HIGHWAY RESEARCH BOARD

Bulletin 58

Compaction of Embankments^ Subgrades^ and Bases

kGADEMY

R£$£ARCH

Ncitioncii Accsdemy of Sciences— Nationol Research Council

publication 240 HIGHWAY RESEARCH BOARD

1952

R. H. BALDOCK, Chairman W. H. ROOT, Vice Chairman FRED BURGGRAF, Director

Executive Committee

THOMAS H. MACDONALD, Commissioner, Bureau of Public Roads

HAL H. HALE, Executive Secretary, American Association of State Highway Officials

LOUIS JORDAN, Executive Secretary, Division of Engineering and Industrial Research, National Research Council

R. H. BALDOCK, State Highway Engineer, Oregon State Highway Commission

W. H. ROOT, Maintenance Engineer, Iowa State Highway Commission H. P. BiGLER, Former Executive Vice President, Connors Steel Company

PYKE JOHNSON, President, Automotive Safety Foundation

G. DONALD KENNEDY, Consulting Engineer and Assistant to President, Portland Cement Association

BURTON W. MARSH, Director, Safety and Traffic Engineering Department, American Automobile Association

R. A. MOVER, Research Engineer, Institute of Transportation and Traffic Engineering, University of California

F. V. REAGEL, Engineer of Materials, Missouri State Highway Department

Editorial Staff

FRED BURGGRAF W. N. CAREY, JR. W. J. MILLER 2101 Constitution Avenue, Washington 25, D. C.

The opinions and conrlu.sions expressed in this publication are those of the authors and not necessai'ily those of the Hi^hwiiy Research Board. HIGHWAY RESEARCH BOARD

Bulletin 58

Compaction of Embankments^ Suhgrades^ and Bases

1952 Washington, D. C. DEPARTMENT OF SOILS Harold Allen, Chairman; Principal Highway Engineer Bureau of Public Roads

COMMITTEE ON COMPACTION OF SUBGRADES AND EMBANKMENTS

L. D. Hicks, Chairman; North Carolina State Highway and Public Works Commission

W. F. Abercrombie, Engineer of Materials and Tests, Georgia Depart• ment of Highways C. W. Allen, Research Engineer, Ohio Department of Highways W. H. Campen, Director, Omaha Testing Laboratories C. A. Hogentogler Jr., Chevy Chase, Maryland T. A. Middlebrooks, Chief, Soil Mechanics Branch, Office Chief of Engineers W. H. Mills, District Engineer, Asphalt Institute, Atlanta O. J. Porter, Consulting Engineer, Newark, New Jersey T. B. Pringle, Chief, Roads and Airfields Section, Office, Chief of Engineers C. R. Reid, Los Angeles, California L. J. Ritter, Professor of Civil Engineering, New York University J. R. Schuyler, Principal Engineer (Soils), New Jersey State Highway Department T. E. Shelbume, Director of Research, Virginia Council of Highway Investigation and Research S. E. Sime, Supervising Design Engineer, Bureau of Public Roads, Kansas City W. T. Spencer, Soils Engineer, Indiana State Highway Commission

iv Preface

• THE ORIGINAL Wartime Road Problems No. 11 "Compaction of Subgrades and Embankments" was published in August 1945 during World War n. It presented infor• mation on the mechanics of compaction, on moisture-density relationships, soil clas• sification, suitability of soils for embankments, methods for controlling moisture content and density during compaction, and maximum limiting slopes for embankment construction. It also presented a review of practices current in 1945 and gave a list of selected references on compaction and allied subject matter. During and following the war, highways were subjected to a larger number of heavier wheel loads than prior to the publication of Wartime Road Problems No. 11. That in• crease in heavy vehicles has emphasized the need for compaction of subgrades and bases for pavements. Also, since that time more information has been developed on the amount of compaction needed in highway and airport subgrades and bases and the rela• tive permanence of moisture content and density. Recent data are available from care• fully controlled e}Q>eriments in field rolling which throw some light on the practicable limits of field compaction for different types and weights of equipment Some in• vestigations have been completed and others are in progress to determine the feasi• bility of using vibration as a means of compacting soils, especially soils of a granular nature. During the war, attention was given to the use of sheepsfoot rollers having high tamping-foot contact pressures. Also, efforts were made to use heavy pneumatic- tire wheel loads for compacting subgrades and bases on some airfields. The result of some of those efforts has been a trend toward the manufacture of heavier compaction equipment, both in the sheepsfoot and rubber-tired types on the premise that they offer possibilities for greater densities or con4>action to greater depths. This bulletin is the result of efforts by the Committee to list practices pertaining to compaction equipment and its use and specifications which govern compaction of embankments, subgrade soils, and bases. In addition, this bulletin attempts to present latest developments in the technology of soil compaction with special reference to the use of equipment heavier than that discussed in Wartime Road Problems No. 11. Contents

PREFACE V DEFINITIONS OF TERMS 1 FUNDAMENTALS OF COMPACTION 2 Factors Influencing Density, 2 Influence of Soil Moisture Content, 2 Influence of Soil Type, 2 Influence of Compactive Effort, 4 Other Factors Which Influence Soil Density, 5 INFLUENCE OF DENSIFICATION ON PHYSICAL PROPERTIES OF SOILS 6 FACTORS INFLUENCING PERMANENCE OF DENSIFICATION 9 DEGREE OF DENSIFICATION NEEDED 10 Embankments, 10 Subgrades, Subbases and Bases, 12 Practicable Limits of Densification, 13 Correlation of Need, Practicable Densification Limits and Permanence, 17 Embankments, 18 Subgrade Materials and Bases, 18 Shoulder Materials, 21 METHODS OF SPECIFYING COMPACTION REQUIREMENTS 21 Control of Density, 21 Control of Compactive Effort, 22 SELECTION AND USE OF EQUIPMENT 23 Ehimping and Spreading, 23 Adding Water to Soil, 25 Handling Excessively Wet Soil, 25 Sheepsfoot-Type Rollers, 25 Methods of Rolling, 27 Smooth-Wheel Power Rollers, 29 Pneumatic-Tire Rollers, 32 Roller Performance on Different Types of Soil, 33 NEW TYPES OF COMPACTION EQUIPMENT 34 Pneumatic-Tire Compactor with Vibratory Unit, 34 Heavy Pneumatic-Tire Rollers, 34 Grid-Type Steel-Wheel Rollers, 36 Three-Wheel Type with Scalloped Ribs on Rolls, 36 Tandem Type with Segmented Front Roll, 36 Tandem Type with Vibratory Intermediate Roll, 36 Vibrating-Base Compactors, 36 Tampers, 36 FIELD CONTROL OF COMPACTION 38 Moisture Content and Density Control, 38 Inspection and Test Methods, 38 Examination Methods, 39 Proctor Penetration Needle, 39 Drying to Constant Weight, 40 In-Place Density Measurement, 41 Moisture-Density Relationship, 42 Correcting for Coarse-Aggregate Content, 46 vii CURRENT PRACTICES IN COMPACTION METHODS AND EQUIPMENT 50 Lift Thickness in Embankment Construction, 51 Control of Compaction, 51 Embankments, 51 Subgrades, 51 Bases, 51 Cost of Compaction, 51 Methods of Testing, 55 Backfilling of Trenches, Pipe Culverts and Sewers, 55 Group A - Compaction Without Density Control, 58 Tamping Methods and Equipment, 58 Lift Thickness, 58 Moisture Control, 59 Materials Requirements, 59 Provision for Saturating, Flooding or Puddling, 59 Group B - Compaction With Density Control, 59 Density Requirements, 59 Lift Thickness, 62 Moisture Control, 63 Materials Reqmrements, 63 Provision for Saturating, Flooding or Puddling, 63 Statement of Requirements for Backfilling Sewers, 63 Backfilling Structural Excavation, 66 Lift Thickness, 67 Compaction, 67 COMPACTION EQUIPMENT 67 Sheepsfoot-Type Rollers, 67 Contact Area of Tamper Feet, 67 Contact Pressure, 67 Pneumatic-Tire Rollers, 76 Smooth-Wheeled Power Rollers, 76 Granular-Base Compaction, 76 Smooth-Wheel Power Rollers, 76 APPENDIX: MANUFACTURERS' SPECIFICATIONS 78

viii Compaction of Embankments, Subgrades, and Bases

• THIS BULLETIN discusses fundamen• Aggregate, and Fill Materials, AASHO tals of compaction, the purpose for which Designation: M 146-49, except as noted. the compaction is intended, and the amount needed for various soils in different parts Settlement of Embankment. Decrease of the road structure in the light of how in elevation of the surface of an embank• compaction is affected by climatic, load, ment due to consolidation of the soil in the and road conditions. From those con• embankment due to its own weight and the siderations, suggestions are made on effect of traffic, over a period of time recommended practice for compacting following construction. embankments, subgrades, and granular Subsidence of Embankment. Decrease bases and for the control of compaction. in the elevation of the surface of an em• Soils work for highways maybe classi• bankment due to consolidation or displace• fied broadly into four categories: (1) ment of the foundation soil over a period selection of soil as to quality; (2) pre• of time during or following construction. diction and control of behavior of soil Embankment Foundation. The mate• under load; (3) protection of soils against rial on which an embankment is placed. effects of climate; and (4) improvement Embankment (Fill). A raised structure of bearing value of soil by drainage, in• of soil, soil-aggregate, or rock. corporation of admixtures, or compaction. Subgrade Material (Basement Soil). There is no other single treatment The material in excavation (cuts), em- which can be applied to natural soils bankment (fills), and embankment foun• which produces so marked a change in dations immediately below the first layer their physical properties at so low a cost of subbase, base, or pavement and to as does compaction, when it is controlled such depth as may affect the structural to meet the desired needs. The bearing design. value of some soils may be increased Subbase. Specified or selected mate• several times by increase in density of rial of planned thickness placed as a the order 3 to 5 pcf. Because compaction foundation for a base. has great influence on the manner in which Base. Specified or selected material soils behave, it is worthwhile presenting of planned thickness placed as foundation not only a discussion of factors which in• for a pavement. fluence compaction and how compaction is Compaction. The practice of artifi• obtained but also how it influences the cially densifying and incorporating defi• nature of soils and how it is affected once nite density into the soil mass by rolling, it is obtained. The committee believes tamping, or other means. this broad perspective of compaction is Consolidation. The decrease in the necessary if it is to be used to the fullest volume of voids, or the increase in den• advantage in the preparation of embank• sity, for the most part inelastic, which is ments, subgrade materials and bases for caused by the stresses imposed in the pavements. supporting soils by permanent foundation loads, or by the repeated passage of highway or airplane traffic under actual DEFINITIONS OF TERMS service conditions. (P) I Bearing Value. The unit load JSj for a The terms embankment, embankment specified amount of settlement (A) and a foundation, subgrade materials, bases, specified loaded area (A). and subbases, as used here, comply with Bearing Capacity. That unit pressure the definitions set forth in Standard Defini• greater than which progressive settlement tions of Terms Relating to Subgrade, Soil will occur leading to failure. compactingprocess (this includes addition 1051 -Modlfiet AASilO and mixing in of water or removal of \ / water by aeration). _ - • \ ^ . J \ In addition to the above factors there \ are the natural effects of "curing," which A"-lorid o SoId may increase the density of the soil. 95 Influence of Soil Moisture Content If a soil IS compacted under a given com• .90 -AASH pactive effort at each of several moisture \ X Method siano Clay contents, there results a moisture- \, density relationship of the nature shown 85 for the Louisiana clay m the lower right- hand part of Figure 1. There is developed, 80 for each soil, a maximum dry density water Content- Percent of Dry Weigtit at an optimum moisture content for the compactive effort used. The optimum Figure 1. Effect of two compactive ef• moisture content, at which maximum dry forts on the densities of two soils. density is obtained, is the moisture con• dition at which the soil has become suf• ficiently workable under the compactive FUNDAMENTALS OF COMPACTION effort used to cause it to become packed so closely as to expel most of the air. At The term "compaction" refers to the moisture contents less than optimum, the act of artificially densifying the soil. soil (except for cohesionless sands) be• It means the pressing of soil particles comes increasingly more difficult to work together into a closer state of contact and thus to compress. As moisture and in so doing e}q>elling air or water contents are increased above optimum, from the soil mass. The density of soil most soils become increasingly more is measured in terms of its volume- workable. However, a closer packing weight and is usually expressed as pounds is prevented when the water fills the soil of wet soil or dry soil per cubic foot (or pores. Thus the moisture-density re• as porosity in percent of total volume). lationship established in the test is in• Those volume weights are expressed as dicative of the relative workability of the wet density and dry density, respectively. soil at various moisture contents under The term "consolidation," by usage, the compactive effort used. The moisture- refers to closer particle contact obtained density relationships hold for the lab• in the time-consolidation process whereby oratory compaction test and for field a superimposed load causes closer pack• compaction by rolling. Available data ing by expelling water and/or air from the from carefully controlled field studies of soil mass. rolling show moisture-density relation• ships almost identical with those developed Factors Influencing Density from laboratory tests. These are de• scribed later. There are several factors which in• fluence the value of density obtained by compaction. The most important of these Influence of Soil Type. The nature of are: (1) the moisture content of the soil; the soil has great influence on the value (2) the nature of the soil, that is, its grain of density obtained under a given com• size distribution and its physical prop• pactive effort. Soils ranging from light• erties; and (3) the nature (including both weight volcanic and diatomaceous soils type and amount) of the compactive effort and heavy clays to well-graded sandy and used. gravelly soils may, when subjected to The following two factors influence identical compaction procedures, yield density but are of less significance than values of maximum density ranging from the factors given above: (1) The temper• 60 pcf. or less for the volcanic and di• ature of the soil and (2) The amount of atomaceous soils, about 9U to lOU pcf. manipulation given the soil during the for the clays and up to about 135 pcf. or SOIL TEXTURE AND PLASTICITY DATA No Description Sand Silt Qay LL PI 1 Well Graded Loomy Sand 88 10 2 16 NP 2 Well Graded Sandy Loom 72 15 13 16 0 3 Med Graded Sandy Loam 73 9 18 22 4 4 Lean Sandy Silty Clay 32 33 35 28 9 5 Loessial Silt 5 85 10 26 2 6 Heovy Cloy 6 22 72 67 40 7 Very Poorly Graded Sand 94 6 NP

Zero Air Voids (G0265)

10 12 14 16 20 22 Moisture - Percent

Figure 2. Moisture-density relationships for seven scils compacted according to AASHO Method AASHO T99 (in part after 'Public Roads"). more for the better-graded, coarse differences in optimum moisture content granular soils. and maximum density, but also dif• Examples illustrative of the differ• ferences in how the soils react to the ences in soil densities obtained under a given compactive effort at moisture con• given compactive effort (AASHO Method tents less than optimum. This is illus• T 99) on seven different soils ranging trated by the curve for the heavy clay' in texture from clays to sands are shown in Figure 2. It may be seen from the moisture-density relationships in Figure ' A "heavy" clay Is a clayey soil which is difficult to manip• ulate. It usually contains more than 50 percent of parUcles 2 that the different soils reflect not only smaller than 0.005 mm. in diameter than about 35 percent causes a marked y decrease in density of the soil mortar Stona and yields no significant increase in i . •. density of the total mixture. a a r o Influence of Compactive Effort The tit Dry Dm tty of results of compaction at different com• -3 Solkto ne MIxtu • 1— pactive efforts on each of several soils ' no '-^—i gives evidence of the comparative effect

X of soil moisture content and soil t3rpe on the degree of compaction obtained. For Dry Oenflit y of S< II Mortar each compactive effort applied m com• • 90i pacting a soil, there is a corresponding es optimum moisture content and maxi• 0 e 20 90 40 so 60 mum density. The maximum density Pareatitoga of Stone in Dry Soil-stona Hliture increases and the optimum moisture CI 20 Soil Mo •to • ^ content decreases with increase m com• 29% 1".j^Slon a 1 1 Soil Mortar Only pactive effort. That is illustrated in \^ Figure 1 which shows moisture-density Saturotion'Lln a • relationships for the AASHO standard method T 99 (25 blows of a 5y2-lb. ham• • mer with 2 sq. in. of striking face drop• ping 12 in. on each of three layers in a Soil Mortar « 90% 1/30-cu. -ft. mold) and the Corps of i-.J-st*,. 1 Engineers modification of the AASHO 80,9 10 19 20 2 9 30 39 method (25 blows of 10-lb. hammer with Mototura Content of Soil Mortar . % of Dry Soil 2 sq. In. striking face dropping 18 in. Figure 3. Elfect of addition of coerse on each of five layers in a 1/30-cu. -ft. aggregate on density of soil. mold). Moisture-density relationship curves for each of the two compactive (No. 6). Moisture content is less critical efforts on a Louisiana clay soil are shown for heavy clays than for the feebly plastic soils in which sand and silt grain sizes predominate. Heavy clays may be com• pacted through a relatively wide range of moisture content below optimum with 190 relatively small changes in density. In contrast, the more granular and better- 1251 graded soils, whichproduce high densities under the same compactive effort, react sharply to small changes m moisture con• tent, producing marked changes in density, as shown by the curves for Soils 1 and 2 tiio in Figure 2. Relatively clean, poorly SIOS I SOILS DATA graded, nonplastic sands of the type Na Li- PI Souree-TMim 1 22 2« Calif Sandy Loom indicated by Soil 7 in Figure 2 having small 2 22 NP Com Sand r 3 18 2 Mlu Clam Sand silt and clay content are relatively in• 4 NP - FlaSond sensitive to moisture changes. \ 99 9 26 2 Mill. Silt Compoctin Effort 6 82 91 TwoaCloy 7 49 19 Calif Cloy The gravel content in a soil also has 90 an influence on the compaction character• Compoctln Effort AJk.SHjai Mathod istics of that soil. The effect of increas• 89 ing the proportion of coarse material on the density of the soil mortar and on the 80 density of the total mix is illustrated in Figure 3. Increasing the content of coarse 100 900 1000 9000ICOOO 50000 100000 material above 25 percent causes a small Compaetln Effort-Ft Lb Par Co Ft decrease in density of the soil mortar, Figure 4. nelationship between compac• while increasing coarse materials to more tive effort and tnaximun- dry density. in solid lines in the right-hand side of at about 24-percent compactive effort. Figure 1. Similar curves for a poorly Thus twice as much compactive effort graded, fine Florida sand are shown in is required to compact the clay to 95 the left of Figure 1. These graphs show percent as is needed to compact the sand that the optimum moisture content for to the same percentage of maximum the clay soil is decreased 6 percent (29 density. to 23) and the maximum density is in• The effect of compactive effort is as creased 12 pcf. (88 to 100) while for the evident and equally as significant in field Florida sand the corresponding changes rolling as in the laboratory compaction are only 1 percent and 2 pcf. respectively. test. In rolling, the effort applied is a If laboratory compaction tests are made product of the drawbar pull (which re• at each of several different compactive flects the weight) and the number of passes efforts, there is developed for each soil for the width and the depth of the rolled a relationship between maximum density area compacted. Increasing the weight and compactive effort. Similar de• or the number of passes increases the terminations for each of several soils compactive effort applied. The signif• make it possible to compare the relative icance of size of tamping foot, contact effects of compactive effort on the dif• pressure, and lift thickness as related ferent types of soil. The relationships to compactive effort is discussed later. between maximum density (for each com• The density-measurement method is pactive effort) and compactive effort are the only procedure available which gives shown in Figure 4. a direct quantitative measure of the de• The curves in Figure 4 show that there gree of densification (e^ressed in terms is, within the range of compactive efforts of porosity, or in terms of weight per normally used, an almost straight-line unit volume). It should be understood relationship between effort and density however, that the relationship between and that there is a marked difference in density and compactive effort is not the slope of the lines for different types linear and specifying a percentage of of soils. For example, the Florida sand density does not infer that a compactive shows a small gain in density with in• effort of similar proportions will be nec• crease m effort while the California clay essary for compaction. There is how• (No. 7) shows that increase in effort ever, a relation between wheel load and materially increases the density. compactive effort, and hence between Knowledge of the compaction character• compactive effort and bearing capacity. istics of different soils is of particular A knowledge of the significance of the value to the engineer who prepares relationship between density, compac• specifications and to the inspector who tive effort, and bearing capacity is help• must interpret the results of density ful in the preparation of specifications tests. For example, the California sand for compaction, whether it be for sub- (No. 2) in Figure 4 has a maximum den• grades, bases, or embankments. sity of 118. 1 pcf. at the compactive effort Other Factors Which Influence Soil of the AASHO Method T 99 (12,375 ft. - lb. Density. There are several factors which per cu. ft.). The compactive effort nec• influence the density obtained by com• essary to obtain 95 percent of maximum paction but do so in a small degree. Soil density is 3500 ft. -lb. per cu. ft. which temperature has an effect, particularly is about 28 percent of the compactive on soils high in clay content. Hogentogler effort of AASHO Method T 99. However, found from laboratory compaction tests the sand can be poured into place with but on a clayey soil that density (under little if any compactive effort to obtain AASHO T 99 test procedure) was in• a density of 106. 5 pcf. which value is creased 3 pcf. and the optimum moisture slightly greater than 90 percent of maxi• content decreased 3 percentage units mum density. Applying the same analysis when the temperature of the soil was in• to the clay (No. 7) it may be seen that 95 creased from 35 F to 115 F. percent of maximum density (AASHO T 99) Compaction tests on some clayey soils is obtained at about 57-percent compactive show that they are quite sensitive to effort and 90 percent of maximum density manipulation, that is, the more they are structure in the same degree. There• IITFMdOplWCL eojOooiA wkMi uod fore, the engineer should not use com• ISOntMOMWC paction to Improve bearing capacity with• 1,900 WOBUt mM out considering the effect which degree of ILDFhMOptVa 40JOOOU 40^lA»ILLoo4 densification has on volume change and aCwmgM I other properties. IISFtaMOpt wc 4S0»al anntaol One of the prime purposes of com• paction is to prevent settlement within embankments. Because compaction and

Cont Ripmntt Lofteratari settlement each bring about a closer otFMM arrangement of soil particles, it is ob• vious that artificial densification by com• ILi FhM Opt WC tMpf.lSbMpalMI paction will prevent later natural consol• idation and settlement of an embankment under its own weight.

