seepage potential and groutability. Drill holes usually do not provide a realistic characterization of fracture orientations and connectivity. All these data should be integrated to determine rock mass permeability or groutability.

(11) Rules of thumb are not good substitutes for using data and judgment in making decisions in grouting unless specifically developed for the site conditions.

(12) Hydraulic models are a tool that can be used to evaluate seepage potential and groutability but depend on realistic design and data input parameters. Water test-derived permeability and groutability are important parameters for hydraulic models. Water tests must be carefully evaluated to ensure that bad test data are not used in models.

98 WATER TESTING FOR GROUTING

Models large enough to approach characterizing a site are usually very large and expensive. The tendency is to build models that are small and economical and, therefore, have a limited connection with reality. Realistic parameters are difficult to obtain in quality or quantity. Few exploration programs provide a statistically significant sample size to fully characterize a site, especially tunnels. Model input parameters and design should be part of any modeling report so the output can be properly evaluated.

Procedure

Calculations

Permeabilities can be calculated in lugeons, feet per year (ft/yr), centimeters per second (cm/sec), or other units from the same basic field data. Lugeons are used in the following discussion because these units are commonly used in the grouting industry. Chapter 17 has a thorough discussion of testing and calculating in other permeability units. One Lugeon equals:

(1) 1 liter per minute per meter (l/min/m) at a pressure of 10 bars (2) 0.0107 cubic feet per minute (ft3/min) at 142 pounds per inch (psi) (3) 1 x 10-5 cm/sec (4) 10 ft/yr

The formula for calculating Lugeons (lu) is:

10 bar 155. take × take × test pressure() bars test pressure() psi

99 FIELD MANUAL

Take is in liters per meter per minute or cubic feet per foot per minute. One bar equals 14.5 psi. Takes should be measured after flows have stabilized and should be run for 5-10 minutes at each pressure step.

Geologic Data

The geologic data should be examined to determine the optimum drill hole orientations and locations. Geologic structure, such as bedding and rock type, can be used to set the initial maximum water test pressures. Easily jacked or hydrofractured rock should initially be water tested at a pressure of 0.5 psi per foot (2.2 kilogram per square centimeter per meter [kg/cm2/m]) of overburden and increased pressures based on stepped pressure tests or jacking tests.

Stepped Pressure Tests

Stepped pressure tests are the best method of conducting water tests. Pressures are stepped up to the maximum pressure and then stepped down through the original pressures. Comparison of the calculated permeability values and the pressure versus flow curves for the steps can provide clues as to whether the flow is laminar, if jacking or hydrofracturing is occurring, and if fractures are being washed out or plugged. Single pressure tests can be misleading because of all the unknown pressure and flow variables affecting the test. The Lugeon value for the test interval should be determined by analysis of the individual test values and not necessarily by an average. The individual tests are used to determine what is happening in the rock, and one value of the five tests is usually the appropriate value to use.

Figures 16-1 through 16-5 are bar chart plots showing the relationship of pressure to Lugeon values for the

100 WATER TESTING FOR GROUTING

Laminar Flow

100

60 PSI / Lugeons 40

0 12345 Pressure 25 50 100 50 25 Lugeons 21 23 22 23 22 Test

Figure 16-1.—Bar chart showing relationship of test pressure and Lugeons in laminar flow.

Turbulent Flow

100

60 PSI / Lugeons 40

0 12345 Pressure 25 50 100 50 25 Lugeons 38 28 15 27 39 Test Figure 16-2.—Bar chart showing relationship of test pressure and Lugeons in turbulent flow.

101 FIELD MANUAL

Washing

100

60 PSI / Lugeons 40

0 12345 Pressure 25 50 100 50 25 Lugeons 21 24 28 33 37 Test

Figure 16-3.—Bar chart showing relationship of test pressure and Lugeons when fractures are washing out.

Filling or Swelling

100

60 PSI / Lugeons 40

0 12345 Pressure 25 50 100 50 25 Lugeons 32 28 21 16 12 Test

Figure 16-4.—Bar chart showing relationship of test pressure and Lugeons when fractures are filling or swelling.

102 WATER TESTING FOR GROUTING

Jacking or Hydrofracturing

100 90 80 70 60 PSI / Lugeons 50 40 30 20 10 0 12345 Pressure 25 50 100 50 25 Lugeons 23 21 43 22 21 Test

Figure 16-5.—Bar chart showing relationship of test pressure and Lugeons when rock is hydrofractured or joints are jacked open. more common types of water test results. Figure 16-1 is a plot of laminar flow in the fractures. The permeability is essentially the same no matter what the pressure and resultant water take. Figure 16-2 is a plot of turbulent flow in the fractures. Permeability decreases as the pressure and resultant flow increases because of the turbulent flow in the fractures. Figure 16- 3 is a plot of flow in fractures that increase in size as the water washes material out of the openings. Permeability increases because fractures are enlarged by the test. Figure 16-4 is a plot of flow in fractures that are being filled and partially blocked as water flows or the fractures are in swelling rock that closes fractures over time because of the introduction of water by the test. Figure 16-5 is a plot of testing in rock that is being jacked along existing fractures or rock that is being fractured by the highest water test pressure. Flow is laminar at the lower pressures.

103 FIELD MANUAL

Combinations of these types of flow can occur and require careful analysis. If the pressures are increased to where jacking or hydrofracturing is occurring, the design grout pressures can be set as high as possible to get effective grout injection yet preclude fracturing or, if appropriate, induce fracturing. Hydrofracture tests are easier to analyze if a continuous pressure and flow recording is obtained. The resolution of a step test may not be adequate to separate hydrofracturing from jacking. Figure 6 is a plot of a continuously recorded hydrofracture/jacking test.

Hydrofracturing/Jacking Test 900 800 700 600 500 400

Pressure 300 200 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Flow (Q) Pressure - Hydrofrac Pressure - Jacking Figure 16-6.—Continuously recorded plot of pressure and flow.

Back Pressures

Back pressures should be measured after every test to determine if the hole holds pressure and if fracturing or jacking has occurred. If the hole holds pressure and backflow occurs while releasing the pressure, hydrofracturing or jacking may have occurred at the test pressure.

104 WATER TESTING FOR GROUTING

Test Equipment

Test equipment can affect the test results. At moderate to high flows, the friction loss caused by the piping and the packer should be considered. Significant loss of pressure occurs between the gauge and the packer. At high flows, the plumbing system “permeability” can be the controlling factor and not the permeability of the test interval. If meters and gauges are located in optimum relation to each other and close to the hole, the arrangement of pipe, hose, etc., will not seriously influence shallow tests although sharp bends in hose, 90-degree fittings on pipes, and unnecessary changes in pipe and hose diameters should be avoided. Laying the system out on the ground and pumping water through the plumbing to determine the capacity of the system is a good idea, especially if using small-diameter piping or wireline packers.

Water Takes Relative to Grout Takes

Water takes alone may be an indication of whether grouting is necessary, and Lugeon calculations may not be necessary after enough water tests with subsequent grouting provide sufficient data to determine a correlation. This shortcut is usually used during the actual grouting because not enough data are available from exploration unless a test grout section is constructed. The correlation can change if the geologic domain in a foundation changes, so any correlation must be continuously checked.

105 FIELD MANUAL

Depth of Grouting

Grouting depth for dam foundations is commonly determined by a rule of thumb related to dam height. A better method is to base the depth on water test data and geologic data. Weathered rock and fracture surfaces are an indication of permeable rock. Grouting to tight, unweathered rock, where practical, makes more sense than trying to grout tight, impermeable rock or not grouting pervious rock because of a rule-of-thumb approach.

Grouting in tunnels should be based on the thickness of the disturbed zone around the periphery of the tunnel and the depth necessary to get the desired results when grouting natural fractures. A machine-bored tunnel will have a much shallower disturbed zone than a conventionally excavated (drill-blast) tunnel and may require less or no grouting.

Bibliography

Ewart, Friedrich-Karl, Rock Permeability and Grouta- bility Related to Dams and Reservoirs, lecture notes, University of Paderborn, Germany, September 1994.

Water Resources Commission N.S.W., Grouting Manual, 3rd edition, Australia, 1980.

106 Chapter 17 WATER TESTING FOR PERMEABILITY

General

Most rock and soil contains numerous open spaces where water may be stored and through which water can move. Permeability, or hydraulic conductivity, is a measure of the ease of movement of fluid and gas through the open spaces and fractures. The properties of soil and rock have significant impact on water movement through the interstitial spaces. Water movement through soil and rock significantly impacts the ability to control water during construction. The movement of water through slopes must be known to understand the stability of slopes. Permeability in this chapter is considered synonymous with the term hydraulic conductivity and is a measurement of the groundwater flow through a cross- sectional area. This chapter discusses how to measure permeability and how to best determine or estimate appropriate permeability values.

In addition to permeability, there are other hydrologic parameters that may impact the understanding of groundwater but are either more difficult to determine or are not a significant consideration in most engineering situations. These other hydraulic parameters of subsurface materials are transmissivity, porosity, and storage. For a more detailed explanation of these hydrologic parameters and the methods used to obtained the values, see chapters 5, 6, and 10 of the Reclamation Groundwater Manual.

Transmissivity

Transmissivity is the average permeability multiplied by the saturated thickness. Transmissivity is particularly important in areas with multiple aquifers. Determining the aquifer thickness may not be practical or necessary FIELD MANUAL if permeability and recharge are relatively low and the need for groundwater control is short term. Transmissivity values are often based on individual permeability values or averaged permeability values. It is important that any permeability value used with the saturated thickness of an aquifer be appropriate and representative. Since most aquifers are rarely homogeneous and isotropic, any field derived data must be qualified by indicating if averaging or selecting the highest or lowest permeability value for a particular site is appropriate.

Porosity

Porosity is the percentage of interstitial space within the soil or rock relative to the total volume of soil or rock. Porosity is not necessarily directly proportional to permeability. Porosity is a significant factor in understanding the stability of soil and rock, but only the effective porosity, the interconnected pores, contribute to permeability. Not all pores or interstitial spaces are connected. Porosities are typically high for sands and gravels (30-40 percent) with high permeabilities (10 to 10-2 cm/sec). Clays have higher porosities (45-55 percent) but have very low permeabilities (10-6 to 10-8 cm/sec). Effective porosity is important in high permeability materials, but the total porosity is rarely relevant except in contaminant transport modeling. In the field, porosity is typically estimated by borehole geophysics.

Storage

Storage is a dimensionless term defined as the volume of water released from or taken into interstitial spaces in the soil or rock. Storage is often interchanged with the terms specific yield, effective porosity, coefficient of storage, and storativity. The water stored within the effective porosity is controlled by the material’s ability to

108 WATER TESTING FOR PERMEABILITY retain and to release water. Understanding storage is particularly important in high permeability materials or localized zones connected with a large source of water.

A glossary of abbreviations and definitions is shown in table 17-1 that are used in the various permeability calculations. Not all the parameters listed in the table are necessary for every calculation. These parameters are derived from the Groundwater Manual, chapter 10. Abbreviations used in the figures and text of this chapter are consistent throughout the chapter. Definitions apply to angled holes as well as vertical wells.

Geologic Conditions

Understanding and measuring the above parameters is important, but understanding the hydrogeologic conditions is essential. Obtaining representative and appropriate hydrologic values is critical in any site investigation. Identifying the water bearing zones and selecting the appropriate test method is very important. Improper test methods, poor well construction, and improper isolation can significantly impact any test design. It is essential that the various aquifers and boundaries in heterogeneous settings be identified and that the various water surfaces existing at the site be located. Obtaining values without a good understanding of subsurface conditions can be misleading and can result in surprises once the actual site conditions are exposed. Obtaining water level data and permeability values has little value without an understanding of the factors controlling the groundwater. Proper evaluation of permeability values requires that the values be correlated with geologic conditions.

109 FIELD MANUAL

Table 17-1.—A glossary of abbreviations and definitions used in permeability calculations

K = Coefficient of permeability in feet (meters) per year under a unit gradient. Q = Steady flow into the well in ft3/sec [m3/sec]. H = The effective head of water in the well in feet (m). For packer tests, determining the effective head is defined in figure 17-5. The effective head may be natural or induced. a = Exposed surface area of the test section in ft2 (m2). Note that this area in an uncased borehole or using a single packer for some tests would include the exposed area at the bottom of the borehole. R = Length of test (packer tests) or screened (perforated) section of well isolated from the adjacent material in feet (m). r = The radius to the borehole sidewall. re = The effective radius to borehole sidewall that is reduced because of an obstruction such as a slotted riser (perforated casing), caved material, gravel, or sand pack. r1 = The outer radius of a riser or casing. rc = The inside radius of a riser or casing. D = Distance from the ground surface to the bottom of the test section. U = Thickness of unsaturated materials above the water surface, including the capillary zone.

Tu = U-D+H = The distance from the induced water surface in the well to the static natural water surface. S = Thickness of saturated material overlying a relatively impermeable layer.

Cu = Conductivity coefficient for unsaturated materials with partially penetrating cylindrical test wells.

Cs = Conductivity coefficient for saturated materials with partially penetrating cylindrical test wells.

110 WATER TESTING FOR PERMEABILITY

Selecting the Appropriate Test

There are numerous ways to determine or estimate permeabilities. The appropriate method for estimating permeabilities must be based on the subsurface conditions and how significantly the values obtained will impact the project. The required level of understanding of the subsurface water conditions should be weighed relative to the cost and the impact on stability and constructability of the feature and on the changes in quality and quantity of water important to the site. Soil classification and Standard Penetration Testing (SPT) blow counts provide crude estimates of soil permeabilities. There are numerous geophysical methods for estimating permeabilities by using flowmeters, acoustic velocities, and gamma borehole logging techniques. The Reclamation Ground Water Manual, chapters 8 and 10, provides detailed explanations of various test methods for determining permeabilities. Except for the aquifer tests, most methods described in this chapter determine the vertical or horizontal permeability.

The most accurate test method for determining permeability is conducting a relatively long-term aquifer test. This method is not covered in this chapter. A full- term aquifer test (pumping test as described in chapter 8 of the Reclamation Ground Water Manual) is rarely justified during initial site investigations because of the cost and time required to perform an aquifer test and possibly handle the discharged water. This chapter discusses the less costly methods used to determine permeability. These methods are less accurate, primarily because these tests are too short in duration and because the interval being tested is not necessarily “truly” undisturbed, open, dimensioned as assumed, and representative.

111 FIELD MANUAL

Stable Boreholes

Packer tests are commonly performed in boreholes because the tests are inexpensive and can be performed quickly, with minimal disruption to the primary task of most site investigations, which is determining the subsurface materials and geology. The Gravity Permeability Test Method 1 for consolidated material is used only within the vadose zone and is the preferred method if the packer test method cannot be used. The principal problem of any gravity permeability test method is that a uniform supply of water is necessary so that a constant head can be maintained above the static water surface. The falling head tests should be used in stable boreholes if the packer test and gravity tests (both above and below the static water surface) cannot be performed.

Unstable Boreholes

There are a number of permeability tests that can be used in unstable materials such as soils that are noncohesive, uncemented, or unindurated or fractured rock that collapses into the borehole. Slug tests are used primarily when water availability or usage is a problem. Piezometer tests are good where water surfaces are high and where water bearing units are relatively thin layered but significant. Unfortunately, the piezometer test is limited to relatively shallow depths (around 20 feet [6 m]) and is rarely successful in cohesionless or gravelly or coarser soils. Gravity permeability tests are used in unstable soils or in rock. Gravity permeability tests require costly construction techniques, delay or prevent further advancement of the borehole, and require a supply of water.

Borehole permeabilities are appropriate for the interval tested unless the test interval is greater than 10 feet

112 WATER TESTING FOR PERMEABILITY

(3 m). For intervals greater than 10 feet (3 m), the test may not be an accurate reflection of the entire saturated column. The permeability values should be plotted on the drill log, along with the water take and test pressures. The test interval should be drawn on the log so that the water test data can be related to fracture data.

Permeability Testing in Rock

Permeability tests are routinely performed in rock, particularly by pressure or packer tests. The permeability calculation assumes laminar flow in an isotropic, homogeneous medium. In reality, the test water take is effectively controlled by fractures because the intact rock permeability is effectively zero in most cases. The water may be flowing into one or into many fractures in the test interval, but the permeability calculation assumes laminar flow in an isotropic, homogeneous medium. The length of the test interval is governed by the rock characteristics. Typically, the test interval may be 10 feet (3 m) long, but the water can be going into one ¼-inch (8-mm) fracture. Test intervals greater than 20 feet (6 m) are inadvisable because, typically, there are a few fractures or a relatively small zone that controls the groundwater flow in bedrock. The calculated permeability of the packer test interval may be a magnitude different from the actual rock mass permeability. Only in the case of a highly fractured rock mass is the calculated permeability relatively reliable and the result is still a relative or effective permeability.

Orientation.—The orientation of the drill hole relative to the fractures significantly affects the number of fractures intercepted by the hole and the perceived permeability. A vertical hole drilled in a material that has predominantly vertical fractures such as flat-bedded sediments will not intercept the predominant control on

113 FIELD MANUAL the rock mass permeability. The drill holes should be oriented to cross as many fractures as possible not only for more meaningful permeability tests, but also to get meaningful rock mass design parameters. If hole orientation is not practical, the results may be corrected for the orientation bias.

Jacking.—The pressure used for the water test should consider geologic structure. Flat-lying, bedded sediments are very susceptible to jacking along bedding planes. The combination of weak bedding planes, typically low vertical confining pressures, or high horizontal in place stresses can result in jacking and apparently high permeabilities. Test pressures of half the typical pressure of 1 pound per square inch per foot (psi/ft) (0.2 kg/cm 2/m) of depth are often appropriate.

Hydrofracturing.—In place stresses in many areas are not lithostatic and horizontal stresses are significantly lower than vertical stresses. The theoretical overburden stress (roughly 1 pound per square inch per foot depth [0.2 kg/cm2/m]) is typically used to determine the test pressure. If the horizontal stress is much lower than the vertical stress, hydrofracturing can occur, resulting in an induced high permeability value.

Stepped Pressure Tests.—Stepped pressure tests are an effective method of conducting water tests. Pressures are stepped up to the maximum pressure and then stepped down through the original pressures. Compari- son of the calculated permeability values and the pressure versus flow curves for the steps can tell you whether the flow is laminar, if jacking or hydrofracturing is occurring, and if fractures are being washed out. If the pressures are increased to where jacking or hydrofracturing is occurring, the design grout pressures can be set as high as possible to get effective grout

114 WATER TESTING FOR PERMEABILITY injection, yet preclude fracturing or induce fracturing if desired. Chapter 16 discusses these tests in detail.

Test Equipment.—The test equipment can affect the test results. At moderate to high flows, the friction loss and restriction because of the piping (plumbing) and the packer is important. Significant pressure loss occurs between the gauge and the packer. At high flows, the plumbing system “permeability” can be the controlling factor rather than the permeability of the test interval. If meters and gauges are located in relation to each other as recommended, the arrangement of pipe, hose, etc., will not seriously influence the tests, although sharp bends in hose, 90-degree fittings on pipes, and unnecessary changes in pipe and hose diameters should be avoided. Laying the system out on the ground and pumping water through the plumbing to determine the capacity of the system is a good idea, especially if using small diameter piping or wireline packers.

In many investigations, information on the permeability of saturated or unsaturated materials is required. Permeability within the vadose zone, including the capillary fringe, is typically estimated by permeameter or gravity permeability tests. Permeability tests within saturated materials are typically performed as a falling head, packer, or aquifer test. Water within the unsaturated zone is suspended within the material but is primarily moving downward by gravity. In unsaturated conditions, the material permeabilities are obtained by one of several field permeameter tests. Since the material is not saturated, permeability tests require more equipment and a lot of water. These tests measure the volume of water flowing laterally while maintaining a constant head.

Laboratory permeability tests of subsurface materials usually are not satisfactory. Test specimens are seldom

115 FIELD MANUAL undisturbed, and a specimen typically represents only a limited portion of the investigated material. Field tests have been devised that are relatively simple and less costly than aquifer pumping tests (although aquifer tests do provide relatively accurate permeability values). These tests are usually conducted in conjunction with exploratory drilling or monitoring existing wells.

Permeability testing of existing monitoring wells may help determine material characteristics when evaluation of existing data indicates gaps or when it is necessary to confirm previous assumptions. Properly conducted and controlled permeability tests will yield reasonably accurate and reliable data. Several locations may need to be tested to provide data on spatial variations of subsurface material characteristics.

The quality of water used in permeability tests is important. The presence of only a few parts per million of turbidity or air dissolved in water can plug soil and rock voids and cause serious errors in test results. Water should be clear and silt free. To avoid plugging the soil pores with air bubbles, use water that is a few degrees warmer than the temperature of the test section.

For some packer tests, pumps of up to 250 gallons per minute (gal/min) (950 liters per minute [L/min]) capacity against a total dynamic head of 160 feet (50 m) may be required.

The tests described below provide semiquantitative values of permeability. There have been numerous types of permeability tests devised with varying degrees of accuracy and usefulness. The tests described below are relatively simple and generally provide useful permeability data. If the tests are performed properly, the values obtained are sufficiently accurate for some engineering purposes. The tests assume laminar flow

116 WATER TESTING FOR PERMEABILITY and a homogeneous medium. These conditions are not often encountered, and fracture flow is what usually occurs in rock. The equations given for computing permeability are applicable to laminar flow. The velocity where turbulent flow occurs depends, in part, on the grain size of the materials tested. A maximum average velocity for laminar flow is about 0.1 foot per second (ft/sec) (25 millimeters per second [mm/sec]). If the quotient of the water intake in cubic units per second divided by the open area of the test section in square units times the estimated porosity of the tested material is greater than 0.10, the various given equations may not be accurate or applicable. The values obtained are not absolute and can vary from the true permeability by plus or minus an order of magnitude.

Length, volume, pressure, and time measurements should be made as accurately as available equipment will permit, and gauges should be checked periodically for accuracy. Keep the accuracy of the results in mind when determining the needed accuracy of the measurements. Results should be reported in feet per year or centimeters per second for most engineering uses.

In an open hole test, the total open area of the test section is computed by:

a = 2BrR+Br2 where:

a = total open area of the hole face plus the hole bottom r = radius of the hole R = length of the test section of the hole

When perforated casing is used and the open area is small, the effective radius, re, is used instead of the actual radius, r.

117 FIELD MANUAL

ap = total open area of perforations a = area of each perforation

If fabricated well screens are used, estimates of the screen open area generally can be obtained from the screen manufacturer.

Permeability tests are divided into four types: pressure tests, constant head gravity tests, falling head gravity tests, and slug tests. In pressure tests and falling head gravity tests, one or two packers are used to isolate the test section in the hole. In pressure tests, water is forced into the test section through combined applied pressure and gravity head or the tests can be performed using gravity head only. In falling head tests, only gravity head is used. In constant head gravity tests, no packers are used, and a constant water level is maintained. Slug tests use only small changes in water level, generally over a short time.

Pressure Permeability Tests in Stable Rock

Pressure permeability tests are run using one or two packers to isolate various zones or lengths of drill hole. The tests may be run in vertical, angled, or horizontal holes. Compression packers, inflatable packers, leather cups, and other types of packers have been used for pressure testing. Inflatable packers are usually more economical and reliable because they reduce testing time and ensure a tighter seal, particularly in rough-walled, oversize, or out-of-round holes. The packer(s) are inflated through tubes extending to a tank of compressed air or nitrogen at the surface. If a pressure sensing instrument is included, pressure in the test section is

118 WATER TESTING FOR PERMEABILITY transmitted to the surface. Although this arrangement permits an accurate determination of test pressures, manual observations should still be made to permit an estimate of permeability if pressure sensors fail. When double packers are used, the hole can be drilled to total depth and then tested. When a single packer is used, the hole is advanced and tested in increments.

Methods of Testing

In stable rock the hole is drilled to the total depth without testing. Two inflatable packers 5 to 10 feet (1.5 to 3 m) apart are installed on the drill rod or pipe used for making the test. The section between the packers is perforated. The perforations should be at least ¼ inch (6 mm) in diameter, and the total area of all perforations should be more than two times the inside cross-sectional area of the pipe or rod. Tests are made beginning at the bottom of the hole. After each test, the packers are raised the length of the test section, and another test is made of the appropriate section of the hole.

In unstable rock, the hole is drilled to the bottom of each test interval. An inflatable packer is set at the top of the interval to be tested. After the test, the hole is then drilled to the bottom of the next test interval.

Cleaning Test Sections

Before testing, the test section should be surged with clear water and bailed or flushed out to clean cuttings and drilling fluid from the hole. If the test section is above the water table and will not hold water, water should be poured into the hole during the surging, then bailed out as rapidly as possible. When a completed hole is tested using two packers, the entire hole can be cleaned in one operation. Although cleaning the hole is frequently omitted, failing to clean the hole may result

119 FIELD MANUAL in a permeable rock appearing to be impermeable because the hole wall is sealed by cuttings or drilling fluid.

Alternatives to surging and bailing a drill hole in indurated or consolidated material before pressure testing include rotating a stiff bristled brush while jetting with water. The jet velocity should be at least 150 ft/sec (45 m/sec). This velocity is approximately 1.4 gal/min per 1/16-inch- (5.3 L/min per 2-mm-) diameter hole in the rod. The drill hole should be blown or bailed out to the bottom after jetting.

Length of Test Section

The length of the test section is governed by the character of the rock, but generally a length of 10 feet (3 m) is acceptable. Occasionally, a good packer seal cannot be obtained at the planned depth because of bridging, raveling, fractures, or a rough hole. If a good seal cannot be obtained, the test section length should be increased or decreased or test sections overlapped to ensure that the test is made with well-seated packers. On some tests, a 10-foot (3-m) section will take more water than the pump can deliver, and no back pressure can be developed. If this occurs, the length of the test section should be shortened until back pressure can be developed, or the falling head test might be tried.

The test sections should have an R/2r ratio greater than 5, where r is the radius of the hole and R is the length of the test section. The packer should not be set inside the casing when making a test unless the casing has been grouted in the hole. Test sections greater than 20 feet (6 m) long may not allow sufficient resolution of permeable zones.

120 WATER TESTING FOR PERMEABILITY

Size of Rod or Pipe to Use in Tests

Drill rods are commonly used to make pressure and permeability tests. NX and NW rods can be used if the take does not exceed 12 to 15 gallons per minute (45 to 60 liters per minute) and the depth to the top of the test section does not exceed 50 feet (15 m). For general use, 1¼-inch (32-mm) or larger pipe is better. Figures 17-1 through 17-4 show head losses at various flow rates per 10-foot (3-m) section for different sizes of drill rod and 1¼-inch (32-mm) pipe. These figures were compiled from experimental tests. Using 1¼-inch (32-mm) pipe, particularly where holes 50 feet (15 m) or deeper are to be tested, is obviously better than using smaller pipe. The couplings on 1¼-inch (32-mm) pipe must be turned down to 1.8 inch (45 mm) outside diameter for use in AX holes.

Pumping Equipment

Mud pumps should not be used for pumping the water for permeability tests. Mud pumps are generally of the multiple cylinder type and produce a uniform but large fluctuation in pressure. Many of these pumps have a maximum capacity of about 25 gal/min (100 L/min), and if not in good condition, capacities may be as small as 18 gal/min (70 L/min). Tests are often bad because pumps do not have sufficient capacity to develop back pressure in the length of hole being tested. When this happens, the tests are generally reported as “took capacity of pump, no pressure developed.” This result does not permit a permeability calculation and only indicates that the permeability is probably high. The fluctuating pressures of multiple cylinder pumps, even when an air chamber is used, are often difficult to read accurately because the high and low readings must be averaged to determine the approximate true effective

121 FIELD MANUAL

Figure 17-1.—Head loss in a 10-foot (3-m) section of AX (1.185-inch- [30.1-mm-] inside diameter [ID] drill rod.

122 WATER TESTING FOR PERMEABILITY

Figure 17-2.—Head loss in a 10-foot (3-m) section of BX (1.655-inch [42.0-mm] ID) drill rod.

123 FIELD MANUAL

Figure 17-3.—Head loss in a 10-foot (3-m) section of NX (2.155-inch [54.7-mm] ID) drill rod.

124 WATER TESTING FOR PERMEABILITY

Figure 17-4.—Head loss in a 10-foot (3-m) section of 1¼-inch (32-mm) steel pipe.

125 FIELD MANUAL pressure. In addition, mud pumps occasionally develop high peak pressures that may fracture the rock or blow out a packer.

Permeability tests made in drill holes should be performed using centrifugal or positive displacement pumps (Moyno type) having sufficient capacity to develop back pressure. A pump with a capacity of up to 250 gal/min (950 L/min) against a total head of 160 feet (48 m) is adequate for most testing. Head and discharge of these pumps are easily controlled by changing rotational speed or adjusting the discharge valve.

Swivels for Use in Tests

Swivels used for pressure testing should be selected for minimum head losses.

Location of Pressure Gauges

The ideal location for a pressure gauge is in the test section, but as close to the packer as possible.

Water Meters

Water deliveries in pressure tests may range from less than 1 gal/min (3.8 L/min) to as much as 400 gal/min (1,500 L/min). No one meter is sufficiently accurate at all ranges. Two meters are recommended: (1) a 4-inch (100-mm) propeller or impeller-type meter to measure flows between 50 and 350 gal/min (200 and 1,300 L/min), and (2) a 1-inch (25-mm) disk-type meter for flows between 1 and 50 gal/min (4 and 200 L/min). Each meter should be equipped with an instantaneous flow indicator and a totalizer. Water meters should be tested frequently.

126 WATER TESTING FOR PERMEABILITY

Inlet pipes should be available to minimize turbulent flow into each meter. The inlet pipes should be at least 10 times the diameter of the meter inlet.

Length of Time for Tests

The minimum length of time to run a test depends on the nature of the material tested. Tests should be run until three or more readings of water take and pressure taken at 5-minute intervals are essentially equal. In tests above the water table, water should be pumped into the test section at the desired pressure for about 10 minutes in coarse materials or 20 minutes in fine-grained materials before making measurements.

Stability is obtained more rapidly in tests below the water table than in unsaturated material. When multiple pressure tests are made, each pressure theoretically should be maintained until stabilization occurs. This procedure is not practical in some cases, but good practice requires that each pressure be maintained for at least 20 minutes, and take and pressure readings should be made at 5-minute intervals as the pressure is increased and for 5 minutes as pressure is decreased.

Pressures Used in Testing

The pressure used in testing should be based on the rock being tested. Relatively flat-lying, bedded rock should be tested at 0.5 lbs/in2 per foot (0.1 kg/cm2/m) of depth to the test interval to prevent uplift or jacking of the rock. Relatively homogeneous but fractured rock can be tested at 1 lb/in2 per foot (0.2 kg/cm 2/m) of test interval depth. Relatively unfractured rock can be tested at 1.5 lb/in2 per foot (0.3kg/cm2/m) of test interval depth.

127 FIELD MANUAL

Arrangement of Equipment

The recommended arrangement of test equipment starting at the source of water is: source of water; suction line; pump; waterline to settling and storage tank or basin, if required; suction line; centrifugal or positive displacement pump; line to water meter inlet pipe; water meter; short length of pipe; valve; waterline to swivel; sub for gauge; and pipe or rod to packer. All connections should be kept as short and straight as possible, and the number of changes in hose diameter, pipe, etc., should be kept as small as possible.

All joints, connections, and hose between the water meter and the packer or casing should be tight, and there should be no water leaks.

Pressure Permeability Tests

A schematic of the following two methods is shown in figure 17-5.

Method 1: The hole is drilled, cleaned, the tools are removed, a packer is seated the test interval distance above the bottom of the hole, water under pressure is pumped into the test section, and readings are recorded. The packer is then removed, the hole is drilled the test interval length deeper, cleaned, the packer is inserted using the length of the newly drilled hole as the test section, and the test performed.

Method 2: The hole is drilled to the final depth, cleaned, and blown out or bailed. Two packers spaced on pipe or drill stem to isolate the desired test section are used. Tests should be started at the bottom of the hole. After each test, the pipe is lifted a distance equal to l, shown on figure 17-5, and the test is repeated until the entire hole is tested.

128 WATER TESTING FOR PERMEABILITY Figure 17-5.—Permeability test for use in saturated or unsaturated consolidated rock and well indurated soils.

129 FIELD MANUAL

Data required for computing the permeability may not be available until the hole has encountered the water table or a relatively impermeable bed. The required data for each test include:

• Radius, r, of the hole, in feet (meters). • Length of test section, R, the distance between the packer and the bottom of the hole, Method 1, or between the packers, Method 2, in feet (meters).

• Depth, h1, from pressure gauge to the bottom of the hole, Method 1, or from gauge to the upper surface of lower packer in Method 2. If a pressure transducer is used, substitute the pressure recorded in the test

section before pumping for the h1 value.

• Applied pressure, h2, at the gauge, in feet (meters), or the pressure recorded during pumping in the test section if a transducer is used. • Steady flow, Q, into well at 5-minute intervals, in cubic feet per second (ft3/sec) (cubic meters per second [m3/sec]). • Nominal diameter in inches (mm) and length of intake pipe in feet (m) between the gauge and upper packer. • Thickness, U, of unsaturated material above the water table, in feet (m). • Thickness, S, of saturated material above a relatively impermeable bed, in feet (m). • Distance, D, from the ground surface to the bottom of the test section, in feet (m). • Time that the test is started and the time measurements are made.

130 WATER TESTING FOR PERMEABILITY

• Effective head, the difference in feet (m) between the elevation of the free water surface in the pipe and the elevation of the gauge plus the applied pressure. If a pressure transducer is used, the effective head in the test section is the difference in pressure before water is pumped into the test section and the pressure readings made during the test.

The following examples show some typical calculations using Methods 1 and 2 in the different zones shown in figure 17-5. Figure 17-6 shows the location of the zone 1 lower boundary for use in unsaturated materials.

Pressure permeability tests examples using Methods 1 and 2:

Figure 17-6.—Location of zone 1 lower boundary for use in unsaturated materials.

131 FIELD MANUAL

Zone 1, Method 1

Given: U = 75 feet, D = 25 feet, R = 10 feet, r = 2 0.5 foot, h1 = 32 feet, h2 = 25 lb/in = 57.8 feet, and Q = 20 gal/min = 0.045 ft3/sec

From figure 17-4: head loss, L, for a 1¼-inch pipe at 20 gal/min is 0.76 foot per 10-foot section. If the distance from the gauge to the bottom of the pipe is 22 feet, the total head loss, L, is (2.2) (0.76) = 1.7 feet.

H = h1 + h2 - L = 32 + 57.8 - 1.7 = 88.1 feet of effective

head, Tu = U - D + H = 75 - 25 + 88.1 = 138.1 feet

R The values for X and Tu/ lie in zone 1 (figure 17-6). To determine the unsaturated conductivity

coefficient, Cu, from figure 17-7:

then:

132 WATER TESTING FOR PERMEABILITY

Figure 17-7.—Conductivity coefficients for permeability determination in unsaturated materials with partially penetrating cylindrical test wells.

Zone 2

R Given: U, , r, h2, Q, and L are as given in example

1, D = 65 feet, and h1 = 72 feet

If the distance from the gauge to the bottom of the intake pipe is 62 feet, the total L is (6.2) (0.76) = 4.7 feet.

H = 72 + 57.8 - 4.7 = 125.1 feet

133 FIELD MANUAL

Tu = 75 - 65 + 125.1 = 135.1 feet

The test section is located in zone 2 (figure 17-6). To

determine the saturated conductivity coefficient, Cs, from figure 17-8:

Figure 17-8.—Conductivity coefficients for semispherical flow in saturated materials through partially penetrating cylindrical test wells.

134 WATER TESTING FOR PERMEABILITY

Method 1:

Method 2:

Zone 3

Given:

R U, , r, h2, Q, and L are as given in example 1, D =

100 feet, h1 = 82 feet, and S = 60 feet

135 FIELD MANUAL

If the distance from the gauge to the bottom of the intake pipe is 97 feet, the total L is (9.7) (0.76) = 7.4 feet.

H = 82 + 57.8 - 7.4 = 132.4 feet

Method 1:

Method 2:

Multiple Pressure Tests

Multiple pressure tests are pressure permeability tests that apply the pressure in three or more approximately equal steps. For example, if the allowable maximum differential pressure is 90 lb/in2 (620 kilopascal [kPa]), the test would be run at pressures of about 30, 60, and 90 lb/in2 (210 kPa, 415 kPa, and 620 kPa).

Each pressure is maintained for 20 minutes, and water take readings are made at 5-minute intervals. The

136 WATER TESTING FOR PERMEABILITY pressure is then raised to the next step. After the highest step, the process is reversed and the pressure maintained for 5 minutes at the same middle and low pressures. A plot of take against pressure for the five steps is then used to evaluate hydraulic conditions. These tests are also discussed in chapter 16.

Hypothetical test results of multiple pressure tests are plotted in figure 17-9. The curves are typical of those often encountered. The test results should be analyzed using confined flow hydraulic principles combined with data obtained from the core or hole logs.

Probable conditions represented by plots in figure 17-9 are:

1. Very narrow, clean fractures. Flow is laminar, permeability is low, and discharge is directly proportional to head.

2. Practically impermeable material with tight fractures. Little or no intake regardless of pressure.

3. Highly permeable, relatively large, open fractures indicated by high rates of water intake and no back pressure. Pressure shown on gauge caused entirely by pipe resistance.

4. Permeability high with fractures that are relatively open and permeable but contain filling material which tends to expand on wetting or dislodges and tends to collect in traps that retard flow. Flow is turbulent.

5. Permeability high, with fracture filling material which washes out, increasing permeability with time. Fractures probably are relatively large. Flow is turbulent.

137 FIELD MANUAL

Figure 17-9.—Plots of simulated, multiple pressure permeability tests.

6. Similar to 4, but fractures are tighter and flow is laminar.

7. Packer failed or fractures are large, and flow is turbulent. Fractures have been washed clean; highly permeable. Test takes capacity of pump with little or no back pressure.

138 WATER TESTING FOR PERMEABILITY

8. Fractures are fairly wide but filled with clay gouge material that tends to pack and seal when under pressure. Takes full pressure with no water intake near end of test.

9. Open fractures with filling that tends to first block and then break under increased pressure. Probably permeable. Flow is turbulent.

Gravity Permeability Tests

Gravity permeability tests are used primarily in unconsolidated or unstable materials. Gravity tests are performed in unconsolidated materials but are typically performed at greater depths. Gravity tests can be run only in vertical or near-vertical holes. A normal test section length is 5 feet (1.5 m). If the material is stable, stands without caving or sloughing, and is relatively uniform, sections up to 10 feet (3 m) long may be tested. Shorter test sections may be used if the length of the water column in the test section is at least five times the diameter of the hole. This length to diameter ratio is used in attempting to eliminate the effect of the bottom of the borehole. The diameter of the borehole sidewalls is the outside of any screen and annular packing of sand and or gravel. After each test, the casing for open hole tests is driven to the bottom of the hole, and a new test section is opened below the casing. If perforated casing is used, the pipe can be driven to the required depth and cleaned out, or the hole can be drilled to the required depth and the casing driven to the bottom of the hole and the hole cleaned out.

139 FIELD MANUAL

Cleaning and Developing Test Sections

Each newly opened test section should be developed by surging and bailing. Development should be done slowly and gently so that a large volume of loosely packed material is not drawn into the hole and only the compaction caused by drilling is broken down and the fines will be removed from the formation.

Measurement of Water Levels Through Protective Pipe

Measuring water depths inside a ¾- to 1½-inch- (20- to 40-mm-) small-diameter perforated pipe in the hole dampens wave or ripple action on the water surface caused by the inflow of water resulting in more accurate water level measurements. Water may also be introduced through the pipe and water level measurements made in the annular space between the pipe and the casing.

In an uncased test section in friable materials liable to wash, the end of the pipe should rest on a 4- to 6-inch (100- to 150-mm) cushion of coarse gravel at the bottom of the hole. In more stable material, the pipe may be suspended above the bottom of the hole, but the bottom of the pipe should be located at least 2 feet (0.6 m) below the top of the water surface maintained in the hole.

Pumping Equipment and Controls

Pressure is not required in the test, but pump capacity should be adequate to maintain a constant head during the test.

140 WATER TESTING FOR PERMEABILITY

Accurate control of the flow of water into the casing is a problem on many gravity tests. The intake of the test section necessary to maintain a constant head is sometimes so small that inflow cannot be sufficiently controlled using a conventional arrangement. A precise method of controlling low flows, such as using needle valves, is important. Many meters are inaccurate at very low flows.

Water Meters

Water deliveries in gravity tests may range from less than 1 gal/min (3.8 L/min) to several hundred gallons per minute. No one meter is sufficiently accurate at all ranges. Two meters are recommended: (1) a 4-inch (100-mm) propeller- or impeller-type meter to measure flows between 50 and 350 gal/min (200 and 1,300 L/min) and (2) a 1-inch (25-mm) disk-type meter for flows between 1 and 50 gal/min (4 and 200 L/min). Each meter should be equipped with an instantaneous flow indicator and a totalizer. Water meters should be tested frequently.

Length of Time for Tests

As in pressure tests, stabilized conditions are very important if good results are to be obtained from gravity tests. Depending on the type of test performed, one of two methods is used. In one method, the inflow of water is controlled until a uniform inflow results in a stabilized water level at a predetermined depth. In the other method, a uniform flow of water is introduced into the hole until the water level stabilizes.

141 FIELD MANUAL

Arrangement of Equipment

A recommended arrangement of test equipment, starting at the source of water, is: suction line; pump; waterline to settling and storage tank or basin, if required; suction line; centrifugal or positive displacement pump; line to water meter inlet pipe; water meter; short length of pipe; valve; and the waterline to the casing. All connections should be kept as short and straight as possible, and the changes in diameter of hose, pipe, etc., should be kept to a minimum. If a constant head tank is used, the tank should be placed so that water flows directly into the casing.

Gravity Permeability Test - Method 1

For tests in unsaturated and unstable material using only one drill hole, Method 1 is the most accurate available. Because of mechanical difficulties, this test cannot be economically carried out at depths greater than about 40 feet (12 m) when gravel fill must be used in the hole. When performing the test, after the observation and intake pipes are set, add gravel in small increments as the casing is pulled back; otherwise, the pipes may become sandlocked in the casing. For tests in unsaturated and unstable material at depths greater than about 12 meters (40 feet), Method 2 should be used (described later).

The procedures for testing soil conditions are:

Unconsolidated Materials – A 6-inch (150-mm) or larger hole is drilled or augered to the test depth and then carefully developed. A cushion of coarse gravel is placed at the bottom of the hole, and the feed pipe

142 WATER TESTING FOR PERMEABILITY

(I) and the observation pipe (O) are set in position (figure 17-10). After the pipes are in position, the hole is filled with medium gravel to a depth at least five times the diameter of the hole. If the drill hole wall material will not stand without support, the hole must be cased to the bottom. After casing, the gravel cushion and pipes are put in, and the casing is pulled back slowly as medium gravel is fed into the hole. The casing should be pulled back only enough to ensure that the water surface to be maintained in the hole will be below the bottom of the casing. About 4 inches (100 mm) of the gravel fill should extend up into the casing.

A metered supply of water is poured into the feed pipe until three or more successive measurements of the water level taken at 5-minute intervals through the observation pipe are within 0.2 foot (5 mm). The water supply should be controlled so that the stabilized water level is not within the casing and is located more than five times the hole diameter above the bottom of the hole. The water flow generally has to be adjusted to obtain the required stabilized level.

Consolidated Materials – The gravel fill and casing may be omitted in consolidated material or unconsolidated material that will stand without support even when saturated. A coarse gravel cushion is appropriate. The test is carried out as in unconsolidated, unstable materials.

Tests should be made at successive depths selected so that the water level in each test is located at or above the bottom of the hole in the preceding test. The permeability coefficients within the limits ordinarily

143 FIELD MANUAL employed in the field can be obtained from figures 17-7 and 17-8. The test zone and applicable equations are shown in figures 17-6 and 17-10.

Data required for computing the permeability may not be available until the hole has penetrated the water table. The required data are:

• Radius of hole, r, in feet (meters)

• Depth of hole, D, in feet (meters)

• Depth to bottom of casing, in feet (meters)

• Depth of water in hole, H, in feet (meters)

• Depth to top of gravel in hole, in feet (meters)

• Length of test section, R, in feet (meters)

• Depth-to-water table, Tu, in feet (meters)

• Steady flow, Q, introduced into the hole to maintain a uniform water level, in ft 3/sec (m3/sec)

• Time test is started and time each measurement is made

Some examples using Method 1 are:

Zone 1, Method 1

Given:

H = R = 5 feet,ÂT = 0.5 foot, D = 15 feet, U = 50 feet, and Q = 0.10 ft3/sec

144 WATER TESTING FOR PERMEABILITY Figure 17-10.—Gravity permeability test (Method 1). (Method test permeability 17-10.—Gravity Figure

145 FIELD MANUAL

R Tu = U-D + H = 50 - 15 + 5 = 40 feet, also Tu / = 40/5 = 8

R The values for X and Tu / lie in zone 1 (figure 17-6). To

determine the unsaturated conductivity coefficient, Cu, from figure 17-7:

Zone 2, Method 1

Given:

H, R, r, U, and Q are as given in example 1, D = 45 feet

R Points Tu / and X lie in zone 2 on figure 17-6.

146 WATER TESTING FOR PERMEABILITY

To determine the saturated conductivity coefficient, Cs, from figure 17-8:

From figure 17-10:

Gravity Permeability Test - Method 2

This method may give erroneous results when used in unconsolidated material because of several uncontrollable factors. However, it is the best of the available pump-in tests for the conditions. The results obtained are adequate in most instances if the test is performed carefully. When permeabilities in streambeds or lakebeds must be determined below water, Method 2 is the only practical gravity test available.

A 5-foot (1.5-m) length of 3- to 6-inch- (75- to 150-mm-) diameter casing uniformly perforated with the maximum number of perforations possible without seriously affecting the strength of the casing is best. The bottom of the perforated section of casing should be beveled on the inside and case hardened for a cutting edge.

The casing is sunk by drilling or jetting and driving, whichever method will give the tightest fit of the casing in the hole. In poorly consolidated material and soils with a nonuniform grain size, development by filling the casing with water to about 3 feet (1 m) above the perforations and gently surging and bailing is advisable

147 FIELD MANUAL before making the test. A 6-inch (150-mm) coarse gravel cushion is poured into the casing, and the observation pipe is set on the cushion.

A uniform flow of water sufficient to maintain the water level in the casing above the top of the perforations is poured into the well. The water should be poured through a pipe and measurements made between the pipe and casing or reversed if necessary. Depth of water measurements are made at 5-minute intervals until three or more measurements are within ±0.2 foot (60 mm) of each other.

When a test is completed, the casing is sunk an additional 5 feet (1.5 m), and the test is repeated.

The test may be run in stable consolidated material using an open hole for the test section. Because the bottom of the casing is seldom tight in the hole and significant error may result from seepage upward along the annular space between the casing and the wall of the hole, this is not recommended. Measurements should be made to the nearest 0.01 foot (3 mm). The values of Cu and Cs within the limits ordinarily employed in the field can be obtained from figures 17-7 and 17-8. The zone in which the test is made and applicable equations can be found in figures 17-6 and 17-11, respectively.

Some data required for computing permeability are not available until the hole has encountered the water table.

The recorded data are supplemented by this information as the data are acquired. The data recorded in each test are:

148 WATER TESTING FOR PERMEABILITY Figure 17-11.—Gravity permeability test (Method 2). (Method test permeability 17-11.—Gravity Figure

149 FIELD MANUAL

• Outside radius of casing, r1 • Length of perforated section of casing, R

• Number and diameter of perforations in length R

• Depth to bottom of hole, D

• Depth-to-water surface in hole

• Depth of water in hole, H

• Depth-to-water table, U

• Thickness of saturated permeable material above underlying relatively impermeable bed, S

• Steady flow into well to maintain a constant water level in hole, Q

• Time test is started, and measurement is made

Some examples using Method 2 are:

Zone 1, Method 2

Given:

R H = 10 feet, = 5 feet, r1 = 0.25 foot, D = 20 feet, U = 50 feet, Q = 0.10 ft3/sec, 128 0.5-inch-diameter perforations, bottom of the hole is sealed

B 2 B 2 Area of perforations = 128 r1 = 128 (0.25) = 25.13 in2 = 0.174 ft2

Area of perforated section = 2BrR = 2B (0.25) (5) = 7.854 ft2

150 WATER TESTING FOR PERMEABILITY

R Points Tu / and X lie in zone 1 on figure 17-6.

Find Cu from figure 17-7:

then, Cu = 1,200

From figure 17-11:

Zone 2, Method 2

Given:

R R Q, H, , r1, re, U, /H, and H/re same as Zone 1, Method 2, D = 40 feet

151 FIELD MANUAL

R Points Tu / and X lie in zone 2 on figure 17-6.

Find Cs from figure 17-8:

From figure 17-11:

Zone 3, Method 2

Given:

R R R Q, H, , r1, re, /H, H/re, U, Cs, and /re are as given in Zone 2, Method 2, S = 60 feet

152 WATER TESTING FOR PERMEABILITY

From figure 17-11:

Gravity Permeability Test - Method 3

This method is a combination of gravity permeability test Methods 1 and 2. The method is the least accurate, but is the only one available for gravelly or coarse soils (figure 17-12).

In some materials, a casing that is beveled and case hardened at the bottom will not stand up to the driving. This is particularly true in gravelly materials where the particle size is greater than about 1 inch (25 mm). Under these conditions, Method 3 would probably not be satisfactory because a drive shoe must be used. Using a drive shoe causes excessive compaction of the materials and forms an annular space around the casing.

On completion of each test, a 3- to 6-inch-diameter (90- to 150-millimeter) perforated casing is advanced 5 feet (1.5 m) by drilling and driving. After each new test section is developed by surging and bailing, a 6-inch (150-mm) gravel cushion is placed on the bottom to support the observation pipe. A uniform flow of water sufficient to maintain the water level in the casing just at the top of the perforations is then poured into the well. The water is poured directly into the casing, and measurements are made through a 1¼-inch (32-mm) observation pipe. The test should be run until three or

153 FIELD MANUAL Figure 17-12.—Gravity permeability test (Method 3). (Method test permeability 17-12.—Gravity Figure

154 WATER TESTING FOR PERMEABILITY more measurements taken at 5-minute intervals are within ±0.2 foot (60 mm) of the top of the perforations.

The values of Cu and Cs, within the limits ordinarily employed in the field, can be obtained from figures 17-7 and 17-8. The zone in which the test is made and applicable equations can be found on figures 17-6 and 17-12, respectively.

The data recorded in each test are:

• Outside radius of casing, r1, in feet (meters)

• Length of perforated section of casing, R, in feet (meters)

• Number and diameter of perforations in length R

• Depth to bottom of hole, D, in feet (meters)

• Depth-to-water surface in hole, in feet (meters)

• Depth of water in hole, in feet (meters)

• Depth-to-water table, in feet (meters)

• Steady flow into well to maintain a constant water level in hole, Q, in ft3/sec (m3/sec)

• Time test is started and time each measurement is made

155 FIELD MANUAL

Zone 1, Method 3

Given: Q = 10.1 gal/min = 0.023 ft3/sec, H = R = 5 feet,

D = 17 feet, U = 71 feet, Tu = 54.5 feet, re = 0.008 foot,

and r1 = 1.75 inches = 0.146 foot (nominal 3-inch casing)

These points lie in zone 1 (figure 17-6).

Find Cu from figure 17-7:

then, Cu = 640

From figure 17-12:

Zone 2, Method 3

R Given: Q, H, , U, re, and r1 are as given in Zone1,

Method 3, D = 66 feet and Tu = 10 feet

156 WATER TESTING FOR PERMEABILITY

These points lie in zone 2 (figure 17-6).

Find Cs from figure 17-8:

From figure 17-12:

Gravity Permeability Test - Method 4

This method can be used to determine the overall average permeability of unsaturated materials above a widespread impermeable layer. The method does not detect permeability variations with depth. The method is actually an application of steady-state pumping test theory.

A well, preferably 6 inches (150 mm) or larger in diameter, is drilled to a relatively impermeable layer of wide areal extent or to the water table. If the saturated thickness is small compared to the height of the water column that can be maintained in the hole, a water table will act as an impermeable layer for this test. The well is uncased in consolidated material, but a perforated casing

157 FIELD MANUAL casing or screen should be set from the bottom to about 5 feet (1.5 m) below the ground surface in unconsolidated material. The well should be developed by pouring water into the hole while surging and bailing before testing.

Before observation wells are drilled, a test run of the intake well should be made to determine the maximum height, H, of the column of water that can be maintained (figure 17-13) above the top of the impermeable layer. A 1- to 1¼-inch (25- to 32-mm) observation pipe should be inserted to near the bottom of the intake well to for water-level measurements. The spacing of the observation wells can be determined from this test run.

A minimum of three observation wells should be installed to the top of the impermeable layer or water table. Suitable pipe, perforated for the bottom 10 to 15 feet (3 to 4.5 m), should be set to the bottom of these wells. The observation wells should be offset from the intake well by distances equal to multiples of one-half the height, H, of the water column that will be maintained in the intake well.

The elevations of the top of the impermeable layer or water table in each well are determined, and the test is started. After water has been poured into the intake at a constant rate for an hour, measurements are made of water levels in the observation wells. Measurements are then made at 15-minute intervals, and each set of measurements is plotted on semi-log paper. The square

158 WATER TESTING FOR PERMEABILITY

Figure 17-13.—Gravity permeability test (Method 4). of the height of the water level above the top of the impermeable bed, h2, is plotted against the distance from the intake well to the observation holes, d, for each hole (figure 17-14). When the plot of a set of measurements is a straight line drawn through the points within the limits of plotting, conditions are stable and the permeability may be computed.

159 FIELD MANUAL

Figure 17-14.—Plot of h2 versus d for gravity permeability test (Method 4).

The data recorded in each test are:

• Ground elevations at the intake well and the observation wells

• Elevations of reference points at the intake well and the observation wells, in feet (meters)

160 WATER TESTING FOR PERMEABILITY

• Distances from center of the observation wells to center

of the intake well, d1, d2, and d3, in feet (meters) • Elevation of top of impermeable bed at the intake well and the observation wells, in feet (meters)

• Depths of water below reference point in the intake well and the observation wells at 15-minute intervals, in feet (meters)

• Uniform flow of water, Q, introduced into well, in ft3/sec (m3/sec)

• Time pumping is started and time each measurement is made

Method 4

3 Given: U = 50 feet, Q = 1 ft /sec, H = 30 feet, d1 =

15 feet, d2 = 30 feet, d3 = 60 feet, h1 = 23.24 feet, 2 2 2 2 h2 = 17.89 feet, h3 = 10.0 feet, h1 = 540 ft , h2 = 320 ft , 2 2 and h3 = 100 ft

A plot of d against h2, as shown on figure 17-14, shows that a straight line can be drawn through the plotted points, meaning that stable conditions exist and the permeability may be computed.

From figure 17-13:

161 FIELD MANUAL

Falling Head Tests

Falling head tests are used primarily in open holes in consolidated rock. Falling head tests use inflatable packers identical to those used for pressure testing and can be used as an alternate method if the pressure transducer or other instrumentation fails. The method of cleaning the hole is the same as that described under pressure testing.

Tests Below the Static Water Level

Tests below the static water level should be done as follows:

• Use inflatable straddle packers at 10-foot (3-m) spacing on a 1¼-inch (32-mm) drop pipe (inside diameter = 1.38 inches [35 mm]). Set packers initially at the bottom of the hole and inflate to 300 lb/in2 (2,000 kPa) of differential pressure.

• After packers are inflated, measure the water level in the drop pipe three or more times at 5-minute intervals until the water level stabilizes. The stabilized level will be the static water level in the test section.

162 WATER TESTING FOR PERMEABILITY

• Pour 2 gallons (8 liters [L]) or more of water as rapidly as possible into the drop pipe after the water level stabilizes. One gallon (4 l) of water will raise the water level in a 1¼-inch (32-mm) pipe 13 feet (4 m) if the section is tight.

• Measure the water level as soon as possible after the water is poured in. Measure the initial depth to water, record the time as soon as possible, and repeat twice at 5-minute intervals. If the rate of decline exceeds 15 feet (4.5 m) in 13 minutes, the transmissivity of a 10-foot (3- m) test section is greater than 200 ft2 (18 m2) per year, and the average permeability is greater than 20 feet (6 m) per year.

The transmissivity value determined is only an approximation, but the value is sufficiently accurate for many engineering purposes.

The equation for analysis is:

where:

T = transmissivity of test section, in ft2/sec (m2/sec)

V = volume of water entering test section in period )t, in ft3 (m3). (A 1-foot [30-cm] decline in 1¼-inch [32-mm] pipe = 0.01 ft3 [0.000283 m3])

s = decline in water level in period )t, in feet (meters)

)t = period of time, in seconds, between successive

water level measurements (i.e., t1 - to, t2 - t1, etc.)