ruFiiM Opt wc Increasing the density by compaction 0>M,900L6 Tractor s increases the resistance to shear de• formation and makes densification by compaction a useful tool in designing and building stable slopes of high embank• Figure 5. Unconfined compressive strength of field-compacted clayey sand con'pared ments, which if not compacted, would not #ith strength of laboratory specimens be stable. having approximately similar densities Other conditions being equal, the bear• (after Corps of Engineers). ing value of a soil increases with in• crease in density. A great many labora• worked, the lower the density for a given tory studies have shown how soil density compactive effort. Manipulation has little and soil moisture content influence bear• effect on the degree of compaction on ing capacity. Only recently (1, 2) have soils which are dominantly silty or sandy. large-scale efforts been made to develop Curing, that is, a drying following comparable data on the relationship be• compaction, is not a factor which in• tween bearing value and soil density under fluences the mechanical process cf com• both field and laboratory conditions. paction, but it may affect an increase in Figure 5 shows unconfined compressive the density of subgrade and base material, strengths of a clayey sand compacted to especially if those materials contain co• various densities at optimum moisture hesive materials. Density may increase content in the laboratory. Figure 5 also on drying as much as 3 to 4 pcf. shows unconfined compressive strengths of undisturbed cylinders cut from field- INFLUENCE OF DENSIFICATION ON compacted lifts. The field lifts were PHYSICAL PROPERTIES OF SOILS compacted with different numbers of passes or coverages of different types of The behavior of a soil in a compact rolling equipment and represent a range state differs from the behavior of the of field compaction. It may be seen that same soil in a loose state. Compaction compressive strengths are approximately under controlled moisture content in• doubled by compaction, yet the greatest fluences all of the physical properties of density shown is not beyond the limits the soil mass related to performance of obtainable in highway construction. embankments, subgrades, and bases in Increasing the density reduces both highways. These major properties are the total porosity and the sizes of the pore bearing value, water movement (capil• spaces of soils which contain sufficient larity, water-retention capacity, and fines to make them compressible. It is permeability), volume change (shrink• that phenomenon, plus the increased age and swell), and resistance to frost friction developed, which increases bear• action. ing capacity and resistance to shear de• Compaction does not improve all soils formation and decreases elastic deforma• for all uses in different parts of the road tions. The reduction in pore spaces re- ISO LEGEND Blows per Weight Drop in ^125 Layers layer hammer inches 1 5 55 0 • 10 lb. 18 (Mod AASHO effort) 1100 a- 5 26 10 Ibi 18 A - 5 12 10 lb l8(Equiv.std AASHO effort) £ 75 NOTES' Specimens compacted in 60in.dia.mold Tested as molded 50 1 25 Figure beside ,126 1 1 1 1 0 curve is molding V Figurm >ldeed besid dry edensit curvey i s water content 140 \ , 128 124 Note X point s 135 e 125 AhtninaH fpmm — center plot 130 _I22 i \\ \\ .Sl25 120 X \ >> > \\. •8 * I'12 0 o 115 > iia 5 10 15 115 120 125 130 5 6 7 8 9 10 II 12 Water content in percent dry weight Molded dry density in lbs. per cu. ft. Molding water content in percent dry weight Molding \M)ter Content vs. Density ond CBR Density vs. CBR Water Content vs. CBR

Figure 6. Relationsliip between CBR values and density and moisture. Tests were made on specimens at the as-moulded moisture content (after Corps of Engineers). 8 duces permeability, thus restricting both in the field and in the laboratory, percolation of water. When compaction to determine the desirable range of is accomplished with proper moisture moisture-density control to hold vol• control for the particular soil, it re• ume change to a minimum. The work of stricts capillary movements, making the Allen and Johnson (3), McDowell (4), soil less susceptible to increase in mois• Russell (5), and the Corps of Engineers ture by absorption, and thus restricts (6) is indicative of the nature of work changes in bearing capacity. done. The importance of reducing the porosity Swell or shrinkage and its relation to in finely grained soils and its relation to initial density and moisture content is bearing capacity may be seen by com• easily determined by direct swell and paring porosities with the porosity at the shrinkage tests. Normal soils (not in• plastic limit The plastic limit is a cluding micaceous, diatomaceous, and critical moisture content affecting the other soils having certain constituents) bearing capacity of fine-grain soils which show a good relationship between swell and are characterized by becoming plastic plasticity index (when correction is made when wet. At or slightly above the plastic for plus No. 4 mesh sieve content). The limit, small increases In load yield large fact that swell is so important has caused increases in deformation. It is practically most investigators to test soils for bear• possible to compact nearly all soils to ing capacity in an expanded condition by densities having porosities less than the fabricating specimens in a wet condition porosity at the plastic limit. Compac• for testing or testing specimens after they tive efforts equal to 100 percent or more have had an opportunity to absorb water of standard (AASHO Method T 99) may be and swell. The work of TurnbuU and required to reduce the porosity below that McRae (8) shown in Figure 6, indicates which holds for the plastic limit for very the relationship between moisture con• heavy clays. That may not be desirable tent, density, and bearing capacity as for subgrades for high-sweUing clay e^qiressed by the California Bearing Ratio soils. Volume change (shrink and swell) (CBR) for a given soiL The work of is an important soil property which af• Benkelman and Olmstead (7), shown in fects the behavior of subgrade materials. Figure 7 and 8, indicates the relationship Soils which exhibit volume change may between soil strength, as determined swell nonuniformly on absorbing water the triaxial testing apparatus, and soil and suffer a reduction in bearing capacity. density and moisture content In swelling they may become the cause of The relationship between soil-density- rough riding pavements. They may also moisture-content and volume change IS, in shrink nonuniformly and cause uneven itself, a broad subject. Space does not settlement and contribute to fractures permit complete coverage here. The best In pavements. results may be obtained by recognizing the Compaction has a marked influence influence of compaction and moisture on the volume change of clay soils. Den• control on the related properties of volume sity influences volume change, the great• change and bearing capacity and com• er the density the greater the potential pacting subgrade soils so that the range swell, unless the soil is restrained by of shrinkage and swell will be a minimum. force. An expansive clay soil should Increasing recognition is being given to be compacted at a water content and to the influence of moisture and density a density at which swelling will be a control on the susceptibility of soils to minimum. Likewise, it should be com• cause segregation of ice on freezing and pacted so shrinkage will be a minimum. subsequent reduction in bearing capacity Although the two conditions may not be during the frost-melting period. Reliable the same, a soil exhibiting volume change data on the influence of controlled com• can be compacted at a moisture content paction on damage due to freezing are yet to a density where both swell and shrink too meager from which to draw con- will be near a minimum for any given condition of exposure. ' Whether interpreted through bearing tests, compression or shear tests Many investigations have been made. 9 elusions on which to base a recommended will be a change as it adjusts itself to the practice. new conditions under the pavement High-volume-change soils, if com• FACTORS INFLUENCING PERMANENCE pacted at moisture contents less than OF DENSinCATION optimum, may gain in moisture, swell, and suffer a reduction in density and There are several factors which tend bearing edacity from the as-built con• to change soil density. The two pri• dition. Contrariwise, if compacted too mary factors are climate and traffic. wet they may lose moisture and shrink Others are of a secondary nature, as for in a degree sufficient to crack the pave• example, condition of pavement surface ment The studies made by several high• and nature of base and subbase or shoul• way departments (9) showed clearly the ders which influence the degree of ex• need for control of moisture content and posure. density to ^proach a condition of least There is no evidence that the main swell and least shrinkage if damaging body of an ordinary embankment suffers effects of moisture and density changes any decrease in density due to swelling of on high-volume-change clays from the clay soils, unless it is subject to pro• as-built to the in-service condition are longed inundation. The surface slopes to be held to a minimum. may increase in porosity with time, but Granular soils retain a large measure for most cases only surface softening will of their compaction. The clayey-sands, result. Likewise, there is no evidence sandy clays, and the silty soils are af• that it continues to settle in detrimental fected in a lesser degree and need to be amounts for some period following ade• compacted in accordance with the de• quate and uniform compaction, either as a gree of protection offered by the type result of climatic or traffic conditions. thickness and cross-section of the pave• For practical purposes normal embank• ment used and other conditions which ments retain their degree of compaction, prevail locally. Seasonal changes which except in the upper and outer portions affect swell and shrinkage are the most subject to seasonal wetting and drying severe in areas near and bordering semi- and frost action: The item of perma• arid regions where long, hot dry periods nence is significant for compacted em• may occur. Even more-severe seasonal bankments only when they are subjected to changes may occur in humid regions where unusual conditions. deep freezing occurs. Subgrade materials, subbases, and The freezing of wet soils results in the bases are subject to more severe ex• formation and often the segregation of ice, posure to climatic changes and traffic which on thawing, may cause a reduction than embankments. Climatic conditions in soil density. Upon the redistribution of may bring about permanent or seasonal the thaw water in the soil, there is a re• reduction or gain in soil moisture and, as gain in soil density. There is evidence a result, may decrease or increase soil that some reduction occurs in the density density and cause distortion of the road of fine-grained soils, if they are in a surface. saturated condition prior to freezing. In considering the permanence of com• The incidence of a greater number of paction, the engineer needs to take into near-legal-axle weights in recent years account two stages in the life of the road. and the experience on airfields give The first concerns the period during which evidence that traffic has an influence on the road adjusts itself to its environment, the permanence of compaction in bases that is, from the "as-built" to the "in- and subbases. Heavy traffic may bring service" condition. The second concerns about an increase in density over that ob• changes in density of the subgrade mate• tained during construction, causing a rials which result from seasonal or long• rutting of a flexible-type pavement or time changes in climatic conditions after subsidence of a rigid pavement. Although the road has been in service for some there are a few factual data, it is quite time. If the soil is compacted too little generally believed that even relatively or too much, too wet or too dry, there clean, coarse granular bases suffer some 10

TABLE 1

REOOV.MENDED MINIMUM REQblREMEl^TS FOR OOMPACIION OF EMBANKMENTS

CONDITION OF EXPOSURE

CONDITION 1 CONDITION 2 a ass of (Not Subject to InundaUon) (Subject to Periods of Inundation) Soil (AA9C M 145-49 Height of CDtnpaction (% Height of Coinpaction (% Fill (ft.) Slope of AASHOMax. D.) Fill (ft.) Slope of AASHO Max. D)

A-1 Not aitical W to 1 95+ Not Critical 2 to 1 95 A-3 Not CiiUcal IK to 1 100+ Not Critical 2 to 1 100+ A-2-4 Less than Less than 10^ 95 2 to 1 95+ 3 to 1 A-2-5 Less than 10 to 50 95 to 100 A-4 Less than 50^ Less than 5( 2 to 1 95+ 3 to 1 95 to 100 A-5 Less than SO A-6 Less than 50 2 to 1 90-95' Less than SO 3 to 1 95 to 100 A-7

REMARKS Recoimiendations for (jondition 2 depends upon height of fills. Higher fills of the order of 35 to 50 ft. should be oompscted to 100 percent, at least for part of fills subject to periods of inundation. Ihusual soils nhich have low resistance to shear deformation should be analyzed by soil-mechanics methods to de• termine permissible slopes and minimum compacted doisities.

'The lower values of minlnmn requirements

reduction in density in frost areas, and Part of that traffic will recompact such granular Road Structure Purpose of Densification bases after the frost leaves the ground. Embankments To prevent detrimental It is now generally accepted that only that settlement compaction can be "maintained" which will To aid in providing stable be regained by traffic. slopes The extent to which the original degree of compaction is preserved depends on the Subgrade To provide bearing protection the soil receives. Full width, Materials capacity impervious pavements or pavements with To control volume change surfaced shoulders provide more protec• To provide uniformity tion against infiltration of surface water than normal-width pavements with shoul• Bases and To provide uniform hig^ ders built of average soils which shrink Subbases bearing capacity and swell seasonally. The use of shoul• ders made of select, dense, low-vol• It should be the aim of the engineer to ume-change material, the maintenance of obtain, as nearly as possible, the densities tight joints, and the provision of good necessary to satisfy the needs for the con• surface drainage all contribute toward ditions involved. maintaining density in subgrade materials. Embankments

The minimum densities necessary in the DEGREE OF DENSIFICATION NEEDED construction of embankments^ depend on the soil type, the height of the embank-

The purpose of compaction in the ' The term "embankment," as used here, refers to that part of the raised structure below the depth of the subgrade mate• different parts of the road structure may rials influenced by traffic loads and effects of climate. be itemized as follows: 11

ment, the design slopes, and the condition produce adequate results. However, of exposure. The necessary minimum re• under conditions of saturation by inun• quirements for compaction should be de• dation it is advisable to increase compac• termined by consideration of all those tion to about 100 percent for high fills of factors and should not be based upon a the order of 35 to 50 ft. single requirement. Sandy and gravelly The plastic soils (A-6 and A-7) show soils of the A-1, A-2, and A-3 groups the greatest improvement from com• (13) can be compacted to relatively high paction. They should be compacted to densities. Some of the very-sandy soils relatively high densities (low porosities) exist in the dry, uncompacted state at if stable slopes are to result for the high• densities of the order of 90 percent of er fills. Recommended minimum require• AASHO maximum densities and attain ments for compaction of embankments are densities of that magnitude or hi gher under given in Table 1. normal construction procedures without Because of their need for greater re• benefit of rolling and have stable slopes sistance to softening,reduction in strength, at those densities. When they are placed and erosion, embankments subject to flood• where they are not subjected to wetting, ing require better compaction than those there is little danger of excessive settle• not subject to inundation. Experience has ment. However, if subjected to satura• shown that well-compacted soils offer tion, they may settle in detrimental amount much-greater resistance to stream eros• unless compacted to about 95 percent of ion during overflows than uncompacted or maximum density. The relatively clean poorly compacted soils. Clay soils are granular soils retain their stability when greatly improved in that respect. saturated. Rigid control of moisture for soils The friable soils of the A-2, A-4, and dryer than optimum is not necessary for A-5 groups can also be compacted with embankments not to be subjected to flood• relative ease but require relatively high ing. The moisture content may be with• densities if stable slopes are to be built. in the range below optimum which permits They are more subject to reduction in obtainingthe desired density with the com• shear strength on saturation and require paction equipment available. Sheepsfoot- higher densities to produce stable slopes. type rollers which produce high unit Normally, 95 percent compaction will pressures and other types of rollers which

V 0* z4 K 7 7 y \ 14 5 y V 2 •^16 • \ 825 o to 3 12 1 II • 2 S 98

'• \

/ NUUE ER IND C«TE! THE NU MSER INOICA ES TH E 2 NUMB ER OF TEST VALUES NUMBER OF TEST VALUES ^ INCLU DED IN AVERAGE OF V-L INCLUDED IN THE AVERAGE / MAX V-L VALUES V-L FOR EACH VALUE OF MOISTURE 2\ 1 1 V •» 5 6,7 4 5 6 7 AVERAGE MAXIMUM (V-O-KIP/SO FT AVERAGE MAXIMUM (V-L)-KIP/SQ FT

Figures 7 and 8. Relation of maximum V-L (tnaxial shear) with density and moisture. 12

SI(VM -US standard Siiei 100 40 eo 10

Sand-Clay

HMViaaz Slltyday andy Clay

HMvyClay SDty Clay Sandy Clay Sand Bnwtl-Sand-Cloy

oa 009 09 I 8 Portlela Sb«-mm Oloimtar

Figure 9. Grain-size distribution and Atterberg linits of soils used in British field-compaction experiments (after Williams). produce heavy wheel loads and high unit design or the depth to which climate pressures permit securing desired densi• affects the soil, whichever is the greater ties at low moisture content. Moderately depth. Because of the effect of climate on plastic soils in Groups A-4 through A-7 bearing capacity and on the permanence should be compacted at moisture contents and effectiveness of compaction, more not greater than 2 or 3 percentage points careful consideration need be given com• over optimum to insure uniform density paction of various types of subgrade mate• and to avoid the unsatisfactory construc• rials for different climatic conditions than tion condition of low stability and rutting is necessary for embankments. The need• under heavy construction eqmpment. ed density and moisture content for ade• High-silt-content soils of low plasticity quate bearing capacity may not be ideal in Groups A-4 and A-5 and sandy silts of for holding volume change within desired Group A-4 should be compacted at mois• limits. ture contents not in excess of optimum to Several state highway departments insure uniform density and to avoid the recognize, in their methods for design• instability and rutting under heavy con• ing flexible type surfaces (11), that the struction equipment which occurs when bearing capacity of the soil must be based these soils are placed at moisture contents on a degree of saturation which occurs which exceed optimum. under service conditions. If compaction Soils compacted at optimum moisture can be controlled to approximate that content have lower permeability and a condition, insofar as is practical under greater resistance to softemng than dry construction methods used, there will soils at equal densities. Therefore, fills result a minimum change in moisture or portions of fills subject to inundation content and density from the as-built or scour should be compacted at moisture to the in-service condition. Because the contents as near optimum as is practicable chief function of a subgrade is to carry and economical for these conditions. loads, that function must be considered with respect to the relative permanence Subgrades, Subbases, and Bases of the densification. The smoothness of the riding surface depends on the uniform• The term subgrade material (base• ity of compaction, hence any factor which ment soil) is intended to include soil to influences uniformity also needs con• the depth which may affect structural sideration. 13

Obviously the highest density obtain• able consistent with a moisture content less than optimum provides the greatest •—S Conn bearing capacity. Nonplastic, granular : 120 wtragn soils and subbase and base materials CL have little or no volume change and re• tain a high degree of their compaction. Thus, it is advantageous from all con• .110 / siderations to compact those soils to high densities. 100 The less-plastic soils of the silty and clayey groups, which have low volume 9 10 19 20 changes, decrease in bearing capacity as Molttura Conttnt- Plrcmt the degree of saturation is increased. 40,000 Lb. Whttl Lood Rubbtr Tin Rolltr hf lotion Protura 97p • I Contoct Prouaro 69p s I 6 Inch Lift* Those soils should be compacted to mod• Dwisily ot le Inch Depth Clayey Sand UL • 18 PI • £ erately high densities. A reduction in density and an accompanying increase in Figure 11. Typical moisture-density data moisture and reduction in bearing capacity from construction lifts on sandy soil occur on soils having high volume change. (after Corps of Engineers). Thus, unless temporary advantage of high bearing capacity during the early life of Practicable Limits of Densification the road is desired, and volume change (and road smoothness) is not a prime The graphs in Figure 4, which illus• factor, those soils should be compacted trate the relationship between density and to densities and at moisture contents compactive effort from laboratory tests, which constitute the best compromise indicate no decrease in rate of density between need and permanence. Because gain with increase in compactive effort for granular soils retain compaction except the greatest compactive efforts shown. in areas of severe frost and because Undoubtedly that is due to compacting soils high densities are desirable, knowledge in a mold whose side-waU friction makes of the practicable maximum field limits that possible. However, for field com• of compaction is important. Hence, rec• paction there is a practicable maximum ommended procedures for selecting the limit of density which can be obtained best densities are given later in this with reasonable economy for each combi• bulletin. nation of soil and compacting equipment. Specifications for bringing about the best results obtainable consistent with the de• sired economy cannot be arrived at with• LEGEND out a foreknowledge of the practicable -• 250IH I Sll«p»tool,9 RlMM- limits for various types of equipment on Sin Li(H,l8in.0«pm 490pt.i Shnpstool,9Pfl«Mt different types of soils. ein Liflt,IPin Depth -•—15001b VIUI>l>Winl,6Cimragn| 3in Litll,9iii D«plh The recent trend towards the use of -a— 40O0O lb. Wh««l Lood.e CowrogeJ I8in D«pth I higher contact pressures and heavier AASHO T99-3eOpl WC equipment has made possible the attain• and Moxifnjm Oaniity ModlfiMAA.SKO Opt «C ment of higher densities on well-graded, ond Maximum Otnsity granular soils and on the more-compress• Soil Cloyay Sand ible clayey soils. Their use has not in• L-ie PI-2 % Sand-SZ creased materially the densities obtain• » SiH • 2 X Cla> 'IS able onvery-sandy materials nor on very- friable silty soils. Data from three in• IS 20 23 Sal tUbtirCartant- Percent vestigations and from several years of compaction practice make it possible to Figure 10. Typical moisture-density data predict with reasonable accuracy the from construction lifts on sandy soil highest degree of compaction practicable (after Corps of Engineers). with present equipment. 14

in rows of 4. Tamping-foot areas 5. 25 water Content - Percent of Dry Weight 10 15 20 25 vi and 5. 5 sq. in. Tamping-foot pressures, Indiana, 209 and 290 psi.: Ohio, 223 and 290 psi. 3-Wheel Type. 10-ton, 325 and 350 lb. 120 per inch of width of rear rolls. Pneumatic-Tire Type- 9-Wheel, 35 psi. Modified A AS.HO / tire pressure, 225 lb. per inch of tire d IIS -~ltt«l Malll \\ width in contact with ground. y ^Zfiro Air \ 'olds RESULTS no / Field Compoctlo n — \ \ Indiana 20,000 on140p00l h Wheel \ \ Load 6 Coverages ^ \ 105 Soils. Silts and silty clay loams, P. I. A range 8 to 17. AASMO » ethod-v/ Moisture Content. Approximately opti• 100 —T99-3( ) 290^000 and 790P.8I mum as determined AASHO Method T //Sh eepsfbot Rollers 6 Poss u 1 1 99. Testa Made an Silty Cloy Sail Having 10% Sond,63%Silt, Density, Lift Thickness, and Number of 27%Clay LL'37PI»I4 SpGf272 Passes. Sheepsfoot Type. 95 to 96 percent of Figure 12. Results of field and labora• AASHO maximum dry density on 6- in. tory compaction on silty clay soil (after loose lifts in 5 to 6 passes. &>rps of Engineers). 3-Wheel Type. 97 to 100 percent of AASHO maximum dry density on 6-in. The first of the investigations referred loose lifts in 1 or 2 coverages. 101 to to were two e:q)erimental fill construc• 104 percent of AASHO maximum dry den• tion projects (12) constructed in 1938, sity on 9-in. loose lifts in 2 to 2% cov• one In Delaware County, Ohio, and the erages. 100 percent of AASHO maximum other in Gibson County, Indiana. The re• dry density in 12-in. loose lifts in 2 cov• sults of the two experiments are sum• erages. marized as follows: Pneumatic Type. 99 percent of AASHO maximum dry density on 6-in. loose lifts Rollers Used (Indiana and Ohio) in 2 coverages. 97 percent of AASHO maximum dry density on 9-in. loose lifts Sheepsfoot Tsrpe. Dual-drum oscillating in 3 coverages. 97 percent of AASHO max• Type 40 and 44-in. -diameter drums 48 imum dry density on 12-in. loose lifts in in. wide, 88 to 112 tamping ft. per drum 4 coverages.

TABLE 2

SUMMARY OF BRITISH FIELD AND LABORATORY COMPACTION STTJDIES ON FIVE SOILS

BRITISH* MODIFIED MAXIMUM FIELD COMPACTION (pcf.)AND STANDARD AASHO OPTIMUM MOISTURE CONTENT (Percent)FOR SOIL TYPE DIFFERENT ROLLERS Density Opt. M.C Density Opt. M.C. 8-Ton I^eunatic •aubfoot" 'Taper Foot" (pcf.) (Percent) (pcf.) (Percoit) 3-Wheel Roller (115 psi.) (249 psi.) Gravel-sand-clay 129 9 138 7 138-7 126-7 129-6 128-5 &nd 121 11 130 9 132-8 127-11 - - - - Sandy-aay 115 14 128 11 116-14 108-19 119-12 120-12 Silty-aay 104 21 120 14 111-16 104-20 116-14 115-14 Heavy-Qay 97 26 113 17 104-20 98-25 107-16 107-15

'ftitidi Standard Test does not differ greatly from AA90 Method T 99. 15

TABLE 3 BRITISH STANDARD COMPACTION ON 5 SOILS BY 4 ROLLERS

Gravel-Sand- Sandy Silty Heavy Roller Clay Sand Clay Clay Clay % % •n % % 8-ton, 3-wheel 107 109 101 106 107 Pneumatic 97 105 94 100 101 Club- foot 100 — 103 111 110 Taper-foot 99 --- 104 110 110

Ohio type 42-in. -diameter by 48-in. drums having 88 ft per drum in rows of four Soils. Approximately equal percentages of with 2V4 by 2% in. (SVw sq. in.) contact sand, silt, and clay. Majority of soils in area and ballasted contact pressure of P. I. range of 15 to 25. 249 psi. Moisture Control. Majority within 1 per• 3-Wheel Type. 8 ton, 186 lb. per in. cent of optimum. of width of front roll 311 lb, per in. of Density, Lift Thickness, and Number of width of rear rolls. Passes. Pneumatic-Tired Type (with pairs of Sheepsfoot Type. 97 to 101 percent of wheels on oscillating axles). 9 wheeL AASHO maximum dry density on 6-in. 36-psi. inflation pressure 39 psi. con• loose lifts in 6 to 9 passes. 97 percent tact pressure, 3,000 1b. per wheel. of AASHO maximum dry density on 9-in. loose lifts in 6 passes. The British studies were unique in two 3-Wheel Type. 101 to 105 percent of respects. They made all tests on one AASHO maximum dry density on 6-in. thickness of lift. They obtained maxi• loose lifts in 2. 5 to 3. 3 coverages. 104 mum compaction for each roller, each percent of AASHO maximum dry density soil being "fully compacted" at each mois• on 9-in. loose lifts in 6 coverages. ture content to enable finding maximum field density and optimum moisture con• The British Road Research laboratory tent for each soil for each roller. From (13) released results in 1950 of rolling 4 to 16 passes were required for full e}q)eriments on five different soils rang• compaction with pneumatic and 3-wheel ing from a gravel-sand-clay to a heavy rollers and from 16 to 64 with sheepsfoot clay. The characteristics of the five types. The results bring out some inter• soils are indicated in Figure 9. The esting relationships between maximum British studies included (among others) field density and field optimum moisture the foUowing types and weights of rollers: content and soil type and equipment. The Sheepsfoot Type. "Club-foot, " fixed- results of the British investigations are frame, dual-drum type. 42-in. -diameter shown in Table 2. by 48-in. drums having 64 tamping feet Tables 3 and 4 show the relative per• per drum in rows of four with 4 in. by centages of British standard compaction 3 in. (12 sq. in.) contact area, and bal• and modified AASHO compaction obtained lasted tamping-foot pressure of 115 psi. by the different types of rollers on the "Taper - foot," dual-drum, oscillating five soils.

TABLE 4 MODIFIED AASHO COMPACTION CW 5 SOILS BY 4 ROLLERS

Gravel-Sand- Sandy Silty Heavy Roller Clay Sand Clay Clay Clay % % % % % 8-ton, 3-wheel 100 101 91 92 92 Pneumatic 91 98 84 87 87 Club- foot 93 — 93 97 95 Taper-foot 93 --- 94 96 95 16

TABLE 5

STANDARD AASHO AND MODIFIED AASHO OOMPACIION OBTAINED ON A aAYEY SAND IN FIELD ROLLING EXPERIMENTS (AHER CORPS OF ENGINEERS)

Equipment Passes Compacted Lift Modified AASHO Standard AASHO Thickness Density Density Afo. m. % % 250-psi. 9 6 94 98 Sheepsfoot 450-pai. 9 6 93-95 97-99 Sheepsfoot 1500-lb. 6 3 94-95 98-99 Wobble-Wheel Pneumatic Tire 20,000-Ib. 4 6 95 99 Wheel-Load Pneumatic Tite 40,000-lb. 4 6 94-96 98-100 Wheel-Load Pneumatic Tire 40,000-lb. 8 6 95-97 99-102 Wheel-Load Pneumatic Tire Laboratory Standard Optimum moisture, content was 11.5 percent. Field optimum moisture contents ranged from 11.5 to 12.2 perceit.

TABLE 6

STANDARD AASHO AND MODIFIED AASHO COMPACTION OBTAINED ON A SILTlf CLAY IN FIELD ROLLING EXPERIMENIS (AHER CORPS OF ENGINEERS)

Equipment Passes Compacted Lift Modified AASHO Standard AASHO Thickness Density Density Wo. m. % %

250 psi. 6 6 92 102 Sheepsfoot 6 500 psi. 6 91-92 102 Sheepsfoot 750 psi. 6 6 91- 92 102- 104 Sheepsfoot 92- 94 10,000 lb. 6 103- 104 Wheel Load Pneumatic Tire 20,000 lb. 92- 93 102- 103 Wheel Load Pneumatic Tire 40,000 lb. 93- 94 103- 104 Wheel Load Pneumatic Tire Laboratory Standard AASHO optimum moisture content was 17.9 percent. Field optimum moisture contents ranged fran 18.5 to 19.5 percent. 17

TABLE 7 Standard AASHO maximum density were AVERAGE DENSITIES OF obtained with relative ease. Five to six HIGHWAY SUBGRADE MATERIALS passes of sheepsfoot rollers having medi• um contact pressures (200 to 250 psL); Type of Subgrade Material . Densities one to two coverages of 10-ton, 3-wheel- AAa» Modified AA30 type rollers and two to three coverages Bases 100.5 96.5 of pneumatic-t}rpe rollers gave 95 percent 96.7 or more of standard compaction on most Granular Materials 101.2 88.8 Silt-Clay Materials 96.8 soils on lift thicknesses of the order of 6 to 9 in. of loose depth (approximately 4 to The Corps of Engineers (14, 15) have 7 in. of compacted depth.) Increasing the conducted field-compaction e:q)eriments contact pressures of the tamping feet on under conditions of close control of mois• sheepsfoot-type rollers without some in• ture content and rolling. The tests were crease in the contact area brought only a made on two types of soils. One soil was small gain in compaction. The higher a clayey sand having a plasticity index of contact pressures were only partly effec• 2, The other was a silty clay having a tive because the bearing capacity of the plasticity index of 14. A significant fea• soils in the loose state could not withstand ture of the tests was that the effectiveness the pressures and the rollers sank deeper of the different rollers was compared on into the soil until the effective contact the basis of the number of passes which pressure equalled the bearing capacity of might be used normally on a construction the soil. Thus, the benefit of higher con• project. tact pressures cannot be realized unless The field and laboratory moisture- the contact area also is adequate for the density relationships obtained on the clay• soil. ey sand are shown in Figures 10 and 11. The e3q)eriments showed that 100 per• The equipment used, number of passes, cent, or more, of standard (AASHO T-99) lift thickness, and relative densities at compaction was obtained by increasing the field optimum moisture content expressed number of passes. Thus it is practicable as percentages of AASHO maximum den• to specify 100-percent compaction for sity (T 99) and modified AASHO maximum special conditions where densities of that density are shown in Table 5. order are desirable. Also, some rollers Field and laboratory moisture-density are more effective on some soils than on relationships for the silty clay soil are others and some soils attain a high degree shown in Figure 12. The equipment used, of compaction with less compactive effort and relative densities at field optimum than others. moisture content expressed as percent• ages of standard AASHO and modified Correlation of Need, Practicable Densi- AASHO maximum densities are shown in fication Limits, and Permanence Table 6. The three rolling experiments showed The data presented are too meager that densities of 95 percent or more of from which to develop firm rules for the

TABLE 8 DENSITIES OF SUBGRADE MATERIALS UNDER RIGID PAVEMENTS IN KANSAS

Description of Average Field Dry Average AASHO Relative Soil Group Density for Group Standard Density Compaction for Group (AASHO T 99) RcL Soils found under pumping 98.9 104.3 94.8 slabs (all soils had less than 50% sand and gravel) Soils having less than 50% 99.8 106.8 93.5 sand and gravel from under non pumping slabs Soils having more than 50% 115.5 117.6 98.3 sand and gravel 18

TABLE 9 MOISTURE CONTENTS OF SUBGRADE MATERIALS UNDER FLEXIBLE PAVEMENTS (After Kersten)

State Textural Soil Sa turation Plastic Limit Optimum M.C. group 2 Minnesota Sandy Loam 78 75 101 Kansas Sandy Loam 65 73 82 Arkansas Sandy Loam 59 72 73 Minnesota Clay 83 91 105 Kansas Clay 92 103 112 Arkansas Clay 92 105 109 promise may need to be made for very TABLE 10 high fills indicating high compaction re• AVERAGE MOISTURE CONTENTS POUND quirements. That must then be done IN THE SUBGRADE GROUPS (after Hicks) by flattening slopes or using selected soils. An analysis of conditionjs for high Class of Soil AA30T99 Plastic Saturation (AA310 W 145-49) Optimum Limit fills should be made by soil mechanics methods which are beyond the scope of A-l-b 82.5 36.4 69.0 this report A-2-4 75.5 43.7 62.9 Subgrade Materials and Bases. The A-2-6 104.3 62.3 85.3 selection of the best density range for 82.6 A-4 106.1 65.0 subgrade soils varies widely because of A-5 114.7 54.0 89.8 A-6 109.1 75.2 85.4 the difference m the behavior of soils A-7-5 118.9 68.2 91.2 under service conditions. It is entirely A-7-6 109.4 70.9 90.9 possible that the compaction which is deemed best from the designers point of selection of the most desirable limits of view is not practicable for construction densification for different types of soils. and contrary, that deemed best from the However, the data do indicate trends which construction point of view may not pro• can be used as a broad basis for applying vide the desired subgrade condition. compaction to a good advantage. This It IS not possible to present in tabular requires a correlation between compac• form recommended compaction limits for tion needs, the limits of compaction which subgrade materials for all types of pave• can be obtained practicably and the rela• ments, loadings, soil types and climatic tive permanence of the compaction under conditions. The best that can be done the conditions of exposure e3q)ected. here is to consider need, permanence, Through such correlation it is possible to and practical limits and set forth a meth• select the range of densities and moisture od of analysis for arriving at the best contents which will result in the 'best' density range. bearing capacity for the service life of Hicks (16) found from his field survey the part of the structure m question. of moisture contents and densities in road Embankments. Because of the wide subgrade materials and bases under difference in the range of values indic• flexible type pavements that heavy ve• ative of the measures of various soil hicles will cause a higher degree of properties, hard-and-fast limiting values densification than will light vehicles and of densities for compaction cannot be drawn. Discussion under "Degree of TABLE 11 Densification Needed" and the range of INFLUENCE OF COMPACTION ON MOISTURE CONTENTS values in Table 1 relate need with design OF GRANULAR BASES (after Hicks) of slopes under the two conditions of (1) inundation and (2) not subject to inunda• Average Standard Optimum Plastic Saturation Density Moisture Content limit tion. The values of relative density % % % % (percent of standard AASHO) are all less (For Densities Under lOOX) than the maximum practicable limits. 98.5 7 5.0 43.8 60.3 Hence no compromise need be made due (For DensiUes 100% and Above) to construction limitations. Such com- lOLl 73.1 40.6 6L1 19

a large volume of traffic will bring about between densities and average moisture density equilibrium quicker than will a contents of granular bases. The average small volume of traffic. Thus traffic is densities (es^ressed as percentages of an important consideration. He found that AASHO T 99 maximum densities) and traffic will maintain densities greater than moisture contents are given in Table 11. 100 percent of AASHO maximum density Studies in Tennessee showed average in granular subgrade material but densities moisture contents of 23 percent compared in silt-clay subgrade material were much to an average plastic limit of 19 for fine lower. Average values from his survey grained plastic subgrade soils (having are given in Table 7. less than SOpercent sand and gravel) under Some of the recent studies of pumping rigid type pavements. The corresponding of rigid type pavements yielded data on values for Kansas were 24. 8 and 19.4 relative densities of subgrade soils under respectively. Moisture contents of the pavements which had been in service more granular soils (having more than several years. The results from the 50% sand and gravel) were 17. 7 and 13. 6 Kansas Investigation (17) which was limited and their plastic limits were 15 and 14.1 largely to the eastern one-half of the State respectively. Moisture contents in Illinois show average values of density for each of subgrade soils underlying granular bases three broad soil groups for that locality. averaged 22. 5 percent and corresponded The results are shown in Table 8. to an average plastic limit of 21.3 percent The densities found in granular soils Thus the fine grain subgrade soils existed under rigid type pavements in service at a condition near saturation while the were found higher than those of the finer granular soils existed at a condition of grained soils. about 83 percent saturation. Kersten's (18, 19) study of the moisture It is recognized that the values given contents of soils under flexible pavements will not hold for all climatic conditions. and the reports of the Highway Research They do however, point out that there is Board Committees on Warping (20) and a range for density and for moisture Pumping (21) of Concrete Pavements pro• content which can be maintained for each vide evidence of the range of moisture type of soil and type of pavement for a contents which exist in subgrade mate• given locality. It follows that the least rials under pavements. The average volume change will occur if compaction is values obtained in three States from aimed at the range which is most apt to Kersten's work indicate the range of soil "stay put" in the subgrade material. The moisture found under flexible pavements range of desirable moisture content can in those localities. The values are given be obtained for any locality by a survey of in Table 9 for only two different types of field conditions on pavements which have soils to show the difference in soil mois• been in service for some time. It should ture content for sandy loam soils and clay be kept in mind that they reflect in some soils. degree the initial moisture contents and Hicks' 1948 report of seasonal meas• densities at which they were compacted. urements of subgrade soil moisture con• In arriving at the best ranges of mois• tents under flexible type pavements also ture content and density, it is desirable showed that soU moisture is related to to make an analysis of the needs for the soil texture. The relationship expressed conditions and correlate those needs with in terms of average moisture contents other factors. One way of making such found in the various Subgrade Soil Groups, analysis consists of stating design and (Soil Classification Method AASHO M construction requirements and the cor• 145-49) IS shown in Table 10. responding ranges of moisture content Generally the soil moisture increased and density. The desirable values for during the fall and winter, reached a one may not coincide with that for the maximum during the month of April and other, necessitating a compromise to receded to a minimum during late sum• obtain the best practicable values. Ex• mer or early fall. amples 1 and 2 illustrate that approach Hicks also reported on the relationship for determining the best range of values. 20 EXAMPLE 1

Conditions: A rigid pavement, a subgrade soil exhibiting high-volume change overlaid by a 4- to 6-in. granular base.

DESIRABLE DESIGN REQUIREMENTS

Description of Requirements Corresponding Approximate Range of Density Moisture Content Maximum bearing values consistent (% of AASHO Maximum Den.) (% of Optimum) with minimum swelling or shrinking from as-built to in-service condition and from season to season for main• tenance of smooth riding surface.

1. Due to soil swell or shrink 90-95 100-115 2. Due to freezing and thawing 90-95 less than 65

CONSTRUCTION REQUIREMENTS AND LIMITATIONS Adequate Bearing Capacity

a. For hauling purposes when 95-100 95-100 subgrade is subject to con• struction traffic

b. When paver and trucks do not No construction requirements. The density use area to be paved and moisture values may be as desired with• in reasonable limits.

^he effect of density on frost action is not well established. Meager data show that, for certain conditions, heaving increases with increases in density to a maximum, then decreases. The effect of moisture content is known to be great. No significant heaving and accompanying softening occurs at moisture contents below the value given. EXAMPLE 2

Conditions: A densely-graded, granular base of nonplastic materials of considerable depth for a flexible pavement carrying a large volume of heavy traffic.

DESIRABLE DESIGN REQUIREMENTS

Description of Requirements Corresponding Approximate Range of Density Moisture Content (% of AASHO Maximum Den.) (% of Optimum) Maximum bearing capacity which can ^ be maintained under the traffic 105-115 95-100 carried

CONSTRUCTION REQUIREMENTS AND LIMITATIONS

Maximum practicable density obtain• able with heavy rollerroll s is only con- 105-110 95+ struction limitation

These values vary with type of materials. It is assumed in this statement that the thickness of the base course is adequate to carry such loads without overstressing the subgrade. 21

The best compromise value for the clay METHODS OF SPECIFYING soil will depend on the exact properties of COMPACTION REQUIREMENTS the soil and conditions under which it must serve. Except for a very-hig^-volume- There are three methods in use for change soil or for semiarid or subhumid stating minimum reqvdrements for com• conditions, a range of density centering paction: (1) controlling soil density, (2) about 95 percent of AASHO T 99 is ade• controlling compactive effort, and (3) quate. For semiarid and subhumid con• a combination of 1 and 2. ditions on the very heavy clay, a value Each of the methods can be made to of 90 percent or less may be necessary. produce satisfactory compaction if it con• Subgrades for intermediate soils of low trols soil moisture content and is properly volume change may well be compacted to applied to the existing conditions. Each densities of 95 to 100 percent. has some advantages as well as dis• The compromise on the granular base advantages. It is the purpose here to material is entirely that of obtaining the point out the advantages and disadvantages maximum density practicable. That may of the methods. require the use of relatively heavy rollers or the use of thin lifts and close control Control of Density of moisture content to obtain the high de• gree of compaction which is desirable The problem of compaction is basically for bases. one of controlling the amount and size of A suggested range of densities for pore spaces of the soil. When the spe• subgrade soils and base materials is cific gravity of the soil is relatively uni• given in Table 12. It is recognized that form, controlling the dry weight per a desirable range of density and moisture cubic foot gives close control of porosity. contentf or a semiarid or subhumid climate A large majority of agencies specifying may differ from that of humid climate. control of compaction do so throu^^ the Likewise, small differences may be desir• medium of controlling dry weight per able in southern compared to northern cubic foot and also stating maximum and climes, especially on soils whose suscep• minimum limiting values of moisture tibility to freeze damage bears a strong content. In most instances the AASHO relationship to degree of densification. T 99 maximum density and optimum moisture content form the basis for the Shoulder Materials. Because of the specification as, for example, specify• severe exposure of shoulder materials to ing a minimum compaction of 95 percent the climatic elements, it is poor economy of AASHO maximum density and a mois• to compact fine-grain clayey soils in road ture content range of 90 to 110 percent shoulders to high densities. If compacted of optimum moisture content to high densities they will swell and pre• Some of the advantages and disad• vent good surface drainage. Moisture vantages of that method may be stated contents for compaction are not critical briefly as follows: and need be only sufficient to obtain good bonding, or knitting, of the soil to mini• Advantages mize erosion. The following tabulation suggests desirable ranges of compaction 1. Because soils seldom differ great• limits for shoulder materials. ly in specific gravity, it constitutes a definite means for measuring the degree of densification obtained. DENSITlf RANGE MOISTURE CON- 2. Unless encumbered with other re• TYPE OF SOIL (% of AASHO TENT RANGE strictions it gives the constructor a wide T 99 Max. D.) (% of Optimum) range in latitude of equipment and methods to acquire the desired compaction. Fine-grained clay 85-90 75-100 Silta and sands 90-95 85-100 Granular material Roll in a moist condiuon Disadvantages with smooth-wheel or cubber-tire roller. 1. It does not tell the constructor 22

field testing. However, if it is accom• larzpief panied by control of moisture it has no e 173% opt wc advantage over the dry density method and has even greater disadvantages. 2l9X-l29Xof opt«q Figure 13 shows a typical dry weight- moisture content relationship and the cor• responding relationship between wet weight per cubic foot and moisture content. Density and optimum moisture content 114 Spitt'90X0(1 values are: maximum dry density 109. 6 per cu. ft., maximum wet density 127.2 per cu. ft, optimum moisture content 15 I09i6p.ci percent, optimum moisture content 17. 5 eisxopt wc. percent If for example, a minimum wet weight of 90 percent of maximum is specified (114.5 per cubic foot wet weight) that wet weight will require a mininium dry weight of 104.9 per cubic foot (equal to 95. 7 percent of maximum dry weight) at 9.2 percent moisture content. If no maximum moisture content is specified 94Zpe.l \ and the field moisture-density relation• B6Xal ship is similar to the wet weight curve, a dry density 90 pcf. (equal to about 82 percent of maximum dry weight) is per• MOISTURE CONTEMT- PERCENT OF DRY WEKSHT mitted at the moisture content approach• ing saturation. If for example, the mois• Figure 13. Interrelationships between ture content is limited to a maximum of specified values based on wet- and dry- 125 percent of optimum* (wet weight per volume weights. cubic foot) or 21. 9 percent, the density requirement of 90 percent of maximum which equipment is best suited, nor how wet weight wiU permit a dry weig^it of much rolling is necessary to obtain the 94. 2 pcf. which is equal to 86 percent specified density. of maximum dry weight Thus, if the 2. It requires field testing equipment specification is stated as a percentage and personneL of maximum wet weight, it permits a 3. It requires some time, depending decrease in dry weight (and a marked on equipment and method and skill of the decrease in bearing capacity) with in• inspector, to measure the dry density. crease in moisture content. That should 4. In unusual cases where sfpecific be taken into consideration and accounted gravities are not known and may differ for in determining specification limits markedly, it does not reflect the true based on wet weight per cubic foot densification of the soil. 5. There is sometimes danger that a soil may be improperly identified and an improper laboratory density value Control of Compactive Effort assigned. Care is needed to compare field and laboratory values for similar There are two methods of specifying materials. control of compaction by specifying re• quirements controlling the compactive The degree of compaction may also effort used. One method which is used by be controlled by specifying limits of wet many agencies is that of specifying types weight per cubic foot. This method has and weights of rollers, and by controlling the advantage in that wet weight per cubic foot can be determined rather quickly in * Normally too wet for ease in handUng 23