163 FIELD MANUAL

• If the log indicates the test section is uniform and without obvious points of concentrated leakage, the average permeability of the test section, in feet per second (m/sec), can be estimated from K = T/R, where R is the length of the test section, in feet (m). If the log indicates a predominantly impervious test section, but includes a zone or zones of concentrated flow, the average K of the zones can be estimated from K = T/RN, where RN is the thickness of the permeable zone or zones, in feet (m).

• After each test, deflate the packers, raise the test string 10 feet (3 m), and repeat the test until the entire hole below the static water level has been tested.

Tests Above the Water Table

Tests above the water table require different procedures and analyses than tests in the saturated zone. Tests made in sections straddling the water table or slightly above the water table will give high computed values if the equations for tests below the static water level are used and low computed values if the following equations are used. For tests above the water table, the following procedure is used:

• Install a 10-foot- (3-m-) spaced straddle packer at the bottom of the hole, if the hole is dry, or with the top of the bottom packer at the water table if the hole contains water. Inflate the packer.

• Fill the drop pipe with water to the surface, if possible, otherwise, to the level permitted by pump capacity.

• Measure the water level in the drop pipe and record with time of measurement. Make two or more similar measurements while the water-table declines.

164 WATER TESTING FOR PERMEABILITY

• Upon completion of a test, raise the packer 10 feet (3 m) and repeat this procedure until all of the open or screened hole is tested.

The equation for analysis is:

where: OO r1 = inside radius of drop pipe, in feet HQQV=OO?HQTKPEJ=OO?RKRG

TG GHHGEVKXG TCFKWU QH VGUV UGEVKQP KP HGGV OO HQQV=OO?HQTCKPEJ=OO?JQNG

)V VKOGKPVGTXCNU VVVV KPUGEQPFU UKPJ KPXGTUGJ[RGTDQNKEUKPG

NP PCVWTCNNQICTKVJO

* NGPIVJ QH YCVGT EQNWOP HTQO DQVVQO QH VGUV KPVGTXCNVQYCVGTUWTHCEGKPUVCPFRKRGKPHGGV O ) (H0, H1, H2 lengths at time of

measurements t0, t1, t2, etc.)

• For the particular equipment specified and a 10-foot (3-m) test section, the equation may be simplified to:

165 FIELD MANUAL

Slug Tests

Slug tests are performed by “rapidly” changing water levels in a borehole. The rapid change is induced by adding or removing small quantities of water, air, or an object that displaces the groundwater. The time required to restore the water level to its original level is used to calculate the permeability. Slug tests are typically performed in areas where access or budget is limited or the extraction or addition of water has a potential impact to the surrounding area. Slug tests are appropriate where the aquifer will not yield enough water to conduct an aquifer test or the introduction of water could change or impact the water quality. A major factor in conducting slug tests is ensuring that the water level during the test reflects the aquifer characteristics and is not unduly affected by the well construction. Where the water surface is shallow and clean water is readily available, water injection or bailing is often the easiest method. The displacement or air injection method may be desirable at locations where the water level is deep and rapid injection or removal of water is difficult.

A number of slug test methods exist. The choice depends on the hydrologic and geologic conditions and the well size and construction.

Selecting the Slug Test

The method of inducing a rise or fall in the water surface depends on the purpose of the test and conditions at the site. Where the water level is shallow and clean water is readily available, water injection or bailing is often the easiest method. One limitation of the test accuracy is the initial water flowing down the inside wall of the well. Causing a rapid rise by displacing water in the well by

166 WATER TESTING FOR PERMEABILITY dropping a pipe or weight or injecting air may be preferable at remote sites where water may not be readily available. The displacement or air injection method may also be desirable at locations where the water level is deep and rapid injection or removal of water may require collection and treatment or at well sites that are being used for water chemistry studies.

Conducting the Slug Test

Before introducing the slug, the well’s sidewall, screen, or filter pack needs to be clear of any obstructions that will impede the movement of water from the riser to the surrounding materials. The riser diameter and length need to be measured as accurately as possible, and the water level must be stabilized and recorded as accurately as possible. The water level measurements must begin immediately following the introduction of the slug. Where the water level changes slowly, measurements may be made by using a water level indicator. For most tests, water levels should be recorded by a pressure transducer and automatic data logger.

Hvorslev Slug Test

The Hvorslev slug test is the simplest method of analysis. This analysis assumes a homogeneous, isotropic, infinite medium in which both the soil and water are incompressible. It neglects well bore storage and is not accurate where a gravel pack or thick sand pack is present. Figure 17-15 is a sketch of the geometry of this test and the method of analysis. This method is used where the slug test is conducted below an existing water surface.

The test analysis requires graphing the change in head versus time. Head changes are given by (H-h)/H-H0 and

167 FIELD MANUAL

Figure 17-15.—Hvorslev piezometer test. should be plotted semi-log against time. The graph should approximate a straight line; and at the point 0.37, the T0 value is defined as the basic time lag. Using the graphical solution for T0, the dimension of the cavity, and the appropriate shape factor, F, a solution for permeability can be found by:

Figure 17-16 provides shape equations for various well geometries.

Bouwer Slug Test

The Bouwer slug test assumes no aquifer storage and finite well bore storage. The well can be partially penetrating and partially screened. The method was

168 WATER TESTING FOR PERMEABILITY Figure 17-16a.—Shape factors for computing permeability from variable head tests.

169 FIELD MANUAL Figure 17-16a (cont.).—Shape factors for computing permeability from variable head

170 WATER TESTING FOR PERMEABILITY

Figure 17-16b.—Shape factor coefficient Fs. originally developed for unconfined aquifers but can also be used for confined or stratified aquifers if the top of the screen or perforated section is located some distance below the upper confining layer. The analysis is based on the Thies equation and determines permeability, K, of the aquifer around the well from the equation:

171 FIELD MANUAL

where: R = length of the perforated section of the casing or riser

s0 = the vertical difference between the water surface inside the well and the static water level at time zero

st = s at time t t = time of reading

rc = inside radius of the riser or casing r = the effective radius of the well, including the perforated casing, sand or gravel pack, and any remaining annular space to the sidewall of the borehole

de = effective radial distance; the distance between the well and the observation well; the distance over which the water level, s, returns to the static level H = the height of water within the well S = aquifer thickness See figure 17-17 for the configuration definition.

The values of de were determined using an electrical resistance analog network. The effective radial distance is influenced by the well diameter, well screen length, well depth, and the aquifer thickness. Various values for R rc, , H, and S were used in the analog network for analysis of their impacts on de.

172 WATER TESTING FOR PERMEABILITY

Figure 17-17.—Slug test on partially penetrating, screened well in unconfined aquifer with gravel pack and developed zone around screen.

The term, ln (de/r), is related to the geometry of the test zone and the amount of aquifer penetration of the well. Two separate solutions are required to address partially penetrating wells and fully penetrating wells. For

173 FIELD MANUAL partially penetrating wells, an empirical equation relating ln (de/r) to the geometry of the test zone is:

In this equation, A and B are dimensionless coefficients that can be read on figure 17-18. An effective upper limit of ln[(S-H)/r] is 6. If the computed value of ln[(S-H)/r] is greater than 6, then 6 should be used in the equation for ln(de /r). When S = H, the well is fully penetrating, and the value of C should be used from figure 17-18 in the equation.

Values of the field test data should be plotted as recovery, s, versus time for each data point reading. The value s should be plotted on a y-axis log scale, and values for corresponding time should be plotted on the x-axis. The points should approximate a straight line, which indicates good test data. Areas of the data that plot as curves (usually at the beginning of the test or near the end of the test) should not be used in the computation.

Piezometer Test

The piezometer test measures the horizontal permeability of individual soil layers below a water surface. This test

174 WATER TESTING FOR PERMEABILITY

Figure 17-18.—Dimensionless parameters A, B, R and C as a function of /re (F for calculation of ln(de/re)). surface. This test may apply to large diameter direct push technology, as well as to any depth that an open hole can be maintained. This test is preferred over the auger-hole test described in section 10-6 of the Ground Water Manual, especially when the soils tested are less than 1.5 feet (0.5 m) thick and are below the water table. This method is particularly good for determining which layer below the capillary zone is an effective barrier.

Equipment

The following items are suggested equipment for the piezometer test.

• Riser between 1- to 2-inch (24- to 50-mm) inside diameter for a depth of around 15 feet (4.5 m) and black iron pipe with smooth inside wall for depths greater than 15 feet (4.5 m)

175 FIELD MANUAL

• Equipment capable of installing the riser and cavity below the riser

• Pump with hose and controller or bailer that will fit inside the casing

• Bottle brush for cleaning soil film from the inside of the test riser if the riser is driven without a protective point that can prevent soils from filling the inside of the tube

• Water level detector, stop watch, and transducer and data logger

Procedure

The test layer should be at least 1 foot (30 cm) thick so that a 4-inch (10-cm) length of cased hole or cavity can be located in the middle of the layer. This placement is especially important if a marked difference in the layers exists above and below the test layer. The differences may be changes in the percentages of fines (>15 percent), overall changes in the soil gradations, soil structure, or degree of cementation or induration within the soil horizon. After selecting an appropriate interval based on the soil investigation, an adjacent hole within 2 feet (0.6 m) of the test hole is advanced to around 2.0 feet (0.6 m) above the bottom of the 4-inch (10-cm) test interval, if using direct push technology, or to the top of the 4-inch (10-cm) interval. Then use a smaller diameter auger to ream the final 4-inch (10-cm) interval for the riser pipe. The final 2.0 feet (0.6 m) are driven to ensure that a reasonably good seal is obtained and also to minimize the disturbance. The lower 4 inches (10 cm) of the borehole are exposed, and the cavity must remain open. After some recovery has occurred, the riser should be cleaned with a brush to remove any soil film unless

176 WATER TESTING FOR PERMEABILITY should be screened within the lower cavity and then cleaned out by gently pumping or bailing water and sediment from the piezometer.

After the water surface has stabilized, the transducer is installed. The riser is bailed or pumped, depending on the diameter of riser and the depth to water. It is not necessary to remove all the water in the screened interval, but the water level should be lowered enough that at least three readings during the first half of the water rise will give consistent results.

Calculations

After completing the piezometer test, the permeability is calculated from:

where:

s1 and s2 = distance from static water level at times t1

and t2, in inches (cm)

t2 - t1 = time for water level change from s1 to s2, in seconds

Ca = a constant for a given flow geometry, in inches (cm) R = length of open cavity, in inches (cm) d = H-R, distance from the static water level to the top of the cavity, in inches (cm) b = distance below the bottom of the cavity to the top of next layer, in inches (cm)

A sample calculation using this equation is shown in figure 17-19. The constant, Ca, may be taken from curves

177 FIELD MANUAL

A sample calculation using this equation is shown in figure 17-19. The constant, Ca, may be taken from curves shown in figures 17-19 or 17-20. The curve on figure 17-19 is valid when d and b are both large compared to R. When b = 0 and d is much greater than R R , the curve will give a Ca factor for = 4 and d = 1 that will be about 25 percent too large.

The chart on figure 17-20 is used for determining Ca when upward pressure exists in the test zone. When pressures are present, additional piezometers must be installed. The tip of the second piezometer should be placed just below the contact between layers in layered soil (figure 17-21). In deep, uniform soils, the second piezometer tip should be placed an arbitrary distance below the test cavity.

After installing the second piezometer, the following measurements should be made:

• Distance, d, in feet (m), between the ends of the riser pipes

• Difference, H, in feet (m), between water surfaces in the two piezometers at static conditions

• Distance, d’, in feet (m), between the center of the lower piezometer cavity and the contact between soil layers in the layered soils

The Ca value from figure 17-20 is used in the equation to determine the permeability.

Limitations

Installation and sealing difficulties encountered in coarse sand and gravel are the principal limitations of the

178 WATER TESTING FOR PERMEABILITY

UV G ÂV [ KV KN D C G O T G ÂR T VG G O Q \ KG ÂR T HQ VÂ G G J ÂU P Q VK VC W R O Q ÂE F P ÂC VC C & Â G T W KI (

179 FIELD MANUAL

Figure 17-20.—Chart for determining Ca if upward pressure exists in the test zone.

180 WATER TESTING FOR PERMEABILITY

Figure 17-21.— Sample calculation for the piezometer test with upward pressure in the test zone. piezometer test for permeability. Also, when the riser bottoms in gravel, a satisfactory cavity cannot be obtained. The practical limit of hole depth is about 20 feet (6 meters). Deeper holes require larger diameters (greater than 2 inches [5cm]), and driving the riser deeper is difficult.

181 FIELD MANUAL

Details on the equipment requirements and procedures are provided in chapter 3 of the Drainage Manual. Permeameter tests are typically restricted to shallow boreholes or excavations and require time to set up the equipment and perform the test. Where the permeability is relatively high (>1,000 feet per year [10-3 cm per second]), these tests require large amounts of water. With material having permeability values greater than 106 feet per year (10 cm/sec), laboratory permeability testing is more cost effective. The samples are collected and tested in the laboratory in accordance with Reclamation Procedure 5605.

Bibliography

Bureau of Reclamation, U.S. Department of the Interior, Drainage Manual, 1993.

Bureau of Reclamation, U.S. Department of the Interior, Ground Water Manual, 1995.

182 Chapter 18

RIPRAP

Introduction

Riprap is preferably a relatively thin layer of large, approximately equidimensional, durable rock fragments or blocks placed on bedding to dissipate water energy and protect a slope, channel bank or shore from erosion caused by the action of runoff, currents, waves or ice (figure 18-1). Bedding is usually a layer of sand and gravel placed under the riprap to prevent erosion of the material from under the riprap. Most dam embankments contain at least one zone that uses rock. Rock is used as riprap for protection against erosion or as rockfill and filter zones that strengthen or drain the embankment.

Figure 18-1.—Riprap properly placed on bedding. The riprap is angular, quarried rock, and the bedding is rounded stream gravel. The backhoe is placing and arranging the rock on the bedding. FIELD MANUAL

The terms “slope protection” and “riprap” are often used interchangeably, but not all slope protection is riprap. Soil cement is also commonly used as slope protection. Riprap is an assemblage of rocks “nested” together to protect a structure or area from the action of water. The stability of an assemblage of rocks is a function of the individual rock’s size, shape, weight, and durability. An assemblage of rocks depends on the individual rock characteristics for stability and also on the site conditions, grading, and thickness. The assemblage of rocks is designed to minimize voids and thickness of the riprap layer to keep the volume of material as low as possible. Proper placement interlocks the individual fragments into a layer of rocks that resists the action of water. Figure 18-2 shows what can happen if riprap is not designed, obtained, and placed properly.

Riprap should be “hand” placed to reduce the void space and maximize the interlocking arrangement, but rarely is this economical (figure 18-3). Most riprap is dumped and falls into place by gravity with little or no additional adjustment (figure 18-4). Because of this, individual pieces of riprap must have appropriate characteristics so that the rocks can be processed, handled, and placed so that the layer remains intact for the life of the project.

This chapter discusses: (1) riprap source evaluation, (2) onsite inspection to ensure that the samples are appropriate and that specified material is being produced from the source, (3) presentation of information to designers and estimators, and (4) waste factors in riprap production. A geologic background, a knowledge of blasting methods and types of explosives, and an understanding of the equipment involved in the processing, hauling, and placing of riprap is important to riprap evaluation, production, and placement. Most of the following discussion applies to rock adequate for aggregate and to larger

184 RIPRAP

Figure 18-2.—Improperly designed, obtained, and placed riprap.

185 FIELD MANUAL

Figure 18-3.—Hand-placed riprap.

186 RIPRAP

Figure 18-4.—Dumped riprap. rock fragments used for roads, breakwaters, and jetties. However, this chapter is oriented toward acquiring suitable material for riprap.

This chapter should be used in conjunction with USBR Procedure 6025, Sampling and Quality Evaluation Testing of Rock for Riprap Slope Protection, and

187 FIELD MANUAL

USBR Design Standard No. 13 for Embankment Dams (DS13). Riprap design is discussed in “Chapter 7, Riprap Slope Protection,” of USBR Design Standard DS13. Other documents, such as the U.S. Army Corps of Engineers’ Engineering Manual 1110-2-2301, Engineering and Design - Test Quarries and Test Fills, and Engineering Manual 1110-20-1601, Engineering and Design - Hydraulic Design of Flood Control Channels, also provide information on design and source evaluation. Note: Test procedures developed to test similar riprap characteristics by different organizations are not necessarily the same. The appropriate test procedure should be selected based on the actual test and the available test equipment.

Evaluation

Much of the following discussion is more guidance than hard and fast rules or requirements. What is unacceptable riprap at one location may be acceptable at another site. Remember that a riprap source must be capable of providing suitable material in sufficient quantities at a reasonable cost. The three elements in every source evaluation are: quality, quantity, and cost.

Quality

Rock quality is determined by laboratory testing, but field personnel input and selection of the samples for testing are critical in determining the riprap quality. There are numerous quarries and pits capable of producing aggregate, but not all sources are suitable for the production of riprap. Riprap sources must produce riprap of the necessary weight, size, shape, gradation, and durability to be processed and placed and then remain “nested” for the life of the project. Performance on

188 RIPRAP existing structures is a valuable method of assessing riprap quality from a particular source.

Shape

The shape of individual rock fragments affects the workability and nesting of the rock assemblage. Natural “stones” from alluvial and glacial deposits are usually rounded to subrounded and are easier to obtain, handle, and place and, therefore, are more workable. Rounded stones are less resistant to movement.

The drag force on rounded stones is less than between angular rock fragments. Rounded stones interlock more poorly than do equal-sized angular rock fragments. As a result, a rounded stone assemblage is more likely to be moved or eroded by water action. Angular-shaped rocks nested together resist movement by water and make the best riprap. The rock fragments should have sharp, angular, clean edges at the intersections of relatively flat faces.

Glacial or alluvial deposits are used as riprap sources only if rock quarries are unavailable, too distant, or incapable of producing the appropriate sizes. Unless the design slope is at an angle to the wave direction or wave energy and the erosive action of water on the slope is low, rounded to subrounded stones are typically used only on the downstream face of embankments, in underlying filters, or as the packing material in gabions.

No more than 30 percent of the riprap fragments should have a 2.5 ratio of longest to shortest axis of the rock. Stones having a ratio greater than 2.5 are either tabular or elongated. These tabular or elongated particles (figure 18-5) tend to bridge across the more blocky pieces or protrude out of the assemblage of rocks. During handling, transporting, and placement, these elongated or

189 FIELD MANUAL

Figure 18-5.—Tabular rock fragment. tabular rock fragments tend to break into smaller fragments and could significantly change the gradation or thickness of the protective layer.

Nearly all durable rock types can provide appropriately shaped material, but not all rock types can be blasted and processed economically into suitable shapes. Mineral alignment and fractures within the rock mass are the primary factors affecting the development of the shape. Most igneous and some sedimentary rocks are capable of making suitably shaped fragments. However, secondary fracturing or shearing will affect the shape. Rocks having closely spaced discontinuities tend to produce fragments that are too small. Sedimentary rocks that have bedding plane partings tend to produce flat shapes. Metamorphic rocks tend to break along jointing, rock cleavage, or mineral banding and often produce elongated shapes.

190 RIPRAP

Weight and Size

The weight and size of individual riprap pieces are essential factors in resisting erosive water forces. The weight of the rock fragment is one design element for riprap but is difficult to obtain in the field for the larger sizes. The relationship between weight and size is approximately:

( 3 Wn = 0.75 Dn

where: Wn - Percentage of total weight of rock where n percent is smaller ( - Unit weight of rock

Dn - Representative diameter of rock where n percent is smaller

This formula assumes the shape of the rock fragment is between a sphere and a cube. The weight and size may be determined in the laboratory or in the field. The unit weight of riprap generally varies from 150 to 175 pounds per cubic foot (2.4 to 2.8 g/cm3) and correlates with surface saturated dry specific gravity (SSSG). Rock having an SSSG above 2.6 is typically suitable for riprap.

Determination of the relationship between weight and size is difficult. Rock is either graded by size or counted and weighed, but rarely are weight and size correlated. Rarely does rock break into perfect cubical shapes; and because of the various shapes and sizes, weighing and sorting the individual pieces is difficult. The American Society for Testing and Materials Procedure D-5519 provides three methods for obtaining size and weight data.

Typically, for sizes up to 36 inches (1 meter) minimum diameter, rock pieces are sorted by size with a sieve or template, and the number of individual pieces is counted

191 FIELD MANUAL within each group. These piles can then be weighed and individual pieces adjusted to determine size. For individual pieces larger than 36 inches, the size is typically determined by using a tape to measure the maximum and minimum size of each piece. The weight is determined from a chart that assumes the shape is between a cube and sphere.

Most rock sources are capable of producing suitable weights and sizes. The size rarely impacts use as a riprap source unless more than 30 percent of the rocks are elongated or flat. In special circumstances, the rock mineralogy and porosity control the weight. The porosity of some sedimentary and extrusive volcanic rock could affect the weight. Rock having an SSSG under 2.3 is typically not considered for riprap. Generally, rock having a low unit weight is weak and tends to break down with handling.

Gradation

The desired gradation consists of size fractions of the individual particles that will nest together and withstand environmental conditions. The gradation design is based on the ability of the source(s) to produce appropriate sizes. Inherent rock mineralogy, cleavage, and fractures control the size of the rock fragments. Blasting, excavating, and processing also affect the size. Most acceptable riprap gradations are obtained by understanding the inherent rock characteristics, by proper blasting techniques, and by processing. Rarely can blending rock sizes achieve an appropriate grading for riprap because the larger fragments tend to separate from the smaller fragments during handling and processing. Processing is typically limited to running the rock fragments over a stationary grizzly (figure 18-6) or sorting with a rock bucket or rock rake (figure 18-7). Rarely is rock processed with jaw or

192 RIPRAP

Figure 18-6.—Stationary grizzly. Rock is dumped on the sloping rails, and the larger material slides off and is separated from the smaller material which falls through.

Figure 18-7.—Rock rake. A dozer-mounted rock rake separates the larger fragments from the smaller material. 193 FIELD MANUAL gyratory crushers except for testing. Segregation of large and small sizes is controlled by reducing the number and amount of drops during handling and processing. Handling should be kept to a minimum.

Most coarse-grained sedimentary and igneous rock quarries are capable of producing suitable riprap gradations. The range of gradations from sedimentary sources depends on the depositional environment. Rock derived from rapid depositional environments is more likely to produce well-graded riprap.

Size range is controlled by discontinuities in the rock. Columnar basalt, some fine-grained sedimentary rock, and metamorphic rock commonly have inherent planes of weakness that limit larger riprap sizes. Intensely to moderately fractured rock rarely produces suitable riprap gradations.

Durability

Riprap durability affects the ability of a source to provide a consistent shape, size, and gradation and the ability to resist weathering and other environmental influences. Durability is typically determined by laboratory test; but durability can be assessed by observing surface exposures, talus, and waste piles or by examining riprap applications already using the potential source or similar source materials. Cracking, spalling, delaminating, splitting, disaggregating, dissolving, and disintegrating are common forms of rock deterioration. Durability is a function of the rock’s mineralogy, porosity, weathering, discontinuities, and site conditions. In rare instances, environmental considerations such as abnormal pH of the water may be a controlling factor in selecting an appropriate riprap source. A high or low pH may accelerate disintegration of the rock.

194 RIPRAP

Alteration of minerals, such as feldspars to softer clays, will impact rock durability. Fine-grained rock types, rocks having high porosity, and chemically altered rocks may tend to slake after cyclic wetting and drying or freezing and thawing. Some rocks tend to break up because of discontinuities such as bedding plane parting, cementation or secondary mineralization, unstable minerals, banding, or foliation. Jointing, rock cleavage, and bedding plane partings often result in excessive finer sizes or tabular and elongated rock fragments.

Rock that breaks down either physically or chemically should be avoided. Obvious examples are most weathered or altered rocks, rock containing soluble or expansive minerals, vesicular basalts, shale, claystone, siltstone, weakly cemented or porous sandstone, schist, or phyllite. Even durable rocks such as slate and some gneisses may generally be unusable because other physical characteristics (cleavage and foliation) will not allow production of large, nearly equidimensional blocks.

Mechanical breakdown and weathering may be accelerated by microfracturing from the blasting, handling, weak cementation or may be the result of alteration of more stable minerals to clay. In addition, there appears to be a significant correlation between porosity, absorption, and durability of rock. Rock that has more than 2 percent absorption is commonly impacted by freezing and thawing and by wetting and drying processes.

Quantity

Every riprap source investigation must provide the estimated quantity required. Estimating realistic quantities depends on an understanding of subsurface geologic conditions. The uniformity of rock and

195 FIELD MANUAL discontinuities within a source area must be assessed. This estimate (often referred to as the reserve) provides not only the amount of riprap available but also provides an understanding of wastage resulting from blasting, handling, processing, haulage, and placement. In stratified deposits such as limestones or sandstones, uniformity must be evaluated because individual beds often differ in character and quality. The dip of stratified rocks and contacts between dissimilar rock types, such as igneous intrusions, must also be considered. The larger the individual pieces required, the more difficult it is for any rock type to supply suitable quantities. Zones or layers of undesirable clay or shale seams may be so large or prevalent that selective quarrying or wasting of undesirable material is required. The geologic conditions, ability of the rock to produce suitable sizes, and the potential reserve should be determined.

Existing commercial sources may be capable of producing riprap but may not be capable of expanding their operation into similar quality rock. In any new source, the amount of burden that must be removed, stability of the cutslopes, uniformity of the rock, depth to water, and ability to blast or process the rock into the appropriate gradation must be evaluated. Since riprap is a surface layer, a smaller sized riprap of increased thickness may be acceptable, or a less durable riprap may be used with the understanding that the riprap may require replacement.

Cost

A primary factor in determining a suitable riprap source is cost. Design and environmental requirements, access, subsurface conditions, testing, depth to water, quantity of suitable rock, and location also affect the cost and should be assessed early in any source investigation.

196 RIPRAP

Producing sources should be located first. Using existing quarries or pits is generally cheaper because there is considerably less cost associated with permitting, developing, and evaluating an existing source. An existing source provides easier access to rock; a history of the source provides an understanding of the source’s ability to provide suitable rock; regulatory requirements are often more easily met; development and processing costs are often known; and often, some testing of material has been performed so that the quality is known. Although existing sources may be known, each of these elements should be evaluated to ensure that information is representative and appropriate for the particular requirement.

In areas where existing sources are not economical, evaluating the surrounding undeveloped areas or abandoned pits or quarries should be considered. Evaluating new or abandoned sources typically involves considerable expense. A new quarry or pit investigation involves understanding subsurface conditions; obtaining, evaluating, and testing subsurface samples; and evaluating subsurface conditions to determine if appropriate riprap can be produced. Factors such as the haul distance, grade, width, and type of roadway should also be assessed.

Investigation Stages

The complexity of investigations for suitable sources of riprap is governed by the development stage and design requirements of the project. Projects are normally developed in four stages: reconnaissance, feasibility, design, and construction.

197 FIELD MANUAL

Reconnaissance

Initial exploration involves field surface reconnaissance using topographic maps, geologic and groundwater maps and reports, and aerial photographs. Supplemental information is provided by records of known developed sources of material. Areas having steep topography could have the best rock exposures. Geology maps provide generalized locations of rock types. Groundwater maps provide indications of rock permeability, depths to water, and information on the need for dewatering or unwatering within the source area. During field reconnaissance, the countryside should be examined for exposed rock outcrops or talus piles. Roadcuts and ditches may also provide useful exposures. Existing sources and any projects that previously used the rock source should be examined.

Service records are an excellent indication of the potential durability of rock. Federal (Reclamation, U.S. Army Corps of Engineers, Department of Transportation), State (highway, environmental quality), and county or local (highway or building) agencies usually maintain lists of sources. The local telephone "Yellow Pages," Internet, and construction companies may also provide information.

Data obtained should define the major advantages or disadvantages of potential material sources within reasonable haul distance. A reconnaissance construction material report should be prepared at this stage.

Feasibility

Information acquired during the feasibility stage is used to prepare preliminary designs and cost estimates. Sufficient information concerning potential sources should be gathered to determine whether the rock should be obtained from an existing source or a new source.

198 RIPRAP

Selection of sources should be limited to those that may eventually be used in specifications. Core drilling and blast tests may be required to confirm fragment size and quantity of material available in each source. The potential material sources should be examined to determine size and character, and particularly to observe joint and fracture spacing, resistance to weathering, and variability of the rock. The spacing of joints, fractures, schistosity, banding, bedding, and other planes of weakness may control the rock fragment sizes and shapes. Weathering resistance of the rock will provide a good indication of durability. Quarry or pit development and the impacts of groundwater should be addressed. Particular attention should be given to location and distribution of unsound seams or beds that must be avoided or wasted during the quarry operation. A general location map and detailed report describing the potential sources and containing estimates of available quantities, overburden, haul roads, and accessibility should be prepared. Representative samples of riprap material from the most promising potential sources should be submitted to the laboratory for testing. A feasibility construction material report should be prepared at this stage.

Design

Investigations during the design stage furnish data and information required for the specifications. Sources indicated by feasibility investigations to be suitable are further investigated to establish quantities, determine the capability to produce the required gradation, and to determine uniformity. Depending on project needs, service records may be used in conjunction with or instead of laboratory testing. Blast and processing testing should be considered for new sources. All sampling and testing and the laboratory’s Riprap Quality Evaluation Report should be completed at this stage. If additional sources are

199 FIELD MANUAL necessary, the new sources must be investigated as throughly as the original sources.

Construction

Investigations during construction provide field and design personnel with additional detailed information for proper source development. This information should be obtained sufficiently ahead of quarrying or excavating to provide for proper processing and placing of material. If unforeseen changes occur in the quality of material in the source, sampling and quality evaluation testing of the material may be required to confirm material suitability or to delineate unsuitable areas.

Reports

Reporting the results of any investigation is important. The level of detailed information requirements increases with each successive stage. Adequate information must be available by the feasibility stage to develop realistic cost estimates and to properly select sources. A suggested outline for reports for rock or riprap obtained from any potential quarry or pit is as follows:

a. Ownership b. Location of source and project shown on a map c. General description of site d. General hydrologic and geologic descriptions e. Structural geology information (distribution and arrangement of rock types and discontinuities within the deposit.) f. Manner and sizes of rock breakage g. Estimate of uniformity and wastage

200 RIPRAP

h. Shape and angularity of source material i. Hardness and density of source material j. Degree and extent of weathering k. Any abnormal properties or conditions not covered above l. Estimate of extent, volume, and depth of suitable deposit(s) m. Accessibility n. Photographs o. Geophysical and geologic data (e.g., drill logs, borehole geophysical logs, and seismic refraction or reflection survey data)

If commercial quarry or pit deposits are considered, obtain, as appropriate, the following information in addition to the data needed for a new source.

• Name, address, and phone number of the plant operator • Location of the plant relative to quarry • Description of the operation and plant with emphasis on capabilities for additional riprap production and maintaining current operation capabilities • Blasting methods and problems related to production of riprap • Transportation facilities and any potential difficulties • Actual or estimated riprap gradations achieved or achievable by current or adjusted operations • Location of scales • Estimate of reserve and wastage

201 FIELD MANUAL

• Approximate prices of riprap material • Service history of material produced • Any other pertinent information

Sampling

Sampling is often the weak link in any source evaluation. The samples should represent the nature and condition of the materials and be appropriate for testing. Sampling is initiated at the specifications stage of the project. Sampling should cover the entire riprap source. The sample size should be at least 600 pounds (275 kilograms) and represent the quality range from poor to best as found at the source in the same proportions as the source can supply. If the material quality is quite variable, it may be preferable to obtain three samples that represent the poorest to best quality material available. The minimum size of individual fragments selected should be at least 0.5 foot (15 cm) square. An estimate of the relative percentages of material at each quality level should be made.

Representative samples may be difficult to obtain. Overburden may limit the areas where material can be obtained and obscure the true characteristics of the deposit. Outcrops will often be more weathered than the subsurface deposits. Samples obtained from talus piles or outer surfaces of rock outcrops are seldom representative of quality, quantity, or gradation. Fresh material may be obtained by breaking away the outer surfaces, or by trenching, blasting, or core drilling. If coring is the only method of obtaining samples, the preferred size is 6 inches (15 cm).

202 RIPRAP

Shipping

Samples of rock fragments can be shipped by conventional transport such as motor freight. Large rock fragments should be securely banded to shipping pallets. Smaller fragments should be transported in bags or containers to preclude loss, contamination, or damage from mishandling during shipment.

Testing

The Riprap Quality Evaluation Report is based on laboratory testing of the shipped representative samples. The quality evaluation tests include detailed petrographic examination, determination of physical properties and absorption, and a rapid freeze-thaw durability evaluation.

Petrographic Examination.—The petrographic examination follows USBR Procedure 4295 or ASTM Procedure C 295, which were developed for concrete aggregate. The decisions concerning specific procedural methods and specimen preparation depend on the nature of the rock and the intended use of the rock.

The rock pieces are visually examined and the different rock facies and types are segregated for individual evaluation. The following are evaluated:

• Size range • Fragment shape • Shape and size control by discontinuities such as joints, banding, or bedding • Surface weathering • Secondary mineralization or alteration • Hardness, toughness, and brittleness

203 FIELD MANUAL

• Voids and pore characteristics and their variations • Texture, internal structure, grain size, cementation, and mineralogy of the various facies and rock types • Thin sections, sometimes supplemented by X-ray diffraction as required

Freeze-Thaw Test.— For freeze-thaw durability testing, two 7/8-inch (73 millimeter) cubes are sawed from rock fragments selected by visual inspection to represent the range from poorest to best quality rock for each rock facies or type. Because the rock pieces could have significant physical or structural discontinuities, the number of cubes obtained for testing will vary from sample to sample. The samples are photographed, the cubes are immersed in water for 72 hours, and specific gravities (bulk, SSSG, and apparent) and absorptions are determined by USBR Procedure 4127 or ASTM Procedure C 127. The cubes are reimmersed in water to maintain a saturated condition for freeze-thaw testing.

Rapid freezing and thawing durability tests are performed on riprap samples according to USBR Procedure 4666 or ASTM Procedure D5312. The rock failure criterion is 25 percent loss of cube mass calculated from the difference in mass between the largest cube fragment remaining after testing and the initial cube mass.

Sodium Sulfate Soundness Test.—Sodium sulfate soundness tests are performed on riprap samples according to USBR Procedure 4088 or ASTM Procedure D5240. The loss after an interval of screening is determined after at least five cycles of saturation and drying of the samples. The test is a good indicator of resistance to freeze-thaw deterioration.

204 RIPRAP

Physical Properties.—Material remaining after the petrographic examination and freeze-thaw testing is crushed into specific size fractions (USBR Procedure 4702). Representative samples of each size fraction are tested for bulk, SSGS, and absorption following USBR Procedure 4127 or ASTM Procedure C 127; abrasion is tested using the Los Angeles abrasion test following USBR Procedure 4131 or ASTM Procedure C 535. Both the Los Angeles abrasion and sodium sulfate soundness tests are durability tests. The Los Angeles abrasion test is used to determine the ability of the rock to withstand handling and processing and water action. The sodium sulfate soundness test simulates weathering of the rock pieces.

Waste in Riprap Production

Production of riprap generally requires drilling, blasting, and processing to obtain the desired sizes. This section is a guide to help estimate the amount of waste that can be expected from riprap production.

Numerous factors in the parent rock contribute to waste in quarrying operations. The natural factors include:

• Weathering • Fracturing (joints, shears, and faults) • Bedding, schistosity, and foliation • Recementing of planar features

Other important, somewhat controllable contributors to waste are:

• Construction inspection • Size and gradation requirements • Drilling and blasting • Processing, hauling, and placement

205 FIELD MANUAL

Factors a through d relate to the geology in the quarry and probably are the most important factors that govern what sizes can be produced. Weathering can extend 20 to 60 feet (6 to 18 meters) below the original ground surface. Weathering breaks down the rock and weakens existing planar features such as bedding, schistosity, and jointing. In rocks such as limestone and dolomite, secondary deposits of calcium carbonate can cement existing joints. When first examined, this cementation appears to be sound; but processing the rock can refracture these planes. Existing quarries, or quarries that have been in operation for many years, probably will produce material with less waste because excavations are partly or completely through the zone of weathering. New quarries, or quarries where rock production has been limited, must contend with the weathered zone and will likely produce a less desirable product.

Gradation Requirements

Gradation requirements and inspection control are governed by the agency issuing the construction specifications. Adjustments in gradation or inspection requirements can drastically change the waste quantities produced. Except in isolated cases, it becomes more difficult to produce riprap when rock sizes are increased and gradations are tightly controlled.

Production Methods

Production methods that include drilling, blasting, processing, and hauling also play an important role in the sizes that can be obtained. Rock that is well-graded and has a large maximum size can be produced more readily when using large diameter, widely spaced shot holes. Close spaced, small diameter shot holes tend to maximize fragmentation. Blasting agents, delays, and loading

206 RIPRAP methods vary considerably and have a significant effect on how the rock fractures. The most efficient and economical drilling and blasting methods must be determined by test blasting and performing gradations on the blasted product. Test shots should be modified to achieve the desired product. Production should not start until it is proven that the required product can be produced with a minimum of waste.

Many rock types, especially those that are banded (bedded or schistose) or contain healed joints, can break down significantly during processing. Some limestones are especially susceptible to breakdown when the rock is dropped during blasting and processing operations. Rock from most quarries will fracture badly when dropped more than 50 feet (15 meters).

Quarries must tailor their blasting techniques to get the required gradations. Quarries that normally produce aggregates for concrete, road metal, and base course usually have a very difficult time producing a reasonably well-graded riprap. This is because their normal operation already has shattered the face at least 100 feet back. To obtain good riprap, a working face or ledge should be reserved for riprap production.

The quantity of quarry waste shown in table 18-1 is typical of riprap quarries. Items that should be considered when using the table include: • Waste includes undersize and excessive intermediate sizes. Oversize riprap is reprocessed to the proper size.

• Rock produced is reasonably well graded from 6± to 36± inches (.15 to 1 m), and the inspection control is very strict. Much less waste will be incurred if smaller rock sizes

207 FIELD MANUAL

Table 18-1.—Rock types and typical usable quantities of riprap

Estimated percent waste to produce Rock type suitable riprap Remarks

IGNEOUS

Intrusive 25 to 75% Average 50%±

Extrusive 40 to 85% Average 60%±

METAMORPHIC

Gneiss 40 to 75% Based on limited data Average 55%±

Schist 50 to 75% Based on limited data Average 65%± Very little riprap would be salvaged in the weathered zone

SEDIMENTARY

Limestone/ 55 to 85 % Based on several good Dolomite Average 65%± quarry sites

Sandstone Average 60%± Based on limited data

are required or if the deposit is shot for rockfill or the specific rock product.

• Drilling, blasting, processing, hauling, and placing are accomplished by a typical contractor.

• Rock quarried is the best material available and is not severely fractured or weathered.

• Riprap production is generally limited to new quarries or unshot ledges or benches.

208 Chapter 19

BLAST DESIGN

Introduction

This chapter is an introduction to blasting techniques based primarily on the Explosives and Blasting Procedures Manual (Dick et al., 1987) and the Blaster’s Handbook (E.I. du Pont de Nemours & Co., Inc., 1978). Blast design is not a precise science. Because of widely varying properties of rock, geologic structure, and explosives, design of a blasting program requires field testing. Tradeoffs frequently must be made when designing the best blast for a given geologic situation. This chapter provides the fundamental concepts of blast design. These concepts are useful as a first approximation for blast design and also in troubleshooting the cause of a bad blast. Field testing is the best tool to refine individual blast designs.

Throughout the blast design process, two overriding principles must be kept in mind:

(1) Explosives function best when there is a free face approximately parallel to the explosive column at the time of detonation.

(2) There must be adequate space for the broken rock to move and expand. Excessive confinement of explosives is the leading cause of poor blasting results such as backbreak, ground vibrations, airblast, unbroken toe, flyrock, and poor fragmentation.

Properties and Geology of the Rock Mass

The rock mass properties are the single most critical variable affecting the design and results of a blast. The FIELD MANUAL rock properties are very qualitative and cannot be sufficiently quantified numerically when applied to blast design. Rock properties often vary greatly from one end of a construction job to another. Explosive selection, blast design, and delay pattern must consider the specific rock mass being blasted.

Characterizing the Rock Mass

The keys to characterizing the rock mass are a good geologist and a good blasting driller. The geologist must concentrate on detailed mapping of the rock surface for blast design. Jointing probably has the most significant effect on blasting design. The geologist should document the direction, density, and spacing between the joint sets. At least three joint sets—one dominant and two less pronounced—are in most sedimentary rocks. The strike and dip of bedding planes, foliation, and schistosity are also important to blast design and should be documented by the geologist. The presence of major zones of weakness such as faults, open joints, open beds, solution cavities, or zones of less competent rock or unconsolidated material are also important to blast design and must be considered. Samples of freshly broken rock can be used to determine the hardness and density of the rock.

An observant blasting driller can be of great help in assessing rock variations that are not apparent from the surface. Slow penetration, excessive drill noise, and vibration indicate a hard rock that will be difficult to break. Fast penetration and a quiet drill indicate a softer, more easily broken zone of rock. Total lack of resistance to penetration, accompanied by a lack of cuttings or return water or air, means that the drill has hit a void. Lack of cuttings or return water may also indicate the presence of an open bedding plane or other crack. A detailed drill log indicating the depth of these various

210 BLAST DESIGN conditions can be very helpful in designing and loading the blast. The log should be kept by the driller. The driller should also document changes in the color or nature of the drill cuttings which will tell the geologist and blaster the location of various beds in the formation.

Rock Density and Hardness

Some displacement is required to prepare a muckpile for efficient excavation. The density of the rock is a major factor in determining how much explosive is needed to displace a given volume of rock (powder factor). The burden-to-charge diameter ratio varies with rock density, changing the powder factor. The average burden-to- charge diameter ratio of 25 to 30 is for average density rocks similar to the typical rocks listed in table 19-1. Denser rocks such as basalt require smaller ratios (higher powder factors). Lighter materials such as some sandstone or bituminous coal can be blasted with higher ratios (lower powder factors).

The hardness or brittleness of rock can have a significant effect on blasting results. If soft rock is slightly under- blasted, the rock probably will still be excavatable. If soft rock is slightly overblasted, excessive violence will not usually occur. On the other hand, slight underblasting of hard rock will often result in a tight muckpile that is difficult to excavate. Overblasting of hard rock is likely to cause excessive flyrock and airblast. Blast designs for hard rock require closer control and tighter tolerances than those for soft rock.

Voids and Zones of Weakness

Undetected voids and zones of weakness such as solution cavities, “mud” seams, and shears are serious problems in

211 FIELD MANUAL

Table 19-1.—Typical rocks, densities, and unit weights

Range of unit weights

Density U.S. range customary Metric Rock type (g/cm3)1 (lb/ft3)2 (kg/m3)3

Limestone 2.5 to 2.8 156 to 174.7 2,500 to 2,800

Schist 2.6 to 2.8 162.2 to 174.7 2,600 to 2,800

Rhyolite 2.2 to 2.7 137.2 to 168.5 2,200 to 2,700

Basalt 2.7 to 2.9 168.5 to 181 2,700 to 2,900

Sandstone 2/0 to 2.6 124.8 to 162.2 2,000 to 2,600

Bituminous 1.2 to 1.5 74.9 to 93.6 1,200 to 1,500 coal

1 Grams per cubic centimeter. 2 Pounds per cubic foot. 3 Kilograms per cubic meter. blasting. Explosive energy always seeks the path of least resistance. Where the rock burden is composed of alternate zones of hard material, weak zones, or voids, the explosive energy will be vented through the weak zones and voids resulting in poor fragmentation. Depending on the orientation of zones of weakness with respect to free faces, excessive violence in the form of airblast and flyrock may occur. When the blasthole intersects a void, particular care must be taken in loading the charge, or the void will be loaded with a heavy concentration of explosive resulting in excessive air-blast and flyrock.

212 BLAST DESIGN

If these voids and zones of weakness can be identified and logged, steps can be taken during borehole loading to improve fragmentation and avoid violence. The best tool for this is a good drill log. The depths of voids and zones of weakness encountered by the drill should be documented. The geologist can help by plotting the trends of “mud” seams and shears. When charging the blasthole, inert stemming materials rather than explosives should be loaded through these weak zones. Voids should be filled with stemming. Where this is impractical because of the size of the void, it may be necessary to block the hole just above the void before continuing the explosive column.

If the condition of the borehole is in doubt, the top of the powder column should be checked frequently as loading proceeds. A void probably exists if the column fails to rise as expected. At this point, a deck of inert stemming material should be loaded before powder loading continues. If the column rises more rapidly than expected, frequent checking will ensure that adequate space is left for stemming.

Alternate zones of hard and soft rock usually result in unacceptably blocky fragmentation. A higher powder factor seldom will correct this problem; it will merely cause the blocks to be displaced farther. Usually, the best way to al- leviate this situation is to use smaller blastholes with smaller blast pattern dimensions to get a better powder distribution. The explosive charges should be concentrated in the hard rock.

Jointing

Jointing can have a pronounced effect on both fragmentation and the stability of the perimeter of the excavation. Close jointing usually results in good fragmentation.

213 FIELD MANUAL

Widely spaced jointing, especially where the jointing is pronounced, often results in a very blocky muckpile because the joint planes tend to isolate large blocks in place. Where the fragmentation is unacceptable, the best solution is to use smaller blast holes with smaller blast pattern dimensions. This extra drilling and blasting expense will be more than justified by the savings in loading, hauling, and crushing costs and the savings in secondary blasting.

Where possible, the perimeter holes of a blast should be aligned with the principal joint sets. This produces a more stable excavation, whereas rows of holes perpendicular to a primary joint set produces a more ragged, unstable perimeter (figure 19-1). The jointing will generally determine how the corners at the back of the blast will break out. To minimize backbreak and flyrock, tight corners, as shown in figure 19-2, should be avoided.

Figure 19-1.—Effect of jointing on the stability of an excavation (plan view).

214 BLAST DESIGN

Figure 19-2.—Tight and open corners caused by jointing (plan view).

The open corner at the left of figure 19-2 is preferable. Given the dominant jointing in figure 19-2, more stable conditions will result if the first blast is opened at the far right and designed so that the hole in the rear inside corner contains the highest numbered delay.

Bedding/Foliation

Bedding has a pronounced effect on both the fragmentation and the stability of the excavation perimeter. Open bedding planes, open joints, or beds of weaker materials should be treated as zones of weakness. Stemming, rather than explosive, should be loaded into the borehole at the location of these zones as shown in figure 19-3. In a bed of hard material (greater than 3 feet [1 m] thick), it is often beneficial to load an explosive of higher density than is used in the remainder of the borehole. To break an isolated bed or zone of hard rock (3 feet [1 m] thick or greater) near the collar of the blasthole, a deck charge is recommended, as shown in figure 19-4, with the deck being fired on the same delay as the main charge or one delay later. Occasionally, satellite holes are used to help break a hard zone in the upper part of the burden. Satellite holes (figure 19-4) are short holes, usually smaller in diameter than the main blastholes drilled between the main blastholes.

215 FIELD MANUAL

Figure 19-3.—Stemming through weak material and open beds.

216 BLAST DESIGN

Figure 19-4.—Two methods of breaking a hard collar zone.

A pronounced foliation, bedding plane, or joint is frequently a convenient location for the bench floor. It not only gives a smoother floor but also may reduce subdrilling requirements.

Dipping beds frequently cause stability problems and difficulty in breaking the toe of the excavation. When bedding or foliation dip into the excavation wall, the stability of the slope is enhanced. When the dip is out of the wall, slip planes exist that increase the likelihood of slope deterioration or failure. Blasthole cutoffs (part of a column of explosives not fired) caused by differential bed movement are also more likely. Beds dipping out of the final slope should be avoided wherever possible.

Although beds dipping into the face improve slope stability, the beds can create toe problems because the toe rock tends to break along the bedding or foliation planes.

217 FIELD MANUAL

Dipping beds such as these require a tradeoff, depending upon which is the more serious problem—a somewhat unstable slope or an uneven toe. In some cases, advancing the opening perpendicular to dipping beds may be a compromise.

Many blasting jobs encounter site-specific geologic conditions not covered in this general discussion. Good blasting techniques require constant study of the geology to make every effort to advantageously use the geology, or at least minimize its unfavorable effects in blast designs.

Surface Blasting

Blast Hole Diameter

The blast hole size is the first consideration of any blast design. The blast hole diameter, along with the type of explosive being used and the type of rock being blasted, determines the burden (distance from the blast hole to the nearest free face). All other blast dimensions are a function of the burden. This discussion assumes that the blaster has the freedom to select the borehole size. Many operations limit borehole size based on available drilling equipment.

Practical blasthole diameters for surface construction excavations range from 3 (75 mm) to approximately 15 inches (38 cm). Large blasthole diameters generally yield low drilling and blasting costs because large holes are cheaper to drill per unit volume, and less sensitive, cheaper blasting agents can be used in larger diameter holes. Larger diameter blastholes also allow large burdens and spacings and can give coarser fragmentation. Figure 19-5 illustrates this comparison using 2- (50-mm) and 20-inch (500-mm)-diameter blastholes as an example.

218 BLAST DESIGN

Figure 19-5.—The effect of large and small blast holes on unit costs.

Pattern A contains four 20-inch (500-mm) blast boles, and pattern B contains 400 2-inch (5-mm) blast holes. In all bench blasting operations, some compromise between these two extremes is chosen. Each pattern represents the same area of excavation—15,000 square feet (1,400 m2)—each involves approximately the same volume of blast holes, and each can be loaded with about the same weight of explosive.

As a general rule, large diameter blast holes (6 to 15 inches [15 to 38 cm]) have limited applications on most construction projects because of the requirements for fine fragmentation and the use of relatively shallow cuts. However, borehole size depends primarily on local conditions. Large holes are most efficient in deep cuts where a free face has already been developed.

219 FIELD MANUAL

In most construction projects, small diameter drilling with high-speed equipment provides relatively low unit costs and permits fairly close spacing of holes. This close spacing provides better distribution of explosives throughout the rock mass, which in turn produces better breakage. An additional advantage of small diameter blast holes is that the reduction in the amount of each explosive used in each hole reduces ground vibrations. Construction blast hole diameters usually vary from 3.5 to 4.5 inches (90 to 114 mm), and the normal drilling depth is less than 40 feet (12 m). Reclamation generally limits blast hole diameters for structural excavation drilling to 3.5 inches (90 mm). Blasting patterns usually range from 6 by 8 feet (1.8 by 2.4 meters) to 8 by 15 feet (2.4 by 4.6 m) and are usually rectangular with the burden being less than the spacing.

In a given rock type, a four-hole pattern will give relatively low drilling and blasting costs. Drilling costs for large blastholes will be low, a low-cost blasting agent will be used, and the cost of detonators will be minimal. In a difficult blasting situation, the broken material will be blocky and nonuniform in size, resulting in higher loading, hauling, and crushing costs as well as requiring more secondary breakage. Insufficient breakage at the toe may also result.

The 400-hole pattern will yield high drilling and blasting costs. Small holes cost more to drill per unit volume, powder for small diameter blastholes is usually more expensive, and the cost of detonators will be higher. The fragmentation will be finer and more uniform, resulting in lower loading, hauling, and crushing costs. Secondary blasting and toe problems will be minimized. Size of equipment, subsequent processing required for the blasted material, and economics will dictate the type of fragmentation needed and the size of blast hole to be used.

220 BLAST DESIGN

Geologic structure is a major factor in determining the blast hole diameter. Planes of weakness (i.e., joints, shears, or zones of soft rock) tend to isolate large blocks of rock in the burden. The larger the blast pattern, the more likely these blocks are to be thrown unbroken into the muckpile. Note that in the top pattern in figure 19-6, some of the blocks are not penetrated by a blast hole. In the smaller bottom pattern, all the blocks contain at least one blast hole. Because of the better explosives distribution, the bottom pattern will give better fragmentation.

Figure 19-6.—The effects of jointing on selection of blast hole size.

221 FIELD MANUAL

Airblast and flyrock often occur because of an insufficient collar distance (stemming column) above the explosive charge. As the blast hole diameter increases, the collar distance required to prevent violence increases. The ratio of collar distance to blast hole diameter required to prevent violence varies from 14:1 to 28:1, depending on the relative densities and velocities of the explosive and rock, the physical condition of the rock, the type of stemming used, and the point of initiation. A larger collar distance is required where the sonic velocity of the rock exceeds the detonation velocity of the explosive or where the rock is heavily fractured or low density. A top- initiated charge requires a larger collar distance than a bottom-initiated charge. As the collar distance increases, the powder distribution becomes poorer, resulting in poorer fragmentation of the rock in the upper part of the bench.

Ground vibrations are controlled by reducing the weight of explosive fired per delay interval. This is done more easily with small blast holes than with large blast holes. In many situations where large diameter blast holes are used near populated areas, several delays, along with decking, must be used within each hole to control vibrations.

Large holes with large blast patterns are best suited to an operation with: (1) a large volume of material to be moved, (2) large loading, hauling, and crushing equipment, (3) no requirement for fine, uniform fragmentation, (4) an easily broken toe, (5) few ground vibration or airblast problems (few nearby buildings), and (6) a relatively homogeneous, easily fragmented rock without many planes of weakness or voids. Many blasting jobs have constraints that require smaller blast holes.

222 BLAST DESIGN

The final selection of blast hole size is based on economics. Savings realized through inappropriate cost cutting in the drilling and blasting program may well be lost through increased loading, hauling, or crushing costs.

Blast Patterns

The three drill patterns commonly used are square, rectangular, and staggered. The square drill pattern (figure 19-7) has equal burdens and spacing, and the rectangular pattern has a larger spacing than burden. In both the square and rectangular patterns, the holes of each row are lined up directly behind the holes in the preceding row. In the staggered pattern (figure 19-8), the holes in each are positioned in the middle of the spacings of the holes in the preceding row. In the staggered pattern, the spacings should be larger than the burden.

Figure 19-7.—Three basic types of drill patterns.

Square or rectangular drilling patterns are used for firing V-cut (figure 19-9) or echelon rounds. The burdens and subsequent rock displacement are at an angle to the original free face either side of the blast round in V-cut or echelon patterns. The staggered drilling pattern is used for row-on-row firing where the holes of one row are fired before the holes in the row immediately behind them as shown in figure 19-9. Looking at figure 19-9, with the burdens developed at a 45-degree angle to the original

223 FIELD MANUAL

Figure 19-8.—Corner cut staggered pattern with simultaneous initiation within rows (blast hole spacing, S, is twice the burden, B).

Figure 19-9.—V-Echelon blast round (true spacing, S, is twice the true burden, B).

224 BLAST DESIGN free face, the original square drilling pattern has been transformed to a staggered blasting pattern with a spacing twice the burden. The three simple patterns discussed here account for nearly all the surface blasting.

Burden

Figure 19-10 is an isometric view showing the relationship of the various dimensions of a bench blast. The burden is defined as the distance from a blast hole to the nearest free face at the instant of detonation. In multiple row blasts, the burden for a blast hole is not necessarily measured in the direction of the original free face. The free faces developed by blast holes fired on lower delay periods must be taken into account. As an

Figure 19-10.—Isometric view of a bench blast.

225 FIELD MANUAL example, in figure 19-8, where one entire row is blasted before the next row begins, the burden is measured perpendicular between rows.

In figure 19-9, the blast progresses in a V-shape. The true burden on most of the holes is measured at an angle of 45 degrees from the original free face.

It is very important that the proper burden be calculated, accounting for the blast hole diameter, relative density of the rock and explosive, and, to some degree, the depth of the blast hole. An insufficient burden will cause excessive airblast and flyrock. Too large a burden will produce inadequate fragmentation, toe problems, and excessive ground vibrations. If it is necessary to drill a round before the previous round has been excavated, it is important to stake out the first row of the second round before the first round is fired. This will ensure a proper burden on the first row of blast holes in the second blast round.

For bulk-loaded charges (the charge is poured down the hole), the charge diameter is equal to the blast hole diameter. For tamped cartridges, the charge diameter will be between the cartridge diameter and the blast hole diameter, depending on the degree of tamping. For untamped cartridges, the charge diameter is equal to the cartridge diameter. When blasting with ANFO (ammonium nitrate/fuel oil mixture) or other low density blasting agents with densities near 53 lb/ft3 (0.85 g/cm3), in typical rock with a density near 170 lb/ft3 (2.7 g/cm3, the normal burden is approximately 25 times the charge diameter. When using denser products such as slurries or dynamites with densities near 75 lb/ft3 (1.2 g/cm3), the normal burden is approximately 30 times the charge diameter. These are first approximations, and field testing usually results in adjustments to these values.

226 BLAST DESIGN

The burden-to-charge-diameter ratio is seldom less than 20 or seldom more than 40, even in extreme cases. For instance, when blasting with a low density blasting agent such as ANFO in a dense formation such as basalt, the desired burden may be about 20 times the charge diameter. When blasting with denser slurries or dynamites in low density formations such as sandstones, the burden may approach 40 times the charge diameter. Table 19-2 summarizes these approximations.