lift thickness and the amount of rolling. The second method has not yet been The amount of rolling is governed by developed. It has the obvious advantages specifying the number of passes or cov• of the density method without the dis• erages or by including roller hours as advantage of present methods which specify a bidding item and placing control of the some percentage, usually less than 100 total effort used under the immediate percent, of the density obtained under supervision of the project engineer. This standard compactive effort. method of control usually includes control Most specifications for compaction of soil moisture content Often this combine density control with control over method also includes specification re• equipment, giving minimum requirements quirements relating the number of com• for equipment (as to size, weight, and paction units to the rate of earth moving ratio of units to rate of earth moving), or requires a maximum output per com• lift thickness, and control of moisture paction unit. content. A second method which has been pro• posed by some engineers differs from the SELECTION AND USE OF EQUIPMENT present density-control method only in the manner m which it is put to use. It con• The success, that is, the economy and sists of specifying a given compactive ef• ease, of obtaining compaction depends in fort for the material to be compacted, if it large measure on the methods and on the be embankment, subgrade, or base. For type and weight of equipment used for roll• example, it is indicated that some base ing. It also depends on the equipment and materials can be compacted in the field to methods used in placing and preparing the the density obtained in the laboratory under soil for rolling. two AASHO T 99 compactive efforts (2 times 12,375 ft-lb. per cu- ft). That Dumping and Spreading compactive effort then forms the basic requirement and the maximum density Compaction depends on the size of the obtained at the compactive effort is the loaded area, the pressure exerted on the density to be obtained in the field. The loaded area, and on the lift thickness. compactive effort can be applied to the Lift thickness is an important factor gov• identical sample removed from the base erning the degree of compaction obtained. in the in-place density test, and used to Many of the difficulties of obtaining the determine the sufficiency of field com• desired compaction can be traced to lift paction. If, for example, it is found that thickness in excess of that which can be a density less than that of Standard AASHO handled by the rolling equipment used. Method T 99 is required for a clay sub- It varies for different types of soils for a grade soil, specifications might be based given piece of rolling equipment on compactive effort equal to 80 percent Proper spreading is largely a matter of of standard effort (9,900 ft-lb. per cu. attention to the job. It can be done di• ft) which would be equivalent to 20 blows rectly by adjusting scrapers during dump• of a 5%-lb. hammer dropping 1 ft on ing. Proper spacing of dumps from each of three layers. wagons makes a simple job of bulldozing The first method given above has the or blading of the loose soil to proper lift advantage of keeping control in the hands thickness. Close attention to the effective• of the engineer. The effectiveness and ness of the roller in early trial runs will economy of the method depend in a large soon indicate the best lift thickness for degree on the care with which the quan• the various types of soils. tities are set up and the resourcefulness It is not possible to predict the exact of the project engineer and his knowledge lift thickness which results in the most of soils and the use of equipment for economical rolling for all soils and types compaction. It has the disadvantage of and weights of equipment However, some preventing resourceful contractors from general rules can be laid down. Gen• developing and using better equipment erally, the heavier the equipment the and methods for compacting soil to ar• greater the lift thickness which can be rive at a lower construction cost. handled. The rule does not hold in the 24

TABLE 12

SUGGESTED RA^GE OF DENSITIES FOR SUBGRADE SOILS AND BASE MATERIALS IN CDNSTRUCTICN

MOISIVRE TYPE OF SOIL TYPE OF PAVEMENT MINIMUM CONTENT RANGE REMARKS DENSITY RANGE (PERCENT (PERCENT OF AASHO OF AASHO MAXIMUM DENSITY) OPTIMUM) Moderate to hi§^ Flexible 95-100 95-100 volime change pre- 90-95 100-110 When construction traffic dcminantly clayey Ihgid Condition 1 does not use prepared sub- soils 95+ <100 grade. Wien construction Condition 2 traffic hauls over pre• pared subgrade.

Predoninantly silty and Flexible 100+3 95-100 sandy soils having little or no volume Rigid 100+3 95-100 change

Good quality granular Flexible 100-110 95-100 Maxmum practicable den• materials suitable for sity varies with type and base and subbase con• grading of material. A struction. maximum range can be se• lected according to material.

Rigid 100-105 95-100 For condition 1 above" 100-110 95-100 For condition 2 above

"The lower range of densities and hi^er rmge of permissible moisture coDtoits for Condition 1 may make It difficult to obtain hi^ densities in base materials.

TABLE 13

EQUIPMENT AND METHODS FOB ADDING WATER PRIOR TO COMPACTION

TYPE OF SOIL EQUIPMENT AND METHODS FOR INCORPORATING WATER WITH SOIL

Heavy Qays Difficult to work and to incorporate water uiifonnly. Beat results usually obtained by sprinkling followed by mixing on grade. Heavy disc harrows are needed to break dry clods and to aid in cutting in water, followed by heavy-duty culUvators and rotary speed mixers. Lift thickness in excess of 6 in. loose measure are difficult to work. Time is needed to obtain uniform moisture distribution.

Medium Qayey Can be worked in pit or on grade as convenience and water hauling conditions dictate. Soils Best results are obtained by sprinkling followed by mixing with cultivators and rotary speed mixers. Can be mixed in lifts up to 8 in. or more loose depth.

Friable SiltvJ-\ These soils take water readily. They can often be handled economically by diking and and Sandy Soils ponding or cutting contour furrows in pit and flooding until the desired depth of moisture penetration has taken place. That method requires watering a few days to 2 or 3 weeks in advance of rolling (depending on the texture and compactness of the soils) to obtain uniform moisture distribution. These soils can alao be handled by sprinkling and mixing, either in-pit ot on-grade, and require relatively little mix• ing. Mixing can be done with cultivators and rotary speed mixers to depths of 8 to 10 in. or more without difficulty.

Granular ftse and These materials take water readily. Best results are obtained by sprinkling and mix• Subbase Materials ing on the grade. Any good mixing equipnbit is adequate. 25 same proportion for sheepsfoot rollers plows, cultivators, or rotary mixers. as for other types, because some stock Rotary speed mixers, with their tail-hood models have about the same length of sections raised, permit good aeration tamping foot regardless of the contact and constitute one of the best methods of pressure and size of tamping feet In facilitating soil drying. any instance, the maximum lift thickness Where wet soils must be used and where which can be compacted in different soils dry soils are also available, the mixing should be determined during the early of the two has proved a good way to reduce stages of rolling on a project Small the excess moisture content in the wet differences in soil moisture may make soil. Rapid mixing can be accomplished the job values differ markedly. with the use of rotary speed mixers. Another method which has been used is Adding Water to Soil alternate-layer construction, where a layer of wet soil about a foot deep is cov• It is often necessary to increase the ered with a layer of dry, stable soil. The moisture content of embankment soils, thickness of the layer of dry soil is ad• subgrade materials, and base materials justed to that necessary to permit hauling to make it possible to obtain the desired equipment to be carried, so both layers degree of compaction and the uniformity. can be compacted sufficiently to provide a Due to the variable conditions encountered, stable embankment. there can be no single method nor piece If wet soils are encountered in only the of equipment which is always superior. surface soils, the simplest method is to The soil can be watered on the grade or in blade off or otherwise remove the ex• the pit Although sprinkling is most com• cessively wet topsoils. That will m many monly used, there are instances where cases permit construction to proceed watering can be done most economically using the subsoils. by flooding the pit, provided that the Wet soils can often be placed in the water soaks in readily to adequate depths. outer part of the embankment where they There are also some differences in the will not endanger the stability of the road• relative efficiency of various pieces of bed section and where they will dry suf• mixing equipment on different soils. ficiently to attain the necessary stability Table 13 summarizes some rules which before being covered with a second layer have been found to be useful in incorporat• of wet material, should the quantity of ing water into soils and base materials. wet material make that necessary.

Handling Excessively Wet Soil Sheepsfoot-Type Rollers

When the soil moisture content marked• The weight of the roller, the area and ly exceeds that needed to obtain the re• shape of the feet, and the spacing of the quired density, the moisture content must feet are variables in the sheepsfoot roller be reduced or the soil must be relegated to which influence compaction. Other var• a use where the excessive moisture con• iables include soil type, moisture content, tent is not detrimental. Drying great initial density, and thickness of lift quantities of soil from highway cuts is at The existence of so many variables makes best a slow and costly process. It has it difficult to present specific recom• been done successfully the use of ag• mendations on the selection and use of that gregate-drying kilns similar to those used type of roller without many reservations. in asphalt plants. However, most drying The best that can be done at this time is to has been air drying, which relies on aera• discuss the effect of the variables and then tion and exposure to the sun's rays to re• make recommendations based on the move excess moisture. In drying by trends which have developed to date. aeration, the object is to manipulate and The contact pressure should be as expose the wet soil to the air and sun and large as possible without greatly exceed• to keep mixing and reexposing wet soil to ing the bearing capacity of the soil. If promote the fastest drymg practicable. that is exceeded, the roller will sink Manipulation can be done by the use of deeper until greater contact area reduces 26

BL0W5 PER LAYER NUUBER OF PASSES LABCRATORY CGHPACT10N FIELD COUPACTION KAVT WEEPSFOOr ROLLER

Figure 15. Relationship between compac- tive effort and dry density (after Ckirps of Engineers). a 4 a 9 toniping fMt, 64 p«r dnim In rowi of 4 en 46 long by 42' In Dion Ttenplng foot pnsnrt tISp 11 lar soils, which depend on their fnctional 2J « zr lompUg fwl, 66 p but the inherent character of the roller "walks up" when contact pressure is sheepsfoot roller is such that stock models not too great (22). can seldom compact efficiently to depths The bearing capacity decreases with greater than 10 to 12 in. of compacted decrease in size of loaded areafor granu- thickness. TABLE 14

CONTACT PRESSURES AND SIZES OF TAVPING FEET BEST SUITED FOR COMPAaiNG DIFFERENT SOILS WITH SHEEPSFOOT HOLLERS

SOIL TYPE CONTACT AREA CONTACT PRESSURE REMARKS (sq. in.) (p.s.i.)

Friable silty and clayey These groupings are based on stock models sandy soils which depend for use m compacting to densities of about largely on their fnctional 7-12 75-125 95% AAEHO T 99 maximum density at moisture qualities for developing contents at or sli^tly below optimuir, when bearing capacity. 6- to 9- in. compacted lift thicknesses are developed. It is also based on the experi• Inteimediate group of ence that rollers are most easily towed clayey silts, clayey sands 6-10 100-200 when their weight allows them to begin to and lean clay soils which 'Vialk up" as rolling progresses. It is have low plasticity. realized that much heavier contact pressures may be more desirable if contact areas are Medium to heavy clays. 5-8 150-300 increased and that such increases are necessary if higher field densities are to be produced. 27

The spacing of the feet has a bearing umt contact pressures far in excess of on contact pressures and percent cov• those shown are being used and are giv• erage, that is, the actual area of tamp• ing good results. However, those rollers ing feet in contact with the ground in are settling to a depth which adjusts the one pass divided by the area passed contact pressure to that of the soil, hence over. Other things being equal, the do not walk up and require greater drawbar greater the tamping-foot area, the fewer pull for towing. It should also be borne passes required to compact the soiL It in mind that plastic soils at moisture has been shown in actual rolling tests (23) contents well below optimum require that random rolling will give 32 percent much greater contact pressures if ade• coverage in 4 passes and 53 percent cov• quate densities are to be obtained. erage in 8 passes of a roller having 64 3- Methods of Rolling. When commencing by-4-in. tamping feet per drum (42 in. compaction on a project, even though op• diameter by 48 in. long) and corresponding erators and inspectors are e:q)erienced, values of 19 and 34 for a roller having' it is well worth while to conduct tests on similar size drum but having 88 2%-by- trial lifts to determine the best rolling 2V4-in. feet per drum (SVis sq. in.). The procedure. Assuming there is no choice relationship between percent coverage and of equipment (as to size of tamping feet), number of passes is shown by the two then test rolling is limited to determining curves in Figure 14. The values given the best lift thickness which can be com• for the two rollers will serve to indicate pacted, the number of passes required comparable values for other rollers. for the major soil types encountered, The number of passes has large in• and the need for increasing or decreas• fluence on the degree of densification ob• ing foot pressures. Such test rollings tained. It has beenfound that the relation• should include a minimum of variables, ship between density and number of passes and the soil should be at optimum mois• is approximately a straight line when ture content. Usually three lifts are suf• plotted on semilogarithmic paper, as is ficient to show minimum rolling neces• the relationship found in the laboratory be• sary to produce the required density. tween number of blows and the density ob• For example, loose lifts of 6, 9, and 12 tained in the laboratory compaction test. in. are spread and strips of each are However, rolling beyond a given number rolled 4, 7, and 10 passes of the roller. of passes is uneconomical. Comparable Density tests will indicate the most effec• relationships are shown in Figure 15. tive combination. If the roller walks up An additional factor influencing selec• too fast and densities are inadequate, the tion of the proper sheepsfoot roller is the hft thickness may need to be reduced or rolling radius, because it determines in the foot pressure increased, or both; some degree the force required for towing contrariwise, if the roller does not walk as well as its maneuverability. The up or sinks deeper with increasing number smaller the rolling diameter (diameter of passes, the shear strength of the soil of drum plus feet) for a given weight, the is being exceeded and the foot pressures greater is the drawbar pull both in the need be decreased by removing ballast straight-away and m turning. from the roller. In either instance the moisture content may need adjustment. The factors to be considered in the selection of a roller which will compact The length of the roUed area, while the soil to the desired density in the otherwise not significant, may have large least amount of time are: (1) select the influence on densities in hot summer maximum contact pressure which the soil months when evaporation is high. Quick can carry without shear failure as evi• handling of soils on the grade often means denced by failure of the soil to compact the difference between adequate densities under rolling, and (2) select the roller with few passes and the addition of and whicH satisfies No. 1 and which also gives mixing m of water. Routing construction the greatest coverage per pass. equipment so its compacting effect is Table 14 may be used as a guide in the well distributed may decrease materially selection o! rollers for three broad groups the rolling required. Roller speed, of soils. It must be borne in mind that within the range normally used in towing 28

TABLE 15 RANGE OF QOHPRESSION OF 3-WHEEL ROLLERS

Weight Gtoup Range of Compression of Drive Ralls Light (5 to 6 tons) ISO to 225 lb. per lin. in. of width of drive rolls Medium (7 to 9 tons) 225 to 300 lb. per lin. in. of width of drive rolls Heavy (10 to 12 tons) 300 to 400 lb. per lin. in. of width of drive rolls sheepsfoot rollers behind tractors, has little influence on effectiveness. The proper balance between earth- moving equipment and compaction equip• ment is necessary if compaction is to be adequate and economical. Productive capacity of a given group of trucks, wagons, or scrapers can be estimated for any given group by the number of units of each size delivered to the dump. The roller capacity of sheepsfoot rollers in I S 4 terms of cubic yards of compacted soil ROLLER SPEED (UPHJ can also be determined with reasonable accuracy. The two values should balance Figure 17. Maximum rolling capacity of as nearly as possible, with ample reserve 3-wheel roller. (Eased on 10- to 12-ton nominal size having 20-in.-wide rear rolls spaced 36 in. apart providing 2-in. over• lap and complete coverage by rear rolls, 6-in. compacted lift).

roller capacity available if conditions change from a soil which rolls with a minimum of rolling to one which requires greater effort Figure 16 shows graphically the maxi• mum possible productive capacity of a given sheepsfoot roller (dual-drum type with 4-ft. drums) for different numbers of passes and different operating speeds when compacting a 6-in. compacted lift. Similar charts may be constructed for other thicknesses of lift Since increases in speed within rea• sonable limits do not change the effec- TABLE 16 RANGE OF (DMPRESSION OF 3-WHEEL HOLLERS OBTAINED BY BALLASTING

Weight Compression Pressures S 4 5 Class in Lb. j>er Un. In. of Width of Rolls RXLER SPEED (UPH) Guide [toll Drive Roll •

Figure 16. Maximum rolling capacity of 5- 6 99-129 153-196 sheepsfoot rollers (based on 6-in. compact• 6- 8 119-162 178-241 ed lift and 8-ft. compacted strip with no r/4-10 136-177 218-284 overlap; continuous operation). 9-12 157-212 236-317 29

type have long been used to obtain com• paction of soils. Tandem-type rollers are not widely used for earth work but are used for final surface compaction of subgrades and bases. Normally the 3- wheel type is used in earthwork com-

XKXX)

2 3 4 9 6 ROLLER SPEED (MPK) Figure 18. Maximum rolling capacity of 3-wheel roller (on same basis as Fig. 15, except 9-in. compacted lift). U400 tiveness of sheepsfoot rollers, it may be seen in Figure 16 that the productive capacity is directly proportional to the operating speed. This makes it worth• while to consider speed when specifying 2 9 4 roller hours. ROLLER SPEED (MPK)

Smooth-Wheel Power Rollers Figure 19. Maximum rolling capacity of 3-wheel roller (on same basis as Fig. 15, Smooth-wheel steel rollers of 3-wheel except 12-in. compacted lift). TABLE 17 PRESSURE AND WEIGHT CLASSES OF 3-WHEEL HOLLERS SUITED FOR COMPACTING DIFFERENT SOILS

Soil Group Weight Group and Pressure (Wt. per Lin. In. of Width of Rear Rolls) Clean, well-graded sands, uniformly Cannot be rolled satisfactorily with graded sands (one size), and some 3-wheel type rollers gravelly sands having little or no silt or clay Friable-silt and clay-sand soils 5 to 6 tons, 150-225 lb. which depend largely on their fric- tional qualities for developing bear• ing capacity Intermediate group of clayey silts and 7 to 9 tons, 225-300 lb. lean clayey soils of low plasticity (<10) Well-graded sand-gravels containing 10 to 12 tons, 300-400 lb. sufficient fines to act as filler and binder Medium to heavy clayey soils 10 to 12 tons, 300-400 lb. 30

vides adequate area to equalize the unit pressure. The 3-wheel type has the advantage of giving complete coverage wherever the drive rolls pass. The passage of the guide roll often compacts the soil suffi• ciently to build up a bearing capacity adequate for the drive rolls. The heavier umts of this type (10 to 12 tons or great• er) can often compact lifts of 10 to 12 m. or greater in depth, especially on friable, fine-grained soils. The proper balance between capacity of hauling equipment and roller capacity is important for 3-wheel rollers. If 1900 IB. W0B8LC WHCEL LOAD, e PUSES sheepsfoot rollers are towed by tractors 20,000 LB WHEEL LOAD 4 PASSES having adequate capacity, they -are more S 40,000 LB WHEEL LOAD. flexible in terms of capacity, because BTAHOARO AASHO HODIFIED AA8H0 their towing speed can be increased or decreased. That range is not so great

WATER CONTENT (PERCENT DRY WEIGHT) for 3-wheel roUers. The charts shown in Figure 17, 18, and 19 permit rapid Figure 20. (Comparison of field and lab• estimate of the rolling capacity of 3-wheel oratory compaction data for clayey sand rollers of lO-to-12-ton capacity for com- (after (Corps of Engineers). paction, because of the greater pressure exerted by the rear (driving) rolls. Rollers of the 3-wheel group may be obtained in a wide range of sizes and weights. The 3-wheel types may, for convenience, be divided into three weight classes. The weight classes and the ^- proximate range of contactpressures, ex• pressed in terms of pounds for linear in. of width of tire on the drive rolls, are given in Table 15. Some manufacturers make no provision for ballasting 3-wheel-type rollers to provide a range of compression for a given weight Others do, however, pro• vide for ballasting to give a range between maximum and minimum pressure suf• ficiently great to be of value in adjusting u 600 a given weight class for best performance on different soils. An example of one manufacturer's specifications is given in Table 16 to illustrate the range of compression which may be obtained by ballasting. The principles which govern the re•

lationship between contact pressures and 4 6 8 compaction apply to 3-wheel type rollers ROLLER SPEED (M.PM) equally as well as to the sheepsfoot tjrpe; Figure 21. Maximum rolling capacity of 3-wheel rollers adjust their contact pres• pneuniatic-tire roller (based on 2-axle, sures to the bearing capacity of the soil 13-wheel, type, rolling width, 84 in, no by simply sinking to that depth which pro• overlap, 6-in. compacted lift). 31

Figure 22. Heavy single-axle, multiple-wheel vibratory, pneumatic- tire compactor. TABLE 18 CONTACT PRESSURE OF PNEUMATIC ROLLER SUITED FOR COMPACTING DIFFERENT SOILS

Soil Group Contact Pressure Clean sands and some gravelly sands. 20 to 40 psi. inflation pressure, the greater pressures with the large size tires. Friable-silty and clayey sands which depend largely on their frictional qualities for developing bearing 40 to 65 psi. inflation pressure. capaci ty. Clayey soils and very gravelly soils.

65 psi. and up inflation pressure.