Table 19-2.—Approximate burden charge diameter ratios for bench blasting

Material Ratio

ANFO (density 53.1 lb/ft3, 0.85 g/cm3) Light rock (density ~ 137.3 lb/ft3, 2.2 g/cm3) 28 Average rock (density ~ 168.6 lb/ft3, 2.7 g/cm3) 25 Dense rock (density ~ 199.8 lb/ft3, 3.2 g/cm3) 23

Slurry, dynamite (density ~ 199.7 lb/ft3, 3.2 g/cm3) Light rock (density ~ 137.3 lb/ft3, 2.2 g/cm3,) 33 Average rock (density ~ 168.6 lb/ft3, 2.7 g/cm3) 30 Dense rock (density ~ 199.8 lb/ft3, 3.2 g/cm3) 27

High-speed photographs of blasts show that flexing of the burden plays an important role in rock fragmentation. A relatively deep, narrow burden flexes and breaks more easily than a shallow, wider burden. Figure 19-11 shows the difference between using a 6-inch (150-mm) blast hole and a 12.25-inch (310-mm) blast hole in a 40-foot (12-m) bench with a burden-to-charge-diameter ratio of 30 and appropriate subdrilling and stemming dimensions. Note the inherent stiffness of the burden with a 12.25-inch (310-mm) blast hole as compared to a 6-inch (150-mm)

227 FIELD MANUAL

Figure 19-11.—Comparison of a 12¼-inch- (300-mm) diameter blast hole (stiff burden) on the left with a 6-inch- (150-mm) diameter blast hole (flexible burden) on the right in a 40-foot (12-m) bench. blast hole. Based on this, lower burden-to-charge- diameter ratios should be used as a first approximation when the blast hole diameter is large in comparison to the bench height. Care must be taken that the burden ratio is not so small as to create violence. Once the ratio has been determined, it becomes the basis for calculating subdrilling, collar distance (stemming), and spacing.

Subdrilling

Subdrilling is the distance drilled below the floor level to ensure that the full face of rock is removed. Where there is a pronounced parting at floor level for the explosive charge to conveniently break, subdrilling may not be required. In coal strip mining, it is common practice to

228 BLAST DESIGN drill down to the coal and then backfill a foot or two before loading explosives, resulting in a negative subdrill. In most surface blasting jobs, some subdrilling is necessary to make sure the shot pulls to grade. In most construction blasting, subdrilling is generally limited to 10 percent or less of the bench height. In blasting for civil engineering structures where a final grade is specified, subdrilling of the final lift is severely restricted. The final lift in structural excavations is usually limited to 5 or 10 feet (1.5 to 3 m). Subdrilling is not allowed in a 5-foot (1.5-m) lift and is limited to 2 feet (0.6 m) for the 10-foot (3-m) lift. To prevent damage to the foundation, the diameter of the blast hole is limited to 3.5 inches (90 mm).

Priming the explosive column at the toe level (bottom of the drill hole) gives maximum confinement and normally gives the best breakage. Toe priming usually requires less subdrilling than collar priming. Toe priming should be restricted in structural foundations because of the potential damage to the unshot rock.

Excessive subdrilling is unnecessary, expensive, and may cause excessive ground vibrations because of the high degree of confinement of the explosive in the bottom of the blast hole, particularly when the primer is placed in the bottom of the hole. In multiple-bench operations, excessive subdrilling may cause undue fracturing in the upper portion of the bench below, creating difficulties in collaring holes in the lower bench. Insufficient subdrilling causes a high bottom, resulting in increased wear and tear on equipment and expensive secondary blasting or hand excavation in structural foundations.

Collar Distance (Stemming)

Collar distance is the distance from the top of the explosive charge to the collar of the blast hole. This zone

229 FIELD MANUAL usually is filled with an inert material called stemming to give some confinement to the explosive gases and to reduce airblast. A well-graded, crushed gravel works best as stemming, but it is common practice to use drill cuttings because of availability and economics. Collar distances that are too short result in excessive violence in the form of airblast and flyrock and may cause backbreak (breaking beyond the back wall). Collar distances that are too long create large blocks in the upper part of the muck pile. The selection of a collar distance is often a tradeoff between fragmentation and the amount of airblast and flyrock that can be tolerated. This is true especially where the upper part of the bench contains rock that is difficult to break or is of a different type. The difference between a violent blast and one that fails to fragment the upper zone properly may be a matter of only a few feet of stemming. Collar or direct priming (placing the primer at or near the collar of the blast hole with the blasting cap pointing toward the bottom of the hole) of blast holes normally causes more violence than center or toe priming and requires the use of a longer collar distance.

Field experience has shown that a collar distance equal to 70 percent of the burden is a good first approximation. Careful observation of airblast, flyrock, and fragmentation will enable further refinement of this dimension. Where adequate fragmentation in the collar zone cannot be attained while still controlling airblast and flyrock, deck charges or satellite (mid-spaced) holes may be required (figure19-4).

A deck charge is an explosive charge near the top of the blast hole, separated from the main charge by inert stemming. If large blocky materials are being created in the collar zone and less stemming would cause excessive airblast or flyrock, the main charge should be reduced

230 BLAST DESIGN slightly and a deck charge added. The deck charge is usually shot on the same delay as the main charge or one delay later. Do not place the deck charge too near the top of the blast hole, or excessive flyrock may result. Alternatively, short satellite holes between the main blast holes can be used. The diameter of the satellite holes is usually smaller than the main blast holes, and the satellite holes are loaded with a light charge of explosives.

Collar distance is a very important blast design variable. One violent blast can permanently alienate neighbors. In a delicate situation, it may be best to start with a collar distance equal to the burden and gradually reduce this if, conditions warrant. Collar distances greater than the burden are seldom necessary.

Spacing

Spacing is defined as the distance between adjacent blast holes, measured perpendicular to the burden. Where the rows are blasted one after the other as in figure 19-8, the spacing is measured between holes in a row. Where the blast progresses at an angle to the original free face, as in figure 19-9, the spacing is measured at an angle from the original free face.

Spacing is calculated as a function of the burden and also depends on the timing between holes. Spacing that is too close causes crushing and cratering between holes, large blocks in the burden, and toe problems. Spacing that is too wide causes inadequate fracturing between holes, toe problems, and is accompanied by humps on the face (figure 19-12).

When the holes in a row are initiated on the same delay period, a spacing equal to twice the burden usually will pull the round satisfactorily. The V-cut round in

231 FIELD MANUAL

Figure 19-12.—Effects of too small and too large spacing. figure 19-9 illustrates simultaneous initiation within a row, with the rows being the angled lines of holes fired on the same delay. The true spacing is twice the true burden, even though the holes originally were drilled on a square pattern.

Field experience has shown that the use of millisecond (ms) delays between holes in a row results in better fragmentation and also reduces ground vibrations produced by the blast. When ms delays are used between holes in a row, the spacing-to-burden ratio must be

232 BLAST DESIGN reduced to somewhere between 1.2 and 1.8, with 1.5 being a good first approximation. Various delay patterns may be used within the rows, including alternate delays (figure 19-13) and progressive delays (figure 19-14). Generally, large diameter blast holes require lower spacing-to-burden ratios (usually 1.2 to 1.5 with ms delays) than small diameter blast holes (usually 1.5 to 1.8). Because of the geology complexities, the interaction of delays, differences in explosive and rock strengths, and other variables, the proper spacing-to-burden ratio must be determined through onsite experimentation, using the preceding values as first approximations.

Except when using controlled blasting techniques such as smooth blasting and cushion blasting, described later, the spacing should never be less than the burden.

Hole Depth

In any blast design, the burden and the blast hole depth (or bench height) must be reasonably compatible. The rule of thumb for bench blasting is that the hole depth-to- burden ratio should be between 1.5 and 4.0. Hole depths

Figure 19-13.—Staggered blast pattern with alternate delays (blast hole spacing, S, is 1.4 times the burden, B).

233 FIELD MANUAL

Figure 19-14.—Staggered blast pattern with progressive delays (blast hole spacing, S, is 1.4 times the burden, B). less than 1.5 times the burden cause excessive air blast and fly rock and, because of the short, thick shape of the burden, give coarse and uneven fragmentation. Where operational conditions require a ratio of less than 1.5, a primer should be placed at the toe of the bench to assure maximum confinement. Keep in mind that placing the primer in the subdrill can cause increased ground vibrations and unacceptably irregular final grades for engineering structures. If the use of a hole depth-to- burden ratio of less than 1.5 is necessary or specified, consideration should be given to increasing the bench height or using smaller drill hole diameters.

Hole depths greater than four times the burden are also undesirable. The longer a hole is with respect to its diameter, the more error there will be in the hole location at toe level (hole wandering), the most critical portion of the blast. A poorly controlled blast will result. Extremely long, slender holes have been known to intersect.

High benches with short burdens can also create safety hazards, such as small equipment having to drill the front

234 BLAST DESIGN row of holes near the edge of a high ledge or a small shovel having to dig at the toe of a precariously high face. The obvious solution to this problem is to use a lower bench height. There is no real advantage to a high bench. Lower benches yield more efficient blasting results, lower drilling costs, less chance of cutoffs, and are safer. If it is impractical to reduce the bench height, larger rock handling and drilling equipment should be used, effectively reducing the blast hole depth-to-burden ratio.

A major problem with long slender charges is the greater potential for cutoffs in the explosive column. If it is necessary to use blast designs with large hole depth-to- burden ratios, multiple priming should be used as insurance against cutoffs.

Delays

Millisecond delays are used between charges in a blast round to:

• To ensure that a proper free face is developed to enable the explosive charge to efficiently fragment and displace the rock

• To enhance fragmentation between adjacent holes

• To reduce the ground vibrations created by the blast

Numerous delay patterns exist, several of which are covered in figures 19-8, 19-9, 19-13, and 19-14. Keep in mind the following:

• The delay time between holes in a row should be between 1 and 5 ms per foot (0.3 m) of burden. Delay times less than 1 ms per foot of burden cause premature shearing between holes, resulting in

235 FIELD MANUAL

coarse fragmentation. If an excessive delay time is used between holes, rock movement from the first hole prevents the adjacent hole from creating additional fractures between the two holes. A delay of 3 ms per foot (0.3 m) of burden gives good results in many types of rock.

• The delay time between rows should be two to three times the delay time between holes in a row. To obtain good fragmentation and to control fly rock, a sufficient delay is needed so that the burden from previously fired holes has enough time to move forward to accommodate moving rock from subsequent rows. If the delay between rows is too short, movement in the back rows will be upward rather than outward (figure19-15).

• Where airblast is a problem, the delay between holes in a row should be at least 2 ms per foot of spacing. This prevents airblast from one charge from adding to that of subsequent charges as the blast proceeds down the row.

• For controlling ground vibrations, most regulatory authorities consider two charges to be separate events if they are separated by a delay of 9 ms or more.

These rules-of-thumb generally yield good blasting results. When using surface delay systems such as detonating cord connectors and sequential timers, the chances for cutoffs will be increased. To solve this problem, in- hole delays should be used in addition to the surface delays. When using surface detonating cord connectors, the use of 100-ms delays in each hole is suggested. This will cause ignition of the in-hole delays well in advance of

236 BLAST DESIGN

Figure 19-15.—The effect of inadequate delays between rows.

rock movement, thus minimizing cutoffs. The same effect can be accomplished with a sequential timer by avoiding the use of electric caps with delays shorter than 75 to 100 ms.

It is best if all the explosive in a blast hole is fired as a single column charge. When firing large blast holes in populated areas, two or more delays within a blast hole can be used to reduce ground vibrations. Blast rounds of this type can become quite complex.

All currently used delay detonators employ pyrotechnic delay elements that depend on a burning powder train for their delay. Although these delays are reasonably accurate, overlaps have been known to occur. When it is essential that one charge fires before an adjacent charge, such as in a tight corner of a blast, it is a good idea to skip a delay period.

Powder Factor

Powder factor, or pounds of explosive per cubic yard (kg/m3) of rock, is not the best tool for designing blasts.

237 FIELD MANUAL

Blast designs should be based on the dimensions discussed earlier in this chapter. Powder factor is a necessary calculation for cost accounting purposes. In construction blasting where the excavated material has little or no inherent value, powder factor is usually expressed in pounds of explosives per cubic yard of material broken. Powder factors for surface blasting can vary from 0.25 to 2.5 pounds per cubic yards (lb/yd3 [0.1 to 1.1 kg/m3]), with 0.5 to 1.0 lb/yd3 (0.2 to 0.45 kg/m3) being most typical.

Powder factor for a single blast hole is calculated by the following: LdD()0340. ()2 PF..= 27BSH

P.F. = Powder factor in pounds of explosive per cubic yard of rock L = Length of explosive charge in feet d = Density of explosive charge in grams per cubic centimeter D = Charge diameter in inches B = Burden in feet S = Spacing in feet H = Bench height

A comparable formula can be developed for metric equivalents. Many companies that provide explosives also publish tables that give loading densities in pounds per foot of blast hole for different combinations of d and D. A common nomograph found in most blasting handbooks can be used to calculate the density in pounds per foot of borehole. The powder factor is a function of the explosive type, rock density, and geologic structure. Table 19-3 includes typical powder factors for surface blasting.

238 BLAST DESIGN

Table 19-3.—Typical powder factors for surface blasting

Powder factor Rock breakage difficulty (lb/yd3) (kg/m3)

Low 0.25-0.40 0.1-0.18

Medium 0.40- 0.75 0.18-0.34

High 0.75-1.25 0.34-0.57

Very high 1.25-2.50 0.57-1.14

Higher energy explosives, such as those containing large amounts of aluminum, can break more rock per unit weight than lower energy explosives. Most of the commonly (lower energy) used explosive products have similar energy values and, thus, have similar rock breaking capabilities. Soft, low density rock requires less explosive than hard, dense rock. Large hole patterns require less explosive per volume of rock because a larger portion of stemming is used. Poor powder distribution in larger diameter blast holes frequently results in coarser fragmentation. Massive rock with few existing planes of weakness requires a higher powder factor than a rock unit with numerous, closely spaced joints or fractures. The more free faces a blast has to break to, the lower the powder factor requirement. A corner cut (figure19-8), with two vertical free faces, requires less powder than a box cut (figure19-9) or angled cuts (figure19-16) with only one vertical free face, which, in turn, will require less powder than a shaft sinking type or parallel cut (figure19-16) where there are no free faces. In a shaft sinking cut, it is desirable to open a second free face by

239 FIELD MANUAL

Figure 19-16.—Types of opening cuts. creating a V-cut somewhere near the center of the round. V-cuts are discussed in the “Underground Blasting” section of this chapter.

When blasted materials have an inherent value per ton, such as aggregate or ore, powder factors are expressed as unit weight of explosives per ton of rock or tons of rock per unit weight of explosive.

240 BLAST DESIGN

Secondary Blasting

Some primary blasts will result in fragments too large to be handled efficiently by the loading equipment and will cause plugging of crushers or preparation plants. Secondary fragmentation techniques must be used to break these oversize fragments. If fragments are too large to be handled, the loader operator will set the rock aside for treatment. Identifying material large enough to cause crusher plugging is not always easy. The loader operator must be knowledgeable enough to watch for material that is small enough for convenient loading but that is too large for the crusher.

Secondary fragmentation can be accomplished by:

• A heavy ball (headache ball) suspended from a crane may be dropped repeatedly on the oversize fragment until it breaks. This is a relatively inefficient method, and breaking a large or tough (nonbrittle) rock may take considerable time. This method is adequate where the number of oversize fragments is small.

• A hole may be drilled into the oversize fragment and a hydraulic wedging device inserted to split the rock. This is also a slow method but may be satisfactory where a limited amount of secondary fragmentation is necessary. An advantage to this method is that it does not create the flyrock associated with explosives and, to some degree, with the headache ball method.

• An explosive may be packed loosely into a crack or depression in the oversize fragment then covered with a damp earth material and fired. This type of charge is called a mudcap, plaster, or adobe charge. This method is inefficient because of the limited

241 FIELD MANUAL

explosive confinement and the relatively large amount of explosives required. Other results are excessive noise, flyrock, and often, inadequate fragmentation. This method is also hazardous because the primed charge lying on the surface is prone to accidental initiation by external impacts from falling rocks or equipment. External charges should be used to break boulders only where drilling is impractical.

• The most efficient method of secondary fragmentation is through the use of small (1- to 3-inch [25- to 75-mm]) blast holes. The blast hole is normally collared at the most convenient location, such as a crack or depression in the rock, and is directed toward the center of the mass. The hole is drilled two-thirds to three-fourths of the way through the rock. Because the powder charge is surrounded by free faces, less explosive is required to break a given amount of rock than in primary blasting. One- quarter pound per cubic yard (0.1 kg/m3) usually is adequate. Careful location of the charge is more important than its precise size. When in doubt, it is best to estimate on the low side and under load the hole. For larger fragments, it is best to drill several holes and distribute the explosive charge rather than place the entire charge in a single hole. All secondary blast holes should be stemmed. Usually, secondary blasts are more violent than primary blasts. Any type of initiation system may be used to initiate a secondary blast and for connecting large numbers of oversize fragments. Detonating cord often is used where noise is not a problem.

Although secondary blasting employs relatively small charges, the potential safety hazards must not be under-

242 BLAST DESIGN estimated. Usually, there is more flyrock, and the flyrock is less predictable than with primary blasting.

Underground Blasting

Underground blast rounds are divided into two basic categories:

(1) Heading, drift, or tunnel rounds, where the only free face is the surface from which the holes are drilled

(2) Bench or stope rounds, where there is one or more free faces in addition to the face where the blast holes are drilled.

In the second category, blast rounds are designed in the same manner as surface blast rounds. Only the blast rounds that are in the first category (those with only one initial free face) are discussed below.

Opening Cuts

The initial and most critical part of a heading round is the opening cut. The essential function of this cut is to provide additional free faces where the rock can be broken. Although there are many specific types of opening cuts and the terminology can be quite confusing, all opening cuts fall into one of two classifications—angled cuts or parallel hole cuts (figure 19-16).

An angled cut, also referred to as a V-cut, draw cut, slab cut, or pyramid cut, breaks out a wedge of rock to create an opening that the remaining burden can move into. Angled cuts are very difficult to drill accurately. The bottoms of each pair of cut holes should be as close

243 FIELD MANUAL together as possible but must not cross. If they cross, the depth of round pulled will be less than designed. If the hole bottoms are more than a foot or so apart, the round may not pull to the proper depth. The angle between the cut holes should be 60 degrees or more to minimize bootlegging. One method to ensure getting a standard angle cut is to supply the drillers with a template with the proper spacing and angles for the angled holes. The selection of the specific type of angled cut is a function of the rock, the type of drilling equipment, and the philosophy of the blasting supervisor. A considerable amount of trial and error usually is involved in determining the best angle cut for a specific site. In small diameter tunnels with narrow headings, it is often impossible to position the drill properly to drill an angled cut. In this case, a parallel hole cut must be used.

Parallel hole cuts, also referred to as Michigan cuts, Cornish cuts, shatter cuts, burn cuts, or Coromant cuts, are basically a series of closely spaced holes, some loaded and some unloaded (figure 19-17) that, when fired, pulverize and eject a cylinder of rock to create an opening where the remaining burden can be broken. Because they require higher powder factors and more drilling per volume of rock blasted, the use of parallel hole cuts usually is restricted to narrow headings where there is not enough room to drill an angled cut.

Parallel hole cuts involve more drilling than angled cuts because the closely spaced holes break relatively small volumes of rock. Parallel cuts are relatively easy to drill because the holes are parallel. Like angled cuts, accurately drilled parallel hole cuts are essential if the blast round is to be effective. Some drill jumbos have automatic controls to ensure that holes are drilled parallel. Drill jumbos of this type are a good investment where parallel hole cuts will be drilled routinely. A template also may

244 BLAST DESIGN

Figure 19-17.—Six designs for parallel hole cuts. be used in drilling a parallel hole cut. The selection of the type of parallel hole cut also depends on the rock, the type of drilling equipment, and the philosophy of the blasting supervisor. As with angled cuts, trial and error usually is involved in determining the best parallel hole cut for a specific site.

All types of opening cuts must pull to the planned depth because the remainder of the round will not pull more deeply than the opening cut. In blasting with burn cuts, care must be exercised to prevent overloading of the burn holes because overloading may cause the cut to “freeze” or not pull properly. The design of the cut depends on the type of rock and often must be designed and refined by trial and error.

245 FIELD MANUAL

The advantage of a large central hole is that the hole gives a dependable free face where succeeding holes can break. This free face is not always obtained with standard burn cuts. The large central hole ensures a more dependable and deeper pull of the blast round. The disadvantages of a large central hole are the requirements for the proper equipment to drill the large central hole as well as extra time. Intermediate-sized holes, usually 4 to 5 inches (100-130 mm) in diameter, are sometimes drilled using the standard blast hole equipment as a compromise.

In some soft materials, particularly coal, the blasted cut is replaced by a sawed kerf, usually at floor level (figure 19-18). In addition to giving the material a dependable void to break into, the sawed cut ensures that the floor of the opening will be smooth.

Blasting Rounds

Once the opening cut has established the necessary free face, the remainder of the blast holes must be designed so that the burden successively breaks into the void space. The progression of the blast round should provide a proper free face parallel or nearly parallel to the hole at its time of initiation. Figure 19-19 gives the typical nomenclature for blast holes in a heading round.

The holes fired immediately after the cut holes are called the relievers. The burden between these holes must be planned carefully. If the burden is too small, the charges will not pull their share of the round. If the burden is too large, the round may freeze because the rock will have insufficient space to expand. After several relievers have been fired, the opening usually is large enough to permit the remainder of the blast to be designed, as discussed under “Surface Blasting.” Where heading rounds are large, the burden and spacing ratio usually is slightly less

246 BLAST DESIGN

Figure 19-18.—Blast round for soft rock using sawed kerf (numbers on loaded holes show delay in milliseconds.) than that for surface blasts. In small headings where space is limited, the burden and spacing ratio will be still smaller. Trial and error plays an important part in this type of blast design.

The last holes to be fired in an underground round are the back holes at the top, the rib holes at the sides, and the lifters at the bottom of the heading. Unless controlled blasting is used (discussed below), the spacing between these perimeter holes is about 20 to 25 blast hole diameters. Figure 19-20 shows two typical angled cut blast rounds. After the initial wedge of rock is extracted by the cut, the angles of the subsequent blast holes are

247 FIELD MANUAL

Figure 19-19.—Nomenclature for blast holes in a heading round.

Figure 19-20.—Angled cut blast rounds.

248 BLAST DESIGN reduced progressively until the perimeter holes are parallel to the heading or looking slightly outward. In designing burden and spacing dimensions for angled cut blast rounds, the location of the bottom of the hole is considered rather than the collar.

Figure 19-21 shows two typical parallel hole cut blast rounds. These rounds are simpler to drill than angled cut rounds. Once the central opening has been established, the round resembles a bench round turned on its side. Figure 19-22 shows a comparison of typical muckpiles obtained from V-cut and burn-cut blast rounds. Burn cuts give more uniform fragmentation and a more compact muckpile than V-cuts. V-cut muckpiles are more spread out and vary in fragmentation. Powder factors and the amount of drilling required are higher for burn cuts.

Figure 19-21.—Parallel hole cut blast rounds.

249 FIELD MANUAL

Figure 19-22.—Fragmentation and shape of muckpile as a function of type of cut.

Delays

Two series of delays are available for underground blasting—millisecond delays, the same as those used in surface blasting; and slow, or tunnel delays. The choice of delay depends on the size of the heading being blasted and on the fragmentation and type of muckpile desired. Slow delays give coarser fragmentation and a more compact muckpile. Millisecond delays give finer fragmentation and a looser muckpile (figure19-23). In small headings where space is limited, particularly when using parallel hole cut rounds, slow delays are necessary to ensure that the rock from each blast hole has time to be ejected before the next hole fires. Where delays intermediate between millisecond delays and slow delays is desired, use millisecond delays and skip delay periods.

250 BLAST DESIGN

Figure 19-23.—Fragmentation and shape of muckpile as a function of delay.

In an underground blast round, the delay pattern must be designed so that at the time of firing each hole has a good free face where the burden can be displaced. Figure 19-24 shows a typical delay pattern for a burn cut blast round in a heading in hard rock. Figure 19-25 shows a delay pattern for a V-cut blast round.

The shape of the muckpile is affected by the order that the delays are fired (figure19-26). If the blast is designed so that the back holes at the roof are fired last, a cascading effect is obtained, resulting in a compact muckpile. If the lifters are fired last, the muckpile will be displaced away from the face.

Powder Factor

As with surface blasting, powder factors for underground blasting vary depending on several things. Powder factors for underground blasting may vary from 1.5 to

251 FIELD MANUAL

Figure 19-24.—Typical burn cut blast round delay pattern (numbers on loaded holes show delay in milliseconds).

Figure 19-25.—Typical V-cut blast round delay pattern (numbers on loaded holes show delay in milliseconds).

252 BLAST DESIGN

Figure 19-26.—Shape of muckpile as a function of firing order.

12 lb/yd3 (0.7 to 5.5 kg/m3). Soft, light weight rock, headings with large cross sections, large blast holes, and angle cut rounds all tend to require lower powder factors than hard, dense rock, small headings, small blast holes, and parallel hole cuts.

Controlled Blasting Techniques

The term, controlled blasting, is used to describe several techniques that limit damage to the rock at the perimeter of the excavation by preventing the force of a blast from continuing into the side walls. Normal blasting propagates cracks into the surrounding rock. These cracks can reduce the stability of the opening. The purpose of controlled blasting is to reduce this perimeter cracking and,

253 FIELD MANUAL thus, increase stability of the final surface. Much of the following discussion on controlled blasting techniques has been determined through years of on-the-job testing and evaluation. The results of controlled blasting are a function of the geology, especially the number and orientation of joint and fracture planes and the quality of the final rock surface that is required.

Line Drilling

Line drilling consists of drilling a row of closely spaced holes along the final excavation limits and not loading the holes with explosive. The line-drilled holes provide a plane of weakness to which the final row of blast holes can break and also reflect a portion of the blast’s shock wave. Line drilling is used mostly in small blasting operations and involves small holes in the range of 2 to 3 inches (50-75 mm) in diameter. Line drilling holes are spaced (center to center) two to four diameters apart but are more closely spaced at the corners. The maximum practical depth to which line drilling can be done is governed by how accurately the alignment of the holes can be held at depth (seldom more than 30 feet [10 m]).

To further protect the final perimeter, the blast holes adjacent to the line drill are spaced more closely and loaded more lightly than the rest of the blast, and deck charges are used as necessary. Best results are obtained in a homogeneous rock with few joints or bedding planes or when the holes are aligned with a major joint plane. Line drilling is sometimes used in conjunction with presplitting where the corners are line drilled and the remainder of the perimeter is presplit.

The use of line drilling is limited to jobs where even a light load of explosives in the perimeter holes would cause unacceptable damage. The results of line drilling are

254 BLAST DESIGN often unpredictable, the cost of drilling is high, and the results depend on the accuracy of the drilling.

Presplitting

Presplitting, sometimes called preshearing, is similar to line drilling except that the holes are drilled slightly farther apart and are loaded very lightly. Presplit holes are fired before any of the adjacent main blast holes. The light explosive charges propagate a crack between the holes. In badly fractured rock, unloaded guide holes may be drilled between the loaded holes. The light powder load may be obtained by using specially designed slender cartridges, partial or whole cartridges taped to a detonating cord downline, an explosive cut from a continuous reel, or heavy grain detonating cord. A heavier charge of tamped cartridges is used in the bottom few feet of hole. Figure 19-27 shows three types of blast hole loads used for presplitting. Cartridges ¾ or I inch by 2 feet (19 or 22 mm by 0.6 m) connected with couplers are available. Manufacturers now produce continuous, small diameter, long-tubular water gel columns for loading presplit holes. The diameter of these continuous tubular columns usually is 1 inch (25 mm), and they come with a built-in downline. They can be loaded easily in rough and inclined holes. The continuous column presplit explosives produce increased loading rates and reduced labor costs.

If possible, stem completely around and between the cartridges in the blast hole; and, although not essential, fire in advance of the main blast. The maximum depth for a single presplit is limited by the accuracy of the drillholes and is usually about 50 feet (15 m). Depths between 20 and 40 feet (6 and 12 m) are recommended. A deviation of greater than 6 inches (152 mm) from the desired plane or shear will give inferior results. Avoid presplitting too

255 FIELD MANUAL

Figure 19-27.—Typical presplit blast hole loading. far ahead of the production blast. If possible, presplit a short section and dig that section out so that the quality of the presplit can be checked. If the presplit results are unsatisfactory, adjustments can be made in subsequent blasts.

Presplitting is usually done in a separate operation and well in advance of drilling and loading the main blast. The presplit holes can be fired with the main blast by

256 BLAST DESIGN firing the presplit holes on the first delay period. The increased hole spacing compared with line drilling reduces drilling costs. Table 19-4 gives parameters for presplitting.

Smooth Blasting

Smooth blasting, also called contour blasting, perimeter blasting, or sculpture blasting, is the most widely used method of controlling overbreak in underground openings such as drifts and stopes (benches). Smooth blasting is similar to presplitting in that an additional row of holes is drilled at the perimeter of the excavation. These holes contain light loads and are more closely spaced than the other holes in the round (figure19-28). The light powder load usually is continuously “string loaded” (loaded end to end) with slender cartridges or continuous reel explosive is used as shown in figure 19-27. Unlike presplitting, the smooth blast holes are fired after the main blast. Usually, this is done by loading and connecting the entire round and firing the perimeter holes one delay later than the last hole in the round. The burden on the perimeter holes should be approximately 1.5 times the spacing. Table 19-5 gives parameters for smooth blasting.

A compromise for smooth wall blasting is to slightly reduce the spacing of the perimeter holes, compared to a standard design, and “string load” regular cartridges of explosive. The explosive column should be sealed with a tamping plug, clay plug, or other type of stemming to prevent the string-loaded charges from being extracted from the hole by charges on earlier delays. Smooth blasting reduces overbreak and reduces the need for ground support. These advantages usually outweigh the cost of the additional perimeter holes.

257 FIELD MANUAL 3-0.4646-0.6 0.08-0.256-1.0 0.03-0.1 .08-0.25 0.03-0.1 0.13-0.50 0.05-0.23 Table 19-4.—Parameters for presplitting for 19-4.—Parameters Table Table 19-5.—Parameters for smooth blasting smooth for 19-5.—Parameters Table Hole diameterHole Spacing charge Explosive (inch) (mm) (feet) (m) (lb/ft) (kg/m) 1.50-1.752.00-2.50 38-443.00-3.50 50-64 1.00-1.504.00 75-90 1.50-2.00 0. 1.50-3.00 0. 0. 100 2.00-4.00 0.6-1.2 0.25-0.75 0.23-0.34 Hole diameterHole Spacing Burden charge Explosive (inch) (mm) (feet) (m) (feet) (m) (lb/ft) (kg/m) 1.50-1.75 38-442.0 2.00 0.6 50 3.00 2.50 1 0.75 0.12-0.25 3.50 0.05-0.55 1.06 0.12-0.25 0.05-0.55

258 BLAST DESIGN

Figure 19-28.—Typical smooth blasting pattern (Burden, B, is larger than spacing, S). Numbers on holes show delay in milliseconds.

Cushion Blasting

Cushion blasting, also called trimming, slabbing, or slashing, is the surface equivalent of smooth blasting. Like other controlled blasting techniques, cushion blasting involves a row of closely spaced, lightly loaded holes at the perimeter of the excavation. Holes up to

259 FIELD MANUAL

6½ inches (165 mm) in diameter have been used in cushion blasting. Drilling accuracy with this larger size borehole permits depths of up to 90 feet (27 m) for cushion blasting. After the explosives have been loaded, stemming is placed in the void space around the charges for the entire length of the column. Stemming “cushions” the shock from the finished wall minimizing the stresses and fractures in the finished wall. The cushion blast holes are fired after the main excavation is removed (figure19-29). A minimum delay between the cushion blast holes is

Figure 19-29.—Cushion blasting techniques.

260 BLAST DESIGN desirable. The same loading techniques that apply to presplitting are used with cushion blasting. The burden on the cushion holes should always be less than the width of the berm being removed.

The large diameter holes associated with cushion blasting result in larger spacings as compared with presplitting reducing drilling costs. Better results can be obtained in poorly lithified and weathered formations than with presplitting, and the larger holes permit better alignment at depth. Table 19-6 gives parameters for cushion blasting.

Riprap Blasting Techniques

Riprap blasting follows the usual rules for blast designs. A few special techniques can aid production of quality riprap.

Powder distribution is the key to satisfactory results. If the above principles of good blast design are followed, satisfactory results should be achieved. The blast design must be monitored continually and changed to produce the best results.

Full column loading is usually the best for initial shots. The starting burden for riprap production should be larger than predicted from table 19-1. If a burden of 7 feet (2.1 m) is predicted, a starting burden of approximately 9 feet (2.7 m) should be tried. Further adjustments can be made to optimize the breakage.

In typical quarry blasting, a spacing of 1.5 times the burden is a good first estimate. The spacing should be about equal to the burden but not smaller than the burden for riprap. Either a square or a staggered drill

261 FIELD MANUAL Table 19-6.—Parameters for cushion blasting cushion for 19-6.—Parameters Table Hole diameterHole Spacing Burden charge Explosive (inch) (mm) (feet) (m) (feet) (m) (lb/ft) (kg/m) 2.00-2.503.00-3.50 50-644.00-4.50 75-90 3.00 100-1155.00-5.50 1.0 4.00 127-140 5.006.00-6.50 1.2 4.00 152-165 1.5 6.00 5.00 1.8 7.00 6.00 1.2 2.1 7.00 1.5 0.08-0.25 1.8 0.03-0.1 9.00 0.13-0.5 2.1 0.25-0.75 0.05-0.2 0.1-0.3 2.7 0.75-1.00 0.3-0.45 1.00-1.50 0.45-0.7

262 BLAST DESIGN pattern should be used. The square pattern often gives a coarser product but also may give more erratic toe conditions. Where possible, rows of blast holes should be perpendicular to the major vertical plane of weakness such as the primary vertical joint set.

If a reasonably well graded riprap is specified, it will be necessary to perform test or trial blasts. The product should be analyzed for gradation, and further test blasts made and gradations checked until the specifications have been met. If insufficient coarse product is produced, the burden and spacing of subsequent rounds should be increased by 1 foot (0.3 m) per round until the amount of coarse product is adequate. If toe problems occur before the amount of coarse product is adequate, reduce the burden and spacing again and increase the stemming or try deck loading in the upper part of the lift.

If too much coarse product is produced, determine whether the material comes from the top or bottom part of the bench face. If the material comes from the bottom or is generally well-distributed, decrease the burden and spacing in 1-foot (0.3-m) increments until the oversize is controlled. If the oversize comes from the top, try using satellite holes (short, smaller diameter holes between the main blast holes, figure19-4) or less stemming.

It is essential that each blast be laid out accurately and drilled and loaded so that there is a known baseline to adjust from if early results are not good. Keeping good records is essential for later adjustments to the blast design. Single row firing, at least for the early shots, also simplifies blast pattern adjustments.

In dry conditions, ANFO will work well. A good, fast, bottom primer should be used. In wet conditions, an emulsion, water gel, slurry, or gelatin dynamite should be

263 FIELD MANUAL used. The bottom of the blast hole should be primed. Excessive orange smoke from a blast indicates the need for a water resistant product or for a better proportional mix of the ANFO.

Bibliography

Dick, R.A., L.R. Fletcher, and D.V. Andrea, Explosives and Blasting Procedures Manual. Bureau of Mines Information Circular 8925, pp. 57-74, 1987.

E. I. du Pont de Nemours & Co., Inc., Blaster’s Handbook. 16th edition, pp. 494, Wilmington, Delaware, 1978.

Glossary

Acoustical impedance - The mathematical expression characterizing a material energy transfer property. The product of a material unit density and sonic velocity.

Adobe charge - See mud cap.

Airblast - An airborne shock wave resulting from the detonation of explosives; may be caused by burden movement or the release of expanding gas into the air. Airblast may or may not be audible.

Airdox - System that uses 10,000 lb/in2 compressed air to break undercut coal. Airdox will not ignite a gassy or dusty atmosphere.

264 BLAST DESIGN

Aluminum - A metal commonly used as a fuel or sen- sitizing agent in explosives and blasting agents; normally used in finely divided particle or flake form.

American Table of Distance - A quantity-distance table published by the Institute of Makers of Explosives (IME) as pamphlet No. 2, which specifies safe explosive storage distances from inhabited buildings, public highways, passenger railways, and other stored explosive materials.

Ammonium nitrate (AN) - The most commonly used

oxidizer in explosives and blasting agents, NH4NO3.

ANFO - An explosive material consisting of a mixture of ammonium nitrate and fuel oil. The most commonly used blasting agent.

ATF - Bureau of Alcohol, Tobacco and Firearms, U.S. Department of the Treasury, which enforces explosives control and security regulations.

Axial priming - A system for priming blasting agents where a core of priming materials extends through most or all of the blasting agent charge length.

Back break - Rock broken beyond the limits of the last row of holes.

Back holes - The top holes in a tunnel or drift round.

Base charge - The main explosive charge in a detonator.

265 FIELD MANUAL

Bench - The horizontal ledge in a quarry face along where holes are drilled. Benching is the process of excavating where terraces or ledges are worked in a stepped sequence.

Binary explosive - An explosive based on two nonexplosive ingredients, such as nitromethane and ammonium nitrate. Materials are shipped and stored separately and mixed at the jobsite to form a high explosive.

Black powder - A low energy explosive consisting of sodium or potassium nitrate, carbon, and sulfur. Black powder is seldom used today because of the low energy, poor fume quality, and extreme sensitivity to sparks.

Blast - The detonation of explosives to break rock.

Blast area - The area near a blast within the influence of flying rock or concussion.

Blaster - A qualified person in charge of a blast. Also, a person (blaster-in-charge) who has passed test approved by Office of Surface Mining (OSM) which certifies the blaster’s qualifications to supervise blasting activities.

Blasters’ galvanometer - Blasters' multimeter; see galvanometer, multimeter.

Blast hole - A hole drilled in rock or other material for the placement of explosives.

Blasting agent - An explosive that meets prescribed criteria for insensitivity to initiation. For storage, any material or mixture consisting of a fuel and oxidizer,

266 BLAST DESIGN

intended for blasting, not otherwise defined as an explosive, provided that the finished product, as mixed and packaged for use or shipment, cannot be detonated by means of a No. 8 test blasting cap when unconfined (ATF). For transportation, a material designed for blasting that has been tested in accordance with the Code of Federal Regulations (CFR) Title 49, Section 173.14a, and found to be so insensitive that there is very little probability of accidental initiation to explosion or transition from deflagration to detonation (Department of Transportation [DOT]).

Blasting cap - A detonator that is initiated by safety fuse (Mine Safety and Health Administration [MSHA]). See detonator.

Blasting circuit - The circuit used to fire one or more blasting caps.

Blasting crew - A crew whose job is to load explosive charges.

Blasting machine - Any machine built expressly for the purpose of energizing blasting caps or other types of initiators.

Blasting mat - See mat.

Blasting switch - A switch used to connect a power source to a blasting circuit.

Blistering - See mud cap.

Blockhole - A hole drilled into a boulder to allow the placement of a small charge to break the boulder.

267 FIELD MANUAL

Booster - A unit of explosive or blasting agent used for perpetuating or intensifying an explosive reaction. A booster does not contain an initiating device but is often cap sensitive.

Bootleg - That portion of a borehole that remains relatively intact after having been charged with explosive and fired. A bootleg may contain unfired explosive and may be hazardous.

Borehole (blast hole) - A drilled hole, usually in rock, that is loaded with explosives.

Borehole pressure - The pressure that the hot gases of detonation exert on the borehole wall. Borehole pressure is primarily a function of the density of the explosive and the heat of explosion.

Bridge wire - A very fine filament wire imbedded in the ignition element of an electric blasting cap. An electric current passing through the wire causes a sudden heat rise, causing the ignition element to be ignited.

Brisance - A property of an explosive roughly equivalent to detonation velocity. An explosive with a high detonation velocity has high brisance.

Bubble energy - The expanding gas energy of an explosive, as measured in an underwater test.

Bulk mix - An explosive material prepared for use without packaging.

Bulk strength - The strength of an explosive per unit volume.

Bulldoze - See mud cap.

268 BLAST DESIGN

Burden - The distance to the nearest free or open face from an explosive charge. There may be apparent burden and a true burden, the latter being measured in the direction broken rock will be displaced following firing of the explosive charge. Also, the amount of material to be blasted by a given hole in tons or cubic yards (m3).

Burn cut - A parallel hole cut employing several closely spaced blast holes. Not all of the holes are loaded with explosive. The cut creates a cylindrical opening by shattering the rock.

Bus wires - The two wires joined to the connecting wire where the leg wires of the electric caps are connected in a parallel circuit. Each leg wire of each cap is connected to a different bus wire. In a series-in- parallel circuit, each end of each series is connected to a different bus wire.

Butt - See bootleg.

Cap - See detonator.

Capped fuse - A length of safety fuse with an attached blasting cap.

Capped primer - A package or cartridge of cap-sensitive explosive that is specifically designed to transmit detonation to other explosives and which contains a detonator (MSHA).

Cap sensitivity - The sensitivity of an explosive to initiation, relative to an IME No. 8 test detonator.

269 FIELD MANUAL

Carbon monoxide - A poisonous gas created by detonating explosive materials. Excessive carbon monoxide is caused by an inadequate amount of oxygen in the explosive mixture (excessive fuel).

Cardox - A system that uses a cartridge filled with liquid carbon dioxide, which when initiated by a mixture of potassium perchlorate and charcoal, creates a pressure adequate to break undercut coal.

Cartridge - A rigid or semirigid container of explosive or blasting agent of a specified length or diameter.

Cartridge count - The number of 1¼- by 8-inch (32- by 203-mm) cartridges of explosives per 50-pound (22.7-kg) case.

Cartridge strength - A rating that compares a given volume of explosive with an equivalent volume of straight nitroglycerin dynamite expressed as a percentage.

Cast primer - A cast unit of explosive, usually pentolite or composition B, commonly used to initiate detonation in a blasting agent.

Chambering - The process of enlarging a portion of blast hole (usually the bottom) by firing a series of small explosive charges. Chambering can also be done by mechanical or thermal methods.

Chapman-Jougeut (C-J) plane - The plane that defines the rear boundary of the primary reaction zone in a detonating explosive column.

Circuit tester - See galvanometer or multimeter.

270 BLAST DESIGN

Class A explosive - Defined by the U.S. Department of Transportation (DOT) as an explosive that possesses detonating or otherwise maximum hazard; such as, but not limited to, dynamite, nitroglycerin, lead azide, black powder, blasting caps, and detonating primers.

Class B explosive - Defined by DOT as an explosive that possesses flammable hazard, such as, but not limited to, propellant explosives, photographic flash powders, and some special fireworks.

Class C explosive - Defined by DOT as an explosive that contains Class A or Class B explosives, or both, as components but in restricted quantities. For example, blasting caps or electric blasting caps in lots of less than 1,000.

Collar - The top or opening of a borehole or shaft. To “collar” in drilling means the act of starting a borehole.

Collar distance - The distance from the top of the powder column to the collar of the blast hole, usually filled with stemming.

Column charge - A long, continuous charge of explosive or blasting agent in a borehole.

Commercial explosives - Explosives designed and used for commercial or industrial, rather than military applications.

Composition B - A mixture of RDX and TNT that has a density of 1.65 g/cm3 and a velocity of 25,000 feet per second (7,622 m/sec), when cast. It is useful as a primer for blasting agents.

271 FIELD MANUAL

Condenser-discharge blasting machine - A blasting machine that uses batteries or magnets to energize one or more condensers (capacitors) whose stored energy is released into a blasting circuit.

Confined detonation velocity - The detonation velocity of an explosive or blasting agent under confinement such as in a borehole.

Connecting wire - A wire, smaller in gage than the lead wire, used in a blasting circuit to connect the cap circuit with the lead wire or to extend leg wires from one borehole to another. Usually considered expendable.

Connector - See MS connector.

Controlled blasting - Techniques used to control overbreak and produce a competent final excavation wall. See line drilling, presplitting, smooth blasting, and cushion blasting.

Cordeau detonant fuse - A term used to define detonating cord.

Cornish cut - See parallel hole cut.

Coromant cut - See parallel hole cut.

Coupling - The degree that an explosive fills the borehole. Untamped cartridges are decoupled; also capacitive and inductive coupling from power lines to an electric blasting circuit.

272 BLAST DESIGN

Coyote blasting - The practice of driving tunnels horizontally into a rock face at the foot of the shot. Explosives are loaded into these tunnels. Coyote blasting is used where it is impractical to drill vertically.

Critical diameter - The minimum diameter of any explosive for propagation of a stable detonation. Critical diameter is effected by confinement, temperature, and pressure on the explosive.

Crosslinking agent - The final ingredient added to a water gel or slurry, causing the material to change from a liquid to a gel.

Current limiting device - A device used to prevent arcing in electric blasting caps by limiting the amount or duration of current flow. Also used in a blasters’ galvanometer or multimeter to ensure a safe current output.

Cushion blasting - A surface blasting technique used to produce competent slopes. The cushion holes, fired after the main charge, have a reduced spacing and employ decoupled charges.

Cushion stick - A cartridge of explosive loaded into a small diameter borehole before the primer. The use of a cushion stick is not generally recommended because of possible bootlegs.

Cut - An arrangement of holes used in underground mining and tunnel blasting providing a free face for the remainder of the round to break.

273 FIELD MANUAL

Cutoffs - A portion of a column of explosives that has failed to detonate owing to bridging or a shifting of the rock formation, often due to an improper delay system; also a cessation of detonation in detonating cord.

Dead pressing - Desensitization of an explosive caused by pressurization. Tiny air bubbles required for sensitivity are literally squeezed from the mixture.

Decibel - The unit of sound pressure commonly used to measure airblast from explosives. The decibel scale is logarithmic.

Deck - A small charge or portion of a blast hole loaded with explosives that is separated from other charges by stemming or an air cushion.

Decoupling - The use of cartridged products significantly smaller in diameter than the borehole. Decoupled charges are normally not used except in cushion blasting, smooth blasting, presplitting, and other situations where crushing is undesirable.

Deflagration - A subsonic but extremely rapid explosive reaction accompanied by gas formation and borehole pressure but without shock.

Delay blasting - The use of delay detonators or connectors that cause separate charges to detonate at different times rather than simultaneously.

Delay connector - A nonelectric, short-interval delay device for use in delaying blasts that are initiated by detonating cord.

274 BLAST DESIGN

Delay detonator - An electric or nonelectric detonator with a built-in element that creates a delay between the input of energy and the explosion of the detonator.

Delay electric blasting cap - An electric blasting cap with a built-in delay that delays cap detonation in predetermined time intervals from milliseconds up to a second or more.

Delay element - The portion of a blasting cap that causes a delay between the application of energy to the cap and the time of detonation of the base charge of the cap.

Density - The weight per unit volume of explosive, expressed as cartridge count or grams per cubic centimeter. See loading density.

Department of Transportation (DOT) - A Federal agency that regulates safety in interstate shipping of explosives and other hazardous materials.

Detaline System - A nonelectric system for initiating blasting caps where the energy is transmitted through the circuit by a low-energy detonating cord.

Detonating cord - A plastic covered core of high-velocity explosive, usually PETN, used to detonate explosives. The plastic covering is covered with various combinations of textiles and waterproofing.

Detonation - A supersonic explosive reaction where a shock wave propagates through the explosive accompanied by a chemical reaction that furnishes energy to sustain stable shock wave propagation. Detonation creates both a detonation pressure and a borehole pressure.

275 FIELD MANUAL

Detonation pressure - The head-on pressure created by the detonation proceeding down the explosive column. Detonation pressure is a function of the explosive density and the square of the explosive velocity.

Detonation velocity - See velocity.

Detonator - Any device containing a detonating charge that is used to initiate an explosive. Includes, but is not limited to, blasting caps, electric blasting caps, and nonelectric instantaneous or delay blasting caps.

Ditch blasting - See propagation blasting.

DOT - See Department of Transportation.

Downline - The line of detonating cord in the borehole that transmits energy from the trunkline down the hole to the primer.

Drilling pattern - See pattern.

Drop ball - Known also as a headache ball. An iron or steel weight held on a wire rope that is dropped from a height onto large boulders to break them into smaller fragments.

Dynamite - The high explosive invented by Alfred Nobel. Any high explosive where the sensitizer is nitroglycerin or a similar explosive oil.

Echelon pattern - A delay pattern that causes the true burden at the time of detonation to be at an oblique angle from the original free face.

276 BLAST DESIGN

Electric blasting cap - A blasting cap designed to be initiated by an electric current.

Electric storm - An atmospheric disturbance of intense electrical activity presenting a hazard in all blasting activities.

Emulsion - An explosive material containing substantial amounts of oxidizers dissolved in water droplets surrounded by an immiscible fuel. Similar to a slurry.

Exploding bridge wire (EBW) - A wire that explodes upon application of current. The wire takes the place of the primary explosive in an electric detonator. An exploding bridge wire detonator is an electric detonator that employs an exploding bridge wire rather than a primary explosive. An exploding bridge wire detonator is instantaneous.

Explosion - A thermochemical process where mixtures of gases, solids, or liquids react with the almost instantaneous formation of gas pressures and sudden heat release.

Explosion pressure - See borehole pressure.

Explosive - Any chemical mixture that reacts at high velocity to liberate gas and heat causing very high pressures. ATF classifications include high explosives and low explosives. Also, any substance classified as an explosive by DOT.

Explosive materials - A term that includes, but is not necessarily limited to, dynamite and other high explosives, slurries, water gels, emulsions, blasting agents, black powder, pellet powder, initiating explosives, detonators, safety fuses, squibs, detonating cord, igniter cord, and igniters.

277 FIELD MANUAL

Extra dynamite - Also called ammonia dynamite, a dynamite that derives the major portion of its energy from ammonium nitrate.

Extraneous electricity - Electrical energy other than actual firing current that may be a hazard with electric blasting caps. Includes stray current, static electricity, lightning, radio frequency energy, and capacitive or inductive coupling.

Face - A rock surface exposed to air. Also called a free face, a face provides the rock with room to expand upon fragmentation.

Firing current - Electric current purposely introduced into a blasting circuit for initiation. Also, the amount of current required to activate an electric blasting cap.

Firing line - A line, often permanent, extending from the firing location to the electric blasting cap circuit. Also called lead wire.

Flash over - Sympathetic detonation between explosive charges or between charged blast holes.

Flyrock - Rock that is propelled through the air from a blast. Excessive flyrock may be caused by poor blast design or unexpected weak zones in the rock.

Fracturing - The breaking of rock with or without movement of the broken pieces.

Fragmentation - The extent that a rock is broken into pieces by blasting. Also the act of breaking rock.

278 BLAST DESIGN

Fuel - An ingredient in an explosive that reacts with an oxidizer to form gaseous products of detonation.

Fuel oil - The fuel in ANFO, usually No. 2 diesel.

Fume Classification - An IME quantification of the amount of fumes generated by an explosive or blasting agent.

Fume quality - A measure of the toxic fumes to be expected when a specific explosive is properly detonated. See fumes.

Fumes - Noxious or poisonous gases liberated from a blast. May be due to a low fume quality explosive or inefficient detonation.

Fuse - See safety fuse.

Fuse lighter - A pyrotechnic device for rapid and dependable lighting of safety fuse.

Galvanometer - (More properly called blasters’ galvanometer.) A measuring instrument containing a silver chloride cell and/or a current limiting device that is used to measure resistance in an electric blasting circuit. Only a device specifically identified as a blasting galvanometer or blasting multimeter should be used for this purpose.

Gap sensitivity - The gap distance an explosive can propagate across. The gap may be air or a defined solid material. Gap sensitivity is a measure of the likelihood of sympathetic propagation.

279 FIELD MANUAL

Gas detonation system - A system for initiating caps where the energy is transmitted through the circuit by a gas detonation inside a hollow plastic tube.

Gelatin - An explosive or blasting agent that has a gelatinous consistency. The term is usually applied to a gelatin dynamite but may also be a water gel.

Gelatin dynamite - A highly water-resistant dynamite with a gelatinous consistency.

Generator blasting machine - A blasting machine operated by vigorously pushing down a rack bar or twisting a handle. Now largely replaced by condensor discharge blasting machines.

Grains - A weight measurement unit where 7,000 grains equal 1 pound.

Ground vibration - Ground shaking caused by the elastic wave emanating from a blast. Excessive vibrations may cause damage to structures.

Hangfire - The detonation of an explosive charge after the designed firing time. A source of serious accidents.

Heading - The working face or end of an excavation driven in an underground mine.

Hercudet - See gas detonation system.

Hertz - A term used to express the frequency of ground vibrations and airblast. One hertz is one cycle per second.

280 BLAST DESIGN

High explosive - Any product used in blasting that is sensitive to a No. 8 test blasting cap and reacts at a speed faster than that of sound in the explosive medium. A classification used by ATF for explosive storage.

Highwall - The bench, bluff, or ledge on the edge of a surface excavation. This term is most commonly used in coal strip mining.

Ignitacord – A cordlike fuse that burns progressively along its length with an external flame at the zone of burning and is used for lighting a series of safety fuses in sequence. Burns with a spitting flame similar to a Fourth-of-July sparkler.

IME - The Institute of Makers of Explosives. A trade organization dealing with the use of explosives and concerned with safety in manufacture, transportation, storage, handling, and use. The IME publishes a series of blasting safety pamphlets.

Initiation - The act of detonating a high explosive by means of a cap, mechanical device, or other means. Also the act of detonating the initiator.

Instantaneous detonator - A detonator that contains no delay element.

Jet 1oader - A system for loading ANFO into small blastholes where the ANFO is sucked from a container and blown into the hole at high velocity through a loading hose.

281 FIELD MANUAL

Jumbo - A machine designed to mount two or more drilling units that may or may not be operated independently.

Kerf - A slot cut in a coal or soft rock face by a mechanical cutter to provide a free face for blasting.

Lead wire - The wire connecting the electrical power source with the leg wires or connecting wires of a blasting circuit. Also called a firing line.

LEDC - Low-energy detonating cord used to initiate nonelectric blasting caps.

Leg wires - Wires connected to the bridge wire of an electric blasting cap and extending from the waterproof plug. The opposite ends are used to connect the cap into a circuit.

Lifters - The bottom holes in a tunnel or drift round.

Line drilling - An overbreak control method where a series of very closely spaced holes are drilled at the perimeter of the excavation. These holes are not loaded with explosive.

Liquid oxygen explosive - A high explosive made by soaking cartridges of carbonaceous materials in liquid oxygen. This explosive is rarely used today.

282 BLAST DESIGN

Loading density - The pounds of explosive per foot of charge of a specific diameter.

Loading factor - See powder factor.

Loading pole - A pole made of nonsparking material used to push explosive cartridges into a borehole and to break and tightly pack the explosive cartridges into the hole.

Low explosive - An explosive where the speed of reaction is slower than the speed of sound, such as black powder. A classification used by ATF for explosive storage.

LOX - See liquid oxygen explosive.

Magazine - A building, structure, or container specially constructed for storing explosives, blasting agents, detonators, or other explosive materials.

Mat - A covering placed over a shot to hold down flying material. The mat is usually made of woven wire cable, rope, or scrap tires.

Maximum firing current - The highest current (amperage) recommended for the safe and effective initiation of an electric blasting cap.

Metallized - Sensitized or energized with finely divided metal flakes, powders, or granules, usually aluminum.

Michigan cut - See parallel hole cut.

283 FIELD MANUAL

Microballoons - Tiny hollow spheres of glass or plastic that are added to explosive materials to enhance sensitivity by assuring adequate entrapped air content.

Millisecond (ms) - Short delay intervals equal to 1/1,000 of a second.

Millisecond delay caps - Delay detonators that have built-in time delays of various lengths. The interval between the delays at the lower end of the series is usually 25 ms. The interval between delays at the upper end of the series may be 100 to 300 ms.

Minimum firing current - The lowest current (amperage) that will initiate an electric blasting cap within a specified short interval of time.

Misfire - A charge or part of a charge that has failed to fire as planned. All misfires are dangerous.

Monomethylaminenitrate - A compound used to sensi- tize some water gels.

MS connector - A device used as a delay in a detonating cord circuit connecting one hole in the circuit with another or one row of holes to other rows of holes.

MSHA - The Mine Safety and Health Administration. An agency under the Department of Labor that enforces health and safety regulations in the mining industry.

Muckpile - A pile of broken rock or dirt that is to be loaded for removal.

Mud cap - Referred to also as adobe, bulldoze, blistering, or plaster shot. A charge of explosive fired in contact

284 BLAST DESIGN

with the surface of a rock usually covered with a quantity of mud, wet earth, or similar substance. No borehole is used.

Multimeter - A multipurpose test instrument used to check line voltages, firing currents, current leakage, stray currents, and other measurements pertinent to electric blasting. (More properly called blasters’ multimeter.) Only a meter specifically designated as a blasters’ multimeter or blasters’ galvanometer should be used to test electric blasting circuits.