Figure 23. Grid Compactor. 32

Figure 24. Heavy, oscillating multipie-wheel pneurr.atic-tire compactor. pacted lift thicknesses of 6, 9, and 12 in. lift with a 1, 500-lb. wheel load as is ob• The use of test strips to determine tained in a 6-in. compacted lift with a the best lift thickness is equally as worth• 10, 000-lb. wheel load. That does not hold while for the 3-wheel type as for the equally true for cohesionless soils, which sheepsfoot type, if the most economical depend largely on their frictional quality compaction is to result. Table 17 may be for developing support. Here the larger used as a general guide to estimate the the size of tire, the greater is the size of range of lift thickness for the weight of the the loaded area and the greater the con• roller. Those values, however, do not fining effect. hold if moisture contents differ materially The experiments of the Corps of Engi• from optimum. neers (24) furnishproof of the above state• Some 3-wheel rollers have little or no ment. Figure 20 shows that the 1, 500-lb. provision for ballasting; therefore, it is wobble-wheel roller and the 20,000 and important to select the best weight for the 40, 000-lb. wheel loads developed densities prevailing conditions. Table 17 gives within about 2 lb. of each other. The data the approximate ranges of pressure and are not directly comparable because six weight classes of 3-wheel rollers suited passes of the 1, 500-lb.-wheel-load rol• for compacting different soils. ler were used, and the lift thicknesses may not have been proportional to the Pneumatic-Tire Rollers wheel load, but they do illustrate the relationships involved. The pneumatic-tire roller, like the Thus, the contact pressure is a major 3-wheel type, depends on area of contact factor in obtaining densities and the pressure (the contact pressure is equal to wheel load and number of passes are the inflation pressure plus some pressure due to sidewall stiffness), number of cov• erages, and thickness of lift. The area of contact and the contact pressure bear a relation to each other and to the total load of each wheel. If the contact pressure is constant, for given tire equipment, in• creasing the total load will not increase the density obtained in rolling. However, increasing the load will increase the size of the loaded area and the effective depth of compaction. Thus, for example, it is Figure 25. Heavy mu1tipie-wheel oscil• possible on a given soil to obtain approxi• lating, pneuir a ti c - ti re compactor with mately equal density in a 3-in. compacted indivi

Figure 26. Very-heavy, tnul tip 1 e-wheel , oscillating, pneumatic- tire conr^pactor. 34

ROGER H.COWKNm OAYTON.O

V

.-5

Figure 27. Tanderr. roller with segmented guide roll.

NEW TYPES OF ported by the axle, and held in place by COMPACTION EQUIPMENT flexibly mounted linkages; and a pair of unbalanced, weighted shafts which rotate Several new types of compacting e- and are timed with gears to produce a quipment, some of which have shown vertical vibrating force which will operate promise of giving effective and eco• at speeds of 600 to 1, 400 rpm. A photo• nomical compaction have recently come graph of one of the units is shown in Fig• on the market: ure 2.

Pneumatic -Tire Compactor with Vibratory Heavy Pneumatic-Tire Rollers Unit Several manufacturers are now pro• This unit is built in two sizes, 30-ton ducing pneumatic-tire rollers of much and 12y2-ton. The 30-ton unit has two 24- greater weight than the multiple-wheel by-33 tires (36 ply). The 12y2-ton unit types which have been produced and in has four 12-by-20 tires (14 ply). The common use for many years. It is now unit consists of a heavily loaded frame• possible to obtain heavy pneumatic-tire- work superimposed on coil springs, sup• roller units of 50-, 100-, 150-, and 200- 35

Figure 28. Tanden roller with vibratory intermediate roll. ton gross weights with maximum wheel types, oscillating units with two wheels loads of 50 tons. Tire pressures range per axle, and individually loaded wheel upwards to a maximum of about 150 psi. units. Examples of some of the heavy The units include single- and dual-axle and very heavy pneumatic-tire roller

#1*

Figure 29. Small, hand-operated self-propelled, vibrating-baseplate compactor. 36 units are shown in Figures 24, 25, and 26.

Grid-Type Steel-Wheel Rollers

This type may consist of a towed type somewhat like a sheepsfoot roller, ex• cept that the tamping feet are replaced by an open, square-mesh grid work, as is indicated in Figure 23, or may consist of a 3-wheel roller in which the com• pression rolls are equipped with grids. The towed units, when equipped with ballast boxes, can be loaded toproduce compression pressures in excess of 300 lb. per lin. in. of drum width. Figure 30. Large, hand-operated, self- Three-Wheel Type with Scalloped Ribs on propelled vibrating-baseplate compactor. Rolls Vibrating- Base Compactors A 16-ton, 3-wheel type of roller now comes equipped with a series of scalloped This type consists of a vibratory unit ribs on the wheels. Rear rolls have five mounted on a base plate. Previbration scalloped ribs around the periphery of each set up in the base plate is transmitted to wheel, the scallops being 4 in. high, 2 in. the ground setting up a movement in the wide, and 13 in. long at the base and soil which has been found effective in spaced 272 in. apart from one inside compacting granular materials. One type edge to the other (4V2 in. center to cen• of unit is a light-weight compactor similar ter). The position of the scallops in each to that illustrated in Figure 29. Another row is staggered, and the transverse type is illustrated in Figure 30. This angle (with the axle) of the scallops is larger unit is constructed in different reversed on the two wheels. The guide sizes ranging from small self-propelled roll has 2-in. -high scallops about 8 in. units to large tractor-towed units. Fig• long. The heavy weight (11,470 1b. per ure 30 illustrates the self-propelled unit. drive wheel) permits a wide range of compression pressures, depending on Tampers the area of scallops in contact with the ground. Tamping of trench backfill has been done largely by hand tampers (see Cur• Tandem Type with Segmented Front Roll rent Practice) or by hand-manipulated mechanical tampers (largely pneumatic A conventional tandem roller has been type). Recently a pneumatic-type pave• built with the guide roll constructed in ment breaker has been used successfully segments somewhat resemblii^ a sheeps• in compacting trench backfill. Two ad• foot roller with large rectangular tamp• aptations of thepavementbreakerforcom• ing feet. This type is illustrated in Fig• pacting backfill are illustrated in Fig• ure 27. ures 31 and 32. Figure 31 shows one of the smaller machines which straddles the Tandem Type with Vibratory Intermediate trench. Figure 32 illustrates one of the Roll larger machines capable of compacting backfill in wide, deep ditches. The unit consists of a heavy-duty tan• A gasoline-driven, manually-operated dem-type roller in which the center roll rammer has been used in compacting back• is energized by a motor unit mounted fill adjacent to structures, in trenches, directly above the center roll. Its prin• and in restricted areas which cannot be cipal use, to date, has been in the com• reached by motor-driven equipment. paction of macadam bases (Fig. 28). This type is illustrated in Figure 33. 37

Figure 31. Pneumatic-driven pavement breaker adapted for con pacting trench backfill.

euaco

Figure 32. Pneumatic-dnven pavement breaker fitted on unit for compacting backfill in wide trenches. 38

The rammer operates on regular grade until thoroughly compacted," some control gasoline. It makes 50 to 60 jumps per of density can be insured through control minute, the height of jumps being about 13 of moisture content to give the best re• to 14 in. Productive capacity may range sults. Under conditions of control of from about 150 to 250 cu. yd. per 8-hr. moisture the standard AASHO compaction day, the rate depending on the nature of and field density tests can serve as useful the soil and the degree of densification guides for obtaining compaction. required. Moisture Content and Density Control FIELD CONTROL OF COMPACTION Inspection and Test Methods. Inspec• The nature of the specifications de• tion and testing for control of moisture termines, in large measure, the nature content and density begin with determina• of methods of testing and inspection for tion of moisture-density relationships the control of compaction. If specifica• for the soils to be compacted. The pro• tions govern only the number of passes or cedure given for "Standard Method of Test coverages, control lies only in inspection for the Compaction and Density of Soils by counting the number of passes actually AASHO Designation: T 99-49" is recom• made or, on a general basis, by bal• mended for use. The method "is also ap• ancing the equipment and inspecting to see plicable for determining the moisture- that rolling is continuous as long as mate• density relations of soils compacted at rials are moved. It provision is made for other degrees of intensity produced by controlling the moisture content as well varying the weight of the rammer, the as the number of passes, or "rolling height of drop of the rammer, the num-

Figure 33. Gasoline-driven rammers for compacting soil in re- stricted areas. 39 ber of blows per layer, or the number Proctor penetrometer method of deter• of layers of soil compacted. " That com- mining soil moisture is sufficiently ac• pactive effort which is necessary and curate for most field purposes. It con• practicable to produce the desired den• sists of determining the resistance to sity should be used. penetration when the point is forced There are several factors which may steadily into the soil (when compacted influence the values of maximum density in the mold under a standard procedure) and optimum moisture content obtained in at the rate of V2 in. per sec. to a depth the test Individually they seldom intro• of 3 in. (25). The penetration resistance duce serious errors, except in some types must be measured in the mold and not in of soil. However, if the individual er• rors are added, the standard values may be difficult to use as a basis for inter• zpoo preting the results of rolling. Some of those factors are: (1) initial moisture content of the soil (before increments are 1,600 added in the test); (2) temperature used in drying to determine moisture content; (3) rigidity of the mold during compaction; 1^00 (4) degradation of soft granular particles Wet Density Penetration during preparation of sample and testing; Resistance (5) method of handling large proportions of 800 plus-4 aggregates; and (6) amount of manipulation during the test. Determinations of moisture content and density of rolled soils are often 400 done under one overall test procedure. However, because there are several ac• ceptable methods in use, they are de• scribed here separately. There is no one best way of determining moisture con• tent, because the reliability and speed of any method depends, in a large measure, on the individual making the determina• Dry Density tion. The following methods are de• scribed: Examination Methods. Experienced engineers, after they have become famil• iar with soils, can often judge moisture contents of soils very closely by exam• ination. Friable soils contain sufficient moisture at optimum to permit forming 14 18 22 a strong cast by compressing the soil in Mosttire Content - Percent the hand. Some clay soils have optimum moisture contents (AASHO T 99) approx• Figure 34. Density and penetration curves imately equal to their plastic limits. (after 'Public Roads"). Often the amount of moisture in those soils the rolled material. It can be used in the can be judged closely at those moisture rolled soil as an approximate means of contents at which a ribbon, thread, or estimating density, provided the operator cube can be formed of the sample. Stand• has developed the experience necessary to ard rules have not been written for those interpret density by that means. Ex• means of appraising the amount of soil amples of density-moisture relations and moisture. They can be learned only relation between penetration resistance by practice and should be used by the and moisture are shown in Figure 34. experienced. Caution should be taken in the use of Proctor Penetration Needle. The the penetrometer. If the soils contain 40

f/a 2 100 Ue

16 18 20 22 24 26 28 MOISTURE CONTENT {PERCENT OF DRY WEIGHT)

Figure 35. Wet-weight - dry-weight relationships for determin• ing moisture content from in-place wet densities and laboratory moisture-density data (after Goldman). gravel, the penetrometer is apt to give wet density was found to be 120 pcf. That erroneous results. It may be seen from density line intersects the dry-density Figure 34 that the penetrometer becomes curve at 101. 5 pcf. (dry weig^it) and 18. 2 less and less sensitive to moisture percent moisture. Since the samples change the wetter the soil becomes above were identical in moisture content, that optimum. of the rolled earth-work was also 18. 2 When laboratory moisture-to-density- percent The wet-rolled density of 115 relationship curves are available, the pcf. corresponds to a dry density of 97. 3 moisture content and dry density can be pcf. estimated with reasonable accuracy with• Drying to Constant Weight The most- out the aid of the penetrometer by using accurate method of determining mois• the wet weight of the soil after recom- ture content is that of drying to constant pacting it in the mold after obtaining the weight in an oven at a temperature of 110 in-place wet density. C (230 F,) - see AASHO T 99-49. It is First, the lines showing the wet den• not often that temperature-controlled sities corresponding to various com• ovens can be set up on construction pro• binations of dry density and moisture con• jects. Small ovens which can be heated tent are drawn on the graph of the dry- by gasoline stoves can be used. Another density - moisture - content relationships alternate is that of drying in an open pan as indicated in Figure 35. The following over a stove. These methods can be example will illustrate the method: handled satisfactorily only if the operator A soil sample from the rolled earth• IS cautious in keeping the temperature work was found to have a wet density of under control and does not overheat the 115 pcf. The same material taken from soil. the rolled earthwork was recompacted in Evaporating to dryness may be done the compaction mold to determine the re- in accordance with the foUowingprocedure: compacted wet density. The recompacted 1. Obtain a representative sample of 41 about 100 grams or less, the size to be consists of thoroughly dispersing the soil convenient and within the accuracy of the in alcohol and determimng the amount of scale used. water removed from the soil by the alcohol 2. Weight sample and record weight. by measuring the change in specific 3. Spread soil to uniform depth in a gravity of the alcohol by means of a pan. hydrometer. 4. Place in oven or, if drying over Another method (29) involves the use of burner, place in a second pan to aid in a pressure-type volumeter which can be preventing burning. used to measure the volume of specimens 5. Dry to constant weight at a temper• and to determine the percentage of water ature of 230 F. (110 C.). If over stove, in the soil by means of air pressure. stir often to prevent overheating. There are several other methods for 6. Allow to cool sufficiently to handle. determining soil moisture which are in 7. Compute moisture content as the developmental stage but which have follows: not been used sufficiently to test their reliability. Each of the methods de• Percent _ wt. wet soil - wt dry soil ^ scribed above is reliable. There is some moisture wt. dry soil difference in the relative accuracy of the methods. Drying to constant weight at a The alcohol-burning method may also constanttemperatureof 110 C. is the most be used to evaporate to dryness. That reliable. The alcohol method is equally method consists of mixing damp soil with reliable if at least three burnings are sufficient denatured grain alcohol to form used. The penetrometer and the wet- a slurry in a perforated metal cup, ignit• density methods are reasonably qmck ways ing the alcohol, and allowing it to burn off. of estimating moisture content and are The alcohol method will produce resists not intended to yield values having the ac• equivalent to those obtained under careful curacy of the drying methods. They can, laboratory drying. A perforated metal however, if used by e:q>erienced op• cup (26) is used for drying the soil. The erators, be made to yield values within suggested procedure is as follows: one or two percentage units of the correct value where care is taken in their use. 1. Weigh perforated cup with filter paper in place in bottom. Record weight. In-Place Density Measurement. There 2. Obtain representative sample of are a numt)er of methods which are suit• about 25 to 35 grams. able, both in speed and reliability, for 3. Place sample in cup and weigh use in determining in-place wet and dry sample and cup and record weight. densities of soils. Standard methods of 4. Place perforated cup in outside Test for the Field Determination of Density metal saucer and stir alcohol into the soil of Soil In-Place, AASHO Designation T sample with a glass rod until the mixture 147-49, provides procedures for two gen• has the consistency of a thin mud or eral methods, namely; the undisturbed- slurry. Clean rod. sample method and the disturbed-sample 5. Ignite the alcohol in saucer and method. sample and bum off all alcohol. The undisturbed-sample method con• 6. Repeat the process three times, sists of removing a sample in as nearly each time completely burning off the as is practicable the undisturbed state. alcohol. Properly designed sampling tubes will, 7. Weigh perforated cup and dry soil in most instances, cause only very minor after third burmng. The weight of dry changes in soil moisture content and soil equals this weight minus weight of density. The method of obtaining a sam• cup and filter. ple with a minimum of disturbance con• 8. Calculate moisture content as shown sists of removing the soil, by use of under the previous method shown above. small, sharp hand tools (for example, There are other methods which can be a knife) from around a column of soil. used for field determination of soil mois• The column of soil may then be coated ture. One of these, proposed by Bouyoucos with a known weight and volume of paraf• (27) and further developed by Bonar (28) fin and the volume of the column deter- 42

computing density from volume and weight CEETB mSTUR QF CRY we 0 measurements are generally similar for

TYPICAL various methods and are not given here. MOISTURE Nearly all methods have some weak• DENSITY nesses. Each method must be used with CURVES an understanding of its shortcomings. The sand method is reliable if: 1. The means of depositing the sand in the test hole is uniform from time to time for different operators. The cone method of depositing the sand has given good results. 2. The sand is calibrated frequently to determine its weight per cubic foot. That weight may vary some from hour to hour with changes in temperature and humidity. 3. The sand is uniform in size dis• tribution and yields consistent results. Standard Ottawa sand has given good re• sults. Some operators have found screen• ed concrete sand (usually passing the No. 10 sieve) to deposit to a uniform density. Others use sand fractions, usually be• tween No. 10 and No. 40 sieve. The im• portant thing is to test for uniformity in deposition. 4. There are no large aggregates pro• truding from the edges of the hole which caimot be surrounded with sand or there are no large cavities which cannot be filled by the sand depositing to its natural angle of repose under the method of deposition used. 5. There is no jarring which will M01STUBE=.PERCEMT OF DHY'wpCHB settle the sand, either in the test hole during measurement or in the container Figure 36. Typical moisture-den sity during calibration. curves (prepared by Ohio State Highway Testing Laboratory from tests on 10,000 6. Care is taken to preclude soil from Ohio soil samples). reused sand. The oil method is not satisfactory in mined by means of a syphon-type over• materials which are so porous that oil flow volumeter. permeates into cavities adjacent the test The disturbed sample method consists hole. The rubber-balloon method is ac• of digging a hole and removing the soil curate only if sufficient air pressure is by means of an auger or small hand tools used to insure that the rubber membrane (for example, a spatula and a spoon), completely surrounds protruding aggre• weighing the removed moist soil, and de• gates and completely fills the test hole. termining the moisture content and the The undisturbed - sample - overflow - vol• dry weight of the soil thus removed. The umeter method has no value in soils so volume of the hole represents the volume friable they will not hold together. The occupied by the soil. That volume may drive-tube method, sometimes called the be determined by means of dry sand or "undisturbed - core method," loses its oil of known volume-weight The rubber- value unless it produces a core of length pouch method has also been used. The equal to the depth of removed material. procedures for measuring volume and Moisture - Density Relationship. De- 43

MolstureContent- Psrcent of Dry Weight 6 8 10 12 14 16 18

3200

2600 2400 2200 ^2000

I rypa'A'Soil I—i rype"B"Soil OT 1400 I IjVpeVSoll

9 1200 TypeVrSoil 600 to 32901 Needle VltorMno Range Type's*^! 600 to 2290 N6Sdlo Woffc RQnQ6 I ^ I—: 1 TypeVSoil 600 to 1600 I Needle Range

CTypeTTSoil Maximum Field e'ersoii Rofler Curves rypeVSon

iType'CTSoili IOOO%-77.3% Roller curves move down Working Range and to the right as mois• Type'^Soil i ture ceases to be uniformly IOO.O%-9a3%ofOpt, distributed in the soil Wo{|ilng Range TypeVSoil | 1 1000% to 33.3% of Optimum Moisture Wbrlcing Range

6 8 10 12 14 16 18 Moisture Content - Percent of Dry Weight

Figure 37. Sample embankment-control curves for typical curve chart, sets A, B, and C, Noverber, 1941, (after 'Wyoming Soils Manual," 1949). 44 termination of optimum moisture con• cross the 122 pcf. line and the 800 psi. tent and maximum density in accordance penetration line in Figure 36 gives: with AASHO Method T 99, or some mod• ification thereof, can be determined by GirvB Moisture Content Moisture Content test in the field laboratory as well as in at 122 pcf. at 800 psi. the central laboratory. However, it is P often necessary to make determinations 17.5 18.4 0 19.5 19.3 more rapidly than can be done by Method R 22.5 20.5 T 99 or some modification of it One method for rapid determination of opti• mum moisture content and maximum den• An examination of the above values sity is that developed in Ohio by Woods and indicates that a moisture content of 19. 3 Litehiser (30). They found that moisture- to 19. 5 denotes Curve Q as the one which density curves have characteristic shapes, most nearly fits the soil in question. the curves for the higher-weight materials Wyoming (31) adopted 20 curves and assuming steeper slopes and their maxi• made some revisions. It found that the mum densities occuringat lower optimum moisture content, as determined by dry• moisture contents. Most soils having ing, often was at variance with the mois• similar maximum weight per cubic foot ture content indicated on the standard, give identical moisture-density curves. typical curve chart at the point where the In the original set, based on 1,088 needle penetration readings and the wet Ohio soil samples, 9 typical curves were weight per cubic foot would line up verti• used. The samples tested were placed in cally on a needle-penetration curve and groups depending upon their wet-weight wet-weight curve of the same number. peaks. As additional tests were made, That indicated difference in moisture con• additional typical curves were added. The tent would change the corresponding dry set in current use, based on 10,000 tests, weight IS shown in Figure 36. Soils having practically the same maxi• In determimng the type of curve to mum dry weight would sometimes differ so use for the soil in question, two easily much in the slope of curves to the left of made steps of the field test for embank• optimum that it would not be possible to ment control are required. The first arrive at a correct maximum dry weight consists of compacting the soil, for which and optimum moisture content unless the the density curve is desired, into the penetration reading and wet-weight de• density cylinder in the standard manner terminations were made at nearly opti• and calculating the wet weight per cubic mum. Figure 37 indicates the typical dif• foot. The second consists of determining ferent curve slopes on the dry side of the penetration resistance and then noting optimum for soils which have similar max• all possible typical curves in Figure 36 imum density and optimum moisture con• upon which the wet weight per cubic foot tent. To correct for those differences, in the cylinder just obtained falls and the two additional sets of typical curves were moisture content at these points. The prepared.' One of these had flatter-than- moisture contents from the wet-weight normal forward slopes (Type A in Fig. and penetration curves which most nearly 37) and the other hadsteeper-than-normal coincide designate the curve which most (Type C in Fig. 37), The differences in nearly approaches the true curve for the moisture content were accounted for by a material. special moisture graph placed above the wet - weight and penetration - resistance curves. Example After a sufficient number of four to SIX point curves has been determined by Let 122 pcf. equal the wet wei^t and test to establish the type of curve (A, B, 800 psi. equal the penetration resistance or C), the number of points may be re- of the soil compacted in the density cyl• inder. Tabulating the moisture content Because of space required tor the three sets of 20 typical at which the various wet-weight curves curves, they are not reproduced here 45 I I Unit Dry Weight Total Sample Vs Binder

140

u

130

120

|2 . Binder Is Fraction of Total _ •s Sample Passing ^ In Sieve I I I I 110 -Values Assumed for Rock 3% Absorption 2.46 BulkSpGr

5 OO

60. 80 90 100 110 120 130 140 150 160 Unit Dry Weight of Binder - Lbs. Per Cu. Ft. Figure 38. Chart for determining relation between dry->ol- uir.e weights of minus No. 4 fraction and total sample (after Shockley).