National Fire Protection Association (NFPA) - An industry/government association that publishes standards for explosive material and ammonium nitrate.

Nitrocarbonitrate - A shipping classification once given to a blasting agent by DOT.

Nitrogen oxides - Poisonous gases created by detonating explosive materials. Excessive nitrogen oxides may be caused by an excessive amount of oxygen in the explosive mixture (excessive oxidizer) or by inefficient detonation.

Nitroglycerin (NG) - The explosive oil originally used as

the sensitizer in dynamites, C3H5(ONO2)3.

Nitromethane - A liquid compound used as a fuel in two- component (binary) explosives and as rocket and dragster fuel.

285 FIELD MANUAL

Nitropropane - A liquid fuel that can be combined with pulverized ammonium nitrate prills to make a dense blasting mixture.

Nitrostarch - A solid explosive similar to nitroglycerin used as the base of “nonheadache” powders.

Nonel - See shock tube system.

Nonelectric delay blasting cap - A detonator with a delay element capable of being initiated nonelectrically. See shock tube system; gas detonation system; Detaline System.

No. 8 test blasting cap - See test blasting cap No. 8.

OSHA - The Occupational Safety and Health Administra- tion. An agency under the Department of Labor that enforces health and safety regulations in the construction industry, including blasting.

OSM - The Office of Surface Mining Reclamation and Enforcement. An agency under the Department of the Interior that enforces surface environmental regulations in the coal mining industry.

Overbreak - Excessive breakage of rock beyond the desired excavation limit.

Overburden - Worthless material lying on top of a deposit of useful materials. Overburden often refers to dirt or gravel but can be rock, such as shale over limestone or shale and limestone over coal.

286 BLAST DESIGN

Overdrive - Inducing a velocity higher than the steady state velocity in a powder column by the use of a powerful primer. Overdrive is a temporary pheno- menon, and the powder quickly assumes its steady state velocity.

Oxides of nitrogen - See nitrogen oxides.

Oxidizer - An ingredient in an explosive or blasting agent that supplies oxygen to combine with the fuel to form gaseous or solid detonation products. Ammo- nium nitrate is the most common oxidizer used in commercial explosives.

Oxygen balance - A mixture of fuels and oxidizers where the gaseous products of detonation are predominantly carbon dioxide, water vapor (steam), and free nitrogen. A mixture containing excess oxygen has a negative oxygen balance.

Parallel circuit - A circuit where two wires, called bus wires, extend from the lead wire. One leg wire from each cap in the circuit is hooked to each of the bus wires.

Parallel hole cut - A group of parallel holes, some of which are loaded with explosives, used to establish a free face in tunnel or heading blasting. One or more of the unloaded holes may be larger than the blast holes; also called Coromant, Cornish, burn, shatter, or Michigan cut.

Parallel series circuit - Similar to a parallel circuit but involving two or more series of electric blasting caps.

287 FIELD MANUAL

One end of each series of caps is connected to each of the bus wires; sometimes called series-in-parallel circuit.

Particle velocity - A measure of ground vibration. Describes the velocity of particle vibration when excited by a seismic wave.

Pattern - A drill hole plan laid out on a face or bench to be drilled for blasting.

Pellet powder - Black powder pressed into 2-inch-long, 1¼- to 2-inch diameter cylindrical pellets.

Pentaerythritoltetranitrate (PETN) - A military explosive compound used as the core load of detonating cord and the base charge of blasting caps.

Pentolite - A mixture of PETN and TNT used as a cast primer.

Permissible - A machine, material, apparatus, or device that has been investigated, tested, and approved by the Bureau of Mines or MSHA maintained in permissible condition.

Permissible blasting - Blasting according to MSHA regulations for underground coal mines or other gassy underground mines.

Permissible explosives - Explosives that have been approved by MSHA for use in underground coal mines or other gassy mines.

PETN - See pentaerythritoltetranitrate.

Plaster shot - See mud cap.

288 BLAST DESIGN

Pneumatic 1oader - One of a variety of machines powered by compressed air used to load bulk blasting agents or cartridged water gels.

Powder - Any solid explosive.

Powder chest - A strong, nonconductive portable container equipped with a lid used at blasting sites for temporary explosive storage.

Powder factor - A ratio between the amount of powder loaded and the amount of rock broken, usually expressed as pounds per ton or pounds per cubic yard. In some cases, the reciprocals of these terms are used.

Preblast survey - A documentation of the existing condition of a structure. The survey is used to determine whether subsequent blasting causes damage to the structure.

Premature - A charge that detonates before intended.

Preshearing - See presplitting.

Presplitting - Controlled blasting where decoupled charges are fired in closely spaced holes at the perimeter of the excavation. A presplit blast is fired before the main blast. Also called preshearing.

Pressure vessel - A system for loading ANFO into small diameter blast holes. The ANFO is contained in a sealed vessel where air pressure forces the ANFO through a hose and into the blast hole; also known as pressure pot.

289 FIELD MANUAL

Prill - A small porous sphere of ammonium nitrate capable of absorbing more than 6 percent by weight of fuel oil. Blasting prills have a bulk density of 0.80 to 0.85 g/cm3.

Primary blast - The main blast executed to sustain production.

Primary explosive - An explosive or explosive mixture sensitive to spark, flame, impact, or friction used in a detonator to initiate the explosion.

Primer - A unit, package, or cartridge of cap-sensitive explosive used to initiate other explosives or blasting agents and that contains a detonator.

Propagation - The detonation of explosive charges by an impulse from a nearby explosive charge.

Propagation blasting - The use of closely spaced, sensitive charges. The shock from the first charge propagates through the ground, setting off the adjacent charge and so on. Only one detonator is required; primarily used for ditching in damp ground.

Propellant explosive - An explosive that normally deflagrates and is used for propulsion.

Pull - The quantity of rock or length of advance excavated by a blast round.

Radio frequency energy - Electrical energy traveling through the air as radio or electromagnetic waves. Under ideal conditions this energy can fire an electric blasting cap. IME Pamphlet No. 20 recommends safe distances from transmitters to electric blasting caps.

290 BLAST DESIGN

Radio frequency transmitter - An electric device, such as a stationary or mobile radio transmitting station, that transmits a radio frequency wave.

RDX - Cyclotrimethylenetrinitramine, an explosive substance used in the manufacture of compositions B, C-3, and C-4. Composition B is useful as a cast primer.

Relievers - In a heading round, holes adjacent to the cut holes, used to expand the opening made by the cut holes.

Rib holes - The holes at the sides of a tunnel or drift round that determine the width of the opening.

Riprap - Coarse rocks used for river bank or dam stabilization to reduce erosion by water flow.

Rotational firing - A delay blasting system where each charge successively displaces its burden into a void created by an explosive detonated on an earlier delay period.

Round - A group or set of blast holes used to produce a unit of advance in underground headings or tunnels.

Safety fuse - A core of potassium nitrate black powder, enclosed in a covering of textile and waterproofing, used to initiate a blasting cap or a black powder charge. Safety fuse burns at a continuous, uniform rate.

291 FIELD MANUAL

Scaled distance - A ratio used to predict ground vibrations. Scaled distance equals the distance from the blast to the point of concern in feet divided by the square root of the charge weight of explosive per delay in pounds. When using the equation, the delay period must be at least 9 ms.

Secondary blasting - Using explosives to break boulders or high bottom resulting from the primary blast.

Seismograph - An instrument that measures and may supply a permanent record of earthborne vibrations induced by earthquakes or blasting.

Semiconductive hose - A hose used for pneumatic loading of ANFO that has a minimum electrical resistance of 1,000 ohms per foot, 10,000 ohms total resistance, and a maximum total resistance of 2,000,000 ohms.

Sensitiveness - A measure of an explosive’s ability to propagate a detonation.

Sensitivity - A measure of an explosive’s susceptibility to detonation by an external impulse such as impact, shock, flame, or friction.

Sensitizer - An ingredient used in explosive compounds to promote greater ease in initiation or propagation of the detonation reaction.

Sequential blasting machine - A series of condenser discharge blasting machines in a single unit that can be activated at various accurately timed intervals following the application of electrical current.

292 BLAST DESIGN

Series circuit - A circuit of electric blasting caps where each leg wire of a cap is connected to a leg wire from the adjacent caps so that the electrical current follows a single path through the entire circuit.

Series-in-parallel circuit - See parallel series circuit.

Shatter cut - See parallel hole cut.

Shock energy - The shattering force of an explosive caused by the detonation wave.

Shock tube system - A system for initiating caps where the energy is transmitted to the cap by a shock wave inside a hollow plastic tube.

Shock wave - A pressure pulse that propagates at supersonic velocity.

Shot - See blast.

Shot firer - Also referred to as the shooter. The person who actually fires a blast. A powderman may charge or load blast holes with explosives but may not fire the blast.

Shunt - A piece of metal or metal foil that short circuits the ends of cap leg wires to prevent stray currents from causing accidental detonation of the cap.

Silver chloride cell - A low-current cell used in a blasting galvanometer and other devices to measure continuity in electric blasting caps and circuits.

Slurry - An aqueous solution of ammonium nitrate, sensitized with a fuel, thickened, and crosslinked to provide a gelatinous consistency. Sometimes called a

293 FIELD MANUAL

water gel. DOT may classify a slurry as a Class A explosive, a Class B explosive, or a blasting agent. An explosive or blasting agent containing substantial portions of water (MSHA). See emulsion; water gel.

Smooth blasting - Controlled blasting used underground where a series of closely spaced holes is drilled at the perimeter, loaded with decoupled charges, and fired on the highest delay period of the blast round.

Snake hole - A borehole drilled slightly downward from horizontal into the floor of a quarry face. Also, a hole drilled under a boulder.

Sodium nitrate - An oxidizer used in dynamites and sometimes in blasting agents.

Spacing - The distance between boreholes or charges in a row measured perpendicular to the burden and parallel to the free face of expected rock movement.

Specific gravity - The ratio of the weight of a given volume of any substance to the weight of an equal volume of water.

Spitter cord - See Ignitacord.

Springing - See chambering.

Square pattern - A blast hole pattern where the holes in succeeding rows are drilled directly behind the holes in the front row. In a truly square pattern, the burden and spacing are equal.

Squib - A firing device that burns with a flash. Used to ignite black powder or pellet powder.

294 BLAST DESIGN

Stability - The ability of an explosive material to maintain its physical and chemical properties over a period of time in storage.

Staggered pattern - A blast hole pattern where the holes in each row are drilled between the holes in the preceding row.

Static electricity - Electrical energy stored on a person or object in a manner similar to that of a capacitor. Static electricity may be discharged into electrical initiators, detonating them.

Steady state velocity - The characteristic velocity at which a specific explosive, under specific conditions in a given charge diameter, will detonate.

Stemming - The inert material such as drill cuttings used in the collar portion (or elsewhere) of a blast hole to confine the gaseous products of detonation; also, the length of blast hole left uncharged.

Stick count - See cartridge count.

Stray current - Current flowing outside the desired conductor. Stray current may come from electrical equipment, electrified fences, electric railways, or similar sources. Flow is facilitated by conductive paths such as pipelines and wet ground or other wet materials. Galvanic action of two dissimilar metals in contact or connected by a conductor may cause stray current.

Strength - An explosive property described variously as cartridge or weight strength, seismic strength, shock or bubble energy, crater strength, or ballistic mortar

295 FIELD MANUAL

strength. Not a well-defined property. Used to express an explosive’s capacity to do work.

String 1oading - Loading cartridges end-to-end in a borehole without deforming them. Used mainly in controlled blasting and permissible blasting.

Subdrill - To drill blast holes beyond the planned grade lines or below floor level to insure breakage to the planned grade or floor level.

Subsonic - Slower than the speed of sound.

Supersonic - Faster than the speed of sound.

Swell factor - The ratio of the volume of a material in an undisturbed state to that when broken. May also be expressed as the reciprocal of this number.

Sympathetic propagation (sympathetic detonation) - Detonation of an explosive material by an impulse from another detonation through air, earth, or water.

Tamping - Compressing the stemming or explosive in a blast hole. Sometimes used synonymously with stemming.

Tamping bag - A cylindrical bag containing stemming material used to confine explosive charges in boreholes.

Tamping pole - See loading pole.

296 BLAST DESIGN

Test blasting cap No. 8 - A detonator containing 0.40 to 0.45 g of PETN base charge at a specific gravity of 1.4 g/cm3 primed with standard weights of primer, depending on the manufacturer.

Toe - The burden or distance between the bottom of a borehole and the vertical free face of a bench in an excavation. Also the rock left unbroken at the foot of a quarry blast.

Transient velocity - A velocity different from the steady state velocity that a primer imparts to a column of powder. The powder column quickly attains steady state velocity.

Trinitrotoluene (TNT) - A military explosive compound used industrially as a sensitizer for slurries and as an ingredient in pentolite and composition B. Once used as a free-running pelletized powder.

Trunkline -A detonating cord line used to connect the downlines of other detonating cord lines in a blast pattern. Usually runs along each row of blast holes.

Tunnel - A basically horizontal underground passage.

Two-component explosive - See binary explosive.

Unconfined detonation velocity - The detonation velocity of an explosive material not confined by a borehole or other confining medium.

297 FIELD MANUAL

V-cut - A cut employing several pairs of angled holes meeting at the bottoms used to create free faces for the rest of the blast round.

Velocity - The rate that the detonation wave travels through an explosive. May be measured confined or unconfined. Manufacturer’s data are sometimes measured with explosives confined in a steel pipe.

Venturi 1oader - See jet loader.

Volume strength - See cartridge strength or bulk strength.

Water gel - An aqueous solution of ammonium nitrate, sensitized with a fuel, thickened, and crosslinked to provide a gelatinous consistency; also called a slurry; may be an explosive or a blasting agent.

Water stemming bags - Plastic bags containing a self- sealing device that are filled with water. Classified as a permissible stemming device by MSHA.

Weight strength - A rating that compares the strength of a given weight of explosive with an equivalent weight of straight nitroglycerin dynamite or other explosive standard, expressed as a percentage.

298 Chapter 20

WATER CONTROL

Introduction

This chapter discusses site conditions that need dewatering and the extent and basic requirements for construction dewatering. A more comprehensive discussion of technical requirements and methods for constructing dewatering facilities is available in the Reclamation Ground Water Manual. The subjects that are discussed include:

C Site review C Site investigations C Data collection C Data interpretation, evaluation, and presentation C Specifications paragraphs C Construction considerations C Supervision and oversight C Documentation of results (final construction report)

Water control is lumped into two categories—dewatering and unwatering. Water control is the removal or control of groundwater or seepage from below the surface (dewatering) or the removal or control of ponded or flowing surface water by ditches, surface drains, or sumps (unwatering). Excavation of materials or construction near or below the water table or near surface water bodies usually requires control of the groundwater or seepage. Control may involve isolation with cutoffs, stabilization by freezing, grouting, or other methods, or by a combination of methods. Control of groundwater and seepage usually involves installation and operation of wells or drains. A key operation in most water control in unstable materials is the removal of water from below the ground surface in advance of excavation and maintaining the water level at FIELD MANUAL a suitable depth below the working surface. These steps permit construction “in the dry,” unhampered by the adverse effects of water.

Understanding what factors control water is critical for ensuring short-term stability during construction of any facility and for the long-term stability of any structure. This chapter discusses what should be considered. If water is considered a potential problem, any field investigation must obtain information on the site’s various potential water sources including seasonal precipitation and runoff periods and the identification and understanding of the water bearing zones within a site. This means not only identifying and determining the depths and extent of the various water bearing zones and their water surfaces but also understanding the formation hydraulic parameters (porosity, permeability, and, when necessary, storage).

Figure 20-1 illustrates the importance of understanding the site hydraulic parameters in selecting the appropriate dewatering method. Using the wrong method for the site materials can result in a totally ineffective dewatering system. Figure 20-1 can be used to assess what is the appropriate dewatering method based on the site materials.

In excavations in rock, cemented granular materials, clays, and other stable materials, water removal or unwatering may be by draining to sumps and using surface pumps concurrently with or following completion of the excavation. Subsurface cutoffs such as sheet piling and slurry walls in soil or soft rock and grouting in rock are also used to control ground and surface water and for ground support. Cutoffs are seldom 100-percent effective, and supplementary dewatering or unwatering is usually required. Soils are frozen for short periods such as for a

300 WATER CONTROL Figure 20-1.—Limits of dewatering methods for different materials. for different methods of dewatering 20-1.—Limits Figure

301 FIELD MANUAL temporary excavation, especially in clayey or silty soils that have low permeability and are difficult to drain.

Unwatering methods are commonly used in soils that have high porosity but low permeabilities (clayey or silty soils), bedrock that has solution cavities, and lava tubes that carry large volumes of water in isolated areas. Unwatering methods are commonly used to control surface water.

Unwatering usually is performed in conjunction with dewatering to ensure control of surface water and to permit dewatering to proceed unaffected by recharge or flooding from nearby surface water. Failure to properly remove or control water during unwatering or dewatering may result in:

• Unstable natural or excavated slopes

• Unstable, unworkable, or unsuitable subgrade

• Boils, springs, blowouts, or seeps on slopes or in the subgrade

• Flooding of excavations or structures

• Uplift of constructed features such as concrete slabs

• Dilution, corrosion, or other adverse effects on concrete, metals, or other construction materials

• Instability of nearby structures

• Draining surrounding surface water and groundwater

302 WATER CONTROL

• Instability of cutoff facilities such as cofferdams

• Loss of fines from the foundation

• Safety problems

• Delays in construction

• Increased construction costs

Water control may vary widely in scope, magnitude, and difficulty. Some controlling factors related to the constructed feature include footprint, foundation depth, and construction time. Factors related to site conditions are:

• Subsurface geology including general material types; bedding, attitudes and lateral extent of bedding; and attitudes, continuity, and apertures of fractures

• Subsurface hydraulic conditions including permeabilities and thicknesses of different materials, groundwater occurrence, and levels

• Recharge conditions including proximity to surface water bodies and precipitation

• Other facilities including cofferdams and site access

Conditions that may indicate the need for dewatering and the possibility for difficult dewatering include:

• Site location adjacent to a large body of surface water, a stream, a marshy area, or an area subject to flooding

• An excavation significantly below the water table

303 FIELD MANUAL

• Complex foundation geology

• An artesian zone immediately below grade

• Existing structures or facilities

• Existing use of groundwater

• Poor quality groundwater

• Presence of hazardous materials

• Thick zones of saturated, low-strength materials such as silt or soft clay, especially under artesian conditions

• Presence of cofferdams or other similar features for which dewatering is needed for stability

• Conditions where failure of dewatering facilities could result in catastrophic failure of protective or other features and a hazard to life or property

Sites requiring groundwater or seepage control for construction or proper operation of a facility should be identified as early in the planning or design process as possible.

Exploration Program

Investigations for water control should be part of the general exploration and design data collection program. Advantages of conducting investigations together include:

304 WATER CONTROL

• Maximizing the use of design data collection and lowering exploration costs

• Providing dewatering data early in the program

• Using field personnel efficiently

Water control investigations generally cannot be established in detail until some reconnaissance level drilling has been done and general subsurface geologic and hydrologic conditions are determined. General surface conditions including topography and surface hydrology should be known. A specialist should be consulted as early in the program as possible to maximize the benefits of the obtained data.

Design Data Requirements, Responsibilities, and Methods of Collection and Presentation

Adequate surface and subsurface data are essential to the proper design, installation, and operation of water control facilities. The amount of data required for water control facilities design may equal or exceed the foundation data required for design of the structure. Water control facilities may be designed in-house or by the contractor; but investigations may be extensive, complex, time consuming, and beyond the capability of a contractor to accomplish in the bidding period. An in-house design is generally better because the time is usually available to do the job right, the designer has control over the design data, responsibility for the water control design is clear to the owner and the contractor, and the contractor can bid the water control installation more accurately.

Design data for water control facilities should be obtained regardless of who is ultimately responsible for the design.

305 FIELD MANUAL

The extent and level of data should be appropriate for the anticipated water control requirements and facilities. All subsurface investigations should be sufficiently detailed to determine the groundwater conditions, including the depth of the vadose zone and the various potentiometric water surfaces; and the investigations should provide at least enough data to estimate the permeability of the soil or rock. Crude soil permeabilities can be estimated from blow counts and the visual or laboratory soil classification. Permeability tests should be considered in any exploration program. If aquifer tests are required, the test wells should approximate the size and capacity of anticipated dewatering wells. Facilities should be preserved and made available to prospective contractors for their testing or use, if appropriate.

If the contractor is responsible for the dewatering design, all field design data should be included in the construction specifications. Data include details of drilling and completion of exploratory drill holes, wells, piezometers, and other installations as well as test data. Data should be as concise as possible and clearly show the history, sequence, and location of all exploration. Design data for water control facilities should be obtained concurrently with feature design data if possible. Specialists should be consulted when preparing design data programs, especially programs for foundation drilling and aquifer testing. Water control data are an essential part of the design data package and must be given the required priority in funds, time, and personnel to minimize problems such as construction delays and claims. Where dewatering may have impacts on existing adjacent structures, wells, facilities, or water resources, a study of the area surrounding the site may be necessary to determine and document impacts. In addition to data involving the constructed feature such as a structure

306 WATER CONTROL layout, excavation depth, and time to construct, other information is required on site conditions such as:

Surface Data

• Site and surrounding topography at an appropriate scale and contour interval

• Cultural features on and off site

• Site and surrounding surface geology with descriptions of materials

• Site and adjacent surface water features such as lakes, streams, swamps, bogs, and marshes

• Plan map of all data points, including locations of drill holes, test holes, piezometers, observation wells, test wells, and overlays on the plan of the proposed feature

Surface information should include data on soil erosion or resistance or how erosion relates to runoff or the potential recharge of the groundwater system. Soil infiltration data from Natural Resource Conservation Service mapping should be included if available.

Subsurface Data

Subsurface data should include representative permeabilities, a real distribution of permeabilities, location and potential recharge sources or barriers, and anticipated seasonal changes in the groundwater system. When a project has a relatively high soil or rock permeability and the permeable formation extends laterally over a large area, storage (storativity, effective

307 FIELD MANUAL porosity) of the aquifer requires evaluation. Specific data that may be necessary include:

• General geology of the site and surrounding area including geologic cross sections that show vertical and lateral variations in materials

• Logs of drill holes, test holes, and piezometers showing depths and thicknesses of materials, descriptions of materials, and results of testing

• Results of material sampling including depths, descriptions, mechanical analyses, and hydrometer analyses

• Geophysical logs

• Aquifer or permeability test results including yields and drawdown with time and static water levels

• Layout of test holes and depths and designs of wells and piezometers

• Water quality analyses

Other Data

• Climatic data for the nearest station including daily temperature and precipitation and details on the occurrence of severe storms

• Streamflow and elevation, lake or reservoir depth, elevation, and other similar data

• Groundwater levels for monitored observation wells, piezometers, test wells, drill holes, and pits

308 WATER CONTROL

• If a nearby surface water body and the groundwater are connected, continuous monitoring of both features for a typical hydrologic cycle

Presentation of Data

The presentation of dewatering data may differ from the presentation of conventional geologic data because water control data are subject to a variety of quantitative interpretations and because water levels, flow, and water quality vary with time.

Because of the potential for different interpretations, most dewatering data such as those from aquifer tests and packer tests are presented as observed field data and as interpretations. A complete description of the site, subsurface conditions, and test facilities should be given along with the data (figures 20-2 and 20-3).

Where time related data are presented, the information should be in a form that will ensure maximum recognition and proper interpretation. Hydrographs that plot time versus water levels mean a lot more than a table of readings.

Monitoring

Water control activities must be monitored during construction and, in some cases, up to a year or more before and following completion of the facility. Details of the monitoring program including design and layout of the system, the responsibilities for installing the system, and monitoring and maintaining records must be included in the specifications and construction considerations to ensure adequate reliable data and inform construction personnel of monitoring requirements.

309 FIELD MANUAL Figure 20-3.—Aquifer test data.

310 (KIWTG #SWKHGTVGUVRNCP CPFUGEVKQPU WATER CONTROL

Monitoring is intended to:

• Provide data on base level conditions • Confirm that the specifications requirements are being met • Maintain a general data base on conditions and impacts resulting from the dewatering • Alert personnel to unsuitable, hazardous, or potentially hazardous conditions • Document conditions in the event of claims or litigation • Provide background data for a followup analysis in the event of a slope, foundation, or structural failure

Monitoring of water control parameters, activities, and features should include:

• Groundwater levels • Discharges • Sediment content of discharges • Chemical and biologic quality of water discharged • Horizontal and vertical control on constructed features and natural and excavated slopes • Levels and sizes of nearby surface water bodies • Stability of nearby structures

The monitoring facilities may range from a few observation wells to a complex system involving sophisticated equipment and continuous and possibly remote monitoring. The extent, complexity, and capability of water control facilities depend on the size and complexity

311 FIELD MANUAL of the facilities and the hydrologic and geologic conditions and excavation depths.

Groundwater Monitoring

Monitoring during construction should include groundwater levels in excavations, areas surrounding the excavations, and off-site locations. Excavations of any substantial width (other than trenches) and a depth of more than a few feet below the anticipated water level may need groundwater monitoring instrumentation installed directly in the excavation. Excavations underlain at shallow depths by artesian conditions may need to be monitored because of the potential for blowout.

Groundwater Monitoring Locations

Groundwater monitoring instrumentation located within an excavation may interfere with the contractor during construction, but monitoring groundwater levels within an excavation generally justifies inconveniences. Because the most difficult area to dewater is usually the center of the excavation, groundwater monitoring instruments should be located near the center. Special provisions may be necessary to ensure continued groundwater monitoring of the facilities during all stages of the excavation. In some cases, groundwater monitoring instrumentation may be incorporated into the structure. This may require that the monitoring instrument be embedded in concrete such as a wall or pier to permit continuous monitoring and simplify backfill operations.

Water level monitoring instrumentation should be located in areas surrounding the excavation to monitor representative areas and specific problem areas. Groundwater levels in off-site locations should be monitored to maintain a general record of conditions and to document

312 WATER CONTROL dewatering. Off-site monitoring is especially important in areas where groundwater is widely used, where groundwater levels are crucial to existing activities, or where there might be subsidence or groundwater level decline.

Locations of individual water level monitoring instruments must be based on conditions encountered at the site, construction activities, and the dewatering facilities. Monitoring instrumentation locations generally will have to be selected after other features such as dewatering systems and roads have been located to avoid conflicts and to ensure representative and reliable monitoring. Instru- mentation should be installed and functioning long before construction to obtain trends and base level conditions. Existing instrumentation may be used for monitoring; but unless the instrumentation construction and other details are known, instrumentation designed specifically for the conditions of the site should be installed as a part of construction.

Groundwater Monitoring Instrumentation

Instrumentation for monitoring groundwater levels usually consists of several observation wells or piezometers. The type of instrumentation, depth, and riser and hole diameter depends primarily on subsurface conditions, desired operating life, and type of monitoring. The design of the instrumentation should be tailored to the subsurface and data requirements so that measurements are a true indication of in place conditions.

Observation wells intended to monitor general groundwater levels can be used in areas where the foundation material is relatively uniform in depth, there is little or no layering, and groundwater levels do not vary appreciably

313 FIELD MANUAL with depth. Piezometers should be used where layering exists or perching, artesian, or complex conditions are expected.

Observation wells and piezometers usually consist of a section of well screen, perforated pipe, or porous tube isolated in the zone to be monitored and connected to a length of standpipe, riser, or casing extending to the surface. The section of well screen, perforations, or porous tube must be isolated with a watertight grout or bentonite seal, and a watertight riser must be used. The diameter of the screen and standpipe should conform to ASTM D-5092. Water levels are measured directly in the well or piezometer by use of tape or electric sounder (M-scope). Float-type recorders can be used to continuously record water level fluctuations but may require a minimum 4- to 6-inch (10- to 15-cm) diameter casing or standpipe. A wide range of electronic and pneumatic instruments is available for monitoring and recording groundwater levels.

Special types of monitoring wells or piezometers may be necessary if hazardous materials are present.

Monitoring Discharges From Dewatering Systems

The discharge from dewatering facilities such as wells, well point systems, drains, and sump pumps should be monitored to provide a record of the dewatering quantities. Data should include starting and stopping times, instantaneous rates of discharge, changes in rates, combined daily volumes, and, in some cases, water chemistry, turbidity, and biologic content.

Discharge rates can be monitored by flow meters (propeller, pitot tube, and acoustic), free discharge

314 WATER CONTROL orifices, weirs, flumes, and volumetric (tank-stopwatch) methods. Meters must be calibrated using a volumetric test before flow testing. Measuring devices generally must be accurate within 10 percent.

Sediment content of dewatering facilities including wells, well point systems, and drains should be monitored. Sediment can damage pumping equipment, cause deterioration of water quality in a receiving water body, and create voids in the foundation that result in well collapse and foundation settlement.

Sediment content usually is measured in parts per million by volume of water or in nephelometric turbidity units (NTU) in water taken directly from the discharge. Measurement requires special equipment. If the limits are 50 parts per million or less, a special centrifugal measuring device is required. If the limits are more than 50 parts per million, an Imhoff cone can be used. A turbidity meter typically measures values less than 2,000 NTUs. Values less than 200 NTUs are generally acceptable for discharge. If sediment yield increases rapidly, the facility may need to be shut down to avoid serious damage or contamination.

The chemical and biologic content of water discharged from dewatering systems should be monitored by periodic collection and analysis of samples taken directly from the system discharge. A single representative sample is adequate if there are a number of discharges from the same source. If there is pumping from different sources, multiple samples may be needed. The initial samples should be taken shortly after startup of the dewatering system (or during any test pumping done during exploration) and periodically during operation. Each sample may need biologic and chemical analyses for heavy metals, organics, and pesticides. More frequent

315 FIELD MANUAL sampling and analyses may be made to determine total dissolved solids, conductivity, pH, and sediment content or turbidity.

Monitoring Water and Ground Surfaces and Structures

Well or Piezometer Design.—Most groundwater monitoring for water control investigations is to collect water level information, but some monitoring is to obtain water quality information. All monitoring wells should be constructed according to ASTM D-5092 and constructed for site conditions and purposes. Geologic conditions, available drilling equipment, depth to water, and the frequency of the readings should be factored into the design of a monitoring well. If a monitoring well requires daily or weekly readings, the well may require installation of an automated water level monitoring system. The type and diameter of riser should be based on the intended use of the monitoring well. If monitoring is to continue into construction, protecting the well should be part of the design. Too often, a piezometer or observation well is constructed without any serious attempt to design the well. Typically, monitoring wells are constructed using 1-inch (2.5-cm) diameter PVC risers with a screen slot size of 0.010 inch (0.25 mm) or with or without a 10/20 sand pack. This “low permeability” monitoring well design is appropriate if the well is monitored only for water levels and the adjacent sources of recharge due to precipitation, dewatering, unwatering activities, or other water bodies is not changing rapidly.

All monitoring wells should be completed using the appropriate seals, risers, and openings to allow the water level in the riser or piezometer to respond to the formation rather than to the water within the riser, the screen, or the sand pack. Improper or inadequate removal of

316 WATER CONTROL cuttings and drill fluids, or too fine a slot or sand pack, can delay the response of groundwater within a riser. Too large openings can result in clogging of the monitoring well and impact the chemistry of the groundwater. A water quality monitoring well in soils or decomposed to intensely weathered bedrock should have a minimum of 2-inch (5-cm) risers with an annular space of at least 2 inches (5 cm). All wells with screen or slots should be developed, especially if the well is being used to obtain water quality samples. Clays and humic materials of colloidal sizes can skew water quality tests.

Ground Surface Monitoring.—The ground surface and other pertinent points should be monitored for settlement during dewatering activities. Use standard surveying methods (at least third order) and temporary benchmarks or other facilities to maintain survey control. Horizontal control is necessary in large or deep excavations that may be susceptible to slope failure. Special instrumentation with alarm warning capability may be necessary if ground failure might endanger life or property.

Water Surface Monitoring.—Nearby surface water bodies, swamps, drains, and other similar features should be monitored, if appropriate, for elevation and discharge changes and environmental changes.

Structural Monitoring.—Nearby structures that may be influenced by settlement or horizontal displacement caused by groundwater withdrawal should be monitored. Both horizontal and vertical measurements should be acquired to detect movement.

317 FIELD MANUAL

Performance Evaluation During Construction

The performance of the water control facilities should be evaluated and documented periodically during construction. This will ensure that the specifications are being met and that unusual or unexpected conditions are properly accommodated. Charts and diagrams such as hydrographs or plots of well or system discharge rates should be prepared at the start of dewatering operations and updated throughout the construction period. An evaluation, along with tables and graphs, should be included in monthly reports to provide essential data for final reports. The evaluation should be coordinated with the design staff to ensure complete understanding of conditions.

Final Reporting

The final construction report should include a section on water control. This section should include a chronology of dewatering and an evaluation of the performance of the facilities as well as contractor compliance with the specifications. Problem areas and unusual events such as pump or slope failures should be documented. Mon- itoring results, including groundwater levels and discharge rates, should be presented in the form of hydrographs and other similar plots or tabulated data.

Bibliography

Bureau of Reclamation, U.S. Department of the Interior, Ground Water Manual, 2nd Edition, 1995.

Cedergren, Harry R., Seepage, Drainage and Flow Nets, John Wiley and Sons, Inc., New York, New York, 1967.

318 WATER CONTROL

Driscoll, Fletcher, G., Ground Water and Wells, Johnson Division, St. Paul, Minnesota, 1986.

Joint AEG-ASCE Symposium, Practical Construction Dewatering, Baltimore, Maryland, May 16, 1975.

Leonards, G.A., Editor, Foundation Engineering, McGraw-Hill Book Co., Inc., New York, New York, 1962.

Powers, J. Patrick, Construction Dewatering, John Wiley and Sons, New York, New York, 1981.

U.S. Departments of the Army, the Navy, and the Air Force, Dewatering and Groundwater Control for Deep Excavations, TM5-818-5, NAVFAC P-418, AFM 88-5, Chapter 6, April 1971.

319 Chapter 21

FOUNDATION PREPARATION, TREATMENT, AND CLEANUP

This chapter discusses foundation preparation for and the placement of the first several layers of earthfill and concrete. Preparation includes excavating overburden; shaping the foundation surface with dental concrete; filling surface irregularities with slush grout (usually a cement/water mixture poured in cracks) or dental concrete (conventional concrete used to shape surfaces, fill irregularities, and protect poor rock); treating faults, shears, or weak zones; and cleanup.

Earthfill Dams

Shaping

Shape the foundation to ensure proper compaction of fill and to prevent stress anomalies in the overlying embankment. Fractures and resultant seepage problems in embankment dams may be caused by irregularities in the foundation such as stepped surfaces, abrupt changes in slope, and excessively steep surfaces. Embankment zones may differentially settle adjacent to these areas, resulting in cracks. Arching occurs near stepped surfaces resulting in a zone of low horizontal stress adjacent to the steep surface. Preventing arching is more important in the upper 1/6 to 1/4 of a dam or in low dams where stresses are low and tension zones develop along steep or diverging abutments. Tension zones or areas of low stresses are susceptible to hydraulic fracturing. The foundation surface should be shaped by excavating or by using concrete to obtain a smooth, continuous surface that minimizes crack potential. When an inclined core is used in a rockfill dam, the core derives support from the FIELD MANUAL underlying filter and transition material. The zone beneath the filter and transition should be shaped using core contact criteria.

Foundation outside the core contact must be shaped to facilitate fill placement and compaction, and unsuitable weak or compressible materials must be removed. Impervious materials beneath drainage features which would prevent drainage features from properly functioning must also be removed. Materials may move into the foundation, and erodible foundation materials may move into the embankment. Appropriately graded filters between the drainage materials and foundation may be necessary.

The minimum treatment of any foundation consists of stripping or removing organic material such as roots and stumps, sod, topsoil, wood, trash, and other unsuitable materials. Cobbles and boulders may also require removal depending on the type of embankment material to be placed.

The weak points in earthfill dams are generally within the foundation and especially at the contact of the foundation with the embankment. Foundation seepage control and stability features must be carefully supervised by the inspection force during construction to ensure conformance with the design, specifications, and good practice. Water control methods used in connection with excavating cutoff trenches or stabilizing the foundations should ensure that fine material is not washed out of the foundation because of improper screening of wells and that the water level is far enough below the foundation surface to permit construction “in the dry.” Whenever possible, locate well points and sumps outside the area to be excavated to avoid loosening soil or creating a "quick" bottom caused by the upward flow of water or equipment

322 FOUNDATION PREPARATION vibration. Avoid locating sumps and associated drainage trenches within the impervious zone because of the difficulty in properly grouting them after fill placement and the danger of damaging the impervious zone/foundation contact.

Found cutoff walls or concrete grout caps in the best rock available. Prohibit or strictly control blasting for the excavation of these structures to avoid damaging the foundation. If the material cannot be excavated with a hydraulic excavator fitted with a rock bucket, a grout cap or cutoff wall is probably not needed and grout nipples can be set directly in the foundation. A highly weathered zone can be grouted effectively by:

• Leaving the foundation high.

• Setting grout nipples through the unsuitable material. Long grout nipples may be necessary in poor rock.

• Excavating to final foundation grade after grouting.

In hard, sound rock, neither a grout cap nor a high foundation is necessary.

When overburden is stripped to rock, carefully clean the rock surface and all pockets or depressions of soil and rock fragments before the embankment is placed. This may require compressed air or water cleaning and handwork. Rock surfaces that slake or disintegrate rapidly on exposure must be protected or covered immediately with embankment material or concrete. Foundation rock should be shaped to remove overhangs and steep surfaces (figure 21-1). High rock surfaces must be stable during construction and should be cut back to maintain a

323 FIELD MANUAL

Figure 21-1.—Example foundation treatment details from specifications. smooth, continuous profile to minimize differential settlement and stress concentrations within the embankment. Final slopes should be 0.5:1 (horizontal to vertical [H:V]) or flatter. Beneath the impervious zone, all overhangs should be removed; stepped surfaces steeper than 0.5:1 and higher than 0.5 foot (15 cm) should be excavated or treated with dental concrete to a slope of 0.5:1 or flatter. Outside the impervious zone, all overhangs should be removed, and stepped surfaces steeper than 0.5:1 and higher than 5 ft (1.5 m) (should be excavated or treated with dental concrete to a slope of 0.5:1 or flatter.

324 FOUNDATION PREPARATION

Slush grout or joint mortar should be used to fill narrow cracks in the foundation (figure 21-1). However, they should not be used to cover exposed areas of the foundation. Slush grout and joint mortar are composed of Portland cement and water or, in some cases, Portland cement, sand, and water. The slush grout is preferably used just before fill placement to eliminate any tendency for hardened grout to crack under load. Dental concrete should be used to fill potholes and grooves created by bedding planes and other irregularities such as previously cleaned shear zones and large joints or channels in rock surfaces. Formed dental concrete can be used to fillet steep slopes and fill overhangs.

Care should be used during all blasting to excavate or to shape rock surfaces. Controlled blasting techniques, such as line drilling and smooth blasting, should be used.

Soil Foundations

When the foundation is soil, all organic or other unsuitable materials, such as stumps, brush, sod, and large roots, should be stripped and wasted. Stripping should be performed carefully to ensure the removal of all material that may be unstable because of saturation, shaking, or decomposition; all material that may interfere with the creation of a proper bond between the foundation and the embankment; and all pockets of soil significantly more compressible than the average foundation material. Stripping of pervious materials under the pervious or semipervious zones of an embankment should be limited to the removal of surface debris and roots unless material removal is required for seismic stability. Test pits should be excavated if the stripping operations indicate the presence of unstable or otherwise unsuitable material.

325 FIELD MANUAL

Before placing the first embankment layer (lift) on an earth foundation, moistening and compacting the surface by rolling with a tamping roller is necessary to obtain proper bond. An earth foundation surface sometimes requires scarification by disks or harrows to ensure proper bonding. No additional scarification is usually necessary if the material is penetrated by tamping rollers.

All irregularities, ruts, and washouts should be removed to provide a satisfactory foundation. Cut slopes should be flat enough to prevent sloughing, and not steeper than 1:1. Material that has been loosened to a depth of less than 6 in (15 cm) may be treated by compaction. Loosened material deeper than 6 in (15 cm) cannot be adequately compacted and should be removed.

Foundation materials at the core/foundation contact must be compacted to a density compatible with the overlying fill material. A fine-grained foundation should be compacted and disked to obtain good mixing and bond between the foundation and the first lift of core material.

Fine-grained foundations should be compacted with a roller. If the foundation is too firm for the tamping feet to penetrate, the foundation surface should be disked to a depth of 6 in and moistened before compaction. Smooth surfaces created by construction traffic on a previously compacted foundation surface should be disked to a depth of 2 in (5 cm).

Coarse-grained foundations should be compacted by rubber-tired or vibratory rollers. Vibratory compactors create a more uniform surface for placement of the first earthfill and are the preferred method of compaction.

Cemented and highly overconsolidated soils that break into hard chunks should not be reworked or disked to mix

326 FOUNDATION PREPARATION foundation and core material. The first lift of embankment material should be placed in a manner similar to that required for rock foundations as described above.

Soil foundation compaction requirements beneath filter and shell zones should be the same as those outlined above, except bonding the foundation to the overlying fill is not required.

The moisture content of the upper 6 in (15 cm) of a fine- grained soil foundation should be within 2 percent dry and 1 percent wet of the Proctor optimum moisture content for adequate compaction. Coarse-grained foundation materials should be just wet enough to permit compaction to the specified relative density, but saturation is not permitted. Dry materials must be disked and moistened to provide a homogeneous moisture content within the specified limits in the upper 6 in (15 cm) of the foundation. Wet materials must be dried by disking to bring the upper 6 in of foundation materia1 within the specified moisture content limits. Wet foundations should be unwatered or dewatered sufficiently to prevent saturation of the upper 6 in (15 cm) of foundation material due to capillary rise or pumping caused by construction equipment travel.

All embankment materials should be protected from eroding into coarser soil zones in the foundation by transitions satisfying filter criteria or by select zones of highly plastic, nonerodible material. Transition zones or filters on the downstream face of the cutoff trench and beneath the downstream zones should prevent movement of fine material in the foundation into the embankment. Dispersive embankment materials must be protected from piping into coarse material in the foundation by placing select zones of nondispersive material between the

327 FIELD MANUAL embankment and foundation. Lime-treated or naturally nondispersive earthfill is appropriate for the first several lifts of fill material or filters. Except for areas where an impervious seal between the embankment and foundation is required, filter zone(s) are the preferred method.

Rock Foundations

Rock foundation surfaces should be moistened, but no standing water should be permitted when the first lift is placed. The use of very wet soil for the first lift against the foundation should generally be avoided, but having the soil slightly wet of optimum moisture content is better. Any material more plastic than what is typically available for embankment construction is commonly used on the first few lifts. The foundation should be properly moistened to prevent drying of the soil. On steep, irregular rock abutments, material slightly wetter than optimum may be necessary to obtain good workability and a suitable bond. Be careful when special compaction is used to ensure that suitable bonds are created between successive layers of material. This usually requires light scarification between lifts of compacted material. Where a rock foundation would be damaged by penetration of the tamping roller feet, the first compacted lift can be thicker than that specified. The first lift thickness should never exceed 15 in (40 cm) loose for 9-in-long (23-cm) tamper feet, and additional roller passes are probably required to ensure proper compaction. Special compaction methods, such as hand tamping, should be used in pockets that cannot be compacted by roller instead of permitting an unusually thick initial lift to obtain a uniform surface for compaction. Irregular rock surfaces may prevent proper compaction by rollers, and hand compaction may be necessary. However, where foundation surfaces permit, a pneumatic-tire roller or pneumatic-tire equipment should be used near foundation contact surfaces. An

328 FOUNDATION PREPARATION alternative to using thick lifts is using a pneumatic-tire roller or loader with a full bucket and disking or scarifying the lift surfaces to obtain a bond between lifts. The tamping roller can be used when the fill is sufficiently thick and regular to protect the foundation from the tamping feet. Unit weight and moisture should be carefully monitored in the foundation contact zone, and placing and compacting operations should be carefully inspected.

On steep surfaces, ramping the fill aids compaction; about a 6:1 slope should be used for ramping the fill. The surfaces of structures should be sloped (battered) at about 1:10 to facilitate compaction.

The basic objectives of foundation surface treatment within the impervious core are:

• Obtain a good bond between the impervious core materials and the foundation. The foundation surface must be shaped by excavation or concrete placement to provide a surface suitable for earthfill compaction. Compaction techniques used for initial earthfill placement should result in adequately compacted embankment material in intimate contact with and tightly bonded to the foundation without damaging the foundation during placement of the first lifts. A plastic material is preferred next to the foundation, and special requirements on the plasticity, gradation, and moisture content are commonly specified.

• Defend against erosion of embankment materials into the foundation by filling or covering surface cracks in the foundation, using blanket grouting, protective filters, and nonerodible embankment

329 FIELD MANUAL

materials (natural or manufactured) at the foundation contact.

• Remove erodible, weak, unstable, compressible, loose, or pervious materials to ensure a foundation of adequate strength and appropriate permeability. When in doubt, take it out. In rock foundations, defects such as faults, fractures, erosion channels, or solution cavities or channels sometimes cannot be completely removed. Material defects in the rock mass include fault gouge, rock fragments, soft or pervious soil, or solutioned rock. These materials require removal to an adequate depth and replacement with slush grout, dental concrete, or specially compacted earthfill.

How the exposed rock surface is treated after removal of unsuitable overlying materials depends on the type of rock and the irregularities present. Construction activities such as using tracked equipment on soft rock surfaces, using rippers near foundation grade, or nearby blasting may loosen rock or open joints in originally satisfactory rock. This type of damage should and can be avoided to limit excavation and cleanup. The configuration of exposed rock surfaces is controlled largely by bedding, joints, other discontinuities, and excavation methods. Depending on discontinuity orientations, these features can result in vertical surfaces, benches, overhangs, or sawteeth. Features such as potholes, buried river channels, solution cavities, and shear zones can create additional irregularities requiring treatment. Unsuitable material must be removed from the irregularities, and the foundation surface must be shaped to provide a sufficiently regular surface that earthfill can be placed without differential settlement. If the irregularities are small enough and discontinuous both

330 FOUNDATION PREPARATION horizontally and vertically, overexcavation can be appropriate. Generally, the foundation surface can be shaped adequately by conventional excavation or smooth blasting. When smoothing of irregularities requires excessively large quantities of excavation or requires blasting that may damage the foundation, shaping with dental concrete may be appropriate.

High rock surfaces must be stable during construction and must be laid back to maintain a smooth, continuous profile to minimize differential settlement and stress concentrations. Slopes should be 0.5:1 (H:V) or flatter, depending on the fill material.

Remove overhangs. Stepped surfaces that are steeper than 0.5:1 and higher than 1 foot (30 cm) should be excavated or treated with dental concrete to a resultant slope of 0.5:1 or flatter, depending on the fill material (figure 21-1). In the lower portions of a high dam, this requirement may be relaxed. For example, a vertical surface less than 20 ft (6.1 m) long and 5 ft (1.5 m) high might be tolerated if the surface is well within the impervious zone.

Remove all overhangs under the outer zones of earthfill dams and under transitions and filters of rockfill dams. Stepped surfaces that are steeper than 0.5:1 and higher than 5 ft (1.5 m) should be flattened or treated with dental concrete to a slope of 0.5:1 or flatter. Beneath the outer rockfill zones of rockfill dams, nearly vertical abutment contact slopes have been permitted in high, steep-walled canyons. Overhangs should be trimmed or the undercut below the overhang filled with concrete.

If shaping requires blasting, proper blasting procedures are essential to ensure that the permeability and strength of the rock is not adversely affected and that the rock can

331 FIELD MANUAL stand on the slopes and handle the imposed loads. Existing fractures and joints in a rock mass, as well as poor blasting, often result in unacceptable excavated surfaces. Prior competent review, approval, and enforcement of the Contractor’s blasting plan, control of blasting details, requirements for acceptabi1ity of the excavated surface, and control of vibration levels can help obtain the desired excavation surface.

All loose or objectionable material should be removed by handwork, barring, picking, brooming, water jetting, or air jetting. Remove accumulated water from cleaning operations. When the rock surface softens or slakes by water washing, compressed-air jetting or jetting with a small amount of water added to the air should be used. Loose or unsuitable material in cavities, shear zones, cracks, or seams should be treated as follows (figure 21-1):

• Openings narrower than 2 in (5 cm) should be cleaned to a depth of three times the width of the opening and treated.

• Openings wider than 2 in (5 cm) and narrower than 5 ft (1.5 m) should be cleaned to a depth of three times the width of the opening or to a depth where the opening is 0.5 in (12mm) wide or less, but not to a depth exceeding 5 ft (5 cm) and treated.

• Openings wider than 5 ft (1.5 m) are a special case where the required depth of cleaning and treatment is determined in the field.

Special cleanup procedures are required for foundation materials that deteriorate when exposed to air or water (slake). The foundation must be kept moist if deterioration is caused by exposure to air and kept dry if

332 FOUNDATION PREPARATION deterioration is caused by exposure to water. Spray coating with material (similar to concrete curing compound) designed to reduce slaking may (but probably will not) be effective. Cleanup and placing a lean concrete “mud slab” approximately 4 in (15 cm) thick may be effective. Usually, removing the last few inches of material and doing final cleanup just before first placement of fill is the best approach. A maximum time interval may also be specified between the time of exposure of the final grade and the time that the foundation is protected with earthfill or a suitable protective coating.

Cleanup outside the core is normally less critical. Loose material should be removed so that the embankment is in direct contact with suitable rock. If defects are contained within the foundation area, they may not require cleaning and refill. If a defect crosses the entire foundation area, it may require cleaning similar to the foundation beneath the core.

Dental concrete is used to fill or shape holes, grooves, extensive areas of vertical surfaces, and sawteeth created by bedding planes, joints, and other irregularities such as previously cleaned out solution features, shear zones, large joints, or buried channels. Formed dental concrete can be used to fillet steep slopes and fill overhangs. Placing a concrete mat over a zone of closely spaced irregularities is appropriate in local areas that are not large in relation to the core dimensions. Dental concrete shaping can be used instead of excavation by blasting or when excessive amounts of excavation would otherwise be required.

Slabs of dental concrete should have a minimum thickness of 6 in (15 cm) if the foundation is weak enough to allow cracking of the concrete under load (figure 21-1).

333 FIELD MANUAL

Thin areas of dental concrete over rock projections on a jagged rock surface are likely places for concrete cracking and should be avoided by using a sufficient thickness of dental concrete or by avoiding continuous slabs of concrete over areas containing numerous irregularities on weak foundations. Feathering at the end of concrete slabs on weak foundations should not be permitted, and the edges of slabs should be sloped no flatter than 45 degrees. Formed dental concrete should not be placed on slopes greater than 0.5:1 (H:V). When dental concrete fillets are placed against vertical or nearly vertical surfaces in weak rock, feathering should not be permitted, and a beveled surface with a minimum thickness of 6 in (15 cm) is required at the top of the fillet.

Concrete mix proportions should provide a 28-day strength of 3,000 pounds per square inch (21 MPa). The maximum aggregate size should be less than one-third the depth of slabs or one-fifth the narrowest dimension between the side of a form and the rock surface. Cement type will depend on the concentration of sulfates in the foundation materials and groundwater. Low-alkali cement is required for alkali-reactive aggregates. Cement type should be the same as used in structural concrete on the job. Aggregate and water quality should be equal to that required in structural concrete.

The rock surface should be thoroughly cleaned, as described below, and moistened before concrete placement to obtain a good bond between the concrete and the rock surface. When overhangs are filled with dental concrete, the concrete must be well bonded to the upper surface of the overhang. The overhang should be shaped to allow air to escape during concrete placement to prevent air pockets between the concrete and the upper surface of the overhang. The concrete must be formed and placed so that the head of the concrete is higher than the upper

334 FOUNDATION PREPARATION surface of the overhang. If this is impractical, grout pipes should be installed in the dental concrete for later filling of the air voids. If grouting through dental concrete is done, pressures should be closely controlled to prevent jacking the concrete or fracturing the fill.

Finished horizontal dental concrete slabs should have a roughened, broomed finish for satisfactory bonding of fill to concrete. Dental concrete should be cured by water or an approved curing compound for 7 days or covered by earthfill. Earthfill placement may not be permitted over dental concrete for a minimum of 72 hours or more after concrete placement to allow concrete time to develop sufficient strength to withstand stress caused by placing earthfill. Inadequate curing may result in the concrete cracking.

Slush grout is a neat cement grout or a sand-cement slurry that is applied to cracks in the foundation. Cracks or joints are filled with grout rather than spreading grout on the surface (figure 21-1). Slush grout should be used to fill narrow surface cracks and not used to cover areas of the foundation. Slush grout may consist of cement and water, or sand, cement, and water. To ensure adequate penetration of the crack, the maximum particle size in the slush grout mixture should be no greater than one-third the crack width. Generally, neat cement grout is used. The consistency of the slush grout mix may vary from a very thin mix to mortar as required to penetrate the crack. The grout preferably should be mixed with a mechanical or centrifugal mixer, and the grout should be used within 30 minutes after mixing.

The type of cement required will depend on the concentration of sulfates in the foundation materials and groundwater. Low-alkali cement is required for alkali sensitive aggregates. Cement type should be that

335 FIELD MANUAL specified for structural concrete. Sand and water quality should be equal to that required for structural concrete.

Clean out cracks as described above. All cracks should be wetted before placing slush grout. Slush grout may be applied by brooming over surfaces containing closely spaced cracks or by troweling, pouring, rodding, or funneling into individual cracks. Slush grout is best applied just before material placement so cracking will not occur during compaction.

Shotcrete is concrete or mortar that is sprayed in place. The quality of the shotcrete depends on the skill and experience of the crew, particularly regarding the amount of rebound, thickness, feather edges, and ensuring adequate thickness over protrusions on irregular surfaces. Untreated areas can be inadvertently covered because of the ease and rapidity of placement. Shotcrete should be used beneath impervious zones only when site conditions preclude using dental concrete. If shotcrete is used, close inspection and caution are necessary. Shotcrete is an acceptable alternative to dental concrete outside the core contact area.

The fill compaction method used depends on the steepness of the surface, the nature of the irregularities in the foundation surface, and the soil material.

A hand tamper may be used to compact earthfill in or against irregular surfaces on abutments, in potholes and depressions, and against structures not accessible to heavy compaction equipment. Hand-tamped, specially compacted earthfill is typically placed in 4-in (10-cm) maximum compacted lifts with scarification between lifts.

336 FOUNDATION PREPARATION

Site-specific conditions determine whether hand- compacted earthfill or filling with dental concrete is the best solution.

The feet of the roller must not penetrate the first layer of earthfill and damage the foundation. Penetration can be prevented by using a rubber-tired roller or loader to compact the first few lifts above the foundation surface with scarification between lifts. Earthfill specially compacted by pneumatic-tired equipment is typically placed in 6-in (15-cm) maximum compacted lifts. Placement of horizontal lifts against mildly sloping rock surfaces can result in feathering of the earthfill lift near the rock contact. Placement of the initial lift parallel to the foundation surface (as opposed to a horizontal lift) for foundation surfaces flatter than 10:1 (H:V) is acceptable if the compactor climbing up the slope does not loosen or disturb the previously compacted earthfill.

Core material compacted against steep surfaces is typically placed in 6-in (15-cm) compacted lifts with scarification between lifts. Earthfill 8 to 10 ft (2.4 to 3 m) from a steep surface should be ramped toward the steep surface at a slope of 6:1 to 10:1 so that a component of the compactive force acts toward the steep surface.

Earthfill placed against irregular surfaces should be plastic and deformable so that the material is forced (squished) into all irregularities on the foundation surface by compaction or subsequent loading. The first layer soil moisture contents should range from 0 to 2 percent wet of optimum. Select material with a required plasticity range is commonly specified. A soil plasticity index ranging from 16 to 30 is preferred although not absolutely necessary.

337 FIELD MANUAL

Core materials that are erodible include low plasticity or nonplastic, silty materials and dispersive clays. Preventing erosion of embankment materials into the foundation includes sealing cracks in the foundation with slush grout and dental concrete and using filter zone(s) between the fine-grained material and the foundation. Sealing cracks is not totally reliable because concrete and mortar can crack due to shrinkage or loading. Using natural or manufactured nonerodible material for the first several lifts of embankment at the core-foundation contact is good practice.

If erosion-resistant plastic materials are available, these materials should be used for the first several lifts along the foundation contact to avoid placing erodible nonplastic materials directly against the rock surface. If plastic materials are not available, the natural soil can be mixed with sodium bentonite to produce core material to be placed against the foundation. Laboratory testing should establish the amount of sodium bentonite required to give the soil the characteristics of a lean clay.