Water Content Total Sample Vs Binder

Water Content Ratios Are Independent of Unit Weights of Materials 3% Absorption Assumed for Rock

15 20 25 30 Water Content of Binder - Percent

Figure 39. Chart for determining relation between water con• tents of minus No. 4 fraction and total sample (after Shockley). 46 duced to one to three and the correct on the material passing the No. 4 sieve curve (or tabulated data) used for as• and from specific gravity and absorption sociating the penetration resistance and tests can be used for determining, by wet weight to obtain the correct dry calculation, the theoretical maximum weight dry weight and optimum moisture content It was found from the typical curves of the entire sample. that the amount of field moisture re• Case 1. Where the minus-4 material quired to secure the same percent of is sufficient in quantity to fill the voids compaction with the roller varies with in the plus-4 material. the curve type, i. e., it is necessary to The maximum dry weight of the total work in a narrower moisture range closer soil is computed from the following to optimum with steep-curve soils (Type f orinula: C) than with flat-curve soils (Type A). A WjXW^ method was developed for calculating the approximate minimum moisture content t F W^ + C W^(l + A^) where required for a sheepsfoot roller having a contact pressure of 325 psi. to obtain 90 W. Dry weight per cubic foot of entire to 95 percent of maximum dry weight in sample at its optimum moisture the field when the moisture is well dis• content. tributed through the soil and lifts are 5 in. W, Dry weight per cubic foot of minus- or less loose depth. No. 4-sieve material at its optimum Determination of the minimum moisture moisture content content is done by (1) determining the W = Weight per cubic foot of plus-No. 4- curve type, (2) selecting the percent of sieve material = sp. gr. x 62.4 = maximum dry weight which wUl define 153.5 minimum moisture-content requirements, F = Percent minus-4 material expressed (3) plot the dry weight thus obtained (see as a decimal. Fig. 37) on the dry side of the dry weight C = Percent plus-4 material expressed curve. The vertical line through that as a decimal. point (Fig. 37) indicates the minimum A = Percent absorption of plus-4 ma- moisture content The 95 percent-den• ^ terial expressed as a decimaL sity point, which is usually about the maximum that can be e3q)ected from the roller, is plotted on this line of mini• If test data: mum moisture content Remain on No. 4 Sieve The working moisture content is the average of th^ minimum and optimum 35% = 0. 35 moisture contents. The working range 2. 46 = sp. gr. is between the two values as is indicated Absorp. 3% = 0. 03 in Figure 37. Correcting for Coarse-Aggregate Con• Pass No. 4 Sieve tent The present AASHO Method of Test T 99 requires separation of the dried 65% = 0. 65 material on the No. 4 sieve and compac• ^ 117. 4 = pcf. dry wt. tion of that portion passing the sieve. It opt. m. c. =17% does not provide for determination of the compacted weight of the total soil (in• Then: cluding the plus-4 material) either by test or by computation. The same is true for ^ _ 117. 4 X 153.5 • the corresponding ASTM TestD-698-42T. ^t-.65xlS3.5 + .35 x 117.4 (1 + 0.03) _ 18020.9 _ 0, . Where it is desirable to calculate the weight per cubic foot and optimum mois• - 142. 068 - ^26- 82 pcf. ture content, for the entire sample it is The optimum moisture content of the total necessary to determine the specific material will be: gravity and absorption of the coarse ma• terials. Data from the compaction test Mj = (CA^ + FMj) where 47

M. = Moisture content of the total soil ly down to the bottom of the scale to 100 C = Percent retained on No. 4 sieve ex• pcf. which is the umt weight of minus-4 pressed as a decimal material desired. A = Percent absorption of material re• (B) Moisture content of minus-4- tained on No. 4 sieve expressed as a sieve material. On Figure 39 enter the decimal scale on the left side of the chart at 15 F = Percent passing the No. 4 sieVe percent moisture content and continue expressed as a decimal across to the intersection with the 50- M, = Moisture content of minus-No. -4- percent-plus-4-sieve line. From that '^f sieve material expressed as a deci• line read directly down to the bottom of mal the scale to 27 percent, which is the moisture content of the minus-4 ma• The umt dry weight of the minus-No. - terial. 4-sieve material can be computed from Case 2. Where the minus-4-sieve the formula: material is insufficient to fill the voids FWjW^ in the plus-4 material. Acceptable subgrade and fill material f W^ - W^ C (1 + A^) and base-course material can be obtain• If the test data are as given above then: ed in which the minus-No. -4 material IS not sufficient to fill the voids in the ^ _ 0. 65 X 126. 82 x 153. 5 plus-4 material. Reagel (33) has de• ^f ~ 153. 5 - 126. 82 X 0. 35 (1 + 0.03) veloped a chart and a nomograph to fa• 12653. 5 cilitate determination of standard dry = 107.78 = * P'^*- weights for that condition. The chart is reproduced in Figure 40 and the nomo• The moisture content of the minus- graph in Figure 41. No. -4-sieve portion will be In the chart, the dry weight of the M,- CA. minus-4 material has been determined M, as 112 pcf. and the specific gravity of the plus-4 material is 2. 55. The first step The percentage of rock, moisture con• IS to locate Point A in the parallelogram tent, and dry weight per cubic foot may of the chart at the intersection of the 112- vary from one individual sample to an• Ib. value with specific gravity of 2.55. other. It is desirable to compute the This point on the coordinates is the con• moisture and density relationships be• dition where the plus-4 voids are just tween total samples and the minus-No. - filled and shows the percent passing the 4 fraction and construct families of curves No. 4 sieve to be 33. 5 percent and the for different values of moisture content combined dry weight to be 139. 4 pcf. The and percent rock. Such charts have been material m question has only 32 percent prepared by Shockley (32) and are re• passing the No. 4 sieve. Then locate produced here as Figures^S and 39. The Point B by a 2. 55 line in the parallelo• curves are for coarse aggregate (plus- gram to a point at the intersection of 32 No. -4-sieve material) having a specific percent on the coordinate. The point on gravity of 2. 46 and an absorption value the other coordinate gives Point C and of 3 percent. The use of the curves is the solution as 135. 7 pcf. for the stand• illustrated by the following example: ard weight of the combined material. Given: Unit dry weight of total sample In the case of the nomograph (Fig. 41) = 120 pcf. Plus-No. -4-sieve material = the specific gravity given is 2. 45 and the 50 percent. Moisture content of total dry weight of the minus 4 material is sample = 15 percent. again 112 pcf. A straight line connecting To determine: (A) Unit weight of these values gives a value of 34. 7 percent minus-4 material. On Figure 38 enter (Point A). The material has only 33 the scale on the left side of the chart at percent passing (Point B) which is less 120 pcf. and continue across to the inter• than 34. 7 percent A straight line from section with the 50 percent plus-4-ma- Point B through the specific gravity value terial line. From that point read direct• of 2. 45 intersects the combined weight 48 Percent Passing No. 4 Sieve - By Weight 25 JO 32 35 40

5?

Figure 40. Combined dry-weight per cubic foot of rolled-stone base or stabilized-aggregate base when amount passing No. 4 sieve equals or is less than the voids (42 percent by volume) of the plus No. 4 material. The intersection of the coordinates of the parallelogram gives the conditions of minus No. 4 material ex• actly sufficient to fill the voids in the plus No. 4 material (after Reagel). line at 131. 9 lb. which is the standard dry terial increases until, at 100 percent weight per cubic foot for this material. coarse aggregate, the unit weight is that There are physical limits to any method of solid rock. Practically, according to of calculation of the influence of material Abercrombie (35) and also according to coarser than the No. 4 sieve on the weight Walker and Holtz (34), the weight of the per unit volume (in pounds per cubic foot) total material begins to decrease when of the total materiaL Theoretically, as the coarse aggregate reaches some value, the content of coarse aggregate is in• ranging from about 50 percent to 65 creased, the density of the total ma• percent, until the proportion of coarse 49

121- 122-

123- 124-

125- 126- 127-

128- 129-

130- 131-. 132-' / / 133-

•41 134- 130 t2 20 y 135- 40 2 25 y 136- 39 230 X 137- 125 38 2 35 y 08- 240/ 37 139- .^45 120 36 140- 2 50 141- 2 55 142- 1-34 -260 143- 115 265 33 144- 2 70 145- 32 no 2 75 146- 31 147- 30 148- 105 149-

150-

151- B2-

153- 154-

155- Dry Weight Percent Passing Specific Gravity Combined Weight Lbs PerCu Ft-«4 0^4 By Weight + #4 Lbs Per Cu Ft

Figure 41. Nomograph for determining combined dry-weights of base materials (after Reagel). 50

aggregate approaches 100 percent, when The 1951-52 survey was broadened further the unit weight approaches the unit weight to include data on compaction of granular for the coarse aggregate alone. bases to make this report of current

CURRENT PRACTICES IN COMPACTION METHODS AND EQUIPMENT TABLE 19 LIFT-THICKNESS REQUIREMENTS BY REGIONS The Committee on Compaction of Sub- Number of Organizations grades and Embankments of the Highway Thickness of Layer Before Compaction Total In Each Region Research Board made its first survey of m compaction in 1942. A second survey was 3-5 1 1 - Mountain made in 1946 and a third in 1951 and 1952. 6 13 1 - Pacific Data from the 1942 survey were published 1 - Mountain in Highway Research Board Wartime Road 3 - Middle East Problems 11, "Compaction of Subgrades 4 - Southeast and Embankments" August 1945. Data 4 - North Central from the 1946 survey were published in 6-8 1 1 - South Central Highway Research Board Bulletin 5, "Report of Committee on Compaction of 6-8-24 1 1 - Pacific Subgrades and Embankments" (1946). 8 14 5 - Middle East 1 - Southeast The 1951-52 survey attemptedto obtain 1 - South Central similar data to those obtained in previous 6 - Mountain studies to determine if any trends were 1 - Pacific apparent in current practices. In addition, 9 1 1 - Middle East the 1951-52 study included summaries of 9-12 1 1 - Northeast current state highway standard specifica• 12 10 7 - Northeast tions for compaction equipment and on 1 - Middle East methods of compaction of backfill of 1 - South Central structural excavation and trench backfill. 1 - North Central

DofC

Note Underlined figures give compacted deptli,remaining figures give depth before compaction

Figure 42. Current practices- depth of lift. 51 practices more nearly complete. Report• Control of Compaction ing of the data from the 1951-52 survey is made on the same regional basis as was Embankments. Compaction and mois• made in 1942 and 1946. ture control requirements for embank- mentshave changedsome, butnot greatly, Lift Thickness in Embankment Construc• since the 1946 report The results of the tion 1951-52 survey are given in Table 20 and in Figures 42 and 43. The 1946 report brought out that there Subgrades. The 1951-52 survey sought was a wide variance in lift thickness and information on methods of specifying showed that a majority of state highway compaction and moisture control for sub- departments specified a maximum lift grades. The results of the survey are thickness of 6 to 8 in., 17 organizations shown in Table 21. Thirty-four organiza• using a 6-in. -maximum and 13 using an tions indicated compaction requirements 8-in. -maximum lift thickness. Those did were no different from the requirements not include 7 organizations which had for embankments. The remaining replies more than one class of specifications, one indicated that closer attention, more rigid of which fell in the 6-or 8-in. -depth control, was beinggivento obtaincompac- group. The report also showed 8 organ• tion and moisture content in subgrades. izations which used a 12-in. -maximum Several states specify higher compaction depth of lift The 1942 and 1946 reports for subgrades. Table 21 shows a wide did not bring out whether the depth of lift variance in depth of compaction in the was depth before compaction or compacted subgrade zone. In most instances the thickness. depth was given as 6 m. or was considered The 1951-52 survey showed that of as surface rolling. Others required com• the state highway departments and the paction to a depth of 8, 12, 18 and 30 in., District of Columbia, 42 organizations as may be seen in Table 21. specify thickness of lift before compac• Bases. Previous surveys did not re• tion and 7 specify thickness of lift after cord the compaction given granular bases compaction. (stabilized bases, clay-gravel bases, and A summary of lift thickness require• sand-clay bases and other bases of natural ments of the 42 organizations by regions aggregates; this does not include crushed- is given in Table 19. rock bases nor bases containing plastic or Seven states specify compacted thick• cementitious binders). The 1951-52 sur• ness. Six require 6 in. of compacted lift vey indicates that about three eights of the thickness, and one has two classes of states provide for greater compaction of compaction - requiring 6 and 12 in. of bases than of embankments (see Table 22). compacted depth respectively. Those That is accomplished by decreasing lift states are all in the East. thickness, increasing roller weight, The states specifying the 6-in. lifts specifying higher densities, or otherwise (before compaction) specify slightly lower exercising more rigid control of rolling. average density requirements than does the group which specifies the 8-in. loose Cost of Compaction depth. That may be due inpart to the fact that those states contain fairly large Compaction is paid for directly in 12 areas of clayey soils which are difficult states at an average cost for each state to compact to high densities. ranging from 372 to 25 cents per cu. yd. It is significant that 7 of the 10 states with an overall average cost of slightly requiring a 12-in. depth before com• over 9 cents per cu. yd. Six of the e- paction are in New England, where gen• leven are from the Mountain States re• erally the soils contain hi^ percentages gion; two from the South Central and one of coarse material, and where fine-grained each from the Northeast, North Central, soils are friable and can be compacted and Pacific areas. In the remaimng in lifts of greater thickness than can states the cost of compaction is included heavy clay soils. in the bid price for excavation and borrow TABLE 20 CONTROL OF LAYER THICKNESS. COMPACTION AND MOISTURE CONTENT IN EMBANKMENTS

CONTROL OF COMPACTION CONTROL OF MOISTURE CONTENT

Thickness of Layer Region and State Compaction Requirement and Com• measurement Basis for control Provision for drying excessively wet soils Loose pacted (inches) (inches)

NORTHEAST Connecticut Satisfactory Mm 90% AASHO T 99 in Not speafled Not specified directly special cases Maine 12 max Satisfactory Not specified Not specified directly Massachusetts 12 max Mm 90% AASHO Modified Not specified Not specified directly Moisture content hmited by density required Michigan 12 max (1) Under 12 in layer method—satisfactory As required to obtain density If necessary to obtain density Also select 9 max (2) Controlled density method Min 95% As required to obtam density material having proper moisture content AASHO T 99 for fine grained soils to replace wet soils Min 95% Michigan cone method for granu• lar materials New Hampshire Satisfactory Min 6 passes of tamping type Not specified May be ordered to suspend work roller when "special compaction" Is in• cluded in special provisions New York Min 90% AASHO T 99 Sufficient to obtain required density Yea Rhode Island 12 max Satisfactory Not specified Not specified directly Vermont 12 max Satisfactory Roll until roller is entirely sup• Not specified Not specified directly ported by tamping feet Wisconsin Until no further compaction is evidenced Visual Material to be dried when excessively wet. under rollers

MIDDLE EAST Delaware 6 max Mm 95% of Modified AASHO ± 10% of optimum Yes By manipulation. Distnct of Columbia 6 max 90-100% AASHO T 99 (See compaction At least equal to optimum Yes By manipulation Table 1) Min 90% Max density on wet wt curve Shall not exceed 110% of optimum Yes No additional material may be placed AASHO T 99 Indiana 9 max Mm 96% AASHO T 99 for soils As required to obtain density As required to obtain density Kentucky 12 max Mm 90% AASHO T 99 for granular ma• As required to obtam density As required to obtain density terials Satisfactory Sprinkling reqmred by engineer Yes Shall be permitted to dry before being rolled Maryland 90-100% AASHO T 99 (see compaction Sprinkling if required by engineer Yes Shall be permitted to dry to a mois• Table 2) ture which will allow compaction Must not be above 2 percentage points above optimum percentage New Jersey. (8 passes of sheepsfoot roller), (5 passes of Not specified If too wet to support 3-wheeled roller is pneumatic tire roller), (4 passes of 3- considered necessary to dry wheel 10-ton roller), 90-95% AASHO T 99 (special projects only) Ohio S max 90-102% AASHO T 99 (see compaction Spnnkling if necessary to obtain density Yes Dned to moisture content not greater Tables) than optimum ± 2% Pennsylvania 8 max Satisfactory Not specified Yes Wet material if suiUble when dry shall be allowed to dry Tennessee Min 95% AASHO T 99 Optimum moisture content Air dry excessively wet soils on job Virginia 8 max Minimum 95% AASHO T 99 Optimum moisture content Yes Drying or mixing with dner soils before rolhng West Virginia 8 max 90-100% AASHO T (see compaction As required to obtam density Yes Drying until density can be obtamed. Table 4 SOUTHEAST Alabama 95-100% AASHO T 99 (100% in top layer) As required to obuin density Yes. By windrowmg Florida Average 95% of Modified AASHO with no Not specified test less than 90% Georgia 6 max Mm 96% AASHO T 99 As required to obtain density Yes. By drying until density can be ob• tained Mississippi 6 max Min 90% AASHO T 99 for clay soils, Mm Satisfactory As required to obUin density OUUUl V^tUUllUtt b max mm W7o AAon\7 1 99 unatir ni|[Q lypo I va trying a wo wet pavement SOUTH CENTRAL ArkanBos 12 max Satisfactory Moisture must be such that soil will com• Yea, so soil will compact properly pact properly Louisiana 8 Min 95% AASHO T 99 95% of optimum Yes Oklahoma 6 min Not less than 90% AASHO T 99 When directed by engineer Yes Texas 6 to 8 Minimum 90 to 100% AASHO T 99 For special projects in gumbo soil slightly Specifications require rollinfc immediately above to 6% below optimum after being brought to uniform moisture content No particular method of dry• NORTH CENTRAL ing specified Iowa 6 Usually to satisfaction of engineer Some Usually—as directed by engineer 90-110% Yes percentage of modified AASHO in unusual of optimum in unusual cases Knnffwp 6 max Tj^?eA—Mm 90% AASHO T 99 Sufficient to insure good bonding Yes, by manipulation 6 max Type B—Compaction until roller feet ride Sufficient to insure good bondmg Yes, by manipulation surface of compacted lift 6 max Type C—6-16 passes of sheepsfoot type Sufficient to inure good bonding Yes, by manipulation roller Minnesota 6-12 (1) Ordinary compaction until no evidence Not specified Not specified of further compaction 6 max (2) Specified density method Generally As required to obtain density As required to obtain density. 97-98% AASHO T 99 Mlssoun 6 max Min 90% AASHO T 99 As required to obtain density As required to obtain density Nebraska 6 Min 90% AASHO T 99 (Except in sand 90% optimum ± 4 See Basis for Control hill region where compaction with con• struction equipment is deemed adequate ) North Dakota 12 max Standard compaction—rolling with sheeps• Same as for extra compaction except no Yes Drying until desired compaction is foot roller until no further compaction is specific moisture values nor densities are obtained ^ obtained stated Provision for watering dry soils 12 max Min 95% AASHO T 99 when extra compac• Moisture content as determined by the Yes Drying until specified compaction tion IS specified on plans engineer can be obtained South Dakota 6 max Compaction until tamping feet do not pene• Not specified Sprinkling as ordered by Yes As directed by engmeer. trate appreciably in soil engineer MOUNTAIN Arizona 8 max Min 95% AASHO T 99 specified by special Not specified, but spnnkling is provided for Yes visions for high fills and finegrai n soils. Colorado 8 max 90% Modified AASHO T 99 95% on Optimum ± 2% is objective Yes. rgranular soils. Idaho (c) 8 (a) 90-100% AASHO T 99 (see Compaction Approved moisture content Provision for drying Table 1) (b) Compaction by routing all transporting Satisfactory to engineer Provision for drymg and earth moving equipment over entire width of each layer (c) Same as (b) above except top foot shall Satisfactory to engineer Provision for drymg be constructed in layers not exceeding 4 in loose thickness Montana 8 ihax 90-100% AASHO T 99 (see Compaction Not specified As directed by engineer Yes. Drying to proper consistency Table 4) Nevada 8 max Min 90% California method 85% on some Not specified As directed by engineer Not specified secondary roads New Mexico 6 max Min 95% on soils having AASHO T 99 max• Optimum to optimum minus 5% Yes imum density less than 120 p c ( Min 90% on soils having AASHO T 99 Optimum to optimum minus 6% Yea maximum density more than 120 pcf Utah 8 max 90 to 100% AASHO T 99 (See Compac• Based on optimum Ranges from 5 to 20 Yes tion Table 4) Wyommg 3 max Non-rolled embankment (Compacted with As directed by engineer Yes. Drying to permit acceptable compac• construction equipment.) tion 6 max r Satisfactory Try to obtain minimum 92% As directed by engineer Yes. Drying to permit acceptable compac• AASHO T 99 tion. PACIFIC California 8 max Min 90% California method Optimum or as required to obtain density Oregon 6 max Min 95% AASHO T 99 in top 3 ft Mm As directed by engineer Y^ Permitted to dry when possible 90% below 3 ft Washington <1) 24 max (1) Satisfactory compaction by routing com• Not specified Not specified. paction equipment 8 max (2) Satisfactory compaction by rollmg Not specified Not specified [i! 6 max (3) Minimum 95% AASHO T 99 Optimum db 8% Optimum ± 3%

(a) Using modified AASHO on some current projects. (b) 12 in maximum in sone more than 3 ft. below surface of embankment 6 m maximum in top 8 ft of fill. CO 54

EMBANKMENT COMPACTION REQUIREMENTS TABLE 1

Standard of Compaction or Maximum Density obtained by AASHO Method Minimum Compaction Required T 99 (P C F.) (Percent of Maximum Density)

89 9 or less 100 90 to 99 9 100 100 to 109.9 95 110 to 119 9 95 120 to 129 9 90 130 and above 90

TABLE 2

CONDITION 1 CONDITION 2 Fills 10 ft or less in height and not subject to Fills exceeding 10 ft m height or subject to long extensive floods penods of flooding

Mimmum Field Com• Minimum Field Com• Maximum Laboratory Dry paction Require• Maximum Laboratory Dry paction Requirements Weight (P C F ) ments (Percent of Dry Weight (P.C F.) (Percent of Dry Weight) Weight)