If nondispersive material is available, it should be used instead of dispersive material, at least in critical locations such as along the core-foundation contact. In deposits containing dispersive material, the dispersion potential generally varies greatly over short distances. Selectively excavating nondispersive material from a deposit containing dispersive materials is frequently difficult and unreliable. Lime can be added to dispersive materials to reduce or convert the soil to a nondispersive material. The amount of lime required to treat the dispersive soil should be established by performing dispersivity tests on samples of soils treated with varying percentages of lime. Adding lime to a soil results in reduced plasticity and a more brittle soil. The lime content should be the

338 FOUNDATION PREPARATION minimum required to treat the soil. Do not treat material that has naturally low plasticity with lime if it is not necessary.

Concrete Arch Dams

The entire area to be occupied by the base of a concrete arch dam should be excavated to material capable of withstanding the loads imposed by the dam, reservoir, and appurtenant structures. Blasting operations must not damage the rock foundation. All excavations should conform to the lines and dimensions shown on the construction drawings, where practical, but it may be necessary to vary dimensions or excavation slopes because of local conditions.

Foundations containing seams of shale, siltstone, chalk, or mudstone may require protection against air and water slaking or, in some environments, against freezing. Excavations can be protected by leaving a temporary cover of unexcavated material, by immediately covering the exposed surfaces with a minimum of 12 in (30 cm) of concrete, or by any other method that will prevent damage to the foundation.

Shaping

Although not considered essential, a symmetrical or nearly symmetrical profile is desirable for an arch dam for stress distribution. However, asymmetrical canyons frequently have to be chosen as arch dam sites. The asymmetry may introduce stress problems, but these can be overcome by proper design. Abutment pads between the dam and foundation may be used to overcome some of the detrimental effects of asymmetry or foundation irregularities. Thrust blocks are sometimes used at

339 FIELD MANUAL asymmetrical sites. The primary use of a thrust block is not to provide symmetry but to establish an artificial abutment where a natural one does not exist. Overexcavation of a site to achieve symmetry is not recommended. In all cases, the foundation should be excavated in such a way as to eliminate sharp breaks in the excavated profile because these may cause stress concentrations in both the foundation rock and the dam. The foundation should also be excavated to about radial or part radial lines.

Dental Treatment

Exploratory drilling or final excavation often uncovers faults, seams, or shattered or inferior rock extending to depths that are impracticable to remove. Geologic discontinuities can affect both the stability and the deformation modulus of the foundation. In reality, the foundation modulus need not be known accurately if the ratio of the foundation modulus Ef to the concrete modulus Ec of the dam is known to be greater than 1:4. Canyons with extensive zones of highly deformable materials and, consequently, Ef /Ec ratios less than 1:4 should still be considered potential arch dam sites. The deformation modulus of weak zones can be improved by removing sheared material, gouge, and inferior rock and replacing the material with backfill concrete.

Analytical methods can provide a way to combine the physical properties of different rock types and geologic discontinuities such as faults, shears, and joint sets into a value representative of the stress and deformation in a given segment of the foundation. This also permits substitution of backfill concrete in faults, shears, and zones of weak rock and evaluates the benefit contributed by dental treatment.

340 FOUNDATION PREPARATION

Data required for analysis are the dimensions and composition of the lithologic bodies and geologic discontinuities, deformation moduli for each of the elements incorporated into the study, and the loading pattern imposed by the dam and reservoir.

Dental treatment concrete may also be required to improve the stability of a rock mass. By using data related to the shear strength of faults, shears, joints, intact rock, pore water pressures induced by the reservoir and/or groundwater, the weight of the rock mass, and the driving force induced by the dam and reservoir, a safety factor for a particular rock mass can be calculated.

Frequently, relatively homogeneous rock foundations with only nominal faulting or shearing do not require the sophisticated analytical procedures described above. The following approximate formulas for determining the depth of dental treatment can be used:

d = 0.002 bH + 5 for H _> 150 ft

d = 0.3b+5 for H<150 ft where: H = height of dam above general foundation level in ft b = width of weak zone in ft d = depth of excavation of the weak zone below the surface of adjoining sound rock in ft. In clay gouge seams, d should not be less than 0.1 H.

These rules provide an estimate of how much should be excavated, but final decisions must be made in the field during actual excavation.

341 FIELD MANUAL

Protection Against Piping

The methods described in the preceding paragraphs will satisfy the stress, deformation, and stability requirements for a foundation, but the methods may not provide suitable protection against piping. Faults, shears, and seams may contain pipable material. To protect against piping, upstream and downstream cutoff shafts may be necessary in each seam, shear, or fault, and the shafts backfilled with concrete. The dimension of the shaft perpendicular to the seam should be equal to the width of the weak zone plus a minimum of 1 foot on each end to key the concrete backfill into sound rock. The shaft dimension parallel to the seam should be at least one-half the other dimension. In any instance a minimum shaft dimension of 5 ft (1.6 m) each way should be used to provide working space. The depth of cutoff shafts may be computed by constructing flow nets and computing the cutoff depths required to eliminate piping.

Other adverse foundation conditions may be caused by horizontally bedded clay and shale seams, caverns, or springs. Procedures for treating these conditions will vary and will depend on the characteristics of the particular condition to be remedied.

Foundation Irregularities

Although analyses and designs assume relatively uniform foundation and abutment excavations, the final excavation may vary widely from that which was assumed. Faults or crush zones are often uncovered during excavation, and the excavation of the unsound rock leaves depressions or holes which must be filled with concrete. Unless this backfill concrete has undergone most of its volumetric shrinkage at the time overlying concrete is placed, cracks can occur in the overlying

342 FOUNDATION PREPARATION concrete near the boundaries of the backfill concrete as loss of support occurs because of continuing shrinkage of the backfill concrete. Where dental work is extensive, the backfill concrete should be placed and cooled before additional concrete is placed over the area.

Similar conditions exist where the foundation has abrupt changes in slope. At the break of slope, cracks often develop because of the differential movement that takes place between concrete held in place by rock and concrete held in place by previously placed concrete that has not undergone its full volumetric shrinkage. A forced cooling of the concrete adjacent to and below the break in slope and a delay in placement of concrete over the break in slope can minimize cracking at these locations. If economical, the elimination of these points of high stress concentration is worthwhile. Cracks in lifts near the abutments very often develop leakage and lead to spalling and deterioration of the concrete.

Concrete Gravity Dams

The entire base area of a concrete gravity dam should be excavated to material capable of withstanding the loads imposed by the dam, reservoir, and appurtenant structures. Blasting should not shatter, loosen, or otherwise adversely affect the suitability of the foundation rock. All excavations should conform to the lines and dimensions shown on the construction drawings, where practicable. Dimensions or excavation slopes may vary because of local conditions.

Foundations such as shale, chalk, mudstone, and siltstone may require protection against air and water slaking or, in some environments, against freezing. These excavations can be protected by leaving a temporary cover of

343 FIELD MANUAL unexcavated material, by immediately applying a minimum of 12 in (30 cm) of mortar to the exposed surfaces, or by any other method that will prevent damage to the foundation.

Shaping

If the canyon profile for a damsite is relatively narrow and the walls are steeply sloping, each vertical section of the dam from the center towards the abutments is shorter in height than the preceding one. Consequently, sections closer to the abutments will be deflected less by the reservoir load, and sections toward the center of the canyon will be deflected more. Since most gravity dams are keyed at the contraction joints, a torsional effect on the dam is transmitted to the foundation rock.

A sharp break in the excavated profile of the canyon will result in an abrupt change in the height of the dam. The effect of the irregularity of the foundation rock causes a marked change in stresses in the dam and foundation and in stability factors. For this reason, the foundation should be shaped so that a uniform profile without sharp offsets and breaks is obtained.

Generally, a foundation surface will appear as horizontal in the transverse (upstream-downstream) direction. However, where an increased resistance to sliding is desired, particularly for structures founded on sedimentary rock foundations, the surface can be sloped upward from heel to toe of the dam.

Dental Treatment

Faults, seams, or shattered or inferior rock extending to depths that are impractical to remove require special treatment by removing the weak material and backfilling

344 FOUNDATION PREPARATION the resulting excavations with dental concrete. General rules for how deep transverse seams should be excavated have been formulated based on actual foundation conditions and stresses in dams. Approximate formulas for determining the depth of dental treatment are:

d = 0.002 bH + 5 for H _> 150 ft d = 0.3 b + 5 for H < 150 ft where:

H = height of dam above general foundation level in feet b = width of weak zone in feet d = depth of excavation of weak zone below surface of adjoining sound rock in feet. In clay gouge seams, d should not be less than 0.1 H.

These rules provide guidance for how much should be excavated, but actual quantities should be determined in the field during excavation.

Although the preceding rules are suitable for foundations with a relatively homogeneous rock foundation and nominal faulting, some damsites may have several distinct rock types interspersed with numerous faults and shears. The effect on the overall strength and stability of the foundation of rock differences complicated by large zones of faulting may require extensive analysis. Data required for analysis include the dimensions and composition of the rock mass and geologic discontinuities, deformation moduli for each of the elements incorporated into the study, and the loading pattern imposed on the foundation by the dam and reservoir.

345 FIELD MANUAL

Dental treatment may also be required to improve the stability of the rock mass. A safety factor for a particular rock mass can be calculated using data related to the strength of faults, shear zones, joints, intact rock, pore water pressures induced by the reservoir and/or groundwater, the weight of the rock mass, and the driving forces induced by the dam and reservoir.

Protection Against Piping

The methods discussed above can satisfy the stress, deformation, and stability requirements for a foundation, but they may not provide suitable protection against piping. Faults and seams may contain pipeable material, and concrete backfilled cutoff shafts may be required in each fault or seam. The dimension of the shaft perpendicular to the seam should be equal to the width of the weak zone plus a minimum of 1 foot (0.3 m) on each end to key the concrete backfill into sound rock. The shaft dimension parallel to the seam should be at least one-half the other dimension. A minimum shaft dimension of 5 ft (1.6 m) each way should be provided for working space. The depth of cutoff shafts may be computed by constructing flow nets and calculating the cutoff depths required to eliminate piping.

Other adverse foundation conditions may be caused by horizontally bedded clay and shale seams, caverns, or springs. Procedures for treating these conditions will vary and will depend on field studies of the characteristics of the particular condition to be remedied.

Foundation Irregularities

Although analyses and designs assume relatively uniform foundation and abutment excavations, the final excavation may vary widely from that which was assumed.

346 FOUNDATION PREPARATION

Faults or crush zones are often uncovered during excavation, and the excavation of the unsound rock leaves depressions or holes that must be filled with concrete. Unless this backfill concrete has undergone most of its volumetric shrinkage at the time overlying concrete is placed, cracks can occur in the overlying concrete near the boundaries of the backfill concrete. Shrinkage of the backfill concrete results in loss of support. Where dental work is extensive, the backfill concrete should be placed and cooled before additional concrete is placed over the area.

Similar conditions exist where the foundation has abrupt changes in slope. At the break of slope, cracks often develop because of the differential movement that takes place between concrete held in place by rock and concrete held in place by previously placed concrete that has not undergone its full volumetric shrinkage. A forced cooling of the concrete adjacent to and below the break in slope and a delay in placement of concrete over the break in slope can be employed to minimize cracking at these locations. If economical, the elimination of these points of high stress concentration is worthwhile. Cracks in lifts near the abutments very often leak and lead to spalling and deterioration of the concrete.

Cleanup

Proper cleaning and water control on a foundation before placing fill or concrete allows the structure and soil or rock contact to perform as designed. Good cleanup allows the contact area to have the compressive and shear strength and the permeability anticipated in the design. Poor cleanup reduces the compressive and shear strength resulting in a weak zone under the structure and providing a highly permeable path for seepage.

347 FIELD MANUAL

Cleaning

Foundation cleanup is labor intensive and costly, so it is routinely neglected. The result is substandard foundations that do not meet design requirements. Rock foundations should be cleaned by:

• Barring and prying loose all drummy rock

• Using an air/water jet to remove as much loose material and fluff as possible

• Removing by hand loose material that an air/water jet misses

Soil foundations should be cleaned by removing material missed by machine stripping that will not be suitable foundation after compaction.

Foundations of weak rock or firm soil can be cleaned by placing a steel plate (butter bar) across the teeth of a backhoe or hydraulic excavator and “shaving” or “peeling” objectionable material off the surface, leaving a clean foundation requiring very little hand cleaning.

Water Removal

Water in small quantities can be removed by vacuuming (with a shop vac or air-powered venturi pipe) or blotting with soil and wasting the wet material just before fill placement. Larger water quantities from seeps can be isolated in gravel sumps and pumped. Grout pipes should be installed; the sumps covered with fabric or plastic; fill placed over the fabric; and after the fill is a few feet above the sump, the sump should be cement grouted by gravity pressure. Seeps in concrete foundations can be isolated and gravel sumps constructed and subsequently grouted

348 FOUNDATION PREPARATION as described above or if the seeps are not too large, the concrete can be used to displace the water out of the foundation during placement.

Bibliography

Abutment and Foundation Treatment for High Embank- ment Dams on Rock, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp.1017- 1032, October 1972.

Current Practice in Abutment and Foundation Treatment, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 1033-1052, October 1972.

Earth and Rockfill Dams, New York, John Wiley and Sons, Inc., 1963.

Foundations and Abutments - Bennett and Mica Dams, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 1053-1072, October 1972.

Foundation Practices for Talbingo Dam, Australia, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 1081-1098, October 1972.

Foundation Treatment for Embankment Dams on Rock, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 1073-1080, October 1972.

349 FIELD MANUAL

Foundation Treatment for Rockfill Dams, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 995-1016, October 1972.

Preparation of Rock Foundations for Embankment Dams, Embankment Dams Engineering, New York, John Wiley and Sons, Inc., pp. 355-363, 1973.

Treatment of High Embankment Dam Foundations, Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM10, pp. 1099-1113, October 1972.

350 Chapter 22

PENETRATION TESTING

Introduction

This chapter discusses the Standard Penetration Test (SPT), Becker Penetration Test (BPT), and Cone Penetra- tion Test (CPT). Penetration tests are used to determine foundation strength and to evaluate the liquefaction potential of a material. SPTs for liquefaction evaluations are stressed in the discussion. The significant aspects of the tests and the potential problems that can occur are included.

History

Penetration resistance testing and sampling with an open ended pipe was started in the early 1900s. The Raymond Concrete Pile Company developed the Standard Penetra- tion Test with the split barrel sampler in 1927. Since then, the SPT has been performed worldwide. The SPT or variations of the test are the primary means of collecting geotechnical design data in the United States. An estimated 80-90 percent of geotechnical investigations consist of SPTs.

Standard Penetration Testing

Equipment and Procedures

The SPT consists of driving a 2-inch (5-cm) outside diameter (OD) “split barrel” sampler (figure 22-1) at the bottom of an open borehole with a 140-pound (63.6-kg) hammer dropped 30 inches (75 cm). The “N” value is the number of blows to drive the sampler the last 1 foot (30 cm), expressed in blows per foot. After the penetration FIELD MANUAL

Figure 22-1.—ASTM and Reclamation SPT sampler requirements.

352 PENETRATION TESTING test is completed, the sampler is retrieved from the hole. The split barrel is opened, the soil is classified, and a moisture specimen is obtained. After the test, the borehole is extended to the next test depth and the process is repeated. SPT soil samples are disturbed during the driving process and cannot be used as undisturbed specimens for laboratory testing.

The American Society of Testing and Materials standardized the test in the 1950s. The procedure required a free falling hammer, but the shape and drop method were not standardized. Many hammer systems can be used to perform the test, and many do not really free fall. The predominant hammer system used in the United States is the safety hammer (figure 22-2) that is lifted and dropped with the a rope and cat head. Donut hammers (figure 22-3) are operated by rope and cat head or mechanical tripping. Donut hammers are not recommended because the hammers are more dangerous to operate and are less efficient than safety hammers. Auto- matic hammer systems are used frequently and are preferred because the hammers are safer and offer close to true free fall conditions, and the results are more repeatable.

The SPT should not be confused with other thick-wall drive sampling methods such as described in ASTM Standard D 3550 which covers larger ring-lined split barrel samplers with up to 3-inch (7.6-cm) OD. These samplers are also know as “California” or “Dames & Moore” samplers. These drive samplers do not meet SPT requirements because they use bigger barrels, different hammers, and different drop heights to advance the sampler.

353 FIELD MANUAL

Figure 22-2.—Safety hammer.

354 PENETRATION TESTING

Figure 22-3.—Donut hammer.

The energy delivered to the sampler can vary widely because of the wide variety of acceptable hammer systems. Numerous studies of SPT driving systems indicate that the energy varies from 40 to 95 percent of the theoretical maximum energy. The “N” value is inversely proportional to the energy supplied to the

355 FIELD MANUAL sampler, and the energy delivered to the sampler is critical. Because of energy losses in the impact anvil, energy from the hammer should be measured on the drill rod below the impact surface. Drill rod energy ratio is determined by measuring the force-time history in the drill string. Both acceleration and force-time history can be measured and are important in determining the normalized penetration resistance of sands for liquefaction resistance evaluations (ASTM D 6066). Common practice is to normalize the SPT N value to a 60-percent drill rod energy ratio. Adjustment factors can be as large as 20 to 30 percent.

The largest cause of error in the SPT is drilling disturbance of the material to be tested. This is especially true when testing loose sands below the water table. Field studies have shown that “sanding in” can be prevented by using rotary drilling with drill mud and upward-deflected-discharge bits and by maintaining the fluid level in the drill hole at all times. Hollow-stem augers are especially popular for drilling in the impervious zones in dams but can cause problems when loose sand is encountered below the water table. Many other drilling methods are available for performing SPTs, and each should be evaluated relative to potential problems and how the data will be used.

Information Obtainable by SPT

The SPT does provide a soil sample. Sampling is not continuous because the closest recommended test interval is 2.5 feet (75 cm). Typical sampling is at 5-foot (1.5-m) intervals or at changes in materials. The test recovers a disturbed soil sample that can be classified on site, or the sample can be sent to the laboratory for physical properties tests.

356 PENETRATION TESTING

SPT N values have been correlated to numerous soil properties. In cohesionless soils (sands), the SPT can be used to predict the relative density of sands (i.e., very loose, loose, medium, etc.) (table 22-1).

Table 22-1.—Penetration resistance and soil properties based on the SPT (Peck, et al.)

Sands Clays (Fairly reliable) (Rather reliable)

Number of Number of blows per blows per foot Relative foot (30 m), N density (30 cm), N Consistency

Below 2 Very soft

0-4 Very loose 2-4 Soft

4-10 Loose 4-8 Medium

10-30 Medium 8-15 Stiff

30-50 Dense 15-30 Very stiff

Over 50 Very dense Over 30 Hard

The SPT has been widely used to predict the allowable bearing capacity of footings on sand. There are several empirical methods that are based either on case histories or on drained modulus of deformation predictions. The application of these predictions should be tempered by local experience. There are many proposed methods for estimating bearing capacity. The methods are probably slightly conservative and should be applied carefully.

357 FIELD MANUAL

SPT N values must be corrected for overburden pressures and the location of the water table.

For clays, the SPT is less reliable for predicting strength and compressibility, especially for weaker clays. The SPT is commonly used to assess the consistency of clays by grouping clays as very soft, soft, medium, etc. Predictions of undrained strengths should be used with extreme caution, especially in weak clays, because the SPT barrel remolds the clay, and the penetration resistance is more a measure of remolded strength. For evaluating undrained strength in clays, vane shear, unconfined compression, or CPTs are better than SPTs. SPT data should not be used to estimate the compressibility of clays. To evaluate compression behavior of clays, use either empirical factors based on water content and atterberg limits or obtain undisturbed samples for laboratory consolidation testing.

SPT data routinely have been used for predicting liquefaction triggered by earthquake loading. If liquefaction is predicted, the SPT data can be used to estimate the post-earthquake shear strengths. Extensive case history data have been collected to evaluate liquefaction; however, the data are subject to drilling disturbance errors and the energy delivered by the hammer system must be known. If drilling disturbance is evident or suspected, the CPT is an alternative because the soil can be tested in place. Procedures for evaluating liquefaction from SPTs are given in Reclamation’s Design Standards No. 13, Embankment Dams, “Chapter 13, Seismic Design and Analysis.” SPT N data can be used to estimate the shear modulus of clean sands, but the method is approximate. If the shear modulus is needed, directly measuring the shear wave velocity is preferred.

358 PENETRATION TESTING

Liquefaction occurs when water pressure builds up in granular soils during an earthquake. Soils mostly susceptible to liquefaction are “cohesionless” soils, primarily clean sands and gravels (GP, SP, GW, SW, GP- GM, SP-SM) and silty sands and gravels (SM, GM). The term, “sands,” in the following discussion refers to all these soils. The water pressure buildup results in strength loss and possibly deformation, slippage, and failure. Data collected at liquefaction sites have been used to assess whether a deposit is liquefiable.

Testing Cohesionless Soils

Earthquake induced liquefaction is commonly associated with sands below the water table. Good drilling technique is critical to ensuring that the sands are undisturbed prior to the SPT. Unfortunately, loose sand is one of the most difficult materials to drill.

If disturbed sands are present, take measures to avoid continued disturbance. Perform depth checks to assess the sand depth at the bottom of the drill hole. These depth checks are made by seeing exactly where the sampler rests before testing. Depth checks that can be made during drilling will be discussed below. Do not drill at excessive rates. Signs of disturbance are excessive slough in the SPT barrel, drill fluid in the sample, and failure of the sampler to rest at the proper cleanout depth. Slough is the disturbed material in the drill hole that caves from the sidewalls but can include disturbed sand that heaves or flows upward into the drill hole. Slough can also consist of cuttings which settle from the drill fluid before testing.

The SPT sampler must rest at the intended depth. This depth is to the end of the cleanout bit or the end of the pilot bit in hollow-stem augers. If the sampler rests at an

359 FIELD MANUAL elevation that is 0.4 foot (12 cm) different from the cleanout depth, disturbance of the soil may be occurring, and the hole must be recleaned.

There are a number of advantages to the SPT:

(1) The test is widely used, and often local experience is well developed.

(2) The test is simple, and many drillers can perform the test.

(3) The SPT equipment is rugged, and the test can be performed in a wide range of soil conditions.

(4) There are numerous correlations for predicting engineering properties with a good degree of confidence.

(5) The SPT is the only in place test that collects a soil sample.

Although the SPT is commonly used and is a flexible in place test, there are significant disadvantages. The test does not provide continuous samples. Different soils in the SPT interval tend to be logged as one soil, especially if the soil core is combined into one laboratory test specimen and laboratory data are used in the logs. Hollow-stem augers can give disturbed samples between test intervals, and the intervals between tests can be logged. The greatest disadvantage to SPTs is the lack of reproducibility of the test results. Drilling disturbance, mechanical variability, and operator variability all can cause a significant variation in test results. The SPT should not be used unless the testing is observed and logged in detail. Old data where drilling and test procedures are not documented should be used with

360 PENETRATION TESTING extreme caution. Another disadvantage to SPTs is that progress is slower than other in place tests because of incremental drilling, testing, and sample retrieval, and SPTs may be more expensive than other in place tests. The SPT is influenced by more than just overburden stress and soil density. The soil type, particle size, soil age, and stress history of the soil deposit all influence SPT results.

Drilling Methods

Fluid Rotary Drilling

Rotary drilling with clear water results in N values that are much lower than N values that are obtained when drilling mud is used. Two factors are involved: (1) the water from drilling can jet into the test interval disturbing the sand, and (2) the water level in the borehole can drop and the sand can heave up the borehole when the cleanout string is removed. These two factors must be minimized as much as is practical.

The best way to drill loose, saturated sands is to use bentonite or polymer-enhanced drill fluid and drill bits that minimize jetting disturbance. Also when drilling with fluid, use a pump bypass line to keep the hole full of fluid as the cleanout string is removed from the drill hole. The lack of fluid in the hole is one of the most frequent causes of disturbed sands. If the soils are fine-grained, use a fishtail-type drag bit with baffles that deflect the fluid upwards. A tricone rockbit is acceptable if gravels or harder materials are present, but adjust the flow rates to minimize jetting.

Casing can help keep the borehole stable, but keep the casing back from the test interval a minimum of 2.5 feet

361 FIELD MANUAL

(75 cm) or more if the hole remains stable. Using a bypass line to keep the hole full of fluid is even more important with casing because the chance of sand heave up into the casing is increased if the water in the casing drops below natural groundwater level. The imbalance is focused at the bottom, open end of the casing. In extreme cases, the casing will need to be kept close to the test interval. Under these conditions, set the casing at the base of the previously tested interval before drilling to the next test interval. Intervals of 2.5 feet (75 cm) are recommended as the closest spacing for SPTs.

Use drilling mud when the SPT is performed for liquefaction evaluation when rotary drilling. A bentonite-based drilling mud has the maximum stabilizing benefit of mud. Bentonite provides the maximum weight, density, and wall caking properties needed to keep the drill hole stable. When mixing mud, use enough bentonite for the mud to be effective. There are two ways to test drill mud density or viscosity—a Marsh Funnel or a mud balance. A mud sample is poured through a Marsh Funnel, and the time needed to pass through the funnel is a function of the viscosity. Water has a Marsh Funnel time of 26 seconds. Fine-grained soils require mud with Marsh Funnel times of 35 to 50 seconds. Coarser materials such as gravels may require funnel times of 65 to 85 seconds to carry the cuttings to the surface. If using a mud balance, typical drill mud should weigh 10-11 pounds per gallon (lbs/gal) (1-1.1 kilograms per liter [kg/L]). Water weighs about 8 pounds per gallon (0.8 kg/L).

Exploration holes are often completed as piezometers. Revertible drilling fluids have been improved, and there are synthetic polymers that break down more reliably. If necessary, specific “breaker” compounds can be used to break down the mud and clean the borehole. If the

362 PENETRATION TESTING borehole cannot be kept stable with polymer fluid, bentonite mud should be used and a second hole drilled for the piezometer installation. Do not combine drill hole purposes if the data from SPTs or piezometers are compromised.

Drilling sands with clear water is possible, but only if the driller is very experienced. As long as drilling is carefully performed, drilling with water can result in SPT N values close to those obtained using mud. Disturbance can be avoided; but without drill mud, jetting disturbance, cave, and sand heave caused by fluid imbalance are likely.

If the water level in the sand layer is higher than the ground surface, sand heave is really going to be a problem. Under these conditions, heavy bentonite mud (80 to100 sec on the Marsh Funnel) is required. A fluid bypass to keep the hole full of mud is required, and an elevated casing or drill pad to hold down the sand can be used. Some successful mud improvement is possible with Barite or Ilmenite additives. Mud can be weighted to about 15 lb/gal with these additives. Sodium or calcium chloride can be used to give polymer fluid better gel strength. In artesian conditions, it may not be possible to keep the sand stable. In these cases, other tests such as the CPT can be used to evaluate the sand.

When using fluid rotary drilling, circulate the drill fluid to remove the cuttings. Pull back the cutting bit several feet, cut fluid circulation, and then slowly and gently lower the bit to rest on the bottom of the hole. Check to see if the depth is within 0.4 foot (10 cm) of the cleanout depth. This check determines if there is cuttings settlement, wall cave, or jetting disturbance.

The bottom of the borehole normally heaves when the cleanout drill string is pulled back creating suction. Fluid

363 FIELD MANUAL should be added to the drill hole as the cleanout string is removed to help avoid problems. Once the sampler is placed, check the sampler depth and compare it to the cleanout depth. A difference of 0.4 foot (10 cm) is unsatisfactory. If sands or silty sands heave up into the borehole, the SPT sampler will often sink through most of the slough. The only way to check for this situation is to carefully inspect the top of the sampler and the ball check housing for slough or cuttings. If the ball check area is plugged with cuttings, the SPT N value may have been affected. A thin plastic cover is sometimes used to keep the slough out of the sampler. The cover is either sheared off at the first blow or it is shoved up into the sampler.

The fluid rotary method is probably the best method for determining SPT N values in saturated sands. In the following sections, two other acceptable drilling methods are discussed. If these methods do not work, use the fluid rotary method.

Hollow-Stem Augers

Hollow-stem augers (HSA) have been used successfully to do SPTs in loose saturated sands. With the proper precautions, hollow-stems can be used reliably in sands, but there are some problems with HSAs. The primary problem with the HSA in loose sands is sand heaving into the augers. This occurs when the pilot bit or the HSA sampler barrel is removed in preparation for the SPT. Sometimes, sand can heave 5 to 10 feet (1.5 to 3 m) up inside the augers. SPT N values taken with this amount of disturbance are unacceptable. These problems can be overcome in most cases by using water-filled augers and removing the pilot bit or HSA sampler slowly to avoid the suction. Drilling mud is not usually required and can cause sealing problems.

364 PENETRATION TESTING

There are two types of HSA systems shown in figure 22-4—wireline and rod type. With either type of system, removal of the pilot bit or HSA sampler barrel can result in sand heaving into the augers. The rod type system is best at preventing sample barrel rotation during soil sampling. In sanding conditions, the wireline system is sometimes harder to operate because the withdrawal rate of the bit or HSA sampler is harder to control. Sanding-in also prevents re-latching of the wireline barrel. Rod type systems are recommended when drilling in heaving sands. If sand heaves a considerable height into the augers, the auger will need to be cleaned or retracted in order to continue drilling using either system. If the augers have to be pulled up 3 feet (1 m) to re-latch a pilot bit or sampler barrel, tremendous suction occurs at the base of the boring, which can disturb the next SPT test interval.

When using HSAs below the water table, the hole must be kept full of fluid, just like it must when using fluid rotary methods. A water or mud source and a bypass line are required. Some successful techniques for hollow- stem drilling in flowing sands are:

C When approaching the test interval, slow the auger rotation to just enough to cut the soil; do not continue to rotate without advancement near the test interval. In flowing sands, continued rotation near the test interval will create a large void around the hole annulus and increase the chance of caving and disturbance of the test interval. If high down pressure is used with wireline systems, the pressure should be relaxed; and the augers should be slightly

365 FIELD MANUAL

Figure 22-4.—Example of rod-type and wireline-type hollow-stem augers.

366 PENETRATION TESTING

retracted ½ inch (1 cm) or so to re-latch bits or barrels. There is no need to release down pressure or retract the augers with rod-type systems.

C Add water to a level higher than the surrounding groundwater level before pulling the pilot bit or sampling barrel. In most cases, water can be added to the top of the augers without concern for disturbance. Add water by removing the drive cap using a hose from the bypass line. When removing the drive cap on rod-type systems, be careful to disconnect the drive cap bearing from the inner rods, or the pilot bit or sampler will be pulled prematurely before adding water. When using a wireline system, the latching device can be sent down the hole and latched before adding water.

The water level is not always maintained at the top of the column, especially if there is a thick layer of unsaturated soil above the test zone. Water can leak through the auger joints, and it may be necessary to add a lot of water.

Pulling the Sampler Barrel.—The sample barrel assembly is generally 5 feet (1.5 m) long. This barrel does not have much clearance with the inside of the augers, especially in the bushing at the base of the augers. With the augers full of water, reconnect the drive cap to the inner rods. Pull the barrel slowly up 0.1 to 0.3 foot (3 to 10 cm) and observe the water level in the augers. If water flows upward, out of the augers, there is a seal between the augers and the sampler, and the sampler barrel is acting like a syringe. If water flows from the top with rod type systems, rotate the barrel or work the barrel slightly down and up to try to break the seal and vent. For wireline systems, release the pulling force and re-apply. Pull slowly and attempt to break the seal. Once the seal is broken, remove the sampler slowly. Remember, with

367 FIELD MANUAL rapid withdrawal rates, suction can be created anywhere in the auger column. For rod systems, add water during pulling to account for water level drop. The same rule applies for wireline systems, but less water is needed.

Pulling the Pilot Bit.—Most pilot bits are seated flush in a brass bushing in the end (crown) of the augers. The pilot bit cutting teeth should be set to a lead distance the same as the outer cutting teeth, so that the body of the pilot bit sits correctly in the bushing. Do not drill with the pilot bit in advance of the outer cutting teeth. A useful procedure in heaving sands is to use a pilot bit one size smaller than the augers being used. For example, if a 4.25-inch (11-cm) inside diameter (ID) HSA is used, a 3.75-inch (9.5-cm) ID HSA pilot bit can be used to reduce vacuum and suction effects.

When drilling with the pilot bit, pull the bit back slowly about 0.1 to 0.2 foot (3 to 6 cm) to allow any seal in the bushing to vent. If the bit is withdrawn quickly, suction will likely occur. If water flows out the top of the augers, suction is occurring. If suction is occurring, rotate the pilot bit and work it down and up to try to break the seal. Once the bit clears the bushing, the tendency to bind is reduced. Withdraw the pilot bit slowly and add water, to account for water level drop as the rods are removed. Remember, with rapid withdraw rates, suction effects can be created anywhere in the auger column.

If sanding-in cannot be controlled with fluid or slow pulling, there are special flap valves that can be placed in the pilot bit seat. Drill without the pilot bit with flap valves.

Once the sampler has been inserted to the base of the boring, determine the depth to the sampler tip as a quality check. If there is more than 0.4 foot (12 cm) of

368 PENETRATION TESTING slough or heave, the test may not be acceptable. This guideline is arbitrary, and it is possible to get a reliable test with as much as 0.5 foot (15 cm) or more slough as long as the vent and ball check of the sampler are not plugged. If the SPT barrel is used to test the bottom of the hole, the sampler will often penetrate loose slough or heave. Checks with a weighted tape may be more accurate in determining the depth to the slough. When using the HSA sampler barrel to core before testing, sand falling out of the barrel could be the cause of slough inside the auger. To avoid this problem, use catcher baskets in the HSA sampler barrel.

When testing at close intervals of 2.5 feet (75 cm) or less, it may be necessary to add water to the augers as the SPT sampling string is removed to avoid water level imbalance and possible heave.

It’s a good idea to combine the continuous sampler of the HSA with SPT operations. If SPTs are at 2.5-foot (75-cm) intervals, perform the SPT and then sample the 2.5-foot (75-cm) and over-sample the 1.5-foot (45-cm) test interval. This adds some time, but allows continuous sampling. This sampling method provides a look at the soils between the test intervals. It is also helpful if recovery is low.

Rotary Casing Advancers

Rotary casing advancers can provide good SPT N values in sands. The casing advancer method uses drilling fluid (bentonite and water) as a circulation medium and is a fluid rotary drilling method. This method is successful because the large diameter outer rods remain filled with drill fluid and keep the sand down. The casing advancer normally has a diamond bit but can be equipped with tungsten carbide drag bits on the outside edge to over-cut soil. Typically, an HQ- or HW-size casing advancer is

369 FIELD MANUAL used with or without a pilot bit. The pilot bit can be a tricone bit removed via wire line. Suction is possible when a pilot bit is removed. If suction occurs, drilling without a pilot bit should be tried. An advantage of drilling with a wireline is that when the pilot bit is removed, the line takes up little volume and results in a minor drop in fluid level inside the rod column. Since a good fluid column remains in the rods, a fluid bypass is not needed. The only problem is that whenever adding rods to the SPT drill string, fluid flows out of the advancer.

The casing advancer must be operated very carefully to avoid sand disturbance. Fluid is pumped down the casing and up a narrow annulus along the exterior of the casing. A casing advancer, especially without a pilot bit, is equivalent to a bottom discharge bit. If excessive fluid pressures are used or if circulation is lost, jetting or hydraulic fracturing the material in the SPT test interval is possible. Drilling the material with a slow advance rate and with low pressure while maintaining circulation is necessary to drill successfully with this system. If circulation return stops, blockage may be occurring; and if pump pressures increase, hydraulic fracturing could occur. If the advance rate is too fast, circulation will be blocked. Water is not an acceptable drill fluid with this method, and drill mud must be used.

Summary of Drilling Effects

Table 22-2 illustrates the effects of different drilling and mechanical variables on the SPT N value (items 1 through 5). A typical N value in clean quartz sand is 20 blows per foot (30 cm). The possible range of N for the material is shown if the material is subject to errors in testing.

370 PENETRATION TESTING

Table 22-2 shows that drilling disturbance can have drastic effects on the N value. In fact, zero blows can be obtained. Zero blows may not be realistic because, in many cases, loosened sand settles back to the bottom of the hole. Also, very loose sand normally does not allow the sampler to settle under the weight of the assembly. Drilling disturbance usually results in a low N value. Low blow counts indicate loose, weak soils, and a weak foundation may be assumed. Erroneous low disturbed N values can result in costly over design of structures. The most important aspect of SPT testing is the way the hole is drilled.

Procedure Variables

The recommended 2.5-foot (75-cm) interval is to ensure that the next interval is not disturbed. If material that only has a few thin layers of sand is drilled, continuous sampling is possible, but difficult, and should not be attempted unless necessary.

Hammer Blow Rate

The blow count rate is important when soil drainage needs to be considered. Most test standards request SPT blows at a rate of 20 to 40 blows per minute (bpm). Blows at 55 bpm are not likely to have an effect on clean sand; but at some fines content, blows will be reduced by the lack of drainage. Blows should be between 20 and 40 bpm if a hammer with a controllable rate is used. Some hammer systems are designed to deliver blows at a faster rate. The automatic hammer is designed to deliver blows at a rate of 50 to 55 bpm. The hammer can be set to run at 40 bpm by adding a spacer ring to the impact anvil. If a hammer rate differs from 50 bpm, clearly note it on the drill logs.

371 FIELD MANUAL 10 e1 N=10 in clay SPT value SPT Typical raw 20 17 8-10? e1 0-20 8-10? 25-30 10 e N = 20 clean sand clean Typical raw SPT value in value SPT Cause Table 22-2.—Estimated variability of SPT N Values 7. Using a 3-inch (7.6-cm) OD barrel versus a barrel OD (7.6-cm) 3-inch a Using 7. barrel (5-cm) 2-inch 5. 8-inch (20-cm) diameter hole compared to 4 inches (10 cm) 1. Using bypass fluid mud drilling and 2. Using drill mud no bypass and fluid 3. Using clear water with or without bypass or without with augers hollow-stem Using 4. fluid 20 0-20 0-20 8-10? 10 8-10? minute (bpm) as opposed to 30 bpm Basic Description method Drilling Sampler 6. Using a larger ID barrel, without the liners 17 9 Procedure per blows 55 of rate count blow a Using 8.

372 PENETRATION TESTING 5 8-10 e3 N=10 e2 in clay SPT value SPT Typical raw 22 14 7 3025 15 12 4 18-22 N = 20 e2 clean sand clean Typical raw SPT value in value SPT Energy TransmissionEnergy Factors Cause Table 22-2.—Estimated variability of SPT N Values (continued) 13. Three wraps versus two wraps around the cathead the around wraps two versus wraps Three 13. 14. Using new rope as opposed to old rope cathead on wrap two versus drops cut string Free fall 15. 22 versus two hammer automatic high-efficiency Using 16. hammer safety wrap 16 11 19 8 9 10. SPT at 200 feet (60 m) as opposed to 50 feet (30 m) 11. SPT at less than 10 feet (3 m) as opposed to 50 feet (30 m) with AW rods 12. SPT at less than 10 feet (3 m) as opposed to 50 feet (30 m) with NW rods Basic Description Hammer operation Drill rods 9. AW rod versus NW rod

373 FIELD MANUAL of N=10 in clay SPT value SPT Typical raw 242218 12 11 9 N = 20 clean sand clean Typical raw SPT value in value SPT re efficient; with larger rods, N may be less in clay because er confining pressure at great depth. The difference shown here Cause Energy TransmissionEnergy Factors (continued) Table 22-2.—Estimated variability of SPT N Values (continued) 17. Using a donut hammer with large anvil as opposed to hammer safety 18. Failure to obtain 30-inch (75-cm) drop height (28 inches [70 cm]) 19. Failure to obtain 30-inch (75-cm) drop height (32 inches [80 cm]) testing during hammer safety of tapping Back 20. 25 12 Basic Description Hammer Operation is from energy only and confining pressure was not considered. pressure confining and is from only energy the weight. clay may 3 = N in be lower because of the weight of the rods. 4 = Actual N value will be much higher because of high e = Estimated value. Estimated = e 1 = Difference occurs dirty in only. sands 2 = It is not known whether small drill holes are less or mo

374 PENETRATION TESTING

Limiting Blow Counts

The Reclamation test procedure calls for stopping the test at 50 blows per foot (30 cm). Other agencies sometimes go to 100 blows per foot (30 cm) because the ASTM test standard D 1586 sets a 100-blow limit. The Reclamation standard is lower to reduce equipment wear.

Using the soil liquefaction criteria for sand at a depth of 100 feet (30 m), 50 blows would not be considered liquefiable. SPT data are corrected to a stress level of 1 ton per square foot (ton/ft2). In a typical ground mass, a 1 ton/ft2 stress level occurs at a depth of 20 to 30 feet (6 to 9 m), depending on the location of the groundwater table. Blow counts in a sand of constant density increase with depth. A correction factor is used to adjust for this overburden effect. In earthquake liquefaction clean sand N160 values greater 30 blows per foot (bpf) are not liquefiable. A blow count of 50 bpf at 100 feet (30 m) corrects to about 30 bpf at 1 ton/ft2. Higher blow counts would not be considered liquefiable. If testing is deeper than 100 feet (30 m) it will be necessary to increase the limiting blow counts to 100. The refusal rule still applies; if there is no successive advance after 10 blows, the test can be stopped.

SPT N values in gravels generally are much higher than in sands. Liquefaction criteria for sands are not reliable criteria for gravels.

Penetration per Blow or Blows per 0.1 Foot (3 cm)

Penetration for each blow should be recorded when drilling in gravelly soils. If penetration per blow is recorded, sand layers can be resolved, and the N value of the sand can be estimated. The blow count in sand can be estimated from a graph of penetration per blow. The

375 FIELD MANUAL extrapolation is generally reliable if the blows start in sand. If the interval starts with gravel and then penetrates into sand, the extrapolation is less reliable because the sampler could be plugged by gravel.

The number of blows for 0.1 feet (3 cm) is the minimum penetration rate data that should be collected. If three people are present, it is very easy to record “penetration per blow,” and these data are preferred over the coarser blows per 0.1 feet (3 cm). To record penetration per blow, make a form with three columns. In one column, list the blows 1 through 100. Mark the drill rods in 0.1-foot (3-cm) intervals or use a tape starting at zero from the edge of a reference point. In the second column, record the total penetration as the test is performed. This will require a reader to call off the total penetration. The reader can interpolate between the 0.1-foot (3-cm) increments, or the penetration can be read directly from a tape. After the test is done the incremental penetration can be calculated from the cumulative penetration data and recorded in the third column.

Equipment and Mechanical Variables

Sampler Barrel

The standard sampler barrel is 2 inches (5.1 cm) in OD and is the barrel that should be used. In private industry, 2.5- (6.4-cm) and 3-inch (7.6-cm) OD barrels are occasionally used. If sample recovery in coarse materials is poor, it is acceptable to re-sample with a 3-inch (7.6-cm) barrel equipped with a catcher.

Gravelly soils generally do not provide reliable SPT data for liquefaction evaluations that are based on sands. Other methods use larger samplers and hammers to

376 PENETRATION TESTING evaluate the liquefaction potential of gravelly soils. The BPT is used at gravel sites. Often, the BPT is used at gravel sites after a first round of SPT testing shows considerable gravels present.

Sampler Shoe

The dimensions of the sampler shoe should meet ASTM D 1586 requirements. Some drill equipment catalogs claim to have special “heavy duty” sample barrels and shoes. The “Terzaghi” style does not meet the ASTM and Reclamation requirements. When buying shoes, check their dimensions to be sure they meet test requirements. Figure 22-1 shows both Reclamation and ASTM sampler requirements.

Shoe ruggedness can be improved by “carburizing” the metal. This is a process where the shoe is heated in a carbon gas to improve the surface hardness of the steel. This makes the shoe more rugged but also more brittle. Most drill manufacturers supply untreated low carbon steel such as 1040 alloy. Generally, a local machine shop can “carburize” the shoe, an inexpensive process.

Sample Retainers

A sample retainer should not be used for liquefaction studies except in desperation because the effects are unknown. If the sample cannot be retained, a sample may be taken with a large diameter split barrel sampler with a retainer re-driven through the test interval. The over coring procedure discussed earlier using HSAs could also be used.

There are several types of retainers available and some types are better than others. There is a flap valve device that actually looks like a toilet seat (a small one) that

377 FIELD MANUAL places a large constriction inside the barrel. This device is the least desirable of the retainers if the N value is important. The basket type catcher is made of curved fingers of steel, brass, or plastic. This type of retainer is only a minor constriction because the holding ring fits into the recessed area between the shoe and the barrel. The problem with this catcher is that the fingers may not always fall back into position to hold the core. A better variation of this catcher is the “Ladd” type retainer that combines the finger basket with a plastic sleeve. This retainer is the most successful at retaining flowing sand because the bag adds extra retaining capability.

Sampler Liners

Most of the SPT samplers in the USA accept liners, but the liner is usually omitted. To determine if the sampler will accept a liner, feel for an offset (increased diameter) inside the shoe. If an offset is present, the barrel is 1½-inch (3.8-cm) ID. Log whether a constant diameter or an enlarged diameter barrel is used because the sample type can effect recovery. For liquefaction evaluation, a constant ID barrel is recommended.

A sampler used without liners is actually better for recovery. Average recovery of a constant ID barrel is about 60 percent, and the average for the barrel without liners is about 80 percent. The difference in N value between constant and enlarged diameter barrels is not known, but an increase in blows in the range of 1 to 4 is likely with a constant ID barrel.

378 PENETRATION TESTING

Sampler Length

A 24-inch- (61-cm-) long split barrel can normally accommodate any slough in the drill hole without plugging the ball check device.

Sampler Vent Ports

The required vent ports for the sampler top subassembly in ASTM and Reclamation test procedures are inadequate when drilling with mud. The ASTM standard requires two G-inch (1-cm) diameter vents above the ball check. When drilling with mud, the fluid gets loaded with sand and can easily plug these ports. The sampler and rods fill with mud as they are lowered into the drill hole. A big column of drill mud may try to push the sample out if the ball check does not seat. Drill larger vent ports in the top subassembly to avoid this problem. Some drillers use a 0.5- to 1-foot (15- to 30-cm) drill rod sub just above the sampler with extra holes drilled in it to easily drain drill fluid from the rod column.

Hammers, Anvils, Rods, and Energy Effects

The variables in energy transmission are hammer type, hammer drop height, hammer drop friction, energy losses in impact anvil(s), and energy losses in rods. The energy in the drill rods is called the “Drill Rod Energy Ratio” or ERi.

Some hammers, especially donut (casing type) hammers with large anvils, deliver approximately 50 percent of the total potential energy of a 140-lb (63.6-kg ) hammer dropping 30 inches (75 cm). The N value is proportional to the energy delivered, and the N values can be adjusted to a common energy delivery level. The current practice is to adjust SPT N values to 60-percent drill rod energy.

379 FIELD MANUAL

Safety Hammers

There are many kinds of SPT hammers. Pin-guided and donut type hammers were common in the past, but these hammers have generally been replaced by the “safety” hammer which has an enclosed anvil (figure 22-2). There are also new automatic hammers that improve the repeatability of delivered hammer energy to the sampler.

The safety hammer provides an economical and safe method of performing the SPT. The enclosed anvil removes hazards from flying metal chips, and operators cannot get their hands in the impact surface. Due to their inherent geometry, safety hammer energy transmission can vary only by about 20 percent as long as the hammers are operated correctly and consistently.

Safety hammers should be designed with a total stroke of about 32 inches (80 cm), and there should be a mark on the guide rod so the operator can see the 30-inch (75-cm) drop. The hammer weight should be 140 pounds (63.6 kg). These characteristics should be verified on the hammer. An easy way to weigh the hammer is to place the total assembly on a platform scale, get the total weight, then lift the outer hammer off the anvil, and weigh the guide rod and anvil. The difference in the two weights is the hammer weight. The hammer weight should be 140 +/- 2 lb (63.6 kg +/- 0.9 kg). Hammers should be stamped with an ID number. It is best to keep a given hammer for a specific drill, especially if the energy transmission of the drill has been measured in the past.

The assumption is that safety hammers deliver 60-percent drill rod energy with two wraps of rope around the cathead. Actually, the hammers deliver about 60 to 75 percent depending on their construction. The guide rod is one factor that affects the energy transmission.

380 PENETRATION TESTING

Some safety hammers come with a solid steel guide rod, and others use a hollow AW drill rod. The solid guide rod absorbs energy, and the solid steel guide rod safety hammer will deliver lower energy than the hollow guide rod safety hammer. These differences are not enough to recommend one design over another. Another variable with safety hammers is a vent. Some hammers have vents near the top of the hammer. A vent allows some air to escape as the anvil moves toward the impact surface. These vents allow the best free fall possible.

Donut Hammers

These hammers are not recommended except in special cases such as when clearance is a problem. If the testing is for liquefaction evaluation, it may be necessary to measure the energy of the donut hammer used. The donut hammer is supposed to be inefficient, but if the hammer has a small anvil, efficiencies may be similar to the safety hammer. The larger anvil absorbs part of the hammer energy.

Rope and Cathead Operations

Most SPTs are performed using the rope and cathead method. In this method, the hammer is lifted by a cathead rope that goes over the crown sheaves. ASTM and Reclamation standards require two wraps of rope around the cathead. After the hammer is lifted to the 30-inch (75-cm) drop height, the rope is thrown toward the cathead, allowing the hammer to drop as freely as possible.

Three wraps will reduce the drill rod energy by about 10 percent and will result in a higher N value. As the rope gets old, burned, and dirty, there is more friction on the cathead and across the crown sheaves. New rope is

381 FIELD MANUAL stiffer and is likely to have higher friction than a rope that has been broken in. A wet rope may have less friction, but the energy differences are small enough that it is not necessary to stop testing in the rain. Rain should be noted on the drill report and log. Frozen rope may have considerably more friction. Under wet and freezing conditions, exercise the rope and warm it up prior to testing.

Consistent rope and cathead operations depend on having well maintained crown sheaves on the mast. Crown sheaves should be cleaned and lubricated periodically to ensure that they spin freely.

Automatic Hammers

Automatic hammers are generally safer and provide good repeatability. Central Mine Equipment (CME) made one of the first automatic hammers commercially available in the United States. This hammer uses a chain cam to lift a hammer that is enclosed in a guide tube. The chain cam is driven with a hydraulic motor. The drop height of this hammer depends on the chain cam speed and the anvil length. Problems with this hammer system primarily result from the speed not being correctly adjusted. The hammer should be run at 50 to 55 bpm to obtain a 30-inch (75-cm) drop. There are blow control adjustments on the hammer, and there is a slot on the side of the hammer casing to observe the hammer drop height. Be sure the hammer is providing a 30-inch (75-cm) drop by adjusting the blow control.

The CME automatic hammer is designed to exert a down force on the rods. This down force from the assembly is about 500 lbs (227 kg). A safety hammer assembly weighs from 170 to 230 pounds (77 to 104 kg). In very

382 PENETRATION TESTING soft clays, the sampler will more easily sink under the weight of the assembly, and with the automatic hammer, the blow counts will be lower.

The Foremost Mobile Drilling Company hammer “floats” on a wireline system. The drop mechanism does not depend on rate. Energy transfer is about 60 to 70 percent.

Energy transfer of some automatic hammers is significantly higher than rope and cathead operated hammers. The CME hammer can deliver up to 95 percent energy. This could result in very low blow counts in sands. Energy corrections are usually required for automatic hammers. The Mobile Drilling Company hammer is less efficient because of a large two-piece anvil.

If an automatic hammer is used, report detailed information on the hammer use. Report make, model, blow count rates, and any other specific adjustments on the drilling log. In liquefaction investigations, the energy transfer must be known. For some hammer systems, such as the CME and Mobile Drilling Company, the energy transfer is known if the hammers are operated correctly, but for some systems, energy measurements may be required.

Spooling Winch Hammers

Mobile Drilling Company developed a hammer called the “Safety Driver.” This hammer system used a steel wireline cable connected to an automated spooling winch with magnetic trip contacts. The contacts sensed when the hammer was lifted 30 inches (75 cm), and the hammer then dropped with the spool unrolling at the correct rate for the dropping hammer.

383 FIELD MANUAL

Energy measurements of this hammer system show some extreme energy variations. Apparently, the contacts and spooling systems require continual adjustment to operate correctly. This type of hammer system is not recommended because of energy transmission problems.

Drill Rods

Any rod from AW to NW size is acceptable for testing. There is some concern about whipping or buckling of smaller AW rods at depths greater than 75 feet (23 m). In these cases, use BW rods or larger. There is not much difference in energy transfer between AW and NW rods. The type of rod changes a blow count in sand only by about two blows and maybe less.

SPT drill rods should be relatively tight during testing. Energy measurements on differing locations of the drill rods do not show significant energy loss on joints that are loose. There has to be a real gap on the shoulders to cause significant energy loss. This is because when the rod is resting in the hole, the shoulders of the joints are in contact. There is no need to wrench tighten joints unless rod joints are really loosening during testing. Be sure to firmly hand tighten each joint.

Drill Rod Length

When using very short rods, energy input to the sampler is attenuated early because of a reflected shock wave. The driller can usually hear this because there is a second hammer tap. The early termination of energy is a problem to depths of 30 feet (9 m), but the correction is small and is often ignored. The energy termination is also a function of the size of the drill rods. There is some energy loss for drill rod strings longer than 100 feet (30 m), and a correction is necessary. A constant density

384 PENETRATION TESTING sand will have an increasingly higher penetration resistance as depths increase. This is because the confining pressure increases in the ground mass with depth.

Summary

How Good is the SPT Test

Figure 22-5 is a summary graph of a study performed in Seattle by the American Society of Civil Engineers (ASCE). In this study, several private geotechnical firms and agencies drilled SPTs at the same site. Six drills were used. Some had safety hammers, and others had automatic hammers. One drill was equipped with a 300-lb (136-kg) safety hammer.

The graph shows a wide variation in raw N value versus depth. The soil conditions at the site are not well documented. Some gravel layers are present. Note that the spooling winch system resulted in unreliably high SPT N values.

The variability of SPT drilling can be reduced if drillers are aware of the problems inherent to the SPT. Inter- pretation of the data improves if all unusual occurrences during SPTs are reported. Drill logs should clearly describe in detail the equipment used.

Liquefaction studies are done in loose sands below the water table. Unfortunately, this material is the hardest to drill without disturbance. Fluid rotary drilling is the preferred approach for keeping the sand stable. HSAs and casing advancer systems have also been successfully used.

385 FIELD MANUAL

Figure 22-5.—Results of SPT with six different drills—ASCE Seattle study.

386 PENETRATION TESTING

The drilling part of SPTs is the most important. Generally, disturbance from improper drilling technique results in lower N values.

Energy transfer effects can be important, especially if highly efficient automatic hammers are used.

Becker-Hammer Penetration Testing for Gravelly Soils

Introduction

The BPT is used to test the density of materials that are too coarse for the SPT or the CPT. Gravel can cause misleading results in the SPT and CPT. Because the diameter of the BPT penetrometer tip is much larger than that of the SPT sampler or the cone penetrometer, gravel- sized particles do not seriously affect the BPT.

The BPT consists of driving a plugged steel casing into the ground using a diesel pile-driving hammer. The blows per foot (30 cm) of penetration are recorded and adjusted for driving conditions. An empirical correlation is then used to estimate equivalent SPT values. The BPT is performed with a Becker Drills, Ltd. model AP-1000 or B-180 drill rig, equipped with an International Construction Equipment (ICE) model 180 closed-end diesel hammer. The standard configuration uses 6.6-inch (16.8-cm) OD double-wall casing and a plugged “crowd- out” bit. Some ICE 180 hammers are marked “Linkbelt.”

The BPT is rapid and economical to perform. Production can reach 500 feet (150 m) per day. A disadvantage is that no sample is retrieved with the BPT, so other sampling, such as SPT or coring, is also required. Another disadvantage is the uncertainty in interpretation

387 FIELD MANUAL of the data. Since the BPT is generally used to estimate equivalent SPT blow counts, significant uncertainty is introduced by that step, in addition to the uncertainty that exists in predictions of soil behavior from N values.

The penetration resistance of soils is influenced by a large number of factors, including soil type (grain-size distribution, plasticity, particle sizes, particle shapes), density, confining stress, energy delivered to the penetrometer, size and shape of the penetrometer, and friction on the sides of the penetrometer. The BPT differs from the SPT test in many ways, and correlation between BPT and SPT data is not consistent. The BPT is not performed in an open hole with a diameter greater than the rod diameter, and the penetrometer tip is not open like a SPT tip, so there is substantial friction on the drill string. This greatly complicates the analysis. Like the SPT, the BPT may give misleading results in soils containing boulders, cobbles, or even large amounts of gravel coarser than about 1½ inches (4 cm).

The effect of fines in the relationship between Becker penetration resistance and liquefaction potential has not been established by experiment or field performance. The effect of fines is generally assumed to be similar to what occurs with the SPT. Since the BPT does not return a sample, it is often necessary to estimate the fines content from nearby drill holes or to neglect the potential benefit of fines.

Role of BPT in Exploration

In soils containing gravel, measured SPT or CPT resistance may be misleadingly high, and there is potential for damage to CPT equipment. CPT equipment generally cannot be advanced through thick gravel layers with more than about 30 percent gravel, depending on the size of the

388 PENETRATION TESTING gravel and the density of the soil. Results may be misleading with smaller gravel contents. BPTs are rarely performed at the start of an investigation and are generally done after SPTs or CPTs have been attempted and found to be inappropriate because of too much gravel. BPT testing generally should not be relied on as the sole basis for liquefaction evaluation without site-specific verification of the SPT-BPT correlation, corroboration by shear-wave velocities, or other liquefaction resistance predictors.

A Becker drill can also be used for other tasks such as installation of instrumentation or holes for geophysical testing. Some soil is compacted around each Becker hole, and the holes may be more prone to deviate from vertical than holes drilled by conventional methods. The extent of densification is not known, so if the holes are to be used for geophysical measurements (such as shear-wave velocity), vary the spacings to evaluate the effect of compaction around the hole. Rotary drilling can also be done inside the double-wall Becker casing to socket installations such as inclinometers into bedrock. This is more expensive than standard Becker testing because of delays and the need for a second rig. Becker rigs do not have rotary drilling capability.

Equipment

Becker drills can be operated with a variety of equipment configurations, but for penetration testing, the standard testing setup is as follows:

• Drill rig: Becker Drills, Ltd. model AP-1000 rig

• Hammer: Supercharged ICE model 180 diesel hammer

389 FIELD MANUAL

• Casing (rods): 168-mm (6.6-in) OD, double-wall

• Drive bit: Crowd-out plugged bit

The correlation between BPT and SPT data proposed by Harder and Seed relies on the use of the standard equipment configuration. The method proposed by Sy requires that at least the last two conditions be met. All four conditions should be met because analyses by the Sy method would probably be duplicated by the Harder- Seed method for preliminary calculations and/or verification. Harder and Seed determined that open-bit tests were inconsistent and erroneously low relative to the closed-bit standard. The older model B-180 and HAV-180 rigs, equipped with the same hammer, transfer about 50 percent more of the energy to the drill string than do AP-1000 rigs. This factor has been tentatively confirmed by energy measurements, but it is preferable to avoid the issue by specifying the use of AP-1000 rigs only.

The diesel hammer does not provide consistent energy to the drill string. This is because the energy depends on combustion conditions, which are affected by fuel condition, air mixture, ambient pressure, driving resistance, and throttle control. The closed-end diesel pile hammer is equipped with a “bounce chamber” where air is compressed by the rising ram after each blow; the air acts as a spring to push the ram back down for the next blow (unlike the more common open-ended diesel hammer that uses gravity alone to return the ram). Measuring the bounce-chamber pressure provides an indirect measure of combustion energy.

Harder-Seed Method of BPT Interpretation

The Harder-Seed method of interpreting the BPT uses measurements of bounce-chamber pressure as an

390 PENETRATION TESTING indication of the energy imparted to the rods by each blow. The bounce-chamber pressure is used to adjust the blow count for the actual combustion condition to that produced by a hypothetical constant combustion condition. The measured bounce-chamber pressure must be adjusted at altitudes above 1000 feet (300 m). The throttle should be kept wide open and the supercharger should be operated any time data are being recorded. Some drillers prefer to use a smaller throttle opening or no supercharger at the beginning of driving when the blowcounts are smaller, producing high blow counts. If the blowcounts required for analysis are near the surface, the driller should be instructed to keep the throttle wide open. Instances where full throttle and supercharger are not used should be recorded in the field notes.

The bounce chamber pressure needs to be monitored continuously during testing. An electronic recording system is available to monitor the bounce chamber. The pressure gauge provided by the hammer manufacturer can be used to record the data manually, but the gauge reading is sensitive to the length of hose used to connect the gauge to the hammer.

If a B-180 or HAV-180 rig is used, the data can be adjusted by multiplying by the factor 1.5 to account for the difference in energy transmitted to the rods. This factor is supported by few data and is considered approximate. An AP-1000 rig is preferred.

Testing for the Harder-Seed Method of Interpretation

The Harder-Seed method requires that the number of blows to drive BPT rods each foot (30 cm) of depth and bounce-chamber pressure during that interval be

391 FIELD MANUAL recorded. Record the driving conditions and note if the drillers pull the rods back to loosen them up to reduce the driving friction.

Sy Method of BPT Interpretation

The method proposed by Sy and Campanella is more rigorous, but more costly and time-consuming. Friction on the sides of the rods may contribute a substantial portion of the driving resistance. A pile-driving analyzer (PDA) is used to record acceleration and rod force during individual blows of the hammer. The PDA also measures the driving energy for each blow. The force and acceleration histories are then analyzed to separate the resistance to driving contributed by the bearing capacity of the tip and by the side friction using a computer program called CAPWAP. PDA operation and CAPWAP analyses are usually done by the contractor.

The PDA measurement eliminates concern about the performance of the hammer, effects of altitude, or loss of energy between the hammer and the rods. At least in theory, analyses should eliminate the effects of varying amounts of side friction on the blow count. The primary drawback is the need for PDA measurements and special analyses. These substantially increase the cost of the testing program and slow the process of testing and interpretation.

The side friction can also be measured directly by pullback tests, where the force required to pull the rods back a few inches is measured by a load cell. This measurement can be substituted for some of the CAPWAP data, but it is not recommended that CAPWAP calculations be completely eliminated. CAPWAP data is the standard from which the method was developed.

392 PENETRATION TESTING

Testing for the Sy Method of Interpretation

The Sy method requires:

Using the PDA, record rod force, acceleration, and transmitted energy. Record the number of blows for each 1-foot (30-cm) interval of BPT driving. Record driving conditions, and note if the drillers pull the rods back to loosen them up to reduce the driving friction.

Discussion of Methods

For routine investigations of typical alluvial materials that do not have dense material overlying them, a PDA is generally not necessary, and the Harder-Seed approach should usually be sufficient. In cases where drill rod friction is likely to be a problem (penetration through compacted fill or deep deposits), the Sy method may be better. BPTs can be done after pre-drilling and casing or after pre-driving the BPT with an open bit through compacted fill overlying the tested layers. This reduces the friction but does not necessarily provide valid predictions of SPT N60 with the Harder-Seed method and may cause them to be low.

With either method, the field notes should mention any time that the drillers pull back the rods to reduce the friction. There is no way to explicitly account for this in the Harder-Seed method. When using the Sy method, the locations for calculations should be selected with the pullbacks in mind. Ideally, pullbacks should be done only before and after critical layers are penetrated. This way, the rod friction can be interpolated between analyzed zones with no pullbacks between them to invalidate the interpolation. Zones to be tested and pullbacks should be discussed with the drillers prior to each hole. Substantial uncertainties exist both in the correlations to estimate the

393 FIELD MANUAL

equivalent SPT N60 and in the correlations to estimate soil behavior from the SPT blow count.

Contracting for Becker Drilling Services

In addition to the usual specifications requirements, the work statement for BPT should address:

C Work requirements — explain general work requirements.

C Purpose and scope — state which portions of the work are for liquefaction assessment and which are for instrumentation or other purposes.

C Local conditions and geology — describe anticipated drilling conditions and potential problem areas.

C Equipment and personnel to be furnished by the contractor — specify complete details on the equipment: rig model numbers, hammers, superchargers, and double wall pipe for rods. See above for details.

C Drilling requirements — list special considerations such as staking, calibration requirements, and refusal criteria.

C Hole completion — describe all hole completion or abandonment procedures.

C Driller’s logs — list requirements for the driller’s report, including forms to be used.

C Field measurement — specify method of measurement of depths for payment.

394 PENETRATION TESTING

In the contract for PDA work, specify the following:

C Purpose and scope of testing.

C Estimated number of feet of driving to be monitored by PDA.

Cone Penetration Test

Test History

The CPT was introduced in northern Europe in the 1930s to facilitate the design of driven pile foundations in soft ground. Early devices were mechanical penetrometers that incrementally measured the cone tip resistance. In the 1960s, mechanical cones, known as Begemann friction cones, were developed. This penetrometer measured both the tip resistance and the side resistance along a sleeve above the cone tip (figure 22-6). At about this same time, the CPT was introduced in North America. Using technology from the rapidly advancing electronics industry, an electric cone penetrometer was developed that used electrical transducers to measure the tip and side resistance (figure 22-7). Most of the work today is performed with electronic cone penetrometers, and the manual does not discuss mechanical systems. The use of electronics allows the incorporation of additional sensors in the cone system, including those for pore water stress, temperature, inclination, acoustic emissions, down-hole seismic, and resistivity/conductivity. In the 1990s, sensors such as laser or other energy-induced fluorescence spectroscopy sensors, membrane interface probes, and even video cameras have been added to detect groundwater contamination. Penetrometers capable of measuring dynamic or static pore water pressures are called piezometric cones or piezocones (CPTU). CPT

395 FIELD MANUAL

Figure 22-6.—Mechanical cone penetrometers.

Figure 22-7.—Typical electrical cone penetrometers.

396 PENETRATION TESTING has continued to gain wide acceptance as an effective site investigation tool in North America.

Test Procedure

The procedures for performing CPTs are standardized in Reclamation procedures USBR 7020 and 7021 and ASTM D-5778 and D-6067. The test is highly reproducible as opposed to SPTs. Test standards call for a cone tip 35.7 mm in diameter with a 10-square- centimeter (cm2) projected area and an apex angle of 60 degrees. The friction sleeve is 150 cm2. Larger diameter penetrometers of 15-cm2 projected area are sometimes used in very soft soils. Smaller diameter penetrometers are sometimes used for laboratory studies of soils.

The cone is advanced at a constant rate of 20 mm per second. Since the penetration resistance depends significantly on the advance rate, the push rate must be checked in the field. The basic equipment required to advance any cone penetrometer is a hydraulic jacking system. Trucks or vehicles built for CPT are typically used; but, in some cases, the hydraulics of rotary drill rigs are used. Semi-portable equipment has been developed for remote site testing. Rigs can be mounted on trucks, tracked vehicles, trailers, barges, or diving bells, depending on accessability. The capacity of cone rigs varies from 100 to 200 kilonewtons (kN) (11.2 to 22.4 tons). The upper bound is the maximum allowable thrust on the cone penetration rods.

Electronic cone penetrometers have built in load cells to measure the tip and side resistance simultaneously (Figure 22-7). Bonded strain gauges typically are used in the load cells because of their simplicity and ruggedness. The load cells commonly have a range of 90 kN (10 tons)

397 FIELD MANUAL for tip resistance and 9 kN (1 ton) for side resistance. The load cell capacity can be varied, depending on the strength of the soils to be penetrated. The load cells are usually connected by an electric cable passing through the drill rods to a data acquisition system at the surface. Cordless models are also available that transmit sonically and “Memo” cones that store the data internally until retrieved at the surface. Data are recorded digitally, which greatly enhances the use of CPT results in engineering applications. The data can be sent in daily by e-mail to the engineer and geologist.

Nearly all electronic cone penetrometers are equipped with a pore pressure element. This pore pressure sensor is typically located between the tip and the friction sleeve. The element can record dynamic water pressure as the cone is being pushed, as well as static water pressures during pauses in testing. The typical capacity of the water pressure transducer is 2.2 kN (500 lb/in2), and the accuracy of water pressure head is about ± 3 cm (0.1 foot). Cones are almost always equipped with inclinometers. The inclinometers are used to monitor rod bending during push and are an essential part of protecting the cone from damage. The inclinometer can be monitored by computer, and pushing can be stopped if bending is excessive. Cone rods can bend as much as 10 to 20 degrees. If the cone is used to detect bedrock or hard layers, this error can be significant. The inclinometer is not directional, so the error from bending can only be estimated.

Advantages and Disadvantages

The CPT has several advantages over other routine in place tests. The tests are rapid and inexpensive compared to other geotechnical profiling techniques. Penetration rates of 3 feet (1 m) per minute are common in many soils. Penetration is stopped only to add sections of push rods,

398 PENETRATION TESTING except when pore water stress dissipation measurements are made with the piezocone. With electrical equipment, continuous profiles are recorded and plotted as penetration progresses, and operator effects are minimized. As discussed below, the test results have been correlated to a variety of soil properties. Digital data acquisition with electrical cones enhances interpretation and provides continuous profiles of soil property estimates.

Although the tests are applicable to a wide range of soil conditions, penetration is limited in certain ground conditions. Well-cemented soils, very stiff clays, and soils containing gravel and cobbles may cause damage to the penetrometer tips.

The CPT can be used at nearly any site because portable devices are available. Portable hydraulic jacking systems can be used for soft soils in locations not accessible to standard rigs.

The CPT has several disadvantages. The test does not provide soil samples. The test is unsuited for well- cemented, very dense and gravelly soils because these soils may damage the relatively expensive penetrometer tips.

Local experience with this test is less than that with the SPT. Although the test is rapidly gaining acceptance in the United States, some drilling contractors do not have the equipment or experience necessary to perform the test. The equipment is expensive and may not be available in some locations. Maintaining the electronics for the CPT and CPTU equipment may be a problem in some test locations.

399 FIELD MANUAL

Data Obtainable

The CPT is primarily a logging tool and provides some of the most detailed stratigraphic information of any penetration test. With electronic cones, data are typically recorded at 5-cm-depth intervals, but data can be recorded at closer spacings. Layers as thin as 10 mm can be detected using the CPT, but the tip resistance can be influenced by softer or harder material in the layer below the cone. Full tip resistance of an equivalent thicker layer may not be achieved. The penetration resistance of the soil is a function of the drainage conditions during penetration. In sands that are drained, the penetration resistance is high, but in clays that are undrained, the penetration resistance is low.

A typical CPT data plot is shown in figure 22-8. CPT plots should show all recorded data (i.e., Tip

Resistance, qc , Sleeve Resistance, fs , Pore pressure, u, and for this example, cone inclination and temperature). CPT data should be plotted to consistent scales on a given project so that the plots can be more easily evaluated.

The CPT does not obtain a soil sample. However, the soils may be classified by comparing the tip resistance to the ratio of tip to sleeve resistance which is known as the friction ratio, Fr . Friction ratio should also be shown on the summary plots. Figures 22-9 and 10 show commonly used relationships to estimate the “soil behavior type.” Clay soils have low tip resistance and high friction ratio, while sands have high tip resistance and low friction ratio. Mixed soils fall in zones 4 through 7. There are also classification methods that incorporate the dynamic pore water pressure generation. The CPT cannot exactly classify soil according to the Unified Soil Classification System. Experience at many sites shows that soils give consistent signatures; and even though the soil behavior

400 PENETRATION TESTING

Figure 22-8.—Example CPT data plot.

401 FIELD MANUAL

Figure 22-9.—Chart for estimating the soil behavior type.

402 PENETRATION TESTING

Figure 22-10.—Chart for estimating the soil behavior type and the coefficient of permeability. type is generally correct, the soil types should be confirmed with a sample boring. Soil behavior type prediction in the unsaturated zone is less reliable but often still useful. The summary plot in figure 22-8 also shows the soil behavior group on the right side bar.

Soil permeability can be estimated from CPT because the tip resistance is a function of drainage during penetration. The permeability estimate is generally within an order of magnitude, which is suitable for most groundwater and seepage studies (figure 22-10).

Numerous correlations of CPT data to strength and compressibility of soils have been developed. These correlations are based primarily on tip resistance but are also supplemented by sleeve friction and dynamic pore water pressure data.

403 FIELD MANUAL

CPTs in clean sands have been performed in large calibration chambers where the density and confining pressure have been controlled. Based on the chamber data, the relative density and friction angle of sand can be estimated using relationships such as those shown in figure 22-11. The tip resistance at a constant relative density increases with increasing confining pressure. Once the relative density is estimated, the friction angle

Figure 22-11.—Relationships between cone tip resistance, relative density, and effective vertical stress.

404 PENETRATION TESTING can be estimated. The compressibility of the sand depends on the mineralogy of the sand particles. Highly compressible sands may contain soft particles. If mica is present in the sand at percentages as low as 5 percent, the compressibility will increase. Samples of the sand to determine mineralogy may be necessary. These estimates for sands are not applicable to sands containing more than 10 percent fines.

The CPT can be used to estimate the undrained strength,

Su, for clays because the CPT is like a cone bearing test in rapid, undrained loading. Figure 22-12 shows that the cone factor, Nk, must be estimated for clay. Typically, a factor of 12 to 15 is used. The factor can be refined by cross correlating with sampling and unconfined compression testing or by vane shear testing.

Compressibility of soils can be estimated by the CPT test, but the consolidation behavior should be confirmed by sampling and laboratory testing.

Figure 22-12.—Empirical cone factor, Nk , for clays.

405 FIELD MANUAL

The CPT is the best method for estimating the liquefaction resistance of sandy soils. The SPT is also used but has many problems in drilling and with equipment. The CPT tests the sand in place without disturbance, and the test is highly repeatable. Figure 22-13 shows the chart used to estimate liquefaction triggering. The chart is based on “clean sands,” but the method includes conversion of dirty sands for evaluation. If the CPT can be used for liquefaction evaluation, it should definitely be considered in the exploration plan. SPT should still be performed at a few sites, but the CPT can be used to rapidly and economically

Figure 22-13.—Comparison of various cyclic resistance ratio (CRR) curves and field data.

406 PENETRATION TESTING map the extent of liquefiable strata. CPT is also used extensively for evaluating ground improvement of liquefiable deposits.

The cone is like a miniature pile and is used for evaluating pile capacity. CPT tests are often performed at the abutments of bridges for pile design. Numerous methods exist for estimating pile capacity.

Economics

Equipment costs for CPT range from low for mechanical devices to high for piezocones, and generally two technicians are required to perform CPTs. These personnel should have a working knowledge of the equipment, but highly trained technicians are not required. The equipment mobilization is similar to that required for the SPT, but portable devices can be used for remote locations. Unit costs are difficult to estimate because the tests provide continuous or nearly continuous measurements. Rig costs are comparable to costs for the SPT, with an added capital cost to convert a conventional drilling rig for CPT testing. However, 200 feet (60 m) of penetration per day is typical; and in some cases, maximum production of 400 feet (120 m) per day is possible. This cost is the lowest of any geotechnical drilling, sampling, and logging method.

Bibliography

Harder, L.F., Application of the Becker Penetration Test for Evaluating the Liquefaction Potential of Gravelly Soils, NCEER Workshop on Evaluation of Liquefaction Resistance, held in Salt Lake City, Utah, 1997.

407 FIELD MANUAL

Harder, L.F. and Seed, H.B., Determination of Penetration Resistance for Coarse-Grained Soils Using the Becker Hammer Drill, Report No. UC/EERC-86-06, NTIS PB87- 124210, Earthquake Engineering Research Center, College of Engineering, University of California, Berkeley, California, May 1986.

Peck, Ralph B., Foundation Engineering, Second Edition, John Wiley & Sons, 1973.

Rausche, F., Goble, G.G., and Likins, Jr., G.E., Dynamic Determination of Pile Capacity, Journal of Geotechnical Engineering, ASCE, Vol. 111, No. 3, pp. 367-383, 1985.

Sy, A. and Campanella, R.G., Becker and Standard Penetration Tests (BPT-SPT) Correlations with Consideration of Casing Friction, Canadian Geotechnical Journal, 31(3): 343-356, 1994.

Sy, A., Campanella, R.G., and Stewart, R.A., BPT-SPT Correlations for Evaluation of Liquefaction Resistance of Gravelly Soils, Static and Dynamic Properties of Gravelly Soils, ASCE Special Publication 56, M.D. Evans and R.J. Fragazy, Editors, American Society of Civil Engineers, New York, New York, 1995.

408 Chapter 23

HANDLING AND TRANSPORTING ROCK AND SOIL SAMPLES

Introduction

Subsurface sampling is expensive and time consuming, so it makes sense to obtain all information possible from the investigative process and the retrieved samples. After expending the money and effort to obtain subsurface information, the samples should not be subjected to unacceptable temperature, rough handling, shoddy packaging, or harsh transportation methods. Any type of mishandling of a sample may make the sample useless for testing or logging, and the investigation may have to be repeated.

There are certain procedures in the handling and transporting of samples that should be a part of every investigation. However, some programs might require more demanding techniques in the handling of samples than others, depending on the types and ultimate uses of the samples. Proper handling results in lower overall costs when the cost of repeating an investigation is considered.

The care and handling required for samples collected for hazardous or toxic material investigations can vary considerably, and details for this type of sampling are not provided in this chapter. Information on required volumes of material, types of storage containers, methods of collection and preservation, and maximum holding periods should be obtained from the appropriate regulatory agency.

Poor samples are sometimes the result of poor drilling practices rather than mishandling. Compression fracturing of core, "spun" core, or uneven or wavy core surfaces may indicate that drilling techniques are FIELD MANUAL inappropriate for the conditions. Problems should be noted in the logs and corrections or improvements should be made immediately, if practicable, to the drilling procedures.

When samples requiring extreme care are obtained, personnel involved in the investigation must be totally familiar with the following procedures, and they must have a clear understanding of which geologic features are to be sampled and why they are to be sampled.

The geologic characteristics and the intended use of the rock and soil samples determine the extent and type of care required. If engineering properties are to be determined, the sample must be handled and preserved so that the properties are not significantly influenced by mechanical damage, changes in chemistry, and environmental conditions such as moisture and temperature.

Design requirements for samples range from geologic logging to complex and critical testing in the laboratory. Priorities for multiple uses or different types of tests must sometimes be established when available samples are limited and when a use or test precludes another test. When the required level of protection is unknown, overprotection is better than underprotection. If the sample is intended for geologic logging only, the care and preservation may be entirely different from that which would be needed if testing in the laboratory is required. Even though the sample has been geologically logged, other studies might be necessary, and continuous care in handling and proper storage may be required.

Samples can range from highly disturbed to relatively undisturbed. The methods of obtaining soil samples vary and may range from "grab" samples to samples obtained

410 HANDLING AND TRANSPORTING SAMPLES by highly refined drilling and sampling techniques. Soil can be difficult to sample whether by drilling or test pits, and obtaining an “undisturbed” sample of soil can be an ordeal. To obtain good “undisturbed” (minimally- disturbed) soil samples, extensive knowledge and experience with numerous types of soil sampling equipment, drilling methods, and drilling fluid additives is necessary.

Specific procedures for the disposal of rock core and samples depend on several factors; see chapter 24 for guidelines.

Sample Protection

The following describes recommended procedures for handling rock and soil samples (samples). The sample groupings are based on the type of testing to be performed, rather than any physical condition of the samples, and generally conform with ASTM Standards. Groups 1 through 4 deal with rock core, but note that the change to soil-like characteristics is transitional rather than abrupt. Table 23-1 summarizes the procedures.

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

411

HANDLING AND TRANSPORTING SAMPLES

6JGEQTGUJQWNFDGRJQVQITCRJGFVQRTQXKFGKOCIGUCU UJQYPKPHKIWTG6JGDQZGUUJQWNFDGQTKGPVGFTGNC VKXG VQ VJG ECOGTC VQ OKPKOK\G FKUVQTVKQP CPF NKIJVKPI UJQWNFDGCRRTQRTKCVGVQOCZKOK\GTGUQNWVKQP#RJQVQ ITCRJ[ HTCOG CU UJQYP KP HKIWTG RTQXKFGU EQP UKUVGPVQTKGPVCVKQPCPFKOCIGSWCNKV[

)TQWR 0QPUGPUKVKXG PQPHTCIKNG UCORNGU HQT YJKEJ QPN[IGQNQIKENQIIKPIKUPGEGUUCT[DGNQPIUVQVJKUITQWR

(QTTQEMEQTGFKPVQHQQV VQO TWPUUCORNGU CTG UWHHKEKGPVN[ RTQVGEVGF KH RNCEGF KP UVTQPI YQQF QT RNCUVKE EQTG DQZGU %CTFDQCTF DQZGU CTG WPCEEGRVCDNG DGECWUGVJGDQZGUFGHQTOYJGPYGVTQVCPFCTGTGCFKN[ FGUVTQ[GFD[KPUGEVU+HXGT[NQPIUQNKFEQTGUJCXGDGGP TGEQXGTGFCPFPGGFVQDGRTGUGTXGFKPVCEVRNCEGGCEJEQTG KPCUVKHHVWDGQTVYQJCNHTQWPFUQHVWDKPIQHGSWCNQT UNKIJVN[ ITGCVGT NGPIVJ VJCP VJG EQTG CPF UGEWTG DQVJ GPFU6JGKPUKFGFKCOGVGTQHVJGVWDGUJQWNFDGUNKIJVN[ NCTIGTVJCPVJGEQTGFKCOGVGTCPFVJGVWDGYCNNUOWUVDG TKIKFGPQWIJVQRTGXGPVEQTGDTGCMCIGDGECWUGQHDGPFKPI

Figure 23-1.—Properly boxed and labeled core.

413 FIELD MANUAL

Figure 23-2.—Core storage area with boxes neatly arranged and separated by spacers for ventilation. Note core photography frame in center of photograph.

6JG VWDKPI UJQWNF DG KORGTOGCDNG UWEJ CU .WEKVG QT 28%VQRTGXGPVNQUUQHUVKHHPGUUQHVJGVWDKPIKPOQKUV EQPFKVKQPU

)TQWR4QEMEQTGVJCVKUUWDLGEVVQOQKUVWTGNQUUQT ICKP CPF OWUV DG VGUVGF NCVGT DGNQPIU KP VJKU ITQWR 4GSWKTGOGPVU HQT VJKU NGXGN QH RTQVGEVKQP KPENWFG TGSWKTGOGPVUHQT)TQWR

6JG OQKUVWTG EQPFKVKQP QH UQOG TQEMU CPF GXGP VJG OQKUVWTGJKUVQT[QHTQEMUUWEJCUUJCNGUCHHGEVVJGTQEM RTQRGTVKGU+HVGUVUCTGVQDGRGTHQTOGFQPVJGEQTGCPFKH CEJCPIGKPOQKUVWTGEQPFKVKQPUOC[KPHNWGPEGVJGVGUV TGUWNVUVJGEQTGOWUVDGUGCNGFVQRTGXGPVOQKUVWTGNQUU 6JKUUCOGRTQEGFWTGCRRNKGUVQCP[UCORNGUYJGPKVKU KORQTVCPVVQOCKPVCKPHNWKFUQVJGTVJCPYCVGTUWEJCU J[FTQECTDQPU

414 HANDLING AND TRANSPORTING SAMPLES

6JG VGTO YCZ TGHGTU VQ C RNCUVKE OKETQET[UVCNNKPG OKZVWTGEQORQUGFQHQPGRCTVOKETQET[UVCNNKPGYCZHQT UVTGPIVJCPFCFJGUKQPCPFQPGRCTVRCTCHHKPQTDGGUYCZ HQT RNCUVKEKV[ 6JKU OKZVWTG QRVKOK\GU CFJGTGPEG CPF OKPKOK\GUDTKVVNGPGUUCPFEQQNKPIETCEMUKPVJGYCZ6JKU OCVGTKCNUJQWNFDGCRRNKGFCVPQOQTGVJCPFGITGGU (CJTGPJGKV u( FGITGGU%GPVKITCFG u% CDQXGKVU OGNVKPIRQKPVGURGEKCNN[KHVJGYCZKUCRRNKGFKPFKTGEV EQPVCEVYKVJVJGUCORNGOCVGTKCN9CZVJCVKUVQQJQVECP RGPGVTCVGUCORNGRQTGUCPFETCEMU+HVJGYCZDQPFUVQ VJGUCORNGVJGYCZKUVQQJQV

5GCNKPIUCORNGUVQRTGUGTXGOQKUVWTGUJQWNFEQPUKUVQHC VKIJVN[ HKVVKPI YTCRRKPI QH C RNCUVKE HKNO UWEJ CU XKP[NKFGPG EJNQTKFG 5CTCP YTCR EQXGTGF D[ C VKIJV YTCRRKPI QH CNWOKPWO HQKN 'CEJ QH VJGUG YTCRRKPIU UJQWNF DG CRRNKGF UQ VJCV CU NKVVNG CKT CU RQUUKDNG KU VTCRRGF DGPGCVJ VJG YTCRRKPIU .CR VJG GPFU QH VJG YTCRRKPIUQXGTVJGGPFUQHVJGUCORNGCPFHQNFQXGTVQ UGCN VJG GPFU (KPCNN[ CRRN[ C OKPKOWO QH F KPEJ OO QHYCZQXGTVJGGPVKTGUWTHCEGQHVJGUCORNG# NC[GTQHEJGGUGENQVJCRRNKGFQPVJGHQKNDGHQTGYCZKPIKU CIQQFKFGC6JKUVJKEMPGUUQHYCZUJQWNFEQPUKUVQHCV NGCUVVYQEQCVKPIUCPFRTGHGTCDN[OQTG(QTNQPIRGTKQFU QHUVQTCIGCRRN[COKPKOWOQHKPEJ OO QHYCZ 9CZOC[DGCRRNKGFD[DTWUJKPIKVQPQTD[FKRRKPIVJG YTCRRGF UCORNG KP C EQPVCKPGT QH OGNVGF YCZ #HVGT YCZKPIVJGUCORNGOC[DGRNCEGFCPFVTCPURQTVGFKPC EQTGDQZ

+P UQOG ECUGU CNWOKPWO HQKN YTCRRKPI OKIJV TGCEV EJGOKECNN[YKVJGKVJGTVJGUCORNGQTVJGUCORNG UHNWKFU +HCTGCEVKQPKURQUUKDNGCNWOKPWOHQKNUJQWNFDGTGRNCEGF YKVJUQOGQVJGTOGVCNHQKNVJCVKUPQPTGCEVKXG#NGUU RTGHGTCDNGOGVJQFKUVQQOKVVJGOGVCNHQKNCPFKPETGCUG VJGVJKEMPGUUQHVJGUGCNKPIYCZ+HVJGOGVCNHQKNKUPQV WUGFVJGVJKEMPGUUQHVJGUGCNKPIYCZUJQWNFDGKPETGCUGF VQKPEJ OO YJGPVJGTGSWKTGFUVQTCIGVKOGKUUJQTV

415 FIELD MANUAL

WR VQ OQPVJ (QT C NQPIGT RGTKQF C VJKEMPGUU QH GKPEJ OO KUCFGSWCVG#NC[GTQHEJGGUGENQVJUJQWNF DGKPEQTRQTCVGFKPVQVJGYCZ

)TQWR6JGUGCTGUCORNGUVJCVCTGHTCIKNGQTOQKUVWTG QTVGORGTCVWTGUGPUKVKXG6JKURTQVGEVKQPNGXGNKPENWFGU VJGTGSWKTGOGPVUHQT)TQWRUCPF

+H UJQEM XKDTCVKQP QT XCTKCVKQP KP VGORGTCVWTG OC[ UWDLGEV UCORNGU VQ WPCEEGRVCDNG EQPFKVKQPU FWTKPI VTCPURQTVVJGUCORNGUUJQWNFDGRNCEGFKPEQTGDQZGUVJCV RTQXKFG EWUJKQPKPI QT VJGTOCN KPUWNCVKQP (TCIKNG UCORNGUOC[TGSWKTGRCEMKPIKPCEWUJKQPKPIOCVGTKCN UWEJCUUCYFWUVTWDDGT5V[TQHQCO RQN[ WTGVJCPGHQCO DWDDNG YTCR QT UKOKNCT OCVGTKCN 6JG EWUJKQPKPI DGVYGGPVJGUCORNGUCPFYCNNUQHVJGEQTGDQZGUUJQWNF JCXGCOKPKOWOVJKEMPGUUQHKPEJ OO CPFUJQWNF JCXGCOKPKOWOVJKEMPGUUQHKPEJGU OO QPVJG EQTGDQZDQVVQOCPFNKF6JGUCORNGUOWUVHKVUPWIN[KPVQ VJGDQZGU

5CORNGU VJCV CTG VGORGTCVWTG UGPUKVKXG UJQWNF DG KPUWNCVGF D[ RNCEKPI VJG EQTG EQPVCKPGT DQZ QT VWDG KPUKFGCPQVJGTEQPVCKPGTVJCVKUFGUKIPGFURGEKHKECNN[VQ RTQXKFG VJGTOCN KPUWNCVKQP 6JGUG EQPVCKPGTU CTG IGPGTCNN[ EQPUVTWEVGF QH FQWDNG QT VTKRNG NC[GTU QH KPUWNCVKPIOCVGTKCNCPFCTGWUWCNN[TGNCVKXGN[CKTVKIJV

)TQWR6JGUGOCVGTKCNUCTGUQRQQTN[KPFWTCVGFVJCV UQKNUCORNKPIRTQEGFWTGUOWUVDGWUGFVQQDVCKPKPVCEV RKGEGUQHEQTG%GTVCKPUJCNGQTJKIJN[YGCVJGTGFTQEM VJCVEQPVCKPUVJGUGOCVGTKCNUCUKPVGTDGFUDGNQPIVQVJKU ITQWR)TQWRUCORNGUCTGOQTGUQKNNKMGVJCPTQEMNKMG CPF UJQWNF DG VTGCVGF CEEQTFKPI VQ VJG CRRTQRTKCVG KPUVTWEVKQPUHQT)TQWRU#VJTQWIJ&DGNQY

416 HANDLING AND TRANSPORTING SAMPLES

)TQWR#%QPUKUVUQHUQKNUCORNGUHQTYJKEJQPN[XKUWCN KFGPVKHKECVKQPUQTITCFCVKQPUCTGPGEGUUCT[6JGOCKP EQPEGTP KP FGCNKPI YKVJ VJKU ITQWR KU VQ CXQKF EQPVCOKPCVKQPYKVJQVJGTUQKNU)TQWR#UCORNGUOC[DG VTCPURQTVGF KP CP[ V[RG QH EQPVCKPGT D[ CP[ VTCPURQT VCVKQP OGVJQF +H VTCPURQTVGF EQOOGTEKCNN[ VJG EQP VCKPGT PGGF QPN[ OGGV VJG TGSWKTGOGPVU QH VJG VTCPURQTVKPI CIGPE[ CPF CP[ QVJGT TGSWKTGOGPVU PGEGUUCT[VQRTGXGPVUCORNGNQUU

)TQWR $ 6JGUG CTG UCORNGU HQT YJKEJ QPN[ YCVGT EQPVGPVCPFENCUUKHKECVKQPVGUVUCTGTGSWKTGFQT2TQEVQT EQORCEVKQP TGNCVKXG FGPUKV[ QT RTQHKNG NQIIKPI CTG TGSWKTGF$WNMUCORNGUVJCVYKNNDGTGOQNFGFQTEQO RCEVGFKPVQURGEKOGPUHQTVGUVUUWEJCUUYGNNRTGUUWTG RGTEGPV UYGNN EQPUQNKFCVKQP RGTOGCDKNKV[ CPF UJGCT VGUVKPICTGCNUQKPENWFGF

+PCNNECUGUHQT)TQWRU$%CPF&UQKNUCUCORNGUJQWNF DG QDVCKPGF HQT FGVGTOKPCVKQP QH KP RNCEG OQKUVWTG EQPVGPVCPFVJGFGVGTOKPCVKQPUJQWNFDGRGTHQTOGFCU UQQPCURQUUKDNG

)TQWR$UCORNGUUJQWNFDGRTGUGTXGFCPFVTCPURQTVGFKP UGCNGFOQKUVWTGRTQQHEQPVCKPGTU%QPVCKPGTUUJQWNFDG VJKEM GPQWIJ CPF UVTQPI GPQWIJ VQ RTQVGEV CICKPUV DTGCMCIGCPFOQKUVWTGNQUU6JGEQPVCKPGTV[RGUKPENWFG YCVGTRTQQH RNCUVKE DCIU QT RCKNU INCUU QT RNCUVKE LCTU VJKPYCNNGF VWDGU CPF NKPGTU %[NKPFTKECN CPF EWDG UCORNGU UJQWNF DG YTCRRGF KP UWKVCDNG RNCUVKE HKNO QT EJGGUGENQVJQTDQVJCPFUJQWNFDGEQCVGFYKVJUGXGTCN NC[GTUQHYCZCEEQTFKPIVQVJGKPUVTWEVKQPUHQT)TQWR UCORNGU

+HRNCUVKEDCIUQTYTCRRKPICTGWUGFVJGDCIUUJQWNFDG RNCEGF CU VKIJVN[ CU RQUUKDNG CTQWPF VJG UCORNG USWGG\KPIQTUWEMKPIQWVCUOWEJCKTCURQUUKDNG6JG

417 FIELD MANUAL

RNCUVKEUJQWNFDGVJTGGOKNQTVJKEMGTVQRTGXGPVNGCMCIG +HINCUUQTRNCUVKELCTUCTGWUGFVJCVFQPQVENQUGVKIJVN[ VJGNKFUUJQWNFDGUGCNGFYKVJYCZ+HRNCUVKERCKNUCTG WUGF CPF VJG NKFU CTG PQV CKT VKIJV VJG NKFU UJQWNF DG UGCNGFYKVJVCRGCPFYCZ

6JKPYCNN RWUJ VWDGU ECP DG UGCNGF YKVJ GZRCPFCDNG RCEMGTUYCZGFYQQFFKUMUQTEJGGUGENQVJCPFYCZ6JG RTGHGTTGF CNVJQWIJ GZRGPUKXG OGVJQF HQT UGCNKPI VJKPYCNN VWDGU KU YKVJ RNCUVKE QT OGVCN GZRCPFCDNG RCEMGTUUGCVGFQPVJGUQKNUWTHCEG6JGUGFGXKEGUVKIJVN[ CDWVVKPIVJGUQKNYKNNMGGRVJGUQKNHKTON[HKZGFKPRQUKVKQP KPVJGVWDG+HYCZGFYQQFFKUMUCTGWUGFCFKUMUNKIJVN[ UOCNNGTVJCPVJGKPUKFGFKCOGVGTQHVJGVWDGUJQWNFDG KPUGTVGFKPGCEJGPFQHVJGVWDGDGKPUPWIEQPVCEVYKVJ VJGUQKNCPFVJGPDGUGCNGFYKVJYCZ5GXGTCNVJKPNC[GTU QH YCZ CTG RTGHGTTGF QXGT QPG VJKEM NC[GT 6JG HKPCN VJKEMPGUUUJQWNFDGCVNGCUVKPEJ OO

1VJGTURCEGTUQTRCEMKPIOCVGTKCNUGZVGPFKPIHTQOVJG YCZGFYQQFFKUMQTYCZGFUQKNUWTHCEGVQVJGVWDGGPFCTG PQVTGEQOOGPFGFDGECWUGVJGUGECPCNNQYVJGUCORNGUVQ OQXGKPVJGVWDGU#P[RCEMKPIOCVGTKCNOWUVDGPQPCD UQTDGPV CPF OWUV UWRRQTV VJG UCORNGU VJTQWIJQWV UJKROGPVCPFUVQTCIG

/GVCNTWDDGTQTRNCUVKEGPFECRUUJQWNFDGUGCNGFYKVJ VCRG(QTNQPIVGTOUVQTCIG NQPIGTVJCPOQPVJ VJG VCRGFGPFECRUUJQWNFDGFKRRGFKPYCZCRRN[KPIVYQQT OQTGNC[GTU'PFENQUWTGUUQNGN[QHEJGGUGENQVJCPFYCZ UJQWNFEQPUKUVQHCNVGTPCVKPINC[GTUQH COKPKOWOQHVYQ GCEJ EJGGUGENQVJCPFYCZ

%[NKPFTKECNEWDKECNQTQVJGTUCORNGUYTCRRGFKPRNCUVKE QTHQKNUJQWNFDGRTQVGEVGFYKVJCOKPKOWOQHVJTGGEQCVU QHYCZCPFEJGGUGENQVJ%[NKPFTKECNCPFEWDGUCORNGU YTCRRGFKPEJGGUGENQVJCPFYCZUJQWNFDGUGCNGFYKVJC OKPKOWO QH VJTGG CNVGTPCVKPI NC[GTU %[NKPFTKECN

418 HANDLING AND TRANSPORTING SAMPLES

UCORNGUCPFUOCNNEWDGUCORNGURNCEGFKPECTVQPUOWUV DG RQUKVKQPGF UQ VJCV YCZ ECP DG RQWTGF EQORNGVGN[ CTQWPFVJGUCORNG6JGYCZUJQWNFHKNNVJGXQKFDGVYGGP VJG UCORNG CPF EQPVCKPGT YCNN 6Q HCEKNKVCVG JCPFNKPI YJGP RNCEGF KP ECTVQPU NCTIG EWDG UCORNGU UWEJ CU YCZGF DNQEM UCORNGUUJQWNFDGGPECRUWNCVGFKPFCOR UCYFWUV TCVJGT VJCP YCZ )GPGTCNN[ YCZGF UCORNGU UJQWNF DG YTCRRGF KP RNCUVKE QT HQKN DGHQTG DGKPI UWTTQWPFGFD[YCZKPCECTVQP

6JGUG UCORNGU OC[ DG VTCPURQTVGF D[ CP[ CXCKNCDNG VTCPURQTVCVKQP 6JG UCORNGU UJQWNF DG UJKRRGF CU RTGRCTGF QT RNCEGF KP NCTIGT EQPVCKPGTU UWEJ CU DCIU ECTFDQCTFQTYQQFDQZGUQTDCTTGNU#RRTQRTKCVGRCEMKPI UJQWNFDGRTQXKFGFVQRTGXGPVDTGCMCIGQTRWPEVWTKPIQH VJGKPFKXKFWCNUCORNGYTCRRKPIQTEQPVCKPGT

)TQWR%6JGUGCTGKPVCEVPCVWTCNQTHKGNFEQORCEVGF UCORNGUHQTFGPUKV[FGVGTOKPCVKQPUQTHQTUYGNNRTGUUWTG RGTEGPV UYGNN EQPUQNKFCVKQP RGTOGCDKNKV[ VGUVKPI CPF UJGCTVGUVKPIYKVJQTYKVJQWVUVTGUUUVTCKPCPFXQNWOG EJCPIGOGCUWTGOGPVU

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

419 FIELD MANUAL

5CORNGUVTCPURQTVGFQPUGCVUQHXGJKENGUECPDGRNCEGFKP ECTFDQCTFDQZGUQTUKOKNCTEQPVCKPGTUCPFUCORNGUPGGF VQDGRCEMGFVQRTGXGPVDWORKPITQNNKPICPFFTQRRKPI

+HVJGUCORNGUCTGPQVVTCPURQTVGFQPXGJKENGUGCVUVJG KPFKXKFWCNUCORNGUUJQWNFDGRNCEGFKPYQQFOGVCNQT QVJGTV[RGUQHUWKVCDNGUJKRRKPIEQPVCKPGTUVJCVRTQXKFG EWUJKQPKPIQTKPUWNCVKQPHQTGCEJUCORNG6JGEWUJKQPKPI OCVGTKCN UJQWNF EQORNGVGN[ GPECUG GCEJ UCORNG 6JG EWUJKQPKPIDGVYGGPVJGUCORNGUCPFYCNNUQHVJGUJKRRKPI EQPVCKPGTUUJQWNFJCXGCOKPKOWOVJKEMPGUUQHKPEJ OO # OKPKOWO VJKEMPGUU QH KPEJGU OO UJQWNF DG RTQXKFGF QP VJG EQPVCKPGT DQVVQO 9JGP TGSWKTGFVJGUCORNGUUJQWNFDGMGRVKPVJGUCOGRQUKVKQP KPYJKEJVJG[YGTGUCORNGFHTQOVJGVKOGVJG[NGCXGVJG ITQWPF WPVKN VGUVKPI KU EQORNGVGF 5RGEKCN EQPFKVKQPU UJQWNFDGRTQXKFGFUWEJCUHTGG\KPIEQPVTQNNGFFTCKPCIG QTUWHHKEKGPVEQPHKPGOGPVVQOCKPVCKPUCORNGKPVGITKV[

)TQWR&5CORNGUVJCVCTGHTCIKNGQTJKIJN[UGPUKVKXG CPF VJCV TGSWKTG VGUVU KP )TQWR % CTG CUUKIPGF VQ )TQWR&6JGTGSWKTGOGPVUHQT)TQWR%OWUVDGOGVKP CFFKVKQPVQVJGHQNNQYKPITGSWKTGOGPVU5CORNGUUJQWNF DGJCPFNGFCPFUVQTGFKPENWFKPIFWTKPIVTCPURQTVCVKQP KPVJGUCOGQTKGPVCVKQPKPYJKEJVJG[YGTGUCORNGF

Storage Containers

%QPVCKPGTUUJQWNFDGFGUKIPGFVQKPENWFG

(QTEQTG

%QTGDQZGUOWUVDGEQPUVTWEVGFTKIKFN[GPQWIJVQ RTGXGPVHNGZKPIQHVJGEQTGYJGPVJGDQZKURKEMGFWR D[KVUGPFU9QQFKURTGHGTTGFCPFUJQWNFDGKPEJ PQOKPCN OO VJKEM2CTVKVKQPUDGVYGGPEQTG

420 HANDLING AND TRANSPORTING SAMPLES

TQYUUJQWNFDGHKTON[HKZGFKPRNCEGVQKPETGCUGVJG UVKHHPGUU QH VJG DQZ 6JG NKF UJQWNF JCXG UVTQPI JKPIGUCPFJCURUQTHCUVGPGFYKVJUETGYU&QPQV FTKXG PCKNU KP VJG NKF #P GZCORNG QH EQTG DQZ EQPUVTWEVKQPKUUJQYPKPHKIWTG

6JGEQTGDQZUJQWNFDGFGUKIPGFHQTVJGCPVKEKRCVGF FKCOGVGT QH EQTG KPENWFKPI CP[ RCEMKPI CPF EWUJKQPKPIOCVGTKCNU+HVJGEQTGDQZKUVQQNCTIGHQT VJG EQTG URCEGTU QT RCEMKPI OCVGTKCN UJQWNF DG RNCEGFKPVJGDQZVQUWRRQTVVJGEQTGCPFRTGXGPV VJGEQTGHTQOOQXKPIKPVJGDQZ+HVJGEQTGDQZKU VQQ UOCNN HQT VJG EQTG VJG EQTG UJQWNF PQV DG JCOOGTGFKPVQVJGDQZ

(QTUQKNUKP)TQWRU%CPF&CPFHQTTQEMKP)TQWRUCPF KHTGSWKTGF

6JG EQPVCKPGT UJQWNF DG EQPUVTWEVGF UQ VJCV VJG UCORNGUECPDGOCKPVCKPGFKPVJGUCOGRQUKVKQPCU YJGPUCORNGFQTRCEMGF

6JG EQPVCKPGT UJQWNF KPENWFG UWHHKEKGPV RCEMKPI OCVGTKCN VQ EWUJKQP QT KUQNCVG VJG UCORNGU HTQO XKDTCVKQPCPFUJQEM

6JGEQPVCKPGTUJQWNFKPENWFGUWHHKEKGPVKPUWNCVKPI OCVGTKCNVQRTGXGPVHTGG\KPI

Shipping Containers

6JGHQNNQYKPIHGCVWTGUUJQWNFDGKPENWFGFKPVJGFGUKIPQH UJKRRKPIEQPVCKPGTU

2N[YQQF RTGHGTCDN[OCTKPGRN[YQQF QTKPEJ VQOO VJKEMOC[DGWUGFHQTUJKRRKPI

421 FIELD MANUAL

EQPVCKPGTU6JGVQR EQXGT UJQWNFDGJKPIGFCPF NCVEJGF QT HCUVGPGF YKVJ UETGYU 6JG GPVKTG UJKRRKPIEQPVCKPGTUJQWNFDGNKPGFYKVJKPUWNCVKQP COKPKOWOQHKPEJGU OO VJKEMHQTRTQVGEVKQP CICKPUVHTGG\KPIQTVGORGTCVWTGHNWEVWCVKQP

/GVCNUJKRRKPIEQPVCKPGTUUJQWNFJCXGEWUJKQPKPI CPFKPUWNCVKPIOCVGTKCNUKOKNCTVQYQQFUJKRRKPI EQPVCKPGTU CNVJQWIJ UNKIJVN[ ITGCVGT VJKEMPGUUGU CTG CRRTQRTKCVG %WUJKQPKPI YKVJ C URTKPI UWURGPUKQPU[UVGOQTCP[QVJGTOGCPUVJCVRTQXKFG UKOKNCTRTQVGEVKQPKUCEEGRVCDNG

$WNM5V[TQHQCOYKVJUNQVUQTRQEMGVUKPVJGUJCRGQH VJG UCORNG VWDG QT NKPGT UJQWNF DG GPENQUGF KP C RTQVGEVKXGQWVGTDQZQHRN[YQQFQTECTFDQCTF

2TQRGTN[NKPGFEQPVCKPGTUEQPUVTWEVGFQHNCOKPCVGF HKDGTDQCTF RNCUVKE QT TGKPHQTEGF ECTFDQCTF QWVGT YCNNUCTGCEEGRVCDNG

Core Handling

6JG HQNNQYKPI RTQEGFWTGU CTG PGEGUUCT[ VQ GPUWTG VJCV TQEM EQTG KU HKTON[ HKZGF KP VJG EQTG DQZ CPF KU CRRTQRTKCVGN[NCDGNGFHQTKPURGEVKQPCPFNQIIKPI

1TKGPVVJGEQTGDQZYKVJVJGUNQVUJQTK\QPVCN2NCEG VJGEQTGKPVJGEQTGDQZUVCTVKPIYKVJVJGUJCNNQYGUV FGRVJCVVJGWRRGTNGHVJCPFEQTPGTCPFRTQITGUUKPI CETQUUCPFVJGPFQYPYCTFCUKPTGCFKPICDQQM YKVJ VJG FGGRGUV FGRVJ CV VJG NQYGT TKIJV JCPF EQTPGT

2NCEGEQTGDNQEMUCVVJGGPFUQHGCEJTWPYKVJVJG FGRVJENGCTN[YTKVVGPQPVJGO

422 Figure 23-3.—Example core box construction. HANDLING AND TRANSPORTING SAMPLES

4WPUQHNGUUVJCPRGTEGPVEQTGTGEQXGT[UJQWNF DGUJQYPD[URCEGTDNQEMURNCEGFKPVJGEQTGDQZCV VJG UWURGEVGF OKUUKPI KPVGTXCN CPF ENGCTN[ KFGPVKHKGF

#HVGT RJQVQITCRJKPI CPF CHVGT UCORNGU CTG RTGRCTGFUCORNGUTGOQXGFHTQOVJGEQTGUJQWNFDG TGRNCEGFD[CURCEGT DNQEMGSWCNKPNGPIVJVQVJG EQTG TGOQXGF 6JG DNQEM UJQWNF DG NCDGNGF UCORNG CPFFGRVJUUJQWNFDGPQVGFCPFRNCEGFKP VJGEQTGTWP

$TGCMKPIVJGEQTGUJQWNFDGCXQKFGFDGECWUGKVOC[ TGFWEGVJGPWODGTQHCXCKNCDNGVGUVURGEKOGPU+HKV KUPGEGUUCT[VQOCMGEQTGHKVKPVJGEQTGDQZPQVGQP DQVJVJGFCKN[FTKNNTGRQTVCPFVJGIGQNQIKENQICPF OCTMQPVJGEQTGVQKPFKECVGOGEJCPKECNDTGCMCIG

+HPGGFGFCFFUWHHKEKGPVURCEGTDNQEMUVQRTGXGPVVJG EQTGHTQOUJKHVKPIFWTKPIUWDUGSWGPVDQZJCPFNKPI

(KIWTGKUCPGZCORNGQHRTQRGTN[DQZGFCPFNCDGNGF EQTG

Identification of Samples

#NN UCORNGU YJGVJGT TQEM QT UQKN OWUV DG RTQRGTN[ KFGPVKHKGF CPF VJG HQNNQYKPI KPHQTOCVKQP UJQWNF DG YTKVVGPQPVJGUCORNGQTEQPVCKPGT

2TQLGEVPCOG (GCVWTGPCOG *QNGRKVQTVTGPEJPWODGT 6QRCPFDQVVQOFGRVJUQHUCORNGKPVGTXCN 5CORNKPIFCVG 5CORNGPWODGT

423 FIELD MANUAL

+PCFFKVKQPVQVJGCDQXG

%NGCTN[CPFRTQOKPGPVN[OCTMUCORNGUEQPVCKPKPI UWURGEVGFQTMPQYPJC\CTFQWUOCVGTKCNU

#VVCEJUCORNGVTCEMKPIQT EJCKPQHEWUVQF[ HQTO KHTGSWKTGF

%NGCTN[ OCTM UCORNGU VJCV OWUV DG JCPFNGF CPF UVQTGFKPVJGUCOGQTKGPVCVKQPCUUCORNGFUVCVKPI VJCVTGSWKTGOGPVCPFVJGTGSWKTGFQTKGPVCVKQP

Transportation Requirements and Procedures

(QTCNNOQFGUQHVTCPURQTVCVKQPVJGNQCFKPIVTCPURQTVKPI CPFWPNQCFKPIQHUJKROGPVEQPVCKPGTUUJQWNFDGUWRGT XKUGFCUOWEJCURQUUKDNG6JGHQNNQYKPITGSWKTGOGPVU CPFRTQEGFWTGUUJQWNFDGEQPUKFGTGFYJGPVTCPURQTVKPI EQTG

4GOQXGVJGUCORNGHTQOVJGFTKNNUKVGDGHQTGKVJCU C EJCPEG VQ HTGG\G JGCV WR QT DG FCOCIGF D[ CEVKXKVKGUCVVJGFTKNNUKVG

*CPFNG UCORNGU IGPVN[ FWTKPI NQCFKPI CPF WPNQCFKPI0GXGTFTQRDQZGUQTVWDGUUNKFGVJGO IGPVN[KPVQRQUKVKQP+HCDQZQTVWDGKUFTQRRGF TGEQTFVJKUHCEV

6TCPURQTV D[ CP CRRTQRTKCVG XGJKENG VQ RTGXGPV FCOCIG D[ OGEJCPKECN XKDTCVKQP UJQEM HTGG\KPI CPFJKIJVGORGTCVWTGUCNQPIVJGGPVKTGVTCPURQTV TQWVG+PUQOGECUGUKVOC[DGPGEGUUCT[VQTGOQXG VJG EQTG HTQO VJG XGJKENG CPF RNCEG KV KP C OQVGN TQQOQTUWKVCDNGUVQTCIGCTGCCVPKIJVWPNGUUVJG

424 HANDLING AND TRANSPORTING SAMPLES

XGJKENGECPDGNGHVKFNKPIVQMGGRVJGUCORNGUCVCP CRRTQRTKCVGVGORGTCVWTG

+HTQWIJVGTTCKPOWUVDGETQUUGFRTQVGEVUCORNGUKP VJG )TQWR CPF )TQWR & ECVGIQTKGU D[ RCFFKPI CTQWPF VJG UKFGU DQVVQO CPF VQR QH VJG EQTG EQPVCKPGTU

6TCPURQTVCVKQP D[ RCUUGPIGT ECT QT CKT HTGKIJV TCVJGTVJCPXCPQTVTWEMOC[DGOQTGCRRTQRTKCVG HQT HTCIKNG EQTG *QYGXGT KH CKT HTGKIJV KU WUGF GPUWTG VJCV VJG UCORNGU CTG VTCPURQTVGF KP C JGCVGFRTGUUWTK\GFEQORCTVOGPV+HVJGEQTGKUVQ DGVTCPURQTVGFKPVJGDGFQHCVTWEMVJGTGUJQWNFDG PQ JGCX[ QDLGEVU VJCV EQWNF UNKFG QT TQNN KPVQ VJG UCORNGEQPVCKPGTU

6JG FTKXGT QH VJG XGJKENG ECTT[KPI VJG UCORNGU UJQWNFDGVJQTQWIJN[KPUVTWEVGFKPVJGTGSWKTGFECTG QHVJGUCORNGU

6JGXGJKENGECTT[KPIVJGUCORNGUUJQWNFDGKPIQQF OGEJCPKECNEQPFKVKQP#DTGCMFQYPQPVJGVTCPU RQTV TQWVG EQWNF NGCXG VJG UCORNGU GZRQUGF VQ GZVTGOGYGCVJGTEQPFKVKQPU

%QOOGTEKCN ECTTKGTU UJQWNF DG WUGF QPN[ YJGP UCORNGUCTGPQVUGPUKVKXGVQUJKRRKPIFCOCIGCPF KPJQWUG HQTEGU CPF GSWKROGPV CTG WPCXCKNCDNG %QOOGTEKCN ECTTKGTU UJQWNF DG WUGF QPN[ KH VJG ECTTKGTKUECRCDNGQHFGNKXGTKPIVJGUCORNGUKPVJG FGUKTGF EQPFKVKQP 6JG UCORNG EWUVQFKCP UJQWNF GPUWTGVJCVCNNUCORNGECTGTGSWKTGOGPVUCTGENGCTN[ KPFKECVGFQPVJGNCFKPIFQEWOGPVU

425 FIELD MANUAL

Upright Handling and Shipping of Samples (QT UQOG V[RGU QH UVWFKGU QT VGUVKPI UWEJ CU VJQUG RGTHQTOGFQPNKSWGHKCDNGUCPFUCPFUGPUKVKXGENC[UVJG UCORNGUOWUVPGXGTNGCXGVJGXGTVKECNQTWRTKIJVRQUKVKQP +H UCORNGU UJQWNF PGXGT NGCXG VJG XGTVKECN QT WRTKIJV RQUKVKQPVJGHQNNQYKPIUJQWNFDGEQPUKFGTGF

5CORNGUVJCVOWUVTGOCKPKPVJGXGTVKECNRQUKVKQP UJQWNF DG QDVCKPGF YKVJ C VJKPYCNN RWUJVWDG UCORNGT6JGUGUCORNGUCTGVJGGCUKGUVVQJCPFNG QPEGVJG[CTGQWVQHVJGITQWPF6JGGPFUECPDG GCUKN[UGCNGFYKVJGZRCPFCDNGRCEMGTU

+H VJKPYCNN RWUJ VWDG UCORNGU CTG PQV VCMGP UCORNGNGPIVJUCPFFKCOGVGTUUJQWNFDGMGRVVQC OKPKOWO5KZKPEJ EO FKCOGVGTEQTGVJCVKU HGGV O NQPIKUCDQWVVJGOCZKOWOUK\GVJCV UJQWNFDGQDVCKPGF5CORNGUNCTIGTVJCPVJKUCTG XGT[FKHHKEWNVVQJCPFNGKPCP[RQUKVKQP

5CORNGUUJQWNFPGXGTDGTGOQXGFHTQOVJGNKPGTQT UCORNKPIVWDG

5CORNG VWDGU UJQWNF DG OCTMGF UQ VJCV VQR CPF DQVVQOCTGGCUKN[FKUEGTPCDNG

4CEMU VJCV YKNN JQNF VJG UCORNGU KP CP WRTKIJV RQUKVKQPOWUVDGFGUKIPGFCPFDWKNVHQTVJGUK\GQH UCORNGDGKPIVCMGP

5CORNGU VJCV OWUV DG VTCPURQTVGF EQOOGTEKCNN[ UJQWNF DG RCEMGF KP C YQQF DQZ 6JG[ UJQWNF DG KPUWNCVGF CICKPUV VGORGTCVWTG EJCPIGU CPF RTQVGEVGFCICKPUVOQXGOGPVYKVJKPVJGDQZ6JG RCEMKPIDQZUJQWNFDGENGCTN[OCTMGFVQKPFKECVG YJKEJUKFGKUVQTGOCKPWRVJCVVJGEQPVGPVUCTG HTCIKNG CPF VJCV VJG EQPVGPVU TGSWKTG RTQVGEVKQP HTQOHTGG\KPI

426 HANDLING AND TRANSPORTING SAMPLES

5VQTCIG'PXKTQPOGPV

#NN UCORNGU UJQWNF DG ITQWRGF CEEQTFKPI VQ UVQTCIG TGSWKTGOGPVUCPFUVQTGFUQVJCVCKTECPEKTEWNCVGCTQWPF VJGUCORNGQTUCORNGEQPVCKPGT HKIWTG 5CORNGU VJCVCTGUGPUKVKXGVQOQKUVWTGNQUUUJQWNF DGUVQTGFCV TQQOVGORGTCVWTG u(u% CPFCVCRRTQZKOCVGN[ RGTEGPVTGNCVKXGJWOKFKV[*KIJGTNGXGNUQHTGNCVKXG JWOKFKV[ ECP ECWUG HWPICN ITQYVJ 5CORNGU KP OGVCN VWDGU UJQWNF DG RTQEGUUGF CU UQQP CU RTCEVKECN VQ OKPKOK\G UCORNG EJCPIGU VJCV OKIJV QEEWT DGECWUG QH KPVGTCEVKQPDGVYGGPVJGUCORNGCPFVJGOGVCNQHVJGVWDG

9QQFDQZGUEQPVCKPKPIUCORNGUUJQWNFDGRTQVGEVGFHTQO TGRGCVGFYGVVKPICPFFT[KPI6JKUEQWNFECWUGYCTRKPI CPF FGNCOKPCVKPI QH VJG YQQF 6JG DQZGU UJQWNF DG RTQVGEVGFCICKPUVFCOCIGD[KPUGEVUCPFTQFGPVU

Recommended Equipment

(QNNQYKPI KU C NKUV QH GSWKROGPV PGEGUUCT[ VQ RTQEGUU JCPFNGCPFVTCPURQTVGKVJGTTQEMQTUQKNUCORNGU

8KP[NKFGPGEJNQTKFG 5CTCPYTCR HKNOCNWOKPWO HQKNYCZFQYPURQWV28%QTUKOKNCTVWDKPI

5VQXGVQOGNVYCZ

.WEKVGQT28%VWDKPI

5CYFWUVTWDDGT5V[TQHQCOQTOCVGTKCNQHUKOKNCT TGUKNKGPE[VQEWUJKQPVJGEQTG

/KUEGNNCPGQWU GSWKROGPV UWEJ CU CFJGUKXG VCRG CPFYCVGTRTQQHHGNVVKROCTMGTU

427 FIELD MANUAL

9QQFFKUMURTGYCZGFKPEJ OO VJKEMYKVJC FKCOGVGTUNKIJVN[NGUUVJCPVJGKPUKFGFKCOGVGTQH VJGVJKPYCNNVWDG

6CRGGKVJGTYCVGTRTQQHRNCUVKEQTFWEVVCRG

%JGGUGENQVJ

%CRUGKVJGTRNCUVKETWDDGTQTOGVCNVQDGRNCEGF QXGTVJGGPFQHVJKPYCNNVWDGU

2NCUVKE QT OGVCN GZRCPFCDNG GPF ECRU VQ UGCN VJG GPFU QH UCORNGU YKVJKP VJKP YCNN VWDGU D[ OGEJCPKECNN[ GZRCPFKPI CP 1 TKPI CICKPUV VJG VWDGYCNN

2NCUVKE QT INCUU LCTU YKFGOQWVJGF YKVJ TWDDGT TKPIGFNKFUQTNKFUNKPGFYKVJCEQCVGFRCRGTUGCN EQOOQPN[ RKPV OKNNKNKVGT =O.? CPF SWCTV O.