89 9 and less * 94.9 and less *« 90-99 9 100 95-99 9 100 100-109 9 95 100-109.9 100 110-119 9 95 110-119 9 98 120-129 9 90 120-129.9 95 130 and more 90 130 and more 95

* Soils having maximum dry weights of less than 90 p c f. will be considered unsatisfactory and shall not be used in embank• ment Soils having maximum dry weights of less than 95 p c.f. will be consider^ unsatisfactory and will not be used in embank• ment under condition 2 requirements. TABLE 3

CONDITION 1 CONDITION 2 Fills 10 ft or less in height and not subject to Fills exceeding 10 ft in height or subject to extensive flooding long periods of flooding

Minimum Field Com• Minimum Field Com• paction Requirements paction Requirements Maximum Laboratory Dry (Percent of Labora• Maximum Laboratory Dry (Percent of Labora• Weight (P C F ) tory Maximum Dry Weight (P C F ) tory Maximum Dry Weight) Weight)

89 9 and less * 94 9 and less 90 0-102 9** 100 95.0-102 9 102 103 0-109 9 98 103 0-109.9 100 110 0-119 9 95 110.0-119 9 98 120 0 and more 90 120 0 and more 95

* Soils having maximum weights of less than 90 p c f will be considered unsatisfactory and shall not be used in embankment *• Soils having maximum dry weights of less than 95 p c f will be considered unsatisfactory and shall not be used in embank• ment under condition 2 requirements or in top 8 in. layer of embankment which will make up the subgradc for pavement or sub- base under condition 1 requirements Soil, in addition to the above requirements, shall have a liquid limit of not to exceed 65 and the minimum plasticity index number of soil with liquid limits between 35 and 65 shall be not less than that determined by the formula 0 6 Liquid Limit minus 9.0. TABLE 4

Maximum Density Obtainable by AASHO Method T-99-49—Pounds Minimum Compaction Required—Per Cent Per Cubic Foot of Maximum Density

90-99 100 100-U9 95 120 and over 90 55

S-95

90- ICQ 90-95

S-90-100(e)

b and 90-95 95 Mod DofC90«0 90Mod

kness

(a) Mini mum 6 passes of tamping when special compaction is specified (b) B posses of sheepsfoot roller 5 passes of pneumatic tire roller 4posses of 3 wheel 10 ton roller (c) Usually to satisfaction of engineers Some compoctio percentage of mod AASHO in unusual coses satisfaction engineers (d) Type A-90% AASHO T99 Type B-Solisfoctory Type C-6-15 posses of sheepsfoot roller (e) Includes satisfactory compoction byeorth moving equipment if) Try to obtain minimum at 92 percent AASHO T99

Figure 43. Ciirrent practices minimum compaction requirements for embankments. Values are percentages of AASHO T99-49 except as noted. and is difficult to determine. Five states which rubber-covered rolls operated at in which compaction is paid for indirectly different speeds to provide the mixing estimated its cost as ranging from 1 to 8 action. That machine also provided a good cents per cu. yd. with an overall average means of breaking down soils for making of slightly over 4 cents per cu. yd. the test. Oven drying or drying in open pans over Method of Testing electric, gas, or gasoline stoves were used in almost every state for drying Nine of the states which conduct the field samples for moisture - content laboratory compaction tests reported us• determination. ing new samples for each point on the The sand method of determining the compaction curve, the remainder of the volume of soils in the in-place density group reusing the remaining part of the test was reported in use in 25 states; sample after the sample for moisture the rubber pouch, or "balloon," in 7 content determination has been removed. states; the volumeter method in 4 states, Eleven states reported using mechan• and the oil method in 2 states. Some of ical mixers for incorporating water with the departments reported using more than soils for the laboratory compaction test. one method. Five of those adopted the Hobart food mixer to that use; five used Lancaster Backfilling of Trenches, Pipe Culverts type of laboratory mixer widely used for and Sewers making test batches of concrete, most of them using the 12-in. -diameter bowl with During July 1949 the committee spon• the muUer attachment; and one reported sored the publication of a review of the using a specially constructed mixer in then current "State Highway Standard TABLE 21 CONTROL OF COMPACTION AND MOISTURE CONTENT IN SUBGRADES 03 Depth of subgrade compaction Region and State .Compaction requirements and measuremt nts Moisture control requirements In cuts In previously compacted fills

NORTHEAST Connecticut Thoroughly and uniformly compacted 10-ton 3-wheel roller. No requirements specified Maine Compacted 10-ton, 3-wheel or approved pneu• matic tired roller. No requirements specified Massachusetts Compacted self-propelled roller weighing not less than 12 tons. No requirements specified Michigan When required, same as for embankments Same as for embankments New Hampshire Rolled to a firm unyielding surface with 10- ton, 3-wheel roller No requirements specified New York Min 95 percent AASHO T 99 for top 4 ft be• Not less than 8 inches No requirement low crown grade, 2 ft wider than pavement Sufficient to obtain density Same as for and downward and outward on 1 to 1 slope embankments Rhode Island Compacted uniformly with approved roller weighing not less than 10 tons No requirements specified Vermont Compacted with 3-wheel power roller Wisconsin No requirements specified Same as for embankments No requirements specified

MIDDLE EAST Delaware Minimum 95 percent Modified AASHO Constructing equipment will No requirement Optimum ± 10 percent probably compact sufliciently District of Columbia 90-100 percent AASHO T 99 (See compaction 12 inches 12 inch (old fills) table 1-S). At least equal to optimum Illinois Compaction to the satisfaction of the engineer Covered by special provisions in Same as for other locations Provision for wetting or drying subgrade special cases Indiana Same as for embankments As required to obtain density Must be satisfactory at time of paving or placing Kentucky sub base Satisfactory All soft and yielding material See compaction requirements replaced with suitable material Maryland Compaction with tandem or 3-wheel, 10-ton roller, also sheepsfoot or any other method Soft, unstable material shall be removed to secure required compaction New Jersey Same as for embankments Surface rolling Ohio Surface rolling No requirements specified 95-105 percent AASHO T 99 (See compac• Min 6 inches Mm 6 inches Not greater than optimum +2% (see com• tion table 2-S) paction table) Not greater than opti• mum in elastic soils Pennsylvania Same as for embankments Excavate 9 ins below final grade No requirements specified Excessively wet material removed Tennessee Same as embankments Compaction per• 6 inches max formed with 10-ton roller or pneumatic Control by field and laboratory tests tired roller Virginia Minimum 95 percent AASHO T 99 8 inches 8 inches Optimum moisture content West Virgmia Scarified to not more than 4" and compacted 4 inches 4 inches with 10-ton, 3-wheel roller to firm un• No requirements specified but must be firm yielding surface and unyielding SOUTHEAST

Alabama Minimum 100 percent AASHO T 99 6 inches 6 inches Only as required to obtain density Ma• nipulation until dry enough to compact Florida Same as for embankments (Av , 95% Modified 12 if stabilization is required— Optimum used as guide only Provision for AASHO with no test less than 90% 6 if no stabilization is required drying Ciporgia Same as for embankments, Minimum (95% 6 in except 12 in over solid rock 6 inches AASHO T 99) No requirements specified Mississippi Minimum 95% AASHO T 99 6 inches 6 inches No requirements specified Soft yielding materials removed North Carolina Thoroughly compacted with power driven No requirements specified except at discre• roller weighing not less than 330 lb per tion of engineer inch of width of tread South Carohna Same as for embankments (Min 90% AASHO 6 inches where used 6 inches where used Optimum ± 3 percent T 99 under high type pavements)

SOUTH CENTRAL

Arkansas Same as for embankments 8 inches No requirements specified Louisiana Same as for embankments (95% AASHO 8 inches loose 8 inches loose 95% of optimum T 99) Oklahoma 95% of Standard Proctor Density for sub- 6 inches 6 inches Based on optimum grades Texas Same as for embankments (90 to 100% 6 inches 6 inches Same as for embankments (slightly above to AASHO T 99) 5% below optimum)

NORTH CENTRAL

Iowa Min 95% AASHO T 99 specified for sub- 6 inches 6 inches 90 to 110 percent of optimum for flexible grade for Flexible Type Pavement Sub- sprinkling when necessary for rigid type grade rolling for rigid type pavement Kansas Thoroughly compacted with approx 5-8 ton No requirements specified tandem or 3-wheel rollers for subgrade for PCC pavement Type AA Min 95% AASHO T 99 6 in to 12 in 6 in to 12 in As required to obtain density Type AAA Min 100% AASHO T 99 6 in to 12 m 6 in to 12 in As required to'bbtain density Minnesota Same as for specified density method for em• Generally upper 12 inches Generally upper 12 inches where Min 80% of optimum bankments according to special provision required (generally 97 or 98% AASHO T 99) Missouri Same as for embankments (Mm 90% AASHO 18 inches 18 inches No requirements specified except as required T 99) to obtain density Nebraska Same as for embankments (Mm 90% AASHO 6 inches Same as for embankments 100% ± 3 (concrete pavements only) T 99) North Dakota Same as (or embankments (Mm 95% AASHO Standard scarify and recompact Same as'for embankments (stress As required to obtain compaction T 99 when specified) to 12" to density of adjacent uniformity) fills South Dakota Same as embankments 12 inches Scarify 6 inches and recompact No requirements specified Provisions for drying if necessary to secure stable road• bed MOUNTAIN

Arizona Same as for embankments (Mm 95% AASHO 6 inches when required 6 inches when required No requirement specified Engineer tries to T 99 by special proviaion) obtain approximately optimum Colorado Same as for embankments except when sub- 12 inches 12 inches Optimum ± 2 IS objective grade IS of selected materials Idaho Higher compaction required in subgrades than 12 inches 18 inches No requirement specified except at direction in embankments (see Table 3-S) of engineer Montana Same as for embankments except last 10 ft 8 inches 8 inches Moisture control required as directed by below grade on high fills engineer Nevada Same as for embankments No requirements specified Ne* Mexico Same as for embankments (90 to 95% AASHO 6 inches 6 inches Optimum to optimum—5% Provision for T99) drying Utah Same as for embankments (90 to 100% 8 inches ± 8 inches ± Provision for wetting or drying subgrade at AASHO T 99) '° direction of engineer Wyoming Same as (or embankments to a depth of at Mm 6 inches Mm 6 inches Requirements based on working range of least 6 inches Wyoming A, B and C type curves

PACIFIC

California Mm 90% California method compaction 4 in 30 inches 30 inches Same as for embankment compacted layers for 2H ft below profile grade Oregon No requirement specified Provision for Same as for embankments (95% AASHO T 99) wetting or drying UJ Washington Up to 22 in in special cases 1 to 6 in (surface rolling only) Optimum ± 3 in compaction Method C only. Same as for embankments 58 Group A Compaction Without Density SUBGRADE COMPACTION REQUIREMENTS Control TABLE 1-S Of the 48 states and the District of Standard of compaction or Maximum Minimum compaction Density obtained by Method AASHO required (Percent of Columbia, 41 specify that the soil shall be T 99 (p c f ) Maximum Density) tamped or that the soil shall be thoroughly or carefully, firmly or solidly tamped, 90 to 99 9 100 100 to 109 9 95 rammed or compacted. Nearly all specify 110 to 119 9 95 120 to 129 9 90 quality of compaction in terms of "to the 130 and above 90 satisfaction of the engineer. "

TABLE 2-S Tamping Methods and Equipment. The above group provides the followmg re• Minimum subgrade quirements for tamping methods and compaction require• Maximum laboratory dry weight ments (Percent of equipment (when inaccessible to a roller). (p.c t) laboratory maximum dry weight) Of these 41 states, 11 do not state whether compaction of backfill shall be by 94 9 and less ** hand or mechanical methods, nor do they 95 0-102.9 105 103 0-109 9 102 state requirements for hand tamping 110.0-119 9 100 equipment. 120 0 and more 96 Five states mention hand tamping but

** Soils with a maximum dry weight of less than 95 p c f make no mention of mechanical tamping. shall be unsatisfactory for us^ in the 6-inch compacted soil layer immediately beneath the pavement and shall be replaced Two of these 5 states list no requirements with suitable soil or granular layer for hand tamping equipment. One state The moisture content of all subgrade materials at time of compaction shall not be greater than 2 percent over the opti• provides only that heavy iron tampers be mum. The moisture content at the time of compaction of granular materials containing 15 to 40 percent passing a number used. Two states require "heavy iron 200 sieve, of predominantly silty or sandy sift soils for which the plasticity index is less than 10, or other approved subgrade tampers" having tamping faces not ex• material which displays pronounced elasticity or deformation ceeding 25 sq. in. in area. Nine states under construction equipment shall not exceed optimum specify mechanical tamping only. Six• teen states provide for either mechanical TABLE 3-S or hand tamping methods. Minimum field com• For hand tamping equipment: nine paction requirements Maximum laboratory dry weight (percent of laboratory states require heavy iron tampers with (pounds per cu ft) determined dry tamping faces not exceeding 25 sq. in. weight) in area. One state requires tampers

89 9 and less 100 weighing not less than 12 lb. and having 90 0 to 99 9 100 a tamping face of not more than 50 sq. in. 100 0 to 109 9 100 110 0 to 119 9 100 One state requires tampers weighing 120 0 to 129 9 95 130 0 and over 95 not less than 15 lb. and having a tamping face area 6 in. by 6 in. One state re• quires tampers weighing not less than 20 Specifications on Compaction of Back• lb. and having a tamping face area not fill of Trenches and around Pipe Cul• larger than 6 in. by 6 iiL One state re• verts and Sewers" (36). That was done quires tampers weighing not less than 50 as a result of the increasing quantity of lb. and having a face not exceeding 100 work being done in urban areas. That sq. in. in area. Three states give no summary of practices in compaction of requirements for hand tamping equipment. trench backfill is included in this overall review of current practices. Lift Thickness. All states in this Compaction requirements can beplaced group of 41 states specify some require• into two broad groups: those requiring ment for depth of lift Of this group)35 compaction of backfill but not specifying state clearly the depth of lift either as density requirements and those controlling loose thickness or state that the material compaction of backfill by specifying com• shall be placed in layers of some given paction to some minimum required thickness and compacted. They are tab• density. ulated according to depth of lift as follows: 59

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Gallons Given- A density of 99 lbs. percu.ft with required moisture of 10% locate point A. Reading vertically It Is found that 32 gal percayd will be needed

Figure 44. Chart for determining gallons of water required per cubic yard of embankment (after "Kansas Highway Manual").

Depth of Lift States Specifying or clods, stones, rock, sod, roots, frozen (inches loose) lumps, etc. Three states provide for the 3 5 use of granular materials. Five states 6 29 provide for acceptable selected materials 8 1 or when specified, granular materials. 9 1 Provision for Saturating, Flooding, or 12 1 Puddling. One state permits thorough sat• In addition, one state provides for a uration of granular materials meeting 4-in. depth for hand tamping and a 6-in. certain grading requirements. One state depth (loose) for mechanical tamping, permits flooding and tamping of special another specified layer not exceeding 8 granular materials meeting certain grad• in. for mechanical tamping and that for ing requirements. One state permits hand tamping layers shall not be more than puddling around pipe only. One state 4 in. Four additional states specified 6- permits water puddling up to the natural in. depths of lift but it was not clear ground line as an alternate to hand tamp• whether the depth was loose depth or ing. compacted depth. Moisture Control. Nineteen states Group B - Compaction with Density Control provide for the addition of water, if nec• essary to facilitate compaction. A major Density Requirements. Eight highway portion of those states specify, "Each departments control compaction of back• layer, if dry, shall be moistened and then fill (within the scope of this review) by compacted." One state provides, (in specifying some minimum density re• addition to moistening) for saturation of quirements: Three require not less than sandy and granular soils. The remaining 90 percent of maximum density as deter• states in this group do not provide for mined by Method of Test AASHO Designa• addition of water to facilitate compaction. tion: T 99. One requires not less than Materials Requirements. Thirty-four 95 percent of maximum density as deter• of this group of states specify that the mined by Method of Test AASHO Designa• material shall be approved or shall be tion: T 99. Two require not less than selected material free from large lumps 90 percent relative density as determined o

TABLE 22

CONTROL OF COMPACTION OF GRANULAR BASES

/ COMPACTION REQUIREMENTS REGION AND STATE Compart<^on with Requirements for Embankments or Subgrades

NORTHEAST

Connecticut Rolling to give satisfactory compaction in layers not to exceed 6 in depth (compacted) Maine Use 8-inch loose lifts compared to 12 for embankments Massachusetts Use 12-ton power roller on bases compared to 10-ton for embankments Michigan Subbate—Same as for embankments (95% of Michigan Cone Method) ' Base—(Processed gravel) Satisfactory compaction New Hampshire Use min 10-ton Il-whcel roller and roll to satisfaction of engineer New York Require rolling with 10-ton rollers in separate layers of max 6 in depth Tamping rollers in some areas where roller cannot be used Rhode Island Same as for embankments Vermont Same except 3-wheel power roller is used on bases Wisconsin Provision is made to require power rollers if desired compaction is not attained by hauling equipment Compaction is 3 to 5 in layers

MIDDLE EAST

Delaware Same as for embankments District of Columbia Same as for embankments 90-100% AASHO T 99 Illinois Compacted to satisfaction of engineer Indiana Density and moisture content satisfactory to engineer. Kentucky Must be within 5 lb of Proctor Density Also pneumatic tire roller required with other rollers Maryland No density requirements stated Rolled with lO-ton power roller New Jersey 100% AASHO T 99 for subbase "Type A" Provision for moisture control Ohio No density requirements Compaction with a 3-wheel roller weighing 10 tons or more or an approved pneumatic tire roller to satis• faction of Engineer Pennsylvania Same except pneumatic tire and sheepsfoot rollers are permitted Tennessee Rolling requirements are more rigid than for embankments Thickness of compacted layer is set between 2 5 and 4 inches. Virginia No density requirements Compaction as required by Engineer West Virginia Compaction to the satisfaction of the engineer.

SOUTHEAST

Alabama Density 100 percent AASHO T 99 Moisture content optimum ± 2 percent Florida Same as for embankments Georgia Bases require 100 percent of AASHO T 99. (Embankments require 95 percent) Mississippi Bases require 100 percent of AASHO T 99 (Embankments 90-95 percent) Contractor maintains for 10 days If contractor obtains 105% then maintenance clause is waived North Carolina Bases or subbases are thoroughly compacted by rolling satisfactory to engineer South Carolina Density 95 percent AASHO T 99 required.

SOUTH CENTRAL Arkansas Different layer thickness used Compaction under traffic Louisiana Same as for embankments Oklahoma 95% of Standard Proctor Density for stabilized aggregate base course Provision for moisture control Texas Density requirements based on compaction of individual samples consisting of total matenal up to 2 in top sizes

NORTH CENTRAL

Iowa Density 100 percent AASHO T 99. Moisture content that which will insure maximum compaction Kansas Min. 100% AASHO T 99 Aggregate binder bases min 4 in compacted lifts and not less than 125 p c f. Minnesota Placed in 3 in layers and compacted to 98 percent AASHO T 99 Missouri Density 90-95% AASHO T 99 except when otherwise covered by special provisions Compacted granular base 90% Stabilized aeeregate or rolled stone bases 95% Nebraska Density 90% AASHO T 99 (for concrete pavements) Moisture content 100% optimum db 3 Density 95-100% AASHO T 99 (for flexible pavements). No moisture requirement except as necessary for construction North Dakota Subbase—same as standard compaction for embankments Base—1 33 times dry loose weight of material but not to exceed 140 p c f dry weight in place for material weighing 100 p c f or more loose weight South Dakota Base course density shall be 1 33 times loose dry wt of aggregate or 140 lb. max required Subbases rolled with pneumatic tire roller (250 lb per in width of roller) to an unyielding condition

MOUNTAIN f

Arizona Same as for embankments Colorado No density tests made Rolling to satisfaction of engineer Minimum of 4 passes with suitable rolling equipment. Idaho No density requirements Compaction controlled by layer thickness Montana Watering and rolling required Greater attention is given projects where watering and rolling are paid for as separate items Nevada Rolled with power roller weighing at least 8 tons until maximum compaction is obtained Placed m thinner layers If more than 4 in. place in two or more layers New Mexico No density required as no test deemed satisfactory Compaction to satisfaction of engineer Utah Rolling until maximum feasible compaction has been obtained Wyoming No density requirement Watering, processing and rolling to satisfaction of engineer

PACIFIC

California Minimum relative compaction not specified but minimum amount and type of rolling equipment is specified. Oregon As required by engineer Washington Thinner lifts Rolling with 3-wheel or pneumatic tire rollers until material does not creep under roller.

1 The Michigan Cone Method consists of compacting granular soils into a funnel-shaped approximately 4 inches and stnking it sharply down on a concrete or heavy timber base mold having a solid bottom in the large end and equipped with a stopper for the small end After the third layer has been placed the blows shall be continued with the wood stopper The bottom shall be so shaped that there will be no sharp corners mside the mold The reversed and held firmly over the opening. Sand shall be added at intervals to keep the base or large end of the mold shall be approximately 5'i inches in diameter and the small mold full, and operations continued until no further consolidation occurs The compacted end shall be not less than 2 ?4 inches The mold shall be approximately 8 > -i inches m soil shall be carefully leveled off to the top of the mold and weighed, and the wet and dry height and shall have a volume of approximately 1,300 cubic centimeters or 0 0459 cubic volume weighte determined For complete test procedure and description of equipment feet The sample shall be thoroughly mixed, then compacted in the mold in three equal see "The Use and Treatment of Granular Backfill" by R L Greenman, Michigan Engineer• layers, each layer receiving 25 blows The blows shall be delivered by raising the mold ing Experiment Station, Bulletin 107, 1948 62

by the California method. Two have min• specify mechanical tamping. The remain• imum density requirements similar to ing two specify mechanical tampers or those specified in Standard Specifications hand tampers, havmg a tamping face not for Materials for Embankments and Sub- exceeding 25 sq. in. in area. grades AASHO Designation: M 57. Lift Thickness. Highway Departments Four of the eight departments which specifying the density method of control specify minimum density requirements of compaction of backfill provide the make no reference to method of compac• following requirements for maximum tion or equipment Two departments thickness of l^t during compaction.