$CIUGKVJGTRNCUVKEQTDWTNCRYKVJYCVGTRTQQHNKPGT

2NCUVKERCKNUYKVJCKTVKIJVNKFU

2CEMKPIOCVGTKCNVQRTQVGEVCICKPUVXKDTCVKQPCPF UJQEM

+PUWNCVKQPVQTGUKUVVGORGTCVWTGEJCPIGQHUCORNGU VQRTGXGPVHTGG\KPI

5CORNG EWDG DQZGU HQT VTCPURQTVKPI EWDG DNQEM UCORNGU EQPUVTWEVGF YKVJ VQ KPEJ VQ OO RN[YQQF OCTKPGV[RG

%[NKPFTKECNUCORNGEQPVCKPGTUUQOGYJCVNCTIGTVJCP VJGVJKPYCNNVWDGUQTNKPGTUCORNGU

428 HANDLING AND TRANSPORTING SAMPLES

5JKRRKPIEQPVCKPGTUGKVJGTDQZQTE[NKPFTKECNV[RG QHRTQRGTEQPUVTWEVKQPVQRTQVGEVCICKPUVXKDTCVKQP UJQEMCPFYGCVJGTVJGNGPIVJIKTVJCPFYGKIJVQH VJG EQPVCKPGTU OWUV DG EQPUKFGTGF YJGP WUKPI EQOOGTEKCNVTCPURQTVCVKQP

5RCEGTDNQEMOCVGTKCNVQTGRNCEGUCORNGUVCMGP

429 Chapter 24

CARE, RETENTION, AND DISPOSAL OF DRILL CORE, SOIL, AND ROCK SAMPLES

General

These guidelines for the care, retention, and disposal of drill core, soil, and rock samples apply to (1) foundation exploration for structures, such as dams, canals, tunnels, powerplants and pumping plants, (2) construction materials investigations including riprap and borrow, and (3) safety of existing structures investigations. Sample retention and disposal guidelines for concrete aggregate, pozzolan, land classification, drainage (except for drainage structures), and hazardous waste studies are excluded.

These guidelines are intended to maximize care of samples and cores, minimize storage costs, meet minimum technical requirements, and avoid unnecessarily long storage periods. Special circumstances or needs may require modification of the guidelines.

These guidelines apply to rock and soil core and samples taken without special sampling sleeves, tubes, or containers. When undisturbed samples taken in sleeves or containers or undisturbed hand-cut samples are specifically intended for laboratory examination or testing to supply design data, the samples should be taken, prepared, cared for, and handled in accordance with USBR 7100 [1] and USBR 7105 [2]. Undisturbed samples should be shipped immediately to avoid deterioration and changes in physical properties. Chapter 23 describes proper procedures for protecting and shipping samples. Appropriate logs, sample data sheets, or other pertinent information should be submitted with the samples. FIELD MANUAL

Location of Storage Facilities

The preparation of an adequate log or description of the core or samples should be done before storing and subsequently disposing of samples. If the sampled material, such as slaking shales, breaks down upon drying and loses in-place characteristics during storage, it may be better to drill new holes than to store large quantities of core that will seldom be looked at or will lead to wrong interpretations if inspected or tested after years of storage.

The following are the general requirements for storage of core and samples:

1. Provide minimum storage conditions. (See the next section, “Conditions of Storage.”)

2. Eliminate unsupervised storage. The storage facility should be at or near the site of a project or investigation.

3. Minimize transferring core and samples from one storage facility to another because work on a structure site or project progresses through successive stages of investigation and construction.

4. Provide accessibility so that minimum travel is required for examination of the core and samples. Frequent inspection may be necessary for design purposes and for prospective bidders on construction specifications.

5. Survey existing unused space before constructing or acquiring new space or use space initially provided for other purposes but adaptable to core and sample storage. For example, the lower

432 CARE, RETENTION AND DISPOSAL

floors and galleries of many powerplants and some pumping plants or buildings erected for temporary use during construction have storage space.

Storage During Investigations

Core and samples should be kept at the nearest existing storage facility. A new storage facility should be established only if required by the location, the amount of core and number of samples anticipated, and the duration of investigation or access convenience. In some instances during periods when actual drilling and sampling operations are in progress, temporary storage at the site may be required to facilitate logging, selection of samples, or ready reference while geologic, soils, or other field studies are in progress. Temporary onsite storage should be limited to short periods of actual need and should prevent damage or deterioration of the core and samples.

When a field office maintaining core storage facilities is closed following preliminary investigations, core and samples no longer required should be discarded (see section entitled Retention of Rock Core and Samples), and the remaining core and samples should be transferred to an appropriate location. When exploration is resumed, the core should be examined to determine whether the samples are still useful or whether redrilling is necessary.

Storage During Construction

Core and samples should be stored locally during construction. The core and samples provide foundation and materials data to geologists, designers, and construction personnel during construction and claim processing.

433 FIELD MANUAL

At the close of construction, special samples should be selected for possible future testing (See the section on “Retention of Rock Core and Samples”). Sample selection is better when personnel familiar with the core, samples, and foundation conditions are available.

At the close of construction, arrangements should be made for continued storage of core and samples until applicable core and sample retention criteria have been met. The core and samples should remain at the local storage facility, if practical.

Storage During Operation and Maintenance

Any transfer of a structure from one organization to another should include arrangements for core and sample storage until the applicable standard core and sample retention periods are met.

Conditions of Storage

The minimum conditions for core and sample storage are:

1. Protection against wetting and drying but not against temperature changes. Cores that might be damaged by drying or freezing should be appropriately protected.

2. Protection against unauthorized access, damage, vandalism, and snake or rodent infestation.

3. Grouping core boxes and samples by drill hole number, investigation site, and project and stacking to permit reasonably easy access and examination. The core and samples should be accessible without excessive unstacking and moving of adjacent core boxes and samples. The

434 CARE, RETENTION AND DISPOSAL

safe height of core box or sample stacks depends on the strength of the boxes and reasonable ease of handling. Core box racks should be provided only when repeated reexamination and study are anticipated and when the time saved by having the boxes separated in units of four or five boxes would be cost effective.

4. The office responsible for storage should maintain adequate records including copies of final logs, photographs, inventory, and location map of the core and samples stored at each core and sample storage location. The records should include the name of the feature or investigation site, drill hole number, number of boxes and samples, and whether the cores or samples have been tested.

Length of Storage

Proposed Structures or Projects

All core and samples collected during site investigations should be kept until the proposed structure, unit, or project is built and has performed satisfactorily for a period of time or is abandoned. The following are exceptions.

Appraisal.—Core and samples obtained in investigations for dams, canals, etc., should be disposed of at the end of appraisal stage investigations, such as the abandonment of a proposed structure site or completion of reconnaissance designs and estimates, except in special cases.

Feasibility.—Disturbed soil samples from borrow pit investigations obtained during feasibility stage investigations and not used for testing should be discarded at the end of the investigations unless interest in the project is

435 FIELD MANUAL sufficient to ensure continuing development. If, at the end of 1 year, further development work has not materialized, the samples should be discarded on the assumption that deterioration makes tests on the samples unreliable.

Undisturbed soil samples can be discarded after 1 year.

Design Investigations and Completed Structures or Projects

Requirements for length of storage for various types of samples and core are as follows:

Borrow Pit Investigations for Design.—Borrow pit soil samples collected for design investigations should be retained until construction is complete and all claims are settled except as the samples are consumed in routine testing.

Borrow Investigations for Construction Control.— Soil samples collected for construction control investigations and field laboratory testing should be discarded after completion of the field laboratory testing and all claims are settled.

Record Samples from Fill.—Samples collected for record tests and not consumed should be retained unless the number of samples is more than necessary to represent the materials used for construction.

Foundation Core and Samples.—Foundation core and samples obtained during design and construction investigations and not consumed in testing may be disposed of when the following requirements are met:

436 CARE, RETENTION AND DISPOSAL

1. Canals and distribution systems including pipelines, minor or small engineering structures, and low dikes or embankments are trouble free for 1 year. 2. Large or major engineering structures such as dams, powerplants or pumping plants, main feeder canals, and main power conduits are trouble free for 5 years. The 5-year time period should begin after operating level reservoir filling for large dams. Representative core and samples from a few representative drill holes should be kept for the life of the structure. 3. Contractual negotiations and settlement of claims which might involve reinspection or testing of the core or samples are complete. 4. Initial safety of dams analysis, modification, and construction activities are complete.

Disposal of Core and Samples

Photographs and an adequate log or description of the core and samples should be available before disposal. When the minimum retention periods and other requirements outlined above have been met, concurrence of the design and operation and maintenance (O&M) offices should be obtained by the office responsible for the core or samples before any core or samples are discarded.

The responsible office should consider giving the State Geologist’s Office, technical schools, colleges, museums, or similar groups the opportunity to select samples or retain the core.

The recommended disposal procedure is to place permanent markers in the core boxes, wrap the boxes in plastic, and bury the boxes in a marked location.

437 FIELD MANUAL

Retention of Rock Core and Samples

If selected cores or samples are retained as representative of the foundation and dam, appropriate assistance in selecting the samples is necessary. Assistance can usually be obtained from the design office.

To facilitate storage, handling, and inspection, standard core box sizes and labeling procedures should be used. Core boxes should withstand a reasonable amount of careful handling, stacking, and shipping when filled with rock core.

To help identify the boxes when stacked, information should be shown on one end and the top of each core box. Temporary labeling of core boxes used while drilling a hole should be replaced with permanent labeling of core boxes which will remain legible after handling, stacking, or storing for long periods. A map or an index file of drill hole core should be maintained which shows the location of drill hole core if the boxes are stored in a large or congested storage area.

Bibliography

Bureau of Reclamation, U.S. Department of the Interior, USBR-7100, “Obtaining Undisturbed Block Samples by the Hand and Chain Saw Methods,” Earth Manual, Part II, 3rd edition, 1990.

Bureau of Reclamation, U.S. Department of the Interior, USBR-7105, “Performing Undisturbed Soil Sampling by Mechanical Drilling Methods),” Earth Manual, Part II, 3rd edition, 1990.

438 Chapter 25

GLOBAL POSITIONING SYSTEM

System Description

The Navigation Satellite Time and Ranging (NAVSTAR) Global Positioning System (GPS) is a space-based satellite radio navigation system developed by the U. S. Depart- ment of Defense (DoD). GPS receivers provide land, marine, and airborne users with continuous three- dimensional (3D) position, velocity, and time data (PVT). This information is available free of charge to an unlimited number of users. The system operates under all weather conditions, 24 hours a day, anywhere on Earth. The Union of Soviet Socialist Republics developed a similar system that is generally not used because it is a duplication of the NAVSTAR function.

GPS System Design

The GPS system consists of (1) the space segment, (2) the control segment, and (3) the user segment.

Space Segment.—The space segment consists of a nominal constellation of 24 operational satellites (including 3 spares) that have been placed in 6 orbital planes 10,900 miles (20,200 kilometers [km]) above the Earth’s surface. The satellites are in circular orbits with a 12-hour orbital period and an inclination angle of 55 degrees. This orientation provides a minimum of five satellites in view at any time anywhere on Earth. Each satellite continuously broadcasts two low-power, spread- spectrum, RF Link signals (L1 and L2). The L1 signal is centered at 1575.42 megahertz (MHz), and the L2 signal is centered at 1227.6 MHz.

Control Segment.—The control segment consists of a Master Control Station (in Colorado Springs) and a FIELD MANUAL number of monitor stations at various locations around the world. Each monitor station tracks all the GPS satellites in view and passes the signal measurement data back to the Master Control Station. Computations are performed at the Master Control Station to determine a precise satellite ephemeris and satellite clock errors. These data are then uplinked to the individual satellites and, subsequently, rebroadcast by the satellite as part of a navigation data message.

User Segment.—The user segment is all GPS receivers and their application support equipment such as antennas and processors. This equipment allows users to receive, decode, and process the information necessary to obtain accurate position, velocity, and timing measurements. These data are used by the receiver’s support equipment for specific application requirements.

GPS Basic Operating Concepts

Satellite Signals.—The satellites transmit their signals using spread-spectrum techniques that employ two different spreading functions: a 1.023-MHZ coarse/ acquisition (C/A) code on L1 only and a 10.23-MHz precision (P) code on both L1 and L2. The two spreading techniques provide two levels of GPS service: Precise Positioning Service (PPS) and Standard Positioning Service (SPS). SPS uses C/A code to derive position, while PPS uses the more precise P-code (Y-code).

C/A Code.—The C/A code is a 1,023 bit nonrepeating code sequence with a clock rate of 1.023 MHZ. The satellite repeats the code once every millisecond. Each satellite is assigned a unique C/A code that is chosen from a set of codes known as Gold Codes.

440 GLOBAL POSITIONING SYSTEMS

P(Y)-Code.—The P-code consists of a 2.36e+14 bit nonrepeating code sequence with a clock rate of 10.23 MHZ. The entire code would take 267 days before a repetition occurs; however, each satellite is assigned a unique 1-week segment of this code that restarts every Saturday/Sunday midnight.

The P-code has a number of advantages over C/A code. (1) The P-code rate is 10 times faster; therefore, the wavelength is 1/10th as long, giving the P-code a much higher resolution. (2) The higher rate spreads the signal over a wider frequency range (see figure 25-1). This frequency spreading makes the P-code much more difficult to jam. (3) By encrypting the P-code (creating Y-code), the receiver is not susceptible to spoofing (false GPS signals intended to deceive the receiver).

The drawback of P-code is that it is relatively difficult to acquire because of its length and high speed. For this reason, many PPS receivers first acquire C/A code, then switch over to the P(Y)-code. Y-code is an encrypted

Figure 25-1.—Satellite signal structure.

441 FIELD MANUAL version of P-code that is used for anti-spoofing (A-S). Because of the similarity of these two codes, they are referred to collectively as P(Y)-code.

Navigation (NAV) Message

Superimposed on both the P-code and the C/A code is a navigation (NAV) message containing satellite ephemeris data, atmospheric propagation correction data, satellite clock-bias information, and almanac information for all satellites in the constellation.

The navigation message consists of 25 1,500-bit frames and is broadcast at 50 bits per second. It takes 30 seconds to receive a data frame or 12.5 minutes to receive all 25 data frames. Each satellite repeats its own ephemeris data and clock bias every frame along with a portion of the almanac. The receiver will receive the critical acquisition information within 30 seconds, but a full almanac will require 12.5 minutes to download.

Signal Acquisition.—The GPS satellites use Bi-Phase Shift Keyed (BPSK) modulation to transmit the C/A and P(Y)-codes. The BPSK technique involves reversal of the carrier phase whenever the C/A or P(Y)-code transitions from 0 to 1 or from 1 to 0.

To the casual observer, the very long sequence of ones and zeros that make up the C/A and P-codes appears random and blends into the background noise. For this reason, the codes are known as pseudo-random noise (PRN).

In actuality, the C/A and P-codes generated are precisely predictable to the start time of the code sequence and can be duplicated by the GPS receiver. The amount the receiver must offset its code generator to match the

442 GLOBAL POSITIONING SYSTEMS

Figure 25-2.—Satellite ranging intersections. incoming code from the satellite is directly proportional to the range between the GPS receiver antenna and the satellite.

By the time the spread-spectrum signal arrives at the GPS receiver, the signal power is well below the thermal noise level. To recover the signal, the receiver uses a correlation method to compare the incoming signals with its own generated C/A or P(Y) codes. The receiver shifts its generated code until the two codes are correlated.

Satellite Ranging.—The receiver continuously determines its geographic position by measuring the ranges (the distance between a satellite with known coordinates in space and the receiver’s antenna) of several satellites and computes the geometric intersection of these ranges. To determine a range, the receiver measures the time required for the GPS signal to travel from the satellite to the receiver antenna. The resulting time shift is multiplied by the speed of light, arriving at the range measurement.

443 FIELD MANUAL

Because the resulting range measurement contains propagation delays caused by atmospheric effects as well as satellite and receiver clock errors, the measurement is referred to as a "pseudorange." A minimum of four pseudorange measurements are required by the receiver to mathematically determine time and the three components of position (latitude, longitude, and elevation). The solution of these equations may be visualized as the geometric intersections of ranges from known satellite locations (see figure 25-2). If one of the variables, such as elevation, is known, only three satellite pseudorange measurements are required for a PVT solution, and only three satellites would need to be tracked.

GPS Accuracy

GPS accuracy has a statistical distribution that depends on a number of important factors, including dilution of precision (DOP) satellite position and clock errors, atmospheric delay of the satellite signals, selective availability (SA), signal obstruction, and multipath errors.

Dilution of Precision

Geometric Dilution of Precision (GDOP) is a measure of the amount of error due to the geometry of the satellites. The errors in the range measurements that are used to solve for position may be magnified by poor geometry. The least error results when the lines of sight have the greatest angular separation between satellites.

There are four other DOP components that indicate how the geometry specifically affects errors in horizontal position (HDOP), vertical position (VDOP), position (PDOP), and time (TDOP). DOPs are computed based on

444 GLOBAL POSITIONING SYSTEMS the spatial relationships between the satellites and the user and vary constantly due to the motion of the satellites. Lower DOPs mean more accurate estimates. A PDOP less than six is necessary for accurate GPS positioning.

Satellite Position and Clock Errors

Each satellite follows a known orbit around the earth and contains a precise atomic clock. The monitor stations closely track each satellite to detect any errors in the orbit or the clock. Corrections for errors are sent to each satellite as ephemeris and almanac data. The ephemeris data contain specific position and clock correction data for each satellite while the almanac contains satellite position data for all satellites. The NAV set receives the ephemeris and almanac data from the satellites and uses these data to compensate for the position and clock errors when calculating the NAV data.

Atmospheric Delay of Satellite Signals

Electromagnetic signals (such as GPS signals) travel at the speed of light, which is always a constant in a vacuum but not in the atmosphere. There are two layers of the Earth’s atmosphere that affect satellite signals, the ionosphere and the troposphere.

The ionosphere is a 90-mile (150-km) thick layer of the upper atmosphere in which ultraviolet radiation from the sun has ionized a fraction of the gas molecules, thereby releasing free electrons (ions). The shape of the ionosphere and its electron density varies with latitude, time of day, time of year, number of sunspots, solar flares, and other cosmic activity. The magnitude of the error caused by ionospheric effects can translate to a position error as large as 130 ft (40 m).

445 FIELD MANUAL

The troposphere is the dense, humid layer of atmosphere near the surface of the Earth. This layer refracts the satellite signals in proportion to the humidity and density of the air. The magnitude of the tropospheric error can be as small as 8 ft (2.3 m) at the zenith, or as large as 65 ft (20 m) at 10 degrees above the horizon.

There are two ways to compensate for the atmospheric delays: modeling and direct measurement. The ionospheric and tropospheric delays are inversely proportional to the square of the frequency. If a receiver can receive L1 and L2 frequencies, it can measure the difference between the two signals and calculate the exact atmospheric delay.

Most receivers currently use mathematical models to approximate the atmospheric delay. The tropospheric effects are fairly static and predictable, and a model has been developed that effectively removes 92-95 percent of the error. This reduces the total two-dimensional (2D) position error caused by the troposphere to around 8 ft (2.0 m).

The ionosphere is more difficult to model because of its unusual shape and the number of factors that affect it. A model has been developed that requires eight variable coefficients. Every day, the control segment calculates the coefficients for the ionospheric model and uplinks them to the satellites. The data are then rebroadcast in the NAV messages of the C/A and P(Y)-codes. This model can effectively remove 55 percent of the ionospheric delay, reducing the total 2D position error caused by the ionosphere to around 25 ft (7.5 m).

Selective Availability and Anti-Spoofing

GPS satellites provide two levels of navigation service: Standard Position Service and Precise Position Service.

446 GLOBAL POSITIONING SYSTEMS

SPS receivers use GPS information that is broadcast in the clear and is available to anyone in the world. This information may contain built-in errors that limit the accuracy of the receiver. This is a security technique called Selective Availability (SA). These SA errors are variable. In normal conditions, the U.S. Government guarantees that these errors do not exceed 100 m horizontal, 140 m vertical, and time accuracy of 340 nanoseconds, 95 percent of the time. There are times when an SPS receiver error exceeds these limits. SPS receivers are for civil use, and SA may or may not be on.

PPS receivers use the same information as SPS receivers. PPS receivers also read encoded information that contains the corrections to remove the intentional SA errors. Only users who have crypto keys to decode this information get the PPS accuracy. U.S. Government agencies and some Allies are authorized to have these crypto keys. A receiver with valid crypto keys loaded and verified is a PPS receiver.

To protect authorized users from hostile attempts to imitate the GPS signals, a security technique called anti- spoofing is also used. This is an encrypted signal from the satellites that can be read only by PPS receivers. SPS receivers are not capable of using anti-spoofing. A receiver with valid crypto keys loaded and verified reads this encrypted signal and operates in a spoofing environment.

GPS Signal Obstruction

Normal operation of the GPS receiver requires undisturbed reception of signals from as few as four satellites (in normal 3D mode) or three satellites in fixed-

447 FIELD MANUAL elevation mode. The signals propagating from the satellites cannot penetrate water, soil, walls, or other similar obstacles.

The antenna and the satellites are required to be in "line- of-sight" with each other. GPS cannot be used for underground positioning in tunnels, mines, or subsurface marine navigation. In surface navigation, the signal can be obscured by buildings, bridges, trees, and other matter that might block an antenna’s line-of-sight from the GPS satellites. In airborne applications, the signal can be shaded by the aircraft’s body during high banking angles. For moving users, signal shading or temporary outages are generally transitory and should not degrade the overall positioning solution.

The GPS receiver uses five channels to minimize the effects of obstruction. During normal operation, four channels track the four primary GPS satellites while the fifth channel tracks the remaining visible satellites and recovers the ephemeris data for each satellite. If one or more of the primary satellites are obscured, the receiver contains the data to support rapid acquisition of alternative satellites.

If only three satellites can be tracked, receivers may feature an “Elevation Hold” mode and continue to navigate as previously noted. The accuracy of the PVT in this mode will not be greatly affected unless the elevation changes. The receiver will use either the last computed elevation or an elevation provided by the user or host system. The accuracy of the “Elevation Hold” mode depends on the accuracy of the elevation provided to the receiver.

448 GLOBAL POSITIONING SYSTEMS

Multipath Interference

Multipath errors result from the combination of data from more than one propagation path. These errors distort the signal characteristics of the range measurements and result in pseudorange errors. These errors depend on the nature and location of a reflective surface peculiar to each user location. The effects are less detrimental for a moving user because small antenna movements can completely change the multipath characteristics.

The receiver is designed to reject multipath signals. First, the active patch antennas are designed to have a sharp gain roll-off near the horizon while providing nominal gain for the primary satellite signal. Since most multipath signals are reflected from ground structures, they tend to be attenuated. Second, the antenna is right-hand polarized. When a right-hand polarized GPS signal is reflected off a conductive surface, the signal becomes left- hand polarized and rejected by the antenna. The receiver also has hardware and software designed to reduce the effects of any multipath interference errors.

Differential GPS

Differential GPS (DGPS) may be used to eliminate the effects of SA and correct certain bias-like errors in the GPS signals. A Reference or Base Station Receiver measures ranges from all visible satellites to its surveyed position. Differences between the measured and estimated ranges are computed and saved for post processing or transmitted by radio or other signals to differential equipped receivers. Sub-meter to centimeter position accuracy is possible using local base station differential GPS.

449 FIELD MANUAL

Quality of Measurement

The accuracy with which positions are determined using GPS depends on two factors—satellite geometry and user measurement accuracy.

Satellite Geometry

Satellite geometry effects on specific position solutions can be expressed as dilution of precision. DOP is used to describe the contribution of satellite geometry to total positioning accuracy. An ideal satellite constellation would not dilute the positioning accuracy.

Ideal Satellite Constellation

The term, “current satellite constellation,” refers to the satellites being used in the current position solution. When the current satellite constellation geometry is ideal, the DOP value is 1. This means the current satellite constellation contributes a “dilution factor” of 1 to positioning accuracy. Most of the time, the satellite geometry is not ideal, which means the current satellite constellation geometry "dilutes the precision" of the positioning accuracy. As the satellite constellation becomes less ideal, the adverse effect on positioning accuracy is greater. The dilution will change over time as satellites travel along their orbits, as different satellites are used to solve for GPS position, and as the user moves.

DOP Effects

The effect of satellite geometry is not equally distributed in all three positional vectors (x, y, and z in Earth- centered, Earth-fixed coordinates). Several DOP related values are commonly used. Table 25-1 shows expected values for HDOP, VDOP, and others. The range given for

450 GLOBAL POSITIONING SYSTEMS

Table 25-1.—Expected values of dilution of precision

68-percent 95-percent probability of probability DOP Description obtaining of obtaining

HDOP Horizontal DOP is the 1.50 1.78 satellite geometry factor in the 2D horizontal position solution.

VDOP Vertical DOP is the 2.08 2.70 satellite geometry factor in the vertical position (elevation) solution.

PDOP Positional DOP is the 2.56 3.23 satellite geometry factor in the 3D position solution.

=  22+  PDOP  HDOP VDOP 

TDOP Time DOP is the N/A N/A satellite geometry factor in the time solution. HTDOP Horizontal and time N/A N/A DOP is the satellite geometry factor in the 2D horizontal position and time solutions. HTDOP = SQRT (HDOP2 + TDOP2)

GDOP Geometrical DOP is the 2.79 3.61 satellite geometry factor in the 3D position and time solutions. GDOP = SQRT (HDOP2 + VDOP2 + TDOP2)

451 FIELD MANUAL

VDOP, HDOP, GDOP, and PDOP assumes a 5-degree antenna mask (signals 5 degrees or more above the horizon) and a 24 satellite constellation.

Unique user conditions, such as more than 5 degrees of antenna masking (e.g., in deep canyons), satellite outages, and poor constellation choice may result in a degraded DOP.

Quality Indicators

The indicators of solution quality are computed based on several things. These include uncertainties in receiver measurement processes, current satellite constellation geometry, and errors as reported by the satellites, such as the User Range Accuracy (URA) index. There are different measures of quality. A quality indicator must be selected based on the requirements of the application and how meaningful that measure will be. Some measures of quality indicators are shown below.

Circular Error Probable.—Circular Error Probable (CEP) is an estimate of horizontal accuracy that expresses the radius of a circle in the horizontal plane that will contain at least 50 percent of the GPS 2D positional solutions. CEP is generally expressed in meters; a smaller value indicates a higher quality 2D position solution. CEP is not desirable as a quality measure for navigation systems because a 50-percent probability is too small. This measure can be useful in some applications, for example, a bombing run where a better than 50-percent chance of hitting a target is required. CEP is not available from all GPS units. However, CEP may be estimated by the following equation.

CEP = 0.8323* EHE

EHE is the expected horizontal error.

452 GLOBAL POSITIONING SYSTEMS

R95.—R95 is similar to CEP except that the circle contains at least 95 percent of the GPS 2D positional solutions. R95 is generally expressed in meters, and a smaller value indicates a higher quality 2D position. R95 is better than CEP as a measure for navigation systems because a 95-percent probability is more commonly associated with navigation requirements. R95 is not available from all GPS units. However, it may be estimated by the following equation.

R95 = 1.731 * EHE

Spherical Error Probable.—Spherical error probable (SEP) is an estimate of 3D accuracy that is the radius of a sphere that will contain at least 50 percent of the GPS 3D positional solutions. SEP is generally expressed in meters, and a smaller value indicates a higher quality 3D position solution. SEP is not desirable as a quality measure for navigation systems for the same reason that CEP is not; a 50-percent probability is too small. A spherical model of errors is not well suited to the GPS model because error probabilities in the horizontal plane are of a smaller scale than those in the vertical plane (compare HDOP to VDOP). This leads to more of a football shaped error distribution than a spherical distribution. SEP is not available from all GPS units.

Expected Position Error.—Expected position error (EPE) is a 1-sigma calculation of 3D position solution estimate of error. EPE is expressed in meters, and a smaller EPE indicates a higher quality position solution. Similarly computed values are often referred to, including:

EHE, Expected Horizontal Error (1-sigma estimate of 2D error)

453 FIELD MANUAL

EVE, Expected Vertical Error (1-sigma estimate of one-dimensional error)

EPE=+() EHE22 EVE

EPE is one of the best available indicators of quality for navigation systems.

EPE can also be output as Figure of Merit (FoM). (See below.)

Root Mean Square.—Root Mean Square (RMS) is a 1-sigma calculation of error in position. Horizontal RMS is equivalent to EHE, vertical RMS is equivalent to EVE, and 3D RMS is equivalent to EPE.

The above is true only if the mean values of the error components are zero or the biases of the errors can be independently determined and removed.

Figure of Merit.—Figure of Merit (FOM) is an expression of EPE, as shown in table 25-2.

From a historical perspective, FOM was created at the inception of GPS to provide users with a simple and quick method of indicating the solution accuracy; it is still widely used in many military applications today. It does not have the granularity to take advantage of the significant improvements in accuracies that may be achieved today. FOM is available from some GPS units on the display.

454 GLOBAL POSITIONING SYSTEMS

Table 25-2.—FOM related to EPE EPE FOM (meters)

1 < 25

2 < 50

3 < 75

4 < 100

5 < 200

6 < 500

7 < 1,000

8 < 5,000 9 5,000

Expected Time Error.—Expected Time Error (ETE) is a calculation of time error that is computed similarly to EPE. ETE is a 1-sigma estimate of time solution error. ETE is expressed in seconds, and a lower ETE indicates a higher quality time solution. Some GPS units calculate and output EPE in the form of Time Figure of Merit.

Time Figure of Merit.—Time Figure of Merit (TFOM) is an expression of ETE as shown in table 25-3.

455 FIELD MANUAL

Table 25-3.—TFOM related to ETE

TFOM ETE

1 < 1 nanosec

2 < 10 nanosec

3 < 100 nanosec

4 < 1 microsec

5 < 10 microsec

6 < 100 microsec

7 < 1 millisec

8 < 10 millisec

9≥ 10 millisec

User Measurement Accuracy

Several factors are involved in the receiver’s ability to accurately measure the distance to the satellites. The most significant factors in user measurement accuracy are space and control segment errors, atmospherics, and user equipment (UE) errors. These errors are generally grouped together and referred to as User Equivalent Range Error (UERE).

456 GLOBAL POSITIONING SYSTEMS

User Equivalent Range Error

User Equivalent Range Error represents the combined effect of space and control segment errors (satellite vehicle position [ephemeris] and clock errors), atmospherics (ionospheric and tropospheric), and user equipment errors (receiver measurement uncertainties). UERE cannot be broadcast by the satellites and can be estimated only at the receiver. The point that sets UERE apart from other measures of error is that UERE does not take into account any satellite geometry effects, such as HDOP or VDOP. Table 25-4 shows a typical error budget for a P(Y)-code GPS receiver.

Table 25-4.—Typical GPS receiver error budget

Accuracy factor Error

Space and control segment 4.0 m

Ionospheric 5.0 m

Tropospheric 2.0 m

Receiver noise 1.5 m

Multipath 1.2 m

Miscellaneous 0.5 m

UERE =+++++()452151205222.. 2 2 . 2 7.0 m

457 FIELD MANUAL

Space and Control Segment Errors

Satellites provide an estimate of their own satellite position and clock errors. Each satellite transmits an indication of these errors in the form of User Range Accuracy (URA).

URA is a value transmitted by each GPS satellite that is a statistical indicator (1-sigma estimate) of ranging accuracies obtainable from that satellite. URA includes all errors that the space and control segments are responsible for—for example, satellite clock error and SA error. URA has very coarse granularity, however.

The URA value is received in the form of an index related to URA as shown in table 25-5.

The URA index broadcast by each satellite will change over time. In practice, the control segment will upload correction data to each satellite at least once every 24 hours. When a satellite first receives its upload, it should have a very low URA index. The amount of error will increase over time, because of things such as satellite clock drift, and the URA index for that satellite will grow. Some satellites’ URA index will grow more rapidly than others.

In practice, authorized PPS users should expect to see URA index values in the range of 0 to 5. More commonly, values of 2-4 should be expected. The values depend on the length of time since the last control segment upload to that satellite.

458 GLOBAL POSITIONING SYSTEMS

Table 25-5.—URA index and values

URA URA index (meters)

1 0.00 < URA <= 2.40

2 2.40 < URA <= 3.40

3 3.40 < URA <= 4.85

4 6.85 < URA <= 9.65

5 9.65 < URA <= 13.65

6 13.65 < URA <= 24.00

7 24.00 < URA <= 48.00

8 48.00 < URA <= 96.00

9 96.00 < URA <= 192.00

10 192.00 < URA <= 384.00

11 384.00 < URA <= 768.00

12 768.00 < URA <= 1,536.00

13 1,536 < URA <= 3,072.00

14 3,072.00 < URA <= 6,144

15 6,144 < URA (or no accuracy prediction available)

459 FIELD MANUAL

Wide Area GPS Enhancement

Wide Area GPS Enhancement (WAGE) is a feature available in Precise Positioning Service PLGR+96 receivers. The WAGE feature uses encrypted satellite data to reduce some space and control segment errors.

Each satellite broadcasts WAGE data that are valid for 6 hours after that satellite receives a data upload. These data may be used to correct satellite clock errors on other satellites that have not received an upload recently. These clock corrections are used to reduce the error caused by satellite clock biases when a period of time has passed since the last upload to those satellites. It takes approximately 12.5 minutes to download a complete WAGE data set. Only WAGE data from the most recently updated satellite are used in PLGR.

Atmospheric Errors

Atmospheric errors are those caused by the satellite RF signal passing through the earth’s atmosphere. These errors include ionospheric and tropospheric delays.

Ionospheric delay affects the GPS signal as it passes through the earth’s ionosphere. The ionospheric delay to GPS signals is very dynamic and depends on the time of day, the elevation angle of the satellites, and solar flare activity. Single frequency receivers use a modeled estimate of the range error induced by GPS navigation signals passing through the Earth’s ionosphere. It is very difficult, however, to estimate the error in this model.

Dual frequency receivers measure this delay by tracking both the GPS L1 and L2 signals. The magnitude of the delay is frequency dependent, and the absolute

460 GLOBAL POSITIONING SYSTEMS delay on either frequency can be scaled from the differential delay between L1 and L2.

Tropospheric delay is the expected measure of range error induced by GPS navigation signals passing through the Earth’s troposphere. This measure is based on satellite elevation. Unlike the ionospheric delay, the tropospheric delay is very predictable, and there is very little error in the compensation.

User Equipment Errors

User equipment errors are those uncertainties in the measurements that are inherent in the receiver’s collection and computation of measurements. Several factors influence these uncertainties, including the GPS hardware, the design of the tracking loops, the code type being tracked (C/A or P(Y)), and the strength of the satellite signals. These uncertainties are taken into account in the Kalman filter processing done in a PLGR when computing EPE and ETE.

Multipath effects are caused by a signal arriving at the receiver site over two or more different paths. The difference between the path lengths can cause them to interfere with one another in the receiver. Buildings, parking lots, or other large objects may reflect a signal from a satellite, causing multipath effects. Signal averaging can be used to minimize the effects of multipath signals.

Error Source Summary

There are many factors that influence the accuracy of GPS measurements. Many of the factors do not contribute large errors but cumulatively are important.

461 FIELD MANUAL

In practice, the three major sources of error are (1) performing the survey when satellite geometry is poor, (2) using equipment not designed to provide the desired accuracy, and (3) mixing datums and coordinate systems.

Satellite Geometry

The most useful error measurement available is position dilution of precision (PDOP). PDOP is a number derived from the geometry of the visible satellites and changes as the satellites move in their orbits. The smaller the PDOP number, the better the satellite geometry. The PDOP value should be six, or preferably less, for accurate GPS work. Some GPS units display the PDOP or an accuracy estimate in real time. Software is available that calculates the PDOP for any planned GPS survey and should be used before conducting the survey to determine whether accurate GPS work is possible at the planned location and time. The software also can be used to determine satellite positions and whether terrain or other obstructions will affect the survey. Presurvey planning, especially relative to PDOP, can make the difference between a mediocre or failed GPS survey and a successful survey.

Equipment

Using inappropriate equipment is another major factor in GPS survey problems. The accuracy of the equipment must be known, and the equipment must be used properly. A small, inexpensive hand-held GPS unit can provide an accuracy of 10s of feet when selective availability is off and approximately 100 feet (30 m) when SA is on. A PLGR (military GPS) can provide similar accuracy when SA is on. A mapping grade GPS unit can provide 1- to 2-ft (0.5-m) accuracy if the data are post- processed and 3-ft (1-m) real-time accuracy if a satellite

462 GLOBAL POSITIONING SYSTEMS differential correction signal is available. Centimeter or survey-grade accuracy is possible with a local differential base station providing real-time or post-processing correction of rover data. Do not expect more accuracy than the equipment can deliver. Manufacturer estimates of accuracy are generally better than what is commonly encountered in the field. The equipment must be well maintained. Many apparently satellite related problems are caused by equipment malfunctions, poorly charged batteries, or faulty cable connections.

Datums and Coordinate Systems

An apparent GPS problem is introduced by collecting or comparing position data based on different datums or coordinate systems. Many old topographic maps and surveys use the 1927 North American Datum (NAD27), and most new survey data are based on the 1983 North American Datum (NAD83). Also, some sites use a local reference system that is not related to a regional datum or coordinate system. Systematic errors are a good indication of a datum problem. Software is available that very accurately converts between datums and coordinate systems and is very useful for diagnosing and correcting problems. Chapter 6 of Volume 1 contains a discussion of datums, map projections, and coordinate systems.

463 APPENDIX

ABBREVIATIONS AND ACRONYMS COMMONLY USED IN BUREAU OF RECLAMATION ENGINEERING GEOLOGY AND RELATED TO HAZARDOUS WASTE

(Many are modified from A.A.P.G. Committee on Stratigraphic Correlations)

Acronyms and Abbreviations Commonly Used in Bureau of Reclamation Engineering Geology

A Apparent trace acre-ft Acre-feet acre-ft/d Acre-feet per day acre-ft/yr Acre-feet per year

AGI American Geological Institute

AP Analysis Plan

APSRS Aerial Photography Summary Record System

ARAR Applicable or Relevant and Appropriate Requirement

ASCS Agricultural Stabilization and Conservation Service

ASTM American Society for Testing Materials FIELD MANUAL

ASTM/USCS American Society for Testing Materials/ Unified Soil Classification System b As a suffix, with boulders

BJ Bedding joint c As a suffix, with cobbles

CADD Computer assisted design and drafting

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CH Fat clay

CL Lean clay

CL Cleavage

CL-ML Silty clay cm Centimeter cm2 Square centimeter cm/s Centimeter per second

COC Contaminant of concern

D Dip trace

DI Durability Index

DLS Detail line survey

DNAPL Dense, nonaqueous phase liquid

DQOs Data Quality Objective

420 ABBREVIATIONS

EPA Environmental Protection Agency ft Foot ft2 Square foot ft3 Cubic foot ft3/s Cubic foot per second ft/yr Feet per year

FJ Foliation joint

FSP Field Sampling Plan

FZ Fracture zone g As a prefix, gravelly; as a suffix, with gravel gal Gallon gal/min Gallon per minute

GC Clayey gravel

GC-GM Silty, clayey gravel

GC/MS Gas chromatograph/mass spectrometer

GC Gas chromatograph

GM Silty gravel

GP Poorly graded gravel

GP-GC Poorly graded gravel with clay

GP-GM Poorly graded gravel with silt

421 FIELD MANUAL

GPS Global Positioning System

GW Well graded gravel

GW-GC Well graded gravel with clay

GW-GM Well graded gravel with silt

H1 Extremely hard

H2 Very hard

H3 Hard

H4 Moderately hard

H5 Moderately soft

H6 Soft

H7 Very soft

HASP Health and Safety Plan

HCl Hydrochloric acid

ID Inside diameter

IF Incipient fracture

IJ Incipient joint in Inch in2 Square inch in3 Cubic inch

JT Joint

422 ABBREVIATIONS k Hydraulic conductivity kPa Kilopascal kg/cm2 Kilogram per square centimeter km Kilometer kN Kilonewton kN/m3 Kilonewton per cubic meter

L Liter lbf/in2 Pound-force per square inch lb/in2 Pounds per square inch lb/ft3 Pounds per cubic foot

LCS Laboratory control standard

LL/PI Liquid limit/plasticity index

LNAPL Light nonaqueous phase liquid

L/sec Liter per second m Meter m2 Square meter m3 Cubic meter m3/s Cubic meter per second m3/yr Cubic meter per year

MB Mechanical break

423 FIELD MANUAL

MCL Maximum contaminant level mg/Kg milligram per kilogram

MH Elastic silt mi Mile

ML Silt mm Millimeter

NAD North American Datum

NASC North American Stratigraphic Code

NCC National Cartographic Information Center

NGI Norwegian Geotechnical Institute

NPDES National Pollutant Discharge Elimination System

NTIS National Technical Information Service

NTU Nephelometric turbidity unit

OD Outside diameter

OERR Office of Emergency and Remedial Response

OH Organic clay

OL Organic silt

OSHA Occupational Safety and Health Administration

424 ABBREVIATIONS

Pa Pascals

PRP Possible responsible party

PCB Pentachlorobenzene ppb Part per billion ppm Part per million

PSI Pound-force per square inch

PT Peat

PVC Polyvinyl chloride

QAPP Quality Assurance Project Plan

QC Quality control

RCRA Resource Conservation Recovery Act

Reclamation U.S. Bureau of Reclamation

RF Random fracture

RMR Rock Mass Rating System Geomechanics Classification

RQD Rock Quality Designation

RSR Rock Structure Rating

S Strike trace s As a prefix, sandy; as a suffix, with sand

SAP Sampling and Analysis Plan

SC Clayey sand

425 FIELD MANUAL

SC-SM Silty, clayey sand

SDWA Safe Drinking Water Act

SM Silty sand

SOP Standard operating procedures

SP Poorly graded sand

SP-SC Poorly graded sand with clay

SPT Standard Penetration Test

SP-SM Poorly graded sand with silt

SW Well graded sand

SW-SC Well graded sand with clay

SW-SM Well graded sand with silt

TBM Tunnel boring machine

TCE Trichloroethlyene

TCLP Toxicity characteristic leaching procedure

TRPH Total recoverable petroleum hydrocarbons

URCS Unified Rock Classification System

USCS Unified Soil Classification System

USDA United States Department of Agriculture

USGS United States Geological Survey

426 ABBREVIATIONS

VOC Volatile organic compound

WP Work plan yd3 Cubic yard

µg/L microgram per liter

µm Micrometer

EC degrees Centigrade

EF degrees Fahrenheit

Commonly Used Acronyms and Abbreviations Related to Hazardous Waste

ARAR Applicable or relevant and appropriate requirement

AST Above ground storage tank

AP Analysis plan

BADT Best available demonstrated technology

BAT Best available technology or best available treatment

CAA Clean Air Act

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act (Superfund)

427 FIELD MANUAL

CERCLIS Comprehensive Environmental Response, Compensation, and Liability Information System

COD Chemical oxygen demand

CRP Community Relations Plan

CRZ Contaminant reduction zone

CWA Clean Water Act (aka FWPCA)

DQO Data quality objectives

EPA Environmental Protection Agency

FS Feasibility study

FSP Field sampling plan

HASP Health and safety plan

HRS Hazard ranking system

HS Head space (analysis)

IDL Instrument detection limit

IDLH Immediately dangerous of life and health

LEL Lower explosive limit

LFL Lower flamability limit

LUST Leaking underground storage tank

MCL Maximum contaminant level (SDWA)

MDL Method detection limit

428 ABBREVIATIONS

MSDS Material safety data sheet

NCR Nonconformance report

ND Nondetect

NFRAP No further remedial action planned

NPDES National Pollutant Discharge Elimination System

NPL National Priority List

NTIS National Technical Information Service

OSWER Office of Solid Waste and Emergency Response

PA Preliminary assessment

PCB Polychlorinated biphenyl

PEL Permissible exposure limit or personal exposure limit

PPB Parts per billion

PPM Parts per million

PPT Parts per trillion

PPTh Parts per thousand

PRP Potentially responsible party

PS Point source

PVC Polyvinyl chloride

429 FIELD MANUAL

PWS Public water supply or public water system

QA Quality assurance

QAPP Quality assurance project plan

QC Quality control

QL Quantitation limit

RA Remedial action or removal action or risk assessment

RCRA Resource Conservation Recovery Act

RD Remedial design

RfD Reference dose

RI Remedial investigation

RMCL Recommended maximum contaminant levels

RME Reasonable maximum exposure

ROD Record of decision

RP Responsible party

RPM Remedial project manager

RQ Reportable quantity

SAP Sampling and analysis plan

SAR Start action request

430 ABBREVIATIONS

SARA Superfund Amendments and Reauthorization Act of 1986

SAS Special analytical services

SDWA Safe Drinking Water Act

SF Slope factor

SI Site inspection

SOP Standard operating procedures

SQG Small quantity generator

STEL Short-term exposure limit

STP Sewage treatment plant

SVOC Semivolatile organic chemical (Compound)

SWDA Solid Waste Disposal Act

TCE Trichloroethylene

TCL Target compound list

TCLP Toxicity characteristic leaching procedure

TD Toxic dose

TDS Total dissolved solids

THC Total hydrocarbons

TIC Tentatively identified compound

TLV Threshold limit value

431 FIELD MANUAL

TOA Trace organic analysis

TOC Total organic carbon or total organic compound

TOX Total organic halogens

TPY Tons per year

TRPH Total recoverable petroleum hydrocarbons

TSCA Toxic Substances Control Act

TSDF Treatment, storage, and disposal facility

TSS Total suspended solids

UEL Upper explosive limit

UFL Upper flamability limit

UST Underground storage tank

VOC Volatile organic chemical (compound)

WP Work plan

WSRA Wild and Scenic Rivers Act

WWTP Wastewater treatment plan

432 APPENDIX A

ABBREVIATIONS AND ACRONYMS COMMONLY USED IN BUREAU OF RECLAMATION ENGINEERING GEOLOGY

AGC automatic gain control AN ammonium nitrate A-S anti-spoofing ASCE American Society of Civil Engineers ASTM American Society for Testing Materials ATF Bureau of Alcohol, Tobacco, and Firearms AVIRIS Airborne Visible and Infrared Imaging Spectrometer BIPS Borehole Image Processing System bpf blow per foot bpm blow per minute BPSK bi-phase shift keyed BPT Becker Penetration Test C/A coarse/acquisition CDP common depth point CFR Code of Federal Regulations cm centimeter cm2 centimeter squared CME Central Mine Equipment cm/sec centimeter per second CPE Circular Probable Error CPT Cone Penetration Test CPTU piezometric cones or piezocones CRR cyclic resistance ratio DGPS differential GPS FIELD MANUAL

DoD U.S. Department of Defense DOP dilution of precision DOT Department of Transportation DS13 U.S. Bureau of Reclamation Design Standard No. 13 for Embankment Dams EBW exploding bridge wire EHE expected horizontal error EM electromagnetic EPE expected position error ERi drill rod energy ratio ETE expected time error EVE expected vertical error FoM Figure of Merit

Fr friction ratio fs sleeve resistance ft feet ft/sec feet per second ft3/min cubic feet per minute ft3/sec cubic feet per second gal/min gallons per minute GDOP geometric dilution of precision g/cm3 grams per cubic centimeter GPR ground penetrating radar GPS Global Positioning System HDOP horizontal dilution of precision HSA hollow-stem auger ICE International Construction Equipment ID inside diameter IME Institute of Makers of Explosives in inch

466 APPENDIX A in/sec inch per second JPL Jet Propulsion Laboratory kg kilogram kg/cm2/m kilograms per square centimeter per meter kg/L kilogram per liter kg/m3 kilogram per cubic meter kHz kilohertz km kilometer kPa kilopascal L liter lb/ft3 pounds per cubic foot lb/in2 pounds per square inch lb/gal pounds per gallon lb/yd3 pounds per cubic yard LEDC low-energy detonating cord L/min liter per minute L/min/m liter per minute per meter lu Lugeon LVL low-velocity layer m meter m2 square meters MHz megahertz mL milliliter mm millimeter mm/sec millimeters per second m/sec meters per second m3/sec cubic meters per second ms millisecond MSHA Mine Safety and Health Administration

467 FIELD MANUAL

MSS multispectral scanner NAD27 1927 North American Datum NAD83 1983 North American Datum NASA National Aeronautics and Space Administration NAV navigation NAVSTAR Navigation Satellite Time and Ranging NFPA National Fire Protection Association NG nitroglycerin NIST National Institute of Standards and Technology NTU nephelometric turbidity unit OD outside diameter O&M operation and maintenance OSHA Occupational Safety and Health Administration OSM Office of Surface Mining P compressional wave PDA pile-driving analyzer PDOP position dilution of precision PETN pentaerythritoltetranitrate PMT photomultiplier tube PPS Precise Positioning Service PRN pseudo-random noise psi pounds per square inch psi/ft pounds per square inch per foot PVC polyvinyl chloride PVT position, velocity, and time data qc tip resistance RMS root mean square

468 APPENDIX A rps revolutions per second S shear wave SA selective availability SEP spherical error probable SLAR side-looking airborne radar SP self-potential, spontanious potential SPS Standard Positioning Service SPT Standard Penetration Test SSS side scan sonar SSSG surface saturated dry specific gravity TDOP time dilution of precision TFOM Time Figure of Merit TM thematic mapper TNT trinitrotoluene ton/ft2 ton per square foot UE user equipment UERE User Equivalent Range Error URA User Range Accuracy USGS U.S. Geological Survey VDOP vertical position dilution of precision WAGE Wide Area GPS Enhancement ° C degrees Centigrade ° F degrees Fahrenheit 3D three-dimensional 2D two-dimensional

469 APPENDIX B

NOMOGRAPH RELATING THE DENSITY OF AN EXPLOSIVE IN G/CC, THE DIAMETER OF THE EXPLOSIVE IN INCHES, AND THE POUNDS OF EXPLOSIVE PER LINEAL FOOT

“Column Diameter” equals hole diameter for poured and pumped blasting products. (For cartridged products, estimate the explosives column average diameter, based upon cartridge diameter and amount of tamping or slump.) For example: a line drawn through the 0.8 gm/cc point (for ANFO) and the 3-inch column diameter point intersects the “weight” line at about 2.5 lb/ft. APPENDIX C

CHART SHOWING RIPABILITY VERSUS SEISMIC VELOCITY FOR A D11N BULLDOZER APPENDIX D

CHARTS SHOWING WEIGHT OF MATERIALS REQUIRED FOR TYPICAL LABORATORY TESTS

FIELD MANUAL *Or more to obtain a representative sample Required minimum test specimen Comments 100 g oven dried 10 g 4 Recommended minimum test sample Same as test specimen 4 sample Practical field Practical English Metric English Metric (footnotes are at the end the are at (footnotes of table) the 1,2,3 Weight of material required for ofWeight individual material - 1 of sheet 7 soil tests size in 9 lb 4 kg 2.2 lb, 1 kg Maximum particle No. 4 5 lb 2.3 kg 1.1 lb 500 g

G ¾ in1½ in3 in 18 lb 26 lb 8 kg 12 kg 26 lb 12 kg 4.4 lb, 2 kg 6.6 lb, 3 kg 6.6 lb, 3 kg* No. 40 (425 µm) 0.1 lbNo. 4 40 g 2 lb 800 g 200 g of test Nominal description Specific gravity 4 No. minus Moisture content No. Method A USBR 5320 USBR USBR 5300 USBR 5305 USBR 5310 USBR 5315 USBR Designation ASTM D 854 ASTM ASTM D 2216 ASTM D 4959 ASTM D 4944 ASTM D 4643 ASTM

478 APPENDIX D *10 lb recommended for large mechanical sieve shakers **Air dried Required specimen Comments minimum test 200 g*, ** 2.4 lb, 1.1 kg*, ** **Required of plus weight No. 4 particles, dried air 100 g oven dried 4 4.4 lb, 2 kg** test sampletest test Same as Same Recommended minimum specimen If not air dried, need test need dried, air not If specimen plus weight to equivalent amount content ofweight moisture 4 (footnotes at end at (footnotes of table) n/a 91 kg 150 lb, 68 kg** 4 English Metric English Metric Practical field sample 1,2,3 Weight of material required for ofWeight individual material - 2 of sheet 7 soil tests size in 20 lb** 9.1 kg** in 5 lb* kg* 2.3 particle particle Maximum

G G ¾ in1½ in 15 lb3 in 100 lb 6.8 kg 200 lb 45 kg 20 lb, 9.1 kg** ¾ in1½ in3 in 30 lb** 50 lb** 14 kg**No. 4 200 lb** 23 kg** 91 kg** 5 lb 6.6 lb, 3 kg** 11 lb, 5 kg** 2.3 kg 40 lb, 18 kg** 1.1 lb 500 g of test Nominal description Gradation: 4 No. minus Gradation: gravel sizes Specific and gravity absorption plus No. 4 No. USBR 5335 USBR 5325 USBR USBR 5320 USBR Designation ASTM C 127 ASTM D 2487 ASTM D 2487 ASTM USBR 5330 or USBR Method B or C

479 FIELD MANUAL *Or as more, have to required, soil 120 g of air-dried (150 g if shrinkage included) is limit **Air dried Two 8-g wet-weight Two specimens Required minimum test specimen Comments 100 g** 100 g** 20 g** 30 g** 4 test sampletest Recommended minimum 4 (footnotes at end at (footnotes of table) English Metric English Metric Practical field sample 1,2,3 Weight of material required for ofWeight individual material - 3 of sheet 7 soil tests size particle particle Maximum No. 4 5 lb* 2 kg* 1.1 lb*, ** 500 g*, ** of test Nominal description LL - 1 point LL - 3 point Plastic limit Plastic Shrinkage limit No. USBR 5350 USBR USBR 5355 USBR USBR 5360 USBR USBR 5365 USBR Designation ASTM D 427 ASTM ASTM (none) ASTM D 4318 ASTM ASTM D 4318 ASTM

480 APPENDIX D Required minimum test specimen Comments 4 test sampletest Recommended minimum 4 (footnotes at end at (footnotes of table) English Metric English Metric Practical field sample 100 lb 45 kg 25 lb100 lb 12 kg 45 kg 25 lb, 12 kg 50 lb 23 kg 50 lb, 23 kg or or

1,2,3 G G Weight of material required for ofWeight individual material - 4 of sheet 7 soil tests size particle particle Maximum ¾ in 3 in1½ or 150 lbNo. 4, ¾ in 68kg 3 in1½ or 75 lb 200 lb 34 kg 91 kg 150 lb 75 lb, 34 kg 68 kg 150 lb, 68 kg No. 4 5 lbNo. 4, 2.3 kg 1.1 lb 500 g 500 g of test Nominal description (Wet and (Wet dry maximum) Dispersivity (crumb, pinhole, double hydrometer) Minimum and/or maximum unit index weight or dry(wet maximum) No. and/or USBR 5400 USBR 5405 USBR 5410 USBR 5525 USBR 5530 USBR Designation ASTM (none) ASTM D 4647 ASTM D 4221 ASTM D 4564 ASTM

481 FIELD MANUAL *Or more as needed*Or more 50 lb least have at to No. 4 and at of minus 50 lb of plus least No. 4 Required minimum test specimen Comments 4 test sampletest Recommended minimum 4 (footnotes at end at (footnotes of table) sample Practical field Practical English Metric English Metric 350 lb* 159 kg* 350 lb* 159 kg* 225 lb, 102 kg 1,2,3 size particle particle Weight of material required for individual soil tests - sheet 5 of 7 - sheet individual tests for soil required of material Weight Maximum No. 4 200 lb 91 kg 50 lb** 23 kg** 50 lb, 23 kg** dried **Air 3 in No. 43 in 50 lb 23 kg 350 lb* 15 lb 159 kg* 350 lb* 7 kg 159 kg* 225 lb, 102 kg 15 lb, 7 kg of test Nominal description Laboratory compaction: 4 No. minus Permeability soils gravelly Laboratory compaction: soils gravelly (one specimen) 3 specimensPermeability 4 No. minus 900 lb 409 kg 900 lb 409 kg 900 lb, 409 kg No. USBR 5500 USBR USBR 5515 USBR USBR 5600 USBR Designation ASTM (none) ASTM D 2937 ASTM ASTM D 2434 ASTM

482 APPENDIX D Required minimum test specimen Comments 4 test sampletest Recommended minimum 4 (footnotes at end at (footnotes of table) sample Practical field Practical English Metric English Metric 1,2,3 size particle particle Maximum No. 4 15 lb 7 kg 3 lb 1.4 kg 1.5 lb, 0.7 kg Weight of material required for ofWeight individual material - 6 of sheet 7 soil tests of test Nominal description One-dimensional consolidation, or Expansion Uplift No. USBR 5700 USBR 5705 USBR 5715 USBR Designation ASTM D 2435 ASTM D 3877 ASTM D 3877 ASTM

483 FIELD MANUAL No. 4 Required minimum test specimen Comments 4 test sampletest Recommended minimum 4 sample 4 times the required weight of the test sample. The test sample is sized to yield the Practical field Practical inch - 9.5 mm, ¾ inch - 19.0 mm, 1½ inch - 37.5 mm, 3 inch - 75 mm and 5 inch - 125 mm. 3 inch - 75 mm 1½ inch - 37.5 mm, ¾ inch - 19.0 mm, inch - 9.5 mm, $

English Metric English Metric G 1,2,3 size Weight of material required for ofWeight individual material - 7 of sheet 7 soil tests particle particle Maximum No. 4¾ in 20 lb1½ in 9.1 kg 100 lb 4 lbNo. 4 200 lb 45 kg 50 lb¾in 91 kg 65 lb 1.8 kg 170 lb1½ in 23 kg 30 kg 200 lb 2 lb, 0.9 kg 77 kg 16 lb 700 lb 91 kg One 2-in-dia specimen 45 lb, 20 kg 200 lb 318 kg 7.3 kg 150 lb, 68 kg One 6-in-dia specimen 700 lb One 9-in-dia specimen 91 kg 318 kg 8 lb, 3.6 kg 2-in-dia specimens Four 180 lb, 82 kg 600 lb, 273 kg 6-in-dia specimens Four 9-in dia specimens Four (usu- 0 of test sample is required. is sample Nominal description ally performed in ally performed with conjunction triaxial other tests) UU CU or CD Triaxial K No. Maximum particle size present in original sample. in original present size particle Maximum No. 4 fraction means either maximum particle in original sample was No. 4 or smaller or a representative portion of the minus - 4.75 mm, No. 4 sieve are: equivalents Metric should field sample be the quartering, permit To 1 2 3 4 USBR 5740 USBR 5745 USBR 5740 USBR 5755 USBR Designation ASTM (none) ASTM D 2850 ASTM D 2850 ASTM D 2850 ASTM fraction of original the

required number of specimens. prepared test

484 APPENDIX D

Weight of material required for combinations of soil tests - sheet 1 of 1 Minimum sample required Maximum Test combinations1 particle size2,3 English Metric No. 4 Laboratory G in 50 lb 23 kg classification ¾ in (gradation, Atterberg limits) 1½ in 100 lb 46 kg 3 in 200 lb 91 kg No. 4 50 lb 23 kg Physical properties - Cohesive soil G in (gradation, Atterberg ¾ in 100 lb4 46 kg4 limits, specific gravity, laboratory 1½ in compaction 3 in 200 lb4 91kg4 Physical properties - No. 4 Cohesionless soil 100 lb 46 kg G in (gradation, Atterberg limits, specific ¾ in gravity, maximum 1½ in 200 lb 91 kg and minimum index unit weight) 3 in Soil-cement (for 1½ in 2,000 lb 908 kg 3 cement contents) 1 Assumes field sample will be used for more than one test. If sample is divided to provide separate test samples, add up values for individual soil tests. 2 Maximum particle size present in original sample. 3 Metric equivalents are: No. 4 sieve - 4.75 mm, G inch - 9.5 mm, ¾ inch - 19.0 mm, 1½ inches - 37.5 mm, 3 inches - 75 mm, and 5 inch - 125 mm. 4 Or more, as needed to have 50 lb of minus No. 4.

485 FIELD MANUAL

In place density test requirements - test apparatus and minimum excavation

Cohesive materials Minimum Maximum required particle size volume Apparatus and template (in) (ft3) opening

¾ 0.25 8-in sand cone

1½ 0.5 12-in sand cone

20-in sand cone or 31 24-in-square frame

5 2 30-in square frame

8 8 4-ft-diameter ring

12 27 6-ft-diameter ring

18 90 9-ft-diameter ring >18 Determine on a case-by-case basis

Cohesionless materials

¾ 0.25 20-in sand cone

1½ 0.5 24-in-square frame

3 1 33-in-square frame

5 2 40-in-diameter ring

8 8 62-in-diameter ring

>8 Determine on a case-by-case basis

486 APPENDIX D

Weight of material required for slope protection tests

Minimum required Reclamation sample designation No. English Metric Comments

The minimum dimension of individual rock fragments selected should be at least 0.5 feet 6025 (15 cm). If source Design 600 lb 275 kg material quality is Standard variable, the sample No. 13 should include rock fragments representing the quality range of the source material.

487 APPENDIX E

USEFUL CONVERSION FACTORS METRIC AND ENGLISH UNITS (INCH-POUND)

Length inch (in) 2.540 X 10 1 3.937 X 10-2 millimeter (mm) hundredths of feet 3.048 X 102 3.281 X 10 -3 millimeter (mm) foot (ft) 3.048 X 10 -1 3.281 meter (m) mile (mi) 1.6093 6.2137 X 10-1 kilometer (km) Area square inch (in2) 6.4516 X 10-4 1.550 X 10-3 square meter (m2) square foot (ft2) 9.2903 X 10 -2 1.0764 X 101 square meter (m2) acre 4.0469 X 10 -1 2.4711 hectare square mile (mi2) 0.386 X 10 -2 259.0 hectares Volume cubic inch (in3) 1.6387 X 10-2 6.102 X 10-2 cubic centimeter (cm2) cubic feet (ft3) 2.8317 X 10-2 3.5315 x 101 cubic meter (m3) cubic yard (yd3) 7.6455 X 101 1.3079 cubic meter (ms) cubic feet (ft3) 7.4805 1.3368 x 10-1 gallon (gal) gallon (gal) 3.7854 2.6417 X 10-1 liter (L) acre-feet (acre-ft) 1.2335 X 103 8.1071 X 10 -4 cubic meter (m3) Flow gallon per minute (gal/min) 6.309 X 10-2 1.5850 X 101 liter per second (L/s) cubic foot per second (ft3/s) 4.4883 X 102 2.228 X 10-3 gallons per minute (gal/min) 1.9835 5.0417 X 10-1 acre-feet per day (acre-ft/d) cubic foot per second (ft3/s) 7.2398 X 102 1.3813 X 10-3 acre-feet per year (acre-ft/yr) 2.8317 X 10-2 3.531 X 101 cubic meters per second (m3/s) 8.93 X 105 1.119 X 10-6 cubic meters per year (m3/yr) Permeability k, feet/year 9.651 X 10-7 1.035 X 106 k, centimeter per second (cm/sec) Density pound-mass per cubic foot 1.6018 X 101 6.2429 X 10-2 kilogram per cubic meter (lb/ft3) (kg/m3) Unit Weight pound force per cubic foot 0.157 6.366 kilonewton per cubic meter (lb/ft3) (kN/m3) Pressure pounds per square inch (psi) 7.03 X 10-2 1.4223 X 101 kilogram per square centimeter (kg/cm3) 6.8948 0.145 kiloPascal (kPa) Force ton 8.89644 1.12405 X 10-1 kilonewton (kN) pound-force 4.4482 X 10-3 224.8096 kilonewton (kN) Temperature °C = 5/9 (°F - 32 °) °F = (9/5 °C) + 32 ° Grouting Metric bag cement per meter 3.0 0.33 U.S. bag cement per foot Water:cement ratio 0.7 1.4 water:cement ratio by weight by volume pounds per square inch 0.2296 4.3554 kilogram per square centi- per foot meter per meter (kg/cm2/m) k, feet/year 0.1 10 Lugeon Index

A abandoned mines, 13 absorption, 87, 88, 195, 203, 205 abutment contact slopes, 331 abutment pads, 339 accelerometers, 77 acoustic beams, 61 borehole imaging device, 61, 62 caliper, 75 energy, 57, 61, 91 energy (seismic waves), 57 imaging, 63, 64 imaging device, 64 logging, 19, 57, 58 logging devices, 57, 58 signal, 91 transducer, 74, 75 velocity devices, 61 velocity logger, 56 waves, 61 active remote sensing, 90 adjusting the blow control, 382 adobe charge, 241, 264 aerial photography, 85, 90, 92, 198 aggregate, 184, 188, 203, 207, 240, 334, 335, 431 air injection method, 166, 167 air jetting, 332 air/water jet, 348 air-powered venturi pipe, 348 alkali sensitive aggregates, reactive, 334, 335 alteration of minerals, 195 alternate delays, 233 aluminum foil wrapping, 415 American Society of Testing and Materials, 353 amplitude-modulated devices, 58 ANFO (ammonium nitrate/fuel oil mixture), 226 angled cut, 239, 243, 244, 245, 247, 249 FIELD MANUAL angular-shaped rocks nested together, 189 anti-spoofing, 442, 446, 447 aperture, 67, 73 apparent attenuation, 66 resistance, 42 resistivity, 9, 45 appraisal stage investigations, 435 aquaclude delineation, 11 aquifer, 2, 11, 108, 111, 115, 116, 166, 168, 171-173, 306, 308, 309, aquifer tests, 111, 116, 306, 309 archaeological investigations, 14, 18, 19 arch dam sites, 339, 340 arching, 321 arrival times, 31, 55, 60, 64, 66 artesian conditions, 304, 313, 363 artificial abutment, 340 ASTM D 1586, 377 ASTM D-5778, 397 ASTM D 3550, 353 atmospheric delay, 444-446 atmospheric spectral features, 88 automated spooling winch, 383 automated water level monitoring system, 317 automatic data logger, 167 automatic hammer, 371, 373, 380, 382, 383, 385, 387 axial dipole array, 11

B backfill concrete, 340, 342, 343, 347 backflow, 104 background potentials, 15, 16 backhoe, 183, 348 ball check housing, 364

492 INDEX bar magnet, 17 Barite, 363 barring, 332, 348 basement complex, 17 basket type catcher, 378 Becker Drills, Ltd. model AP-1000, 389 Becker Penetration Test (BPT), 351 bedding, riprap, 183, 190, 195 bedding planes, 114, 210, 215, 254, 325, 333 bedrock delineation studies, 11 depths, 18 topography, 14 Begemann friction cones, 395 bench blasting, 219, 227, 233 bench floor, 217 benches, 234, 235, 257, 298, 330 bentonite, 315, 338, 361-363, 369 BIPS analysis, 73 blanket grouting, 329 blast and processing testing, 199 blast hole size, 218, 221, 223 blast tests, 199 blasthole cutoffs, 217 blasting procedures, techniques, 192, 207, 209, 218, 233, 253, 254, 259, 261, 264, 325, 331 blotting with soil, 348 blow count rate, 371, 372 blow counts, 111, 306, 371, 375, 383, 388, 391 blowout, 302, 313 boils, 302 bond, 325, 326, 328, 329, 334 bonding of fill to concrete, 335 borehole caliper log, surveys, 74 deviation, 75 diameter, 49, 52, 57, 61, 74

493 FIELD MANUAL

effects, 74 electric logs, 38 film camera probe, 73 film camera systems, 69 fluid, 38, 39, 42, 45, 52, 57, 61, 77, 78, 81 acoustic velocity, 57 temperature, 77 gravity log, 74, 78 gravity logger, meter, 78, 79, 80 imaging, 56, 61-63 device, 56, 61, 62 velocity devices, 56 mapping, 69 peculiarities, 38 permeabilities, 112 spacing (distance), 65 television systems, 69 temperature log, 74 wireline surveying, 37 bounce chamber, 390, 391 bounce-chamber pressure, 390, 391 bound water, 41 boundary definition of thick strata, 45 Bouwer slug test, 168 box cut, 239 brooming, 332, 336 buckling of smaller AW rods, 384 bulk and shear moduli, 60 bulk density, 49, 51-53, 78, 80, 290 log, 52 bulk density/porosity logging methods, 80 bulk-loaded charges, 226 burden-to-charge diameter ratio, 211 buried channels, 5, 333 manmade objects, 15 metallic waste, 14

494 INDEX

pipelines, 14, 16, 18, 21 stream channels, 13 burning powder train, 237 bypass line, 361, 362, 365, 367

C calcium chloride, 363 calculated permeability values, 100, 114 calibration chambers, 404 for hole diameter, 52 pits, 49 caliper, 52, 61, 74-76 caliper log, 52, 74 camera, 32, 67-73, 75, 85, 395, 413 canals (and distribution systems), 16, 431, 435, 437 canyon profile for a damsite, 344 capillary fringe, 115 rise, 327 system, 15, 16 zone, 110, 175 CAPWAP, 392 carburizing, 377 care of samples, 431 cased boreholes, 37, 49, 50, 55 casing advancer method, 369 casing advancer systems, 385 cat head, 353 cathodic protection, 1, 10, 11, 21 cavities, 15, 56, 62, 63, 66, 67, 69, 210, 211, 302, 330, 332 cement, 77, 96, 184, 206, 321, 325, 334, 335, 348 cementation, 66, 74, 176, 195, 204, 206 centrifugal mixer, 335

495 FIELD MANUAL channels, 5, 13, 84, 87, 188, 325, 330, 333, 448 channels in rock surfaces, 325 cheese cloth, 415-417 chemical and biologic content of water, 316 quality of water discharged, 312 chemical concentration cells, 15 Cherenkov light, 55 photons, 55 chronology of dewatering, 319 claims, 306, 312, 433, 436, 437 clay plug, 257 cleanout bit, 359 cleanup procedures, 332 clock errors, 440, 444, 445, 457, 458, 460 closed-end diesel pile hammer, 390 CME automatic hammer, 382 coefficient of storage, 108 cofferdams, 303, 304 cold protection, 412 collar distance, 222, 228-231, 271 color of the borehole wall, 67 commercial quarry or pit deposits, 201 sources, 196 compaction, 66, 140, 153, 321, 322, 326-329, 336, 337, 348, 389, 417 techniques, 329 compass/clinometer, 68, 71 compressed air or water cleaning (air jetting), 323, 332 compression fracturing of core, 409 compression packers, 118 compressional energy, 57 (P) wave velocity, 5 wave oscillations, 57

496 INDEX

wave velocities, 3, 5, 61 waves, 5, 6, 57 concrete, 66, 67, 69, 203, 207, 302, 313, 321, 323-325, 329-331, 333-343, 345-349, 351, 431 backfill, 342, 346 backfilled cutoff shafts, 346 cracking, 334, 335 grout caps, 323 joints, 69 modulus, 340 conductive fluid in the borehole, 47 conductivity, 13, 14, 32, 78, 107, 110, 132, 134, 146, 147, 317, 395 cone tip resistance, 395 connectivity, 96-98 cone tip resistance, 395 construction specifications, 206, 306 traffic, 326 contact log, 46 contacts of rock or soil against concrete, 67 contaminant plumes, 10, 14 continuity of geologic strata, 38 continuity of the bedding, 38 continuous acoustic velocity (sonic) logger, 57 continuously recorded hydrofracture/jacking test, 104 contour blasting, 257 contrasting lithologies, 63 contractor compliance, 319 contractual negotiations, 437 control segment, 439, 446, 456-458, 460 controlled blasting techniques, 233, 253, 254, 259, 325 conventional flowmeters, 81 conventionally excavated (drill-blast) tunnel, 106 core box, 411, 412, 413, 415, 416, 420-423, 434, 435, 437, 438

497 FIELD MANUAL

contact area, 336 contact criteria, 322 drilling, 199, 202 materials, 329, 338 storage facilities, 433 core/foundation contact, 326, 338 coring, 202, 377, 387 corner cut, 239 cornish cuts, 244 correlate strata, 41, 45, 48, 51 corrosion, 21, 302 CPT, 351, 358, 363, 387, 388, 395, 397-401, 403, 405-407 crack potential, 321 cracks in the foundation, 325, 329, 335, 338 cross-hole geophones, 64 seismic tomography, 66 test(s), 64, 65 crowd-out plugged bit, 390 crown sheaves, 381, 382 crypto keys, 447 curing compound, 333, 335 curve shapes, 45 cushion blasting, 233, 259-262, 272-274 cushion holes, 261, 273 cushioning material, 416, 420 cutoff depths, 342, 346 facilities, 303 shafts, 342, 346 trench(s), 322, 327 wall, 323 cutoffs, 217, 235-237, 274, 299, 300 cylindrical and cube samples, 417-419

498 INDEX

D daily drill report, 423 dam foundation, 95, 98, 106, 350 dam height, 106 damp sawdust, 419 damsite foundation permeabilities, 96 deck charge, 215, 230, 231 deck of inert stemming material, 213 deformation, 340-342, 345, 346, 357, 359 moduli, 340, 341, 345 degree of compaction, 66 delay interval, 222 pattern, 210, 251, 252, 276 delineating thin strata, 45 densities of materials in the Earth, 18 density contrasts, 18, 19 logger, 49, 78 logging device, 51 dental concrete, 321, 324, 325, 330, 331, 333-338, 345 fillets, 334 treatment, 340, 341, 344-346 concrete, 341 work, 343, 347 depth of geologic materials, 38 of investigation, 11, 14, 47 of investigation for the microlog, 47 of penetration, 45 design data, 304-306, 351, 431 collection program, 304 Design Standards No. 13, Embankment Dams, 358 detecting cavities, 15

499 FIELD MANUAL determination, 18, 41, 52, 119, 133, 191, 203, 408, 417 of lithologies from SP logs, 41 of physical properties, 38, 203 of the relationship between weight and size, 191 of volumetric water content, 52 detonating cord, 236, 242, 255, 272, 274-277, 282, 284, connectors, 236 deviation surveys, 6, 65, 288, 297 dewatering, 96, 198, 299, 300, 302-306, 309, 312, 314-320 design, 306 facilities, 299, 304, 314-316 wells, 306 diesel pile-driving hammer, 387 differential GPS (DGPS), 449 differential movement, 343, 347 settlement, 324, 330, 331 digital processing, 84, 87 dilution, 302, 444, 450, 451, 462 factor, 450 of precision (DOP), 444 direct (non-refracted) arrivals, 64 directional detectors, 64 surveys, 74, 75 discontinuity (discontinuities), 20, 56, 62, 63, 67, 69, 71, 190, 194-196, 200, 203, 204, 330, 340, 341, 345 disk-type meter, 126, 141 disks, 326, 418, 428 disturbed zone, 106 dispersive clays, 338 dispersive embankment materials, 327 material(s), 338 soil, 338 dispersivity tests, 338

500 INDEX disposal guidelines, 431 disposing of samples, 432 ditches, 198, 299 double packers, 119 down-hole probe, 67, 69 drag force, 189 drainage trenches, 323 draining, 300, 302 surrounding surface water and groundwater, 302 drawdown with time, 308 draw cut, 243 drill hole deviation surveys, 6 drill jumbos, 244 drill rod energy ratio, 356, 379 drilling fluid loss, 67 mud, 38, 39, 361, 362, 364, 372 mudcake, 45 drive cap, 367 drive shoe, 153 driving friction, 392, 393 drop pipe, 162-165 drummy rock, 348 dry boreholes, 47 dual frequency receivers, 460 durability tests, 204, 205 durable rock types, 190 dynamic elastic properties of rock, 60 dynamites, 226, 227, 285, 294 D-6067, 397

E earthquake design analysis, 8 liquefaction, 375

501 FIELD MANUAL

Earth’s magnetic field, 80 effective porosity, 50, 56, 61, 108, 308 effects of bed thickness, 45 of mud cake, 52 of traffic, 9 on sensitive equipment, 9 EHE, 452-454 electric log, 37, 38 log correlation, 38 sounder (M-scope), 315 electrical current, 9, 26, 32, 77, 292, 293 field, 9 properties, 2, 10, 11, 13, 37, 38 resistivity, 1, 2, 9-11, 13 surveys, 38, 45 electrode(s), 9-11, 23, 33, 37, 41, 43-45, 47 array, 11, 13, 42, 45 spacing, 10, 11, 43, 45 electrolyte, 16 electromagnetic (EM) conductivity, 13, 14 profiling surveys, 10, 13, 14 induction, 13 radiation, 84 spectrum, 84, 86 surveying, 13 wave propagation, 13 electromagnetically induced telluric, 16 (large scale flow in the earth’s crust) currents, 16 electron density, 51, 445 electro-filtration, 16 electro-mechanical pulse, 57 embankment, 183, 188, 321-329, 333, 338, 349, 350, 358

502 INDEX embankment layer (lift), 326 embankment zones, 321 energy losses in rods, 379 transfer effects, 387 energy/count plot, 55 EPE, 453-455, 461 erodible foundation materials, 322 nonplastic materials, 338 erosion, 90, 183, 291, 307, 329, 330, 338 channels, 330 erosional history, 96 erosive action of water, 189 water forces, 191 erosion-resistant plastic materials, 338 ETE, 455, 456, 461 evaluating an existing source, 197 subsurface conditions, 197 excavated slopes, 302, 312 excavating, 192, 200, 266, 321-323, 338 excavation, 96, 211, 213-215, 217, 220, 229, 253, 254, 257, 259, 260, 272, 280-282, 286, 289, 297, 299, 300, 302, 303, 307, 313, 323, 329-333, 339-343, 345, 347 existing quarries, 197, 206 expandable packers, 418, 426 exploration program(s), 4, 17, 95, 99, 304, 306

F fabricated well screens, 118 falling head test(s), 112, 118, 120, 162 false-color infrared images, 85

503 FIELD MANUAL fault(s), 5, 23, 85, 96, 205, 210, 321, 330, 340-342, 344-347 investigations, 4 studies, 10, 14 feasibility stage, 198, 200, 435 feathering (edges), 334, 336, 337 feathering of the earthfill lift, 337 feeder canals, 437 field laboratory testing, 436 spectra, 88 spectrometer, 88 surface reconnaissance, 198 fill material, 326, 328, 331 fillet steep slopes, 325, 333 film, 67, 69-73, 75, 83-85, 176, 412, 415, 417, 419, 427 film-recording cameras, 67 filter(s), 25, 85, 189, 322, 327-329, 331 criteria, 327 pack, 167 zone(s), 328, 338 first lift, 326-328 fishtail-type drag bit, 361 flap valves, 368 flooding, 302, 303 flow in fractures, 103 flow nets, 319, 342, 346 flowing sands, 365 flowmeter(s), 74, 81, 111 log, 74, 81 fluff, 348 fluid content, 41, 53 density, 51, 78 flow, 81 temperature logging device, 77 velocity, 57

504 INDEX fluid-filled borehole, 57, 64 fluxgate compass, 77 focused device, 47 logs, 45 focused-current, or guard, resistivity device, 43, 45 foliation, 195, 205, 210, 215, 217 FOM, 454, 455 forced cooling, 343, 347 Foremost Mobile Drilling Company hammer, 383 formation water resistivities, 41 foundation and abutment excavations, 342, 346 contact surfaces, 328 data, 305 depth, 303 materials, 322, 326, 327, 332, 334, 335 modulus, 340 strength, 351 studies, 4 surface, 321, 322, 326, 329-331, 336, 337, 344 fracture(s), 60, 62, 74, 78, 81, 97, 98, 100, 103, 106, 107, 113, 114, 120, 137-139, 190, 192, 199, 207, 236, 239, 260, 303, 321, 330, 332 changes, 96 orientations, 98 zones, 66 fracturing, 66, 98, 104, 115, 190, 205, 229, 231, 278, 321, 335, 370, 409 the fill, 335 fragmentation, 9, 206, 209, 212-214, 218-222, 226, 227, 230, 232, 234-236, 239, 241, 242, 249, 250, 278 free face, 209, 218, 219, 223, 225, 226, 231, 235, 239, 243, 246, 251, 273, 276, 278, 282, 287, 294, 297

505 FIELD MANUAL freeze-thaw deterioration, 204 durability testing, 204 testing, 204, 205 freezing, 195, 204, 299, 339, 343, 382, 420-422, 424, 426, 428, 434 French satellite, 89 frequency (number per foot of borehole) of discontinuities, 67 fresh water, 13, 39, 41 sands, 41 friction loss, 105, 115 ratio, Fr, 400 sleeve, 397, 398 frozen rope, 382 fs, 171, 400 full column loading, 261 fully penetrating wells, 173

G gabions, 189 gamma radiation, 49-52 ray(s), 49, 50-52, 55, 61 gamma borehole, 111 logging techniques, 37, 38, 47, 56, 78, 111 gamma ray count, 50, 52 detector, 50, 55 energy, 55 logs, 50 gamma-gamma density log(s), 49, 50

506 INDEX

density logger, 78 logs, 51, 52 gelatin dynamite, 263, 280 geologic photogrammetry, 85 geologic structure, 31, 60, 100, 114, 209, 238 Geometric Dilution of Precision (GDOP), 444 geometric distortions, 86 geophones, 20, 27, 32, 34, 64 geophysical surveys, 1-3, 14, 16, 56 tomography, 66 geotechnical exploration, 37 investigations, 1-3, 5, 8, 15-18, 38, 48, 56, 351 geothermal applications, 16 areas, 16 exploration, 4, 13 investigations, 11 glacial or alluvial deposits, 189 Global Positioning System (GPS), 91, 439-450, 452-455, 457, 458, 460-463 GPR, 14 gradation requirements, 205, 206 grading for riprap, 192 grain density, 18, 51 graphite, 15 gravel deposits, 10, 14 sumps, 348 gravimeter, 26, 78 gravity anomalies, 18, 80 effect, 18 meter, 78, 79 meter density, 78

507 FIELD MANUAL

permeability test, 112, 142, 147, 153, 157 values, 80 grizzly, 192 ground conditions, 95, 399 failure, 318 roll, 7, 34 support, 257, 300 surface electrode, 42 groundwater aquifers, 18 geophysics, 13 investigations, 11, 14 levels, 308, 312-315, 318 in excavations, 300, 313 maps, 198 monitoring, 313, 314 monitoring instrumentation, 313, 314 occurrence, 303 quality investigations, 55 withdrawal, 318 ground-truth, 3 grout cap, 323 injection, 104, 114 nipples, 323 pipes, 335, 348 potential, 97 program, 95 travel, 98 groutability, 95-98 grouting, 19, 69, 95, 98, 99, 105, 106, 299, 300, 323, 329, 335 depth, 106 in rock, 300 in tunnels, 106

508 INDEX

operations, 19, 69 pressures, 98 guard arrays, 47 gyratory crushers, 194 gyroscope, 77 gyroscopic sensors, 77

H hammer drop friction, 379 height, 379, 382 hammer type, 379 hammers, 379 (casing type) hammers, 379 hand cleaning, 348 compaction, 328 tamper(tampering), 328, 336 tighten each joint, 384 Harder-Seed method, 390, 391, 393 harrows, 326 haul distance, 197, 198 hauling, 184, 205, 206, 208, 214, 220, 222, 223 HAV-180 rig, 391 hazardous materials (chemicals), 14, 275, 304, 315, 424 hazardous waste studies (investigations), 10, 14, 17, 431 HDOP, 444, 450-453, 457 headache ball, 241, 276 heading round, 243, 246, 248, 291 heat pulse flowmeter, 81 heavy grain detonating cord, 255 high resolution seismic reflection, 5 high-energy neutrinos, 55 high-frequency acoustic energy, 61

509 FIELD MANUAL hole wandering, 234 hollow AW drill rod, 381 guide rod safety hammer, 381 hollow-stem, 356, 359, 360, 364-366, 372 augers (HSAs), 364, 365, 377, 385 horizontal displacement, 318 permeability, 111, 174 plane, 71, 452, 453 hydraulic conductivity, 107 excavator, 323, 348 fracturing, 321, 370 models, 98 wedging device, 241 hydrofracture tests, 104 hydrofractured rock, 100 hydrofracturing, 98, 100, 104, 114 hydrogen atoms (nuclei), 52 hydrologic studies, 50 hyperspectral data, 88 hydrographs, 309, 319

I igneous rock, 194 Ilmenite additives, 363 Imhoff cone, 316 impact anvil, 356, 371, 379 impeller-type meter, 126, 141 impervious materials, 322 impervious zone(s), 323, 324, 331, 336, 356 foundation contact, 323 inclined core, 321 inclinometer, 398

510 INDEX inert stemming materials, 213 infiltration, 307 inflatable (straddle) packers, 118, 119, 162 initial lift, 328, 337 inspection control, 206, 207 investigations during the design stage, 199 ionosphere, 445, 446, 460 irregular rock surfaces, 328

J jacking, 97, 98, 100, 104, 114, 127, 335, 397, 399 tests, 100 jetting and driving, 147 joint mortar, 325 sets, 210, 214, 340

K kerf, 246, 247, 282

L Landsat, 83, 89, 90 lateral, 1, 10, 13, 16, 24, 43-45, 47, 303, 308 array (resistivity), 43, 44 array spacing, 43 device(s), 43, 45 logs, 45 lava tubes, 302 layer velocities, 4 leakage paths, 16 leather cups, 118 left-hand polarized, 449

511 FIELD MANUAL lifts, 328, 329, 336-338, 343, 347 lime, 328, 338, 339 line drilling, 254, 255, 257, 272, 282, 325 linear features, 63 lining design, 96 liquefaction, 351, 356, 358, 359, 362, 375-378, 381, 383, 385, 388, 389, 394, 406-408 evaluation(s), 351, 362, 376, 378, 381, 389, 406 resistance, 356, 389, 406-408 resistance evaluations, 356 triggering, 406 lithologic contacts, 60, 66 lithology, 38, 39, 41, 48, 53, 74, 96 litigation, 312 load cells, 397, 398 local differential base station, 463 location map of the core and samples, 435 of drill hole core, 438 of stratigraphic contacts, 67 logging tools, 37, 49, 55 long-normal, 43, 45 loss of fines, 303 low permeabilities, 108, 302 plasticity, 338, 339 low-alkali cement, 334, 335 Lugeon value, 100

M machine stripping, 348 machine-bored tunnel, 106 magnetic features, 17 log, 74, 80

512 INDEX

materials, 17, 28 north, 62 surveys, 2, 13, 17, 18 susceptibility, 80 material properties for static and dynamic stress analysis, 65 mechanical breakdown, 195 calipers, 74, 75 penetrometers, 395 metal expandable packers, 418 methods for obtaining size and weight data, 191 Michigan cuts, 244 microlog, 46, 47 electrode spacings, 47 sonde, 47 survey, 47 microsurvey, 46 microwave bands, 84 military GPS, 462 millisecond delays, 235, 250 mineral composition, 38 deposits, 15, 16 exploration, 13, 17 textures, 67 mineralogy, 38, 192, 194, 204, 405 minilog, 47 model input parameters, 99 monitoring during construction, 313 leakage, 17 of water control parameters, 312 well design, 317 wells, 116, 315, 317 mortar, 295, 325, 335, 336, 338, 344 movement by water, 189

513 FIELD MANUAL ms delays, 232, 233, 236 MSS, 86, 89 mud cake, 47, 52 mud pumps, 121 mud slab, 333 mudcap, 241 multiple aquifers, 107 electrode arrays, 42, 43 pressure tests, 127, 136, 137 multiple-arm calipers, 74 multiple-electrode resistivity arrays, 45 sonde, 38 multispectral photographs, 85 multi-beam sonar, 91 multi-beam systems, 91 muon, 55

N N value, 356, 364, 370, 371, 374, 375, 378, 379, 381, 385 NAD27, 463 NAD83, 463 natural color images, 85 natural electrical potential, 15 natural gamma log, 53 logger, 49 radiation, 49, 50, 52 ray detector, 50 ray logging, 61 ray logs, 50 natural potential, 15, 33

514 INDEX

Navigation Satellite Time and Ranging (NAVSTAR), 439 near infrared wavelengths, 83 near-infrared spectrum, 85 neat cement grout, 335 needle valves, 141 negative subdrill, 229 nephelometric turbidity units (NTU), 316 neutron activation, 55 detectors, 52 devices (source), 49, 53, 55 log(s), 50, 52, 53 logger, 49 radiation, 52, 53 water content log, 49 new quarry or pit investigation, 197 Nk, 405 nonconducting fluids, 47 nondispersive earthfill (material), 327, 328, 338 nonerodible embankment materials, 330 normal array(s), 43, 44 devices, 43, 45 resistivity arrays, 43 spacing devices, 47 NTU, 316 nuclear borehole measurements, 49 nuclear logs, 49, 55 nuclear radiation logging systems, 49 tools, 49

515 FIELD MANUAL

O objectives of foundation surface treatment, 329 observation well(s), 158, 160, 161, 172, 307, 308, 312, 314, 315, 317 observed gravity, 18 office responsible for the core or samples, 437 oil exploration, 4, 7 open discontinuities, 62, 67 open holes, 37, 162 open-ended diesel hammer, 390 optical logging systems, 67 optimum drill hole orientations, 100 moisture content, 327, 328 orange smoke, 264 organic material, 322 orientation of the drill hole relative to the fractures, 113 outcrops, 198, 202 overburden (depth), 98, 100, 114, 199, 202, 286, 321, 323, 358, 361, 375 overexcavation, 331, 340 overhangs, 323-325, 330, 331, 333, 334

P packer, 105, 110, 112, 113, 115, 116, 118-120, 126, 128, 130, 138, 164, 165, 309 packer(s), 74, 105, 115, 118-120, 128, 130, 162, 164, 418, 426 seal, 120 test(s), 110, 112, 113, 116, 309 packing material, 189, 418, 421, 428 pails, 417-419, 428 panchromatic photography, 85 parallel hole cuts, 243-245, 253 partially penetrating wells, 173, 174

516 INDEX

PDA measurement, 392 PDOP, 444, 445, 451, 452, 462 peeling, 348 penetration per blow, 375, 376 resistance, 351, 356, 358, 385, 388, 397, 400, 408 penetrometer, 387, 388, 395, 397, 399 tip, 387, 388 perforated pipe, 140, 315 performance, 188, 319, 388, 392 on existing structures, 189 performing gradations on the blasted product, 207 perimeter blasting, 257 cracking, 253 holes of a blast, 214 permafrost, 14 permanent labeling, 438 markers, 437 permeabilities, 45, 95, 96, 99, 108, 111, 112, 114, 115, 147, 302, 306, 307 permeabilities of strata, 45 permeability, 39, 95-100, 103, 105, 106, 107-119, 121, 126, 128, 130, 131, 133, 136-139, 142-145, 147-149, 153, 154, 157, 159-161, 163, 164, 166, 168, 170, 171, 174, 177-179, 181, 182, 198, 300, 302, 306-308, 316330, 331, 347 coefficients, 143 of the soil, 306 test(s), 97, 112-116, 118, 121, 126, 128, 131, 138, 139, 142, 145, 147, 149, 153, 154, 157, 159, 160, 179, 306, 308

517 FIELD MANUAL permeable, 38, 39, 41, 47, 81, 96, 106, 120, 137, 138, 150, 164, 307, 347 path, 347 sand bed, 41 permeameter, 115, 182 pervious rock, 106 petrographic examination, 203, 205 petroleum exploration, 1, 17, 18 traps, 18 pH, 194, 317 photographs, 69, 71, 83, 85, 198, 201, 227, 435, 437 photography, 83, 85, 90, 92, 411, 414 frame, 414 photomultiplier tubes, 55 physical properties, 2, 37, 38, 81, 203, 205, 340, 356, 431 piezoelectric transducer, 61 piezometer(s), 178, 306-308, 314, 315, 362, 363 permeability test, 179 pile-driving analyzer, 392 pilot bit, 359, 364, 365, 367, 368, 370 cutting teeth, 368 seat, 368 pipable material, 342 pipelines, 16, 18, 21, 67, 295 piping, 15, 105, 115, 327, 342, 346 pit development, 199 planar discontinuities, 63, 71 plastic bags, 298, 417, 419 material, 329 pails, 418, 428 plasticity, 329, 337-339, 388, 415 PLGR, 460-462 PLGR+96 receivers, 460 PMT, 55

518 INDEX pneumatic instruments, 315 pneumatic-tire(d) equipment, 328, 337 roller, 328, 329 points of high stress concentration, 343, 347 Poisson’s ratio, 24 polar regions, 17 polymer-enhanced drill fluid, 361 (poly)urethane foam, 416 pore fluid content, 41 spaces, 9 water, 41, 341, 346, 395, 399, 400, 403 water stress, 395, 399 dissipation measurements, 399 porosity, 9, 18, 38, 45, 49-53, 56, 61, 66, 67, 78, 80, 107, 108, 117, 192, 194, 195, 300, 302, 308 porous media, 16 permeable zones, 47 tube, 315 position dilution of precision (PDOP), 462 positive ions, 16 potassium isotope K40, 50 potential electrodes, 11, 43-45 power conduits, 437 powerplants, 431, 433, 437 powder factor, 211, 213, 237-239, 251, 283, 289 PPS accuracy, 447 precipitation, 300, 303, 308, 317 Precise Position (Positioning) Service (PPS), 440, 446, 460 preferred site frequencies, 8 presentation of information, 184 preshearing, 255, 289 presplitting, 254-258, 261, 272, 274, 289

519 FIELD MANUAL pressure transducer, 130, 131, 162, 167, 398 versus flow curves, 100, 114 principal joint sets, 214 production blast, 256 progressive delays, 233, 234 propagation velocities, 57 protecting and shipping samples, 431 Protection against wetting and drying, 434 protective filters, 329 outer box, 422 pseudorange, 444, 449 pseudo-random noise (PRN), 442 pump bypass line, 361 pumping caused by construction equipment travel, 327 pyramid cut, 243 pyrotechnic delay elements, 237 P- and S-wave energies, 57 P- and S-waves, 64 P-code, 440-442 P-wave, 56, 60, 66

R R95, 453 radar interferometry, 90 remote sensing, 90 radiation detector, 47 logging device, 61 logging systems, 49, 50 radioactive isotopes, 50

520 INDEX

material, 53 source (material), 47, 49, 52 ramping the fill, 329 rapid freeze-thaw durability evaluation, 203 real-time viewing, 67 rebound, 336 receiver measurement uncertainties, 457 recharge conditions, 303 record tests, 436 rectangular pattern, 223 reference electrode, 45 reflectance spectra, 87 reflected shock wave, 384 refraction, 2-6, 21, 22, 25-28, 31-33, 35, 57, 64, 66, 201 refusal rule, 375 relationship between weight and size, 191 relative clay content, 49 density, 50, 226, 327, 357, 404, 417 remote sensing, 83, 84, 89-93 interpretations, 83 representative permeabilities, 307 samples, 199, 202, 203, 205 requirements for length of storage, 436 for storage of core and samples, 432 reservoir load, 344 resistance of a circuit, 41 of the conductor, 41 resistivity, 1, 2, 9-11, 13, 32, 33, 38-48, 77, 395 deflection, 41 logs, 39, 43, 46, 77 measurements, 43 revertible drilling fluids, 362 RF Link signals, 439

521 FIELD MANUAL right-hand polarized, 449 rippers, 330 rippability, 4 riprap, 183-189, 191, 192, 194-197, 199-208, 261, 263, 291, 298, 431 characteristics, 188 durability, 194 evaluation, production, and placement, 184 fragments, 189 quality, 188, 189, 199, 203 Quality Evaluation Report, 199, 203 quarries, 207 source(s), 184, 188, 189, 192, 194-196, 202 evaluation, 184 investigation, 195 riser and hole diameter, 314 rock abutments, 328 breakage, 9, 200, 239 bucket, 192, 323 characteristics, 113, 184, 192 durability, 195 failure criterion, 204 foundation(s), 327, 328, 330, 339, 341, 344, 345, 350 surfaces, 328 fragments, 183, 187, 189, 190, 192, 195, 203, 204, 323, 330 mass design parameters, 97, 114 permeability, 97, 98, 113, 114 quarries, 189, 194 rake, 192, 193 rockfill dams, 331, 349, 350 roller, 326, 328, 329, 337 passes, 328

522 INDEX rotary casing advancers, 369 drilling, 356, 361-363, 369, 385, 389 rounded stone assemblage, 189 rover data, 463 rubber-tired roller, 337

S SA, 444, 447, 449, 458, 462 Safety Driver, 383 safety hammer, 353, 373, 374, 380-382, 385 of dams analysis, 437 saline water, 15 salinity, 9, 38, 39, 41, 46 of pore fluids, 46 salt water intrusion, 14 saltwater/fresh water interfaces, 13 sample data sheets, 431 retention (criteria), 431, 434 selection, 434 size, 95, 99, 202 sampler shoe, 377 tip, 368 sand heave, 362, 363 pack, 110, 167, 317, 318 sanding in (sandlocked), 142, 356 sand-cement slurry, 335 satellite(s), 83, 89, 90, 215, 230, 231, 263, 317, 318, 439-452, 456-458, 460-463 differential correction signal, 463 vehicle position, 457

523 FIELD MANUAL saturated low-strength materials, 304 materials, 7, 52, 110, 115 sand, 10, 53 saturation, 38, 53, 66, 204, 325, 327 sawdust, 416, 419, 427 sawed kerf, 246, 247 sawteeth, 330, 333 scarification, 326, 328, 336, 337 scarifying the lift surfaces, 329 schistosity, 199, 205, 206, 210 screen slot size, 317 screening of wells, 322 screens of water wells, 69 sculpture blasting, 257 sealing samples, 415 secondary arrivals, 5 blasting, 214, 220, 229, 241, 242, 292 emission of neutrons and gamma rays, 52 fragmentation, 241, 242 fragmentation techniques, 241 sediment content, 312, 316, 317 seepage, 11, 16, 95-98, 148, 299, 304, 319, 321, 322, 347, 403 control, 96, 304, 322 evaluation, 95 investigations, 11 potential, 95, 98 quantities, 96 seeps, 302, 348, 349 seismic anomalies, 65 energy, 26, 28, 29, 35, 56, 66 pulse, 64 P-wave velocity, 66 refraction interpretation, 4 signal, 32, 66

524 INDEX

source, 6, 64 stability, 325 surveys, 3, 14, 60 tomography, 66 velocities, 6, 56, 57, 60, 61, 64 wave(s), 6, 25, 27, 30, 31, 32, 34, 57, 64, 288 velocities, 64 Seisviewer, 61 Selective Availability (SA), 444, 446, 447, 462 selective quarrying, 196 self-potential surveys, 2, 11, 15, 16 sequential timers, 236 service history of material produced, 202 settlement during dewatering activities, 318 settlement of claims, 437 shaft sinking cut, 239 shale baseline (line), 38, 39 shape of individual rock fragments, 189 shatter cuts, 244 shaving, 348 shear wave velocity (velocities), 2, 5, 6, 57, 61, 64, 358 shear waves, 6, 57 shell zones, 327 shipping containers, 420-422, 429 shop vac, 348 short normal array, 44 short rods, 384 shotcrete, 336 shotpoint depth, 65 shrinkage, 338, 342, 343, 347 Side Scan Sonar (SSS), 91 side-looking airborne radar (SLAR), 90 single column charge, 237 frequency receivers, 460 packer, 110, 119 single-beam systems, 92

525 FIELD MANUAL single-electrode array, 45 single-point array, 43 single-receiver devices, 57 siting studies, 1, 4 slab cut, 243 slabbing, 259 slake (slaking), 195, 323, 332, 333, 339, 343, 432 slashing, 259 slope failure, 318 protection, 184, 187, 188 sloughing, 139, 326 slug tests, 112, 118, 166 slush grout, 321, 325, 330, 335, 336, 338 mix, 335 small-strain dynamic properties, 2 smooth blasting, 233, 257-259, 272, 274, 294, 325, 331 sodium sulfate soundness test, 204, 205 soil cement, 184 foundation compaction requirements, 327 infiltration data, 307 liquefaction criteria, 375 solar flare(s) activity, 445, 460 solid steel guide rod, 381 solution cavities, 56, 63, 66, 67, 210, 211, 302, 330 features, 60, 333 sonde, 37, 38, 43, 45, 47, 49-53, 55-57, 61, 77 electrodes, 45 sonic energy, 56 vibrations, 9 SP log (logging), 38, 41, 43, 50 SP peak, 41 space segment, 439

526 INDEX spacer blocks, 423 ring, 371 spacing-to-burden ratio, 232, 233 spalling, 194, 343, 347 special purpose electric logging devices, 46 specific gravity (gravities), 18, 78, 191, 204, 294, 297 spectral analyses, 55 bands, 87, 88 data, 83, 84 logging sonde, 55 logs, 55 ranges, 83 resolution, 83, 84, 87, 89 signatures, 84 spectrometers, 84 spontaneous potential, 15, 33, 38, 41 spoofing, 441, 442, 446, 447 environment, 447 spray coating, 333 spring suspension system, 422 springs, 74, 302, 342, 346, 439 square drill pattern, 223 SSGS, 205 SSSG, 191, 192, 204 stability requirements, 342, 346 staggered pattern, 223, 224, 295 Standard Penetration Test (SPT), 351 Standard Position Service, 446 standard surveying methods, 318 standing water, 328 standpipe, 165, 315 Stanley waves, 6 static pore water pressures, 395 water levels, 308

527 FIELD MANUAL

Station Receiver, 449 statistically significant sample size, 99 steeply dipping plane, 71 stemming, 213, 215, 222, 227-230, 239, 257, 260, 263, 271, 274, 295, 296, 298 stemming column, 222 stepped pressure tests (step test), 100, 104, 114 surfaces, 321, 324, 331 stereo imaging, 89 storage, 107-109, 128, 142, 167, 168, 265, 266, 281, 283, 289, 295, 300, 307, 409, 410, 414, 415, 418, 420, 424, 427, 431-436, 438 costs, 431 facility, 432-434 of core, 432, 434 periods, 431 storativity, 108, 307 stove to melt wax, 427 straddle packer, 164 strain gauges, 397 strata boundaries, 39, 41, 45 stratum boundary resolution, 45 stream gravel, 183 stress anomalies, 321 caused by placing earthfill, 335 concentrations, 324, 331, 340 relief, 96 strike and dip of planar features (strikes and dips), 63, 73 string loaded, 257 stripping, 322, 325, 348 of pervious materials, 325 operations, 325 structural concrete, 334, 336 Su, 405

528 INDEX subdrilling requirements, 217 subsurface cutoffs, 300 subsurface geologic conditions, 37, 195, 305 hydraulic conditions, 303, 305 layer resistivities, 38 materials, 2, 10, 11, 13, 48, 107, 112, 115 suitable riprap source, 196 sulfates, 334, 335 sulfide, 15 sump pumps, 315 sumps, 299, 300, 322, 323, 348 sunspots, 445 supplementary dewatering, 300 surface and subsurface data, 305 cracks, 329, 335 in the foundation, 329 drains, 299 electrical surveys, 38, 45 saturated dry specific gravity (SSSG), 191 water, 299, 300, 302, 303, 307, 309, 312, 318 wave(s), 5-8, 27, 34, 57, 60 surveying, 8 survey control, 85, 318 susceptibility logs, 80 swelling rock, 103 swivels, 126 S-wave, 33, 57, 60, 64, 65 arrival, 64 cross-hole tests, 65 Sy method, 390, 392, 393 synthetic polymers, 362

529 FIELD MANUAL

T talus, 7, 194, 198, 202 piles, 198, 202 Televiewer, 61 tamped cartridges, 226, 255 tamping (tamper) feet, 326, 328, 329 plug, 257 roller(s), 326, 328, 329 roller feet, 328 TDOP, 444, 451 television cameras, 67 temperature changes, 426, 434 device, 77 logging, 77, 78 probe, 78 variations in the fluid, 77 temporary labeling, 438 storage, 433 tension zones, 321 tensioned mechanical arms, 74 test blasting (blasts), 207, 263, 267, 281, 286, 297 grout section, 105 pressure(s), 96, 100, 103, 104, 113, 114, 119 wells, 110, 133, 134, 306-308 testing subsurface samples, 197 TFOM, 455, 456 theoretical overburden stress, 114 thermal infrared, 84, 86, 87, 90 systems, 86 wavelengths, 87 properties of materials, 86

530 INDEX thermistor (thermal resistor), 77 thick-wall, 353 thickness of the riprap, 184 thrust blocks, 339 tight, impermeable rock, 106 timbers, 15 time-varying, low frequency, electromagnetic fields, 13 top of rock configuration, 19 topographic maps, 198, 463 total dissolved solids (TDS), 317 total porosity, 108 toxic waste studies, 11 tracer elements, 50 tracked equipment, 330 tracking, 424, 460, 461 transferring core, 432 trapped water, 41 travel times, 57 trial blasts, 263 triaxial arrays, 64 tricone bit, 370 rockbit, 361 trimming, 259 troposphere, 445, 446, 461 true orientation (strike and dip), 67 true P- and S-wave velocities, 65 true velocities, 64 tunnel alignments, 95 tunnel delays, 250 tunnel studies, 96 tunnels, 67, 95, 98, 99, 106, 244, 273, 291, 431, 448 turbidity, 116, 315-317 turbulent flow, 103, 117, 127 two-dimensional (2-D) projection, 73

531 FIELD MANUAL

U UERE, 456, 457 ultraviolet radiation, 445 uncased boreholes, 51 unconfined compression, 358, 405 underground blast rounds, 243 underwater surveys, 91 undisturbed soil samples, 436 undrained strength in clays, 358 uniformity of rock, 195 unsaturated conductivity coefficient, 132, 146 unsuitable subgrade, 302 unsupervised storage, 432 unwatering (methods), 198, 299, 300, 302, 317 uplift of constructed features, 302 URA, 452, 458, 459 USBR 7020, 397 user equipment (UE) errors, 456 Equivalent Range Error (UERE), 456 Range Accuracy (URA), 452, 458 segment, 439, 440

V vacuuming, 348 vadose zone, 112, 115, 306 vane shear, 358, 405 testing, 405 variable head tests, 170 variations in fluids, 45 VDOP, 444, 450-453, 457 velocity contrast, 11, 66 reversal, 5

532 INDEX vertical electrical soundings, 11 hammer device, 64 surfaces, 330, 333, 334 very high resolution mapping of near-surface geology, 15 vibration damage, 9 levels, 9, 332 protection, 412 vibratory compactors (rollers), 326 videotaped, 69 vinylidene chloride, 415, 427 visible spectrum, 85 void ratio, 53 vugs, 63, 78

W WAGE, 460 wall irregularity (irregularities), 52 of a borehole, 37 washout zones, 74 wastage, 196, 200, 201 waste piles, 194 water action, 189, 205 content, 38, 46, 49, 52, 53, 358, 417 content (saturation), 38 by weight, 53 of strata, 46 control, 299, 303-306, 309, 312, 317, 319, 322, 347 data, 306, 309 facilities, 305, 306, 312, 319

533 FIELD MANUAL

investigations, 305, 317 methods, 322 energy, 183 gel columns, 255 jetting, 332 level monitoring instrumentation, 313 meters, 126, 141 quality, 166, 308, 309, 316-318, 334, 336 analyses, 308 removal, 300, 348 salinity, 38 table, 7, 15, 119, 127, 130, 144, 148, 150, 155, 157, 158, 164, 175, 299, 303, 356, 358, 359, 365, 385 take(s), 96, 103, 105, 113, 127, 136 test(s), 98, 100, 105, 114 calculation, 97 data, 96, 106, 113 information, 97 pressure, 103 results, 96, 97, 103 washing, 332 watertight riser, 315 wavelength range, 84 wavy core surfaces, 409 wax, 412, 415-419, 427 waxed wood disks, 418 weight of the rock fragment, 191 well(s), 67, 69, 109, 110, 116, 133, 134, 158, 160, 161, 173, 174, 299, 306-308, 312, 314-318, 322 collapse, 316 point systems, 315, 316 points, 322 screen(s), 64, 74, 118, 172, 315 well-graded riprap, 194, 207 wet and dry density, 53

534 INDEX

foundations, 327 rope, 382 whipping, 384 Wide Area GPS Enhancement (WAGE), 460 wireline (wire line), 370 acoustic/seismic logging systems, 56 devices, 73 electrical systems, 42 nuclear radiation systems, 49 packers, 105, 115 wood shipping containers, 422 workability and nesting of the rock assemblage, 189

Y Young’s modulus, 24

535