TABLE 23 HIGHWAY DEPAfflWEM RiXJUIBEMENTS FOR TRiWCH BACXnLLING No. of States Group Bequirementa and D-C. Specifications lequire confjaction but do not specify density .... 41 TanpinR Provisions: Mechanical tamping only specified 9 Hand oi mechanical tamping allowed 16 Hand tonping moitioned only 5 Tamping method not mentioned 11 Depth of Layer or Lift: Depth placed before compaction, in. 4 3 6 29 8 1 9 1 12 1 Depths 4 to 8 in., but with particular requirements for hand tamping 2 Depth 6 in., but not clear as to loose or canpacted .4 Moisture Control Some provision 19 No provision ; 22 Materials Requirements. Provision for select or approved materials 34 Pennissim to Saturate. Flood or Riddle 4 Specifications require density control 8 Tanping Provisions Mechanical tamping specified 2 Hand or mechanical tamping alloved 2 Temping method not mentioned 4 Ccpipaction Requirements Not less than 95% max. density (AASIO 1 99) 1 Not less than 90% max. density (AA310 T 99) 3 Not less than 9(^ rel. density (California Method) 2 Depth of Layer or Lift: Not to exceed Basis 4 in. loose 2 6 in. loose 2 6 in. coTipacted 2 4 to 6 in. loose 1 8 in. loose 1 Moisture Control, provision made 8 Materials Requirements- Granular backfill specified 2 Select or approved backfill specified 6 Provision for puddling 1 63

No. of nate to tamping to obtain the required Dept Depth of Lift Requirements density, but that method must be used on —2 Not to exceed 6 in. compacted material from deposits indicated on plans depth or on material meeting specified grading 2 Not to exceed 6 in. loose depth requirements. 2 Not to exceed 4 in. loose depth 1 Not to exceed 8 in. loose depth 1 Not to exceed 4 and 6 in. loose Statement of Requirements for Backfilling depth depending on construc• Sewers tion method. Twelve States have specification items Moisture ControL All of the eight covering sewers, storm sewers, sanitary highway departments specifying the density sewers, or storm and sanitary sewers. method have provisionf or control of mois• Because these specifications do differ in ture content during compaction. some states from those given for pipe Materials Requirements. Two of the culverts and trench backfill, data on eight departments specify granular back• specifications for sewers are given sep• fill and give grading requirements, and arately in the following summary: one department specifies granular back - State 1. Sanitary sewer. Suitable fill around pipe and selected material for materials are tamped around pipe and the remaining part of the trench. The re- to a depth of 2 ft above the pipe. Re• mainingfive departments call for selected mainder thorou^ly settled and compacted or approved material free from large or by tamping and flooding. No moisture frozen lumps, rocks, roots and similar control given. extraneous material. State 2. Sewer, Suitable materials Provision for Saturating, Flooding or are hand tamped to 1 ft above sewer. Puddling. One highway department in Balance filled to within Va ft. of top and this group provided puddling as an alter• flooded.

u. 90

80 85 90 95 100 105 110 115 120 Probable Rolled Density

Figure 45. Chart for determining shrinkage from cut to fill (after 'Kansas Highway Manual"). TABLE 24

CURRENT STATE HIGHWAY STANDARD SPECIFICATIONS FOR COMPACTION OF BACKFILL FOR STRUCTURAL EXCAVATION

Region and State Depth of Lift Compaction Moisture Control Tamping Equipment and Methods

NORTHEAST

Connecticut 12 in max. loose Mm 95% AASHO T 99 Puddling permitted Power rollers, motonzed equipment or hand equipment of type (b). and vibratory equipment Maine 9 in max loose Thoroughly compacted Not specified Tamping or flushing with water Massachusetts 6 in max loose Thoroughly compacted Not specified Tamped Equipment not shown under excavation for struc• ture but type (a) equipment shown under backfillmg of pipe culverts Puddling of clean granular matenal permitted Michigan 9 in max loose Same as Emb controlled den• Same as for embankments Power and hand equipment. Details on tamping equipment sity method for granular not given Vibratory equipment used extensively Flood• material (95% cone ing permitted on permission of engineer method) New Hampshire 8 m. max loose Thoroughly consolidated Not specifiGd Approved power tamping devices New York 4 in max loose Min 96% AASHO T 99 As required to obtain density Mechanical rolling or tamping Mechanical tampers shall be equal in weight and power to Ingersoll-Rand No. CC45 with a tamping foot area not to exceed 50 sq in. Rhode Island 12 in max loose Well compacted Not specified Equipment not specified under structure excavation and back• fill but mechanical tampers or hand tampers type (a) shown under bedding and backfill for pipe culverts Vermont 12 in max loose Thoroughly compacted Not specified Mechanical or hand tampers. Details on tamping equipment not given. Wisconsin 12 in max loose Thoroughly compacted Not specified Equipment not specified under excavation for structures

MIDDLE EAST

Delaware 6 in max loose (power equip• Min 95% Modified AASHO Optimum ± 10 percent Mechanical tampers Details on tamping equipment not ment) given 4 in max I oose (hand equip ) Distnct of Columbia Same as embankments At least equal to optimum Power rollers or mechanical tampers Mechanical tampers 6 in max loose (90-100% AASHO T 99) capable of exerting a blow equal to 250 lb per sq ft of tamping area and have a dead weight in excess of 40 lb Illinois 6 in max Thoroughly tamped Not specified Mechanical tampers of approved design Indiana Grade B special borrow max Thoroughly compacted Not specified Mechanical tamps (preferably). For small areas hand tamps, 6 in loose rain weight 15 lb having a face area 6 by 6 in Special filling matenal Thoroughly saturated 12 m max loose Kentucky 6 in max loose Thoroughly compacted Sufficient to insure desired Approved mechanical tamping devices compaction and density Maryland 6 in max loose Same as embankments Sufficient to insure proper Mechanical tampers (90-100% AASHO T 99) compaction New Jersey 6 in max (subsurface struc• Satisfactory Not specified Mechanical tampers Puddling of foundation excavation and ture excavation) subsurface structure excavation Details on equipment not specified Ohio 4 in. max loose Same as embankments Sufficient to insure density Pneumatic Umpers (90-102% AASHO T 99) Pennsylvania 4 in max loose Thoroughly tamped or rolled Not specified Mechanical tampers Tennessee 6 in max loose for tamping Thoroughly compacting each Compacted at optimum mois• Tamping rollers and mechanical tampa are used roller 3" max loose for layer ture content as determined mechanical tamp. by laboratory tests on back• fill matenal Virginia 6 in max loose Thoroughly tamped Not specified Mechanical tamper capable of exerting a blow equal to 250 p s r of tamping area West Virginia 6 in max loose for rollinfc Thoroughly compacted Not specified Roller minimum weight 10 tons Pneumatic backfill tamper 4 in max loose for tamping (25 to 35 lb ) having a piston blow rather than a hammer blow SOUTHEAST

Alabama 6 in max. loose Same as embankments Provision for adding water or Mechanical tamping and/or rolling .'95% AASHO T 99) drying Florida 8 m max loose Thoroughly compacted Provision for adding water or Approved mechanical equipment drying 4 in max loose Thoroughly compacted Provision for adding water or Approved hand tampers weighing not less than 50 lb and drj ing having a face area not exceeding 100 sq in Georgia 6 in max compacted Well tamped Not specified (Foundations excavation for bndges) Power dnven tamper 6 in max loose Mm 95% AASHO T 99 Sufficient to allow speafied (Embankment adjacent to structures ) Roller or power dnven compaction mechanical tamper Mississippi 6 in max compacted Thoroughly compacted Not specified (Backfilling for structure) Mechanical or hand tamping Details on tamping equipment not given 6 in max compacted 90-95% AASHO T 99 Satisfactory (Embankment adjacent to structures) Pneumatic tired or sheepsfoot rollers North Carolina 6 in max. loose Same density as adjacent por• Not specified Approved mechanical tamper which will deliver at least 185 tion of embankment p s f of tamping area South Carolina 6 in max loose Thoroughly compacted Not specified Equipment not specified under excavation for structure

SOUTH CENTRAL

Arkansas 6 in max loose (Spec Satisfactorily compacted Not specified Hand or mechanical tampers Liouisiana 6 in max loose Satisfactorily compacted Provision for moistening— If too wet dned in borrow Mechanical rammers or hand tampers of type (a) Oklahoma 6 in max loose Same as emb (90% AASHO Provision for moistening T 99) Equipment not specified under excavation for structures Texas 10 m max loose Same as for emb 90-100% As required to obtain density AASHO T 99 Equipment not specified under structural excavation.

NORTH CENTRAL

Iowa 6 in max loose Compacted Satisfactory to Not specified Approved roller or mechanical tamper. Pneumatic tamper Engineer shall be supplied with air at a pressure of not less tnai 100 p 3 I Kansas 6 in max compacted Mm 90% AASHO T 99 Sufficient for thorough bonu- Rolling, mechanical tampers or hand tampers of type (a) ing and density Minnesota 6 in max compacted Thoroughly compacted Not specified Approved rollers or mechanical tampers Missouri 6 in max loose Same as embankments Provision for moistening Rollers, mechanical tampers or hand tampers of type (a). (90% AASHO T 99) Nebraska 6 in max loose Min 90% AASHO T 99 Same as embankments Rollers, mechanical tampers North Dakota 8 in max loose Extra Comp Mm 95% Provision for moistening AASHO T 99 Rollers, mechanical tampers or hand tampers of type (a) South Dakota 4 in max loose Satisfactorily compacted Not specified Mechanical tampers

MOUNTAIN

Arizona 5 in. max loose (6 in. max To a density satisfactory to Provision for moistening Rollers, mechanical tampers or hand tampers of type (a). alongside pipe) engineer Colorado 6 in max loose Thoroughly compacted Provision for moistening Mechanical tamper, IngersoU-Rand Model 34 Backfill tamped or acceptable equivalent with 6 in diameter butt min operating air pressure 80 p s i Idaho^ 6 in loose Same as embankments As approved by engineer Approved air. gasoline or electric driven tamper (90-100% AASHO T 99) Montana 8 in max loose Thoroughly compacted Not specified Mechanical or hand tampers (excavation for structures) 8 m max loose Same as embankments Provision for wettmg or Tamping, pneumatic or power rollers (Embankments placed (90-100% AASHO T 99) drying around structures) Nevada 4 in max loose Same as embankments Provision for moistenmg Tamped, puddled or rolled (Note this refers to selected (Mm 90% modified AASHO) granular matenal) Pneumatic or hand tampers New Mexico 4 in max loose Same as embankments Provision for moistening or Pneumatic or mechanical tamping units Tamper head area (Min 95% AASHO T 99) non-use of wet maten&J 19-29 sq in and deliver a blow of not less than 175 p s i of tamper head area Utah 8 in max loose Thoroughly compacted Not specified Equipment not specified under excavation for structures Wyommg 5 in max loose To a density satisfactory to Provision for moistening Pro• Mechanical tamper — Thor model 60 BFT Tamper with engineer hibit use of wet material 6 in diameter tamper head or acceptable equivalent Tamper must operate at about 750 strokes per minute under air pres• sure of 70-80 p s 1 Also pneumatic, sheepsfoot or smooth PACIFIC steel roller

California 4 in max loose Ponding of sandy or granular Provision for moistening Tamped or rolled Equipment not specified material Same as em• bankments (90% California method ) Oregon 6 in max loose 95% AASHO T 99 Provision for drying Same As approved by engineer as for embankments Washington 6 in max loose Same as embankments Optimum ± 3 percentage Air driven tampers with tamping foot area of 36-64 sq in mm (95% AASHO T 99) points (Method C) air pressure 75 p s i Gasoline driven tampers Barco or equal with tamping foot area 36-64 sq in Bureau o( Public Roads 12 in max loose Satisfactonly compacted Provision for moistening Mechanical rammers or hand tampers of type (a)

NOTE —Type (a) requires tampers (usually heavy, iron tampers) havmg tamping faces not exceeding 25 sq in in area Type (b) requires tampers weighing not less than 12 lb and having a tamping face not exceeding 50 sq in 66

State 3. Storm sewers. Suitable tamped. Provision is made for adding materials are placed in 4-in. layers and water to dry soils. thoroughly tamped to a depth of 1 ft state 10. Sewers. Suitable materials above the pipe. Materials for the re• passing a 1-in. ring are compacted to the maining depth are placed in 6-in. layers level of the top of the pipe. Water settling and each layer tamped. No moisture con• may be used above top of pipe when trol given. specially permitted by the engineer. No State 4. Storm sewers. Suitable ma• moisture control specified. terials are placed and compacted in ac• state 11. storm sewers. Selected soil, cordance with one of three methods. sand, or rock dust is thoroughly tamped. Method 1. Placed in layers of 6 inch No specified depth of lift nor moisture loose depth and tamped. control are given. Puddling is recom• Method 2. Use Method 1 to 12 in. above mended for sandy or gravelly materials. the pipe. Remaining materials are placed State 12. Storm sewers. Approved in lifts of 12 in. and each lift inundated. materials shall be used. If stone gravel Method 3. Same as Method 2 except that or slag is specified for backfilling, the the trench is filled and jetted to within two sewer pipe shall be covered with clean feet of the pipe. gravel or broken stone or slag placed No moisture control specified for Methods around and above it to a height of not less 1 and 2. than 4 in. above the surface of the pipe. State 5. Storm sewers - If under pave• Material shall be deposited simultaneously ment Selected granular materials are on both sides of the pipe in uniform layers used. If crushed stone is used it is tamp• not to exceed 4 in. in thickness, solidly ed in layers not exceeding 6 in. If sand tamped or rammed with proper tools so as or gravel is used it is placed in 12 -in. not to injure pipe. No moisture control layers, each layer is thoroughly saturated specified. to secure maximum compaction. The foregoing statement of require• If not under pavement. Selected granular ments for backfilling over sewer pipe can and ordinary materials are used. Selected be summarized more briefly as follows: granular materials are placed in 4-in. Six of the twelve states provide only for layers to a height of 1 ft. above the pipe. compaction, with no provision for pud- Ordinary materials are thoroughly tamped dhng, flooding, or jetting. Two states in 6-in. layers for the remainder of the provide for compaction and indicate that depth. No moisture control specified. flooding or puddling may be permitted, State 6. storm and sanitary sewers. one stating specifically that puddling is Ordinary materials are carefully hand recommended only for sandy soils and tamped in 4-in. layers up to a height of gravelly soils. One state specified that 6-in. above the pipe. Remainder tamped the material shall be thoroughly settled in 6-in. lifts. No moisture control spec• by tamping and flooding. One state has ified. provisions for use of compaction, flood• State 7. Pipe sewers. Ordinary ma• ing and jetting. One state provides for terials are used if satisfactory. If not compaction of ordinary and angular satisfactory, pit-run sand with 100 per• (crushed rock) granular materials, per• cent passing a 3-in. sieve is placed in mitting flooding only on rounded granu• layers not exceeding 6-in. and each layer lar materials. Only one state provides thoroughly compacted. No moisture con• simply for "flooding" without any qual• trol specified. ifications or reservations. state 8. storm sewers. Ordinary suit• able materials are placed in layers not Backfilling Structural Excavation exceeding 4 in. loose measure and com• pacted to density requirements given for The 1951-52 survey included a review roadway(AASHO T-99 table of densities). of Current State Highway Standard Spec• Moisture control required but no limits ifications to summarize compaction and given. moisture control requirements for back• state 9. Sewers. Suitable materials filling of structural excavation (see Table are placed in 6-in. layers and solidly 24). 67

Lift Thickness. The specifications scribed as weighing not less than 12 lb. show a wide range of variation in thick• and having a tamping face not exceeding ness of lift Four states specify a 6-in. 50 sq. in. compacted thickness. Two do not specify layer thickness. The remainder (two specifications are shown for some states) are divided in specifying thickness of lift COMPACTION EQUIPMENT (loose measurement): Because of the important part of equip• ment in obtaining compaction, a summary Loose Depth Number of Organizations has been made of State Highway Depart• in. Spec^ying ment Standard Specifications for rolling and tamping equipment. Data on various i 5 items wMch are mentioned in specifica• 6 24" tions are given in Table 25. 8 5 9 2 Sheepsfoot-Type Rollers 10 12 Contact Area of Tamping Feet. Most 4-6 organizations allow a wide range of size 4-8 of tamping-foot contact area. This may 6-12 be seen from the summary of specification Not specified requirements: a Five states required a 6-in. compacted depth. Range in Contact Area No. of (sq. in.) Organizations Uo8 Compaction. Thirty organizations 4 to 9 2 stated their requirements for backfill 4 to 10 2 compaction simply in terms of being 4 to 12 8 thoroughly or satisfactorily compacted 4 to 13 2 or well tamped or in similar terms. 4 to 18 1 Seventeen states which required compac• 5 min. 2 tion in terms of some percent of a maxi• 5 approx. 1 mum density showed identical require• 5 to 8 3 ments for embankments and structural 5 to 10 I backfilL Four specified 90 percent of 5% min. 1 AASHO T 99, seven specified 95 percent, 6 to 8 2 one specified 90-95 percent, 5 specified 8 to 12 1 90-100, one specified 90-102, two re- 13 max. 1 qmred 90 percent and one required 95 (Note: Two states provide for two ranges percent of a modified method. There are of sizes. They are incorporated in the 16 organizations which specify density above tabulation.) control of backfill compared to 39 which specify density control of embankments.

Nearly all organizations provided for An analysis of the specifications on a the use of mechanical tamping equipment; ' regional basis shows no difference in 32 required mechanical tampers; several specifications for contact area for any states provided for hand-tamping equip• specific region. ment The hand equipment referred to Contact Pressure. An analysis of was of two types. Type A was usually standard specifications covering pressures referred to as heavy iron tampers hav• of sheepsfoot-type rollers also showed a ing tamping faces not exceeding 25 sq. wide range in minimum contact pressure in. in area. Type B tampers were de• requirements. The range is: 68

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NORTHEAOT

CflODecticat 10 DUD 150 BO yd. (a) RoDed gravel base—bottom (a) coarse Mune 10 (a) An approved pneumatic tired roller may be osad ManBcbusetts 12 mm (a) 12 mm (a) (a) Requires a s>'lf-propelled roller MiehigBO (a) (a) Reqmred but no specifira- tions covermg pneomatie tire roller New Hampahtre 10 DUD New York .\pproved roller weighing Dot 10 mm less than 10 tons Rhode Tifhtnd Vermont 10 mm Wtseonsio Mm 2S0 10 DUD Mm 250 (a) Max 68% of gross weight on (a> fb) drmng rolb. (b) Max. 72% of groes weight on drmng rods. Haubng Equipment Eogmeer may reqmre. special roDing eqmpment if not attained dor- tng contract Rubber tirvd roUers are used. MIDDLE EAST

Delaware 10 mm (a) (a) For W B MaeadaiD. No requirement for gravel. DiBtnet of Cohimbu »-10 (a) 200-280 8-12 (a) 200-380 (a) Weight an>rov«l for job nbnou 6- iO 200-32S 6- 10 200-^25 (a) Qravel or crushed stone sur• face coarse Type A Indiana 2-aile. 9-wheel. Upto200 10 nun 10 mm Permit use of crawler tread trac• min tors having a bearmg of at least 6 lb per sq m of tread. Vary lift thickniea to obtau desired density Eentqcky 7- 10 7- 10 Maryland 10 (s) 10 (a) (fk) Reamres a K^ton "power roller'* New Jersey 8 nun 225 DUO 8 nun (a) Min 330 (a) OD a tire not more than 24 m. Ohio (a) wide. 10 mm Mm 300 2 (a) Wfligbtt dimeosiaDS of roDer and number and spacing of tires shall be such that spea- fod^mpsetion may be ob- Pennsyhrama 8 250 10 mm Mm 330 Specified for crushed rock. Tennessee 10 2 500 sq yds Virginia 10(a) 10(8) (a) For W B Macadam only Sieepsfoot or other approved types for stabilised and pit nm base courses. West Virgiou Approved type 10 nun (a) (a) Reeoostmeted base course. 1 1 Coarse to Fine gradmgs. 75

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Minimum Permissible No. of tion-Investigation, Report No. 2 Compac• Contact Pressure Organizations tion Studies on Silty Clay, Tech. Memo. by Tamping Feet Specifying No. 3-271, Waterways Experiment Sta• psi. tion, Vicksburg, Mississippi, July, 1949. 550 (loaded) 1 3. Allen, H. and Johnson, A. W. The 450 1 Results of Tests to Determine the Expan• 325 1 sive Properties of Soils, Proc. Highway 300 2 Research Board, Vol. 16, pp. 220-233, 250 3 1936. 200 14 4. McDowell, C. Progress Report on 200 (loaded) 1 Development and Use of Strength Tests for 150 4 Sul^rade Soils and Flexible Base Mate• 135 1 rials, Proc. Highway Research Board, 125 1 Vol. 26, pp. 484-506, 1946. 110 1 5. Russell, H. W., Worsham, W. B. 100 5 and Andrews, R. K. Influence of Initial 90 1 Moisture and Density on the Volume 85 1 Change and Strength Characteristics of 80 1 Two Typical Illinois Soils, Proc. Highway 50 2 Research Board, Vol. 26, pp. 544-550, 1946. Other significant specification require• 6. Corps of Engineers. The California ments for sheepsfoot rollers are given in Bearing Ratio as Applied to the Design of Table 25, "Current State Highway Standard Flexible Pavements for Airports, U. S. Specification Requirements for Tamping Waterways Experiment Station, Tech. (Sheepsfoot) Type Rollers for Embankment Memo. 213-1, July 1945. Construction. " 7. Benkelman, A. C. and Olmstead, Pneumatic-Tire Rollers. Twenty- F. R. The Cooperative Project on Struc• three organizations included some re• tural Design of Non-rigid Pavements, quirements for the pneumatic-tire roller Proc. Highway Research Board, Vol. 16, m specifications for compaction of em• pp. 13-25, 1946. bankments (see Table 26). 8. Turnbull, W. J. and McRae, J. L. Smooth-Wheeled Power Rollers. Thir• Soil Tests Shown Graphically, Eng. News- ty-four organizations have specification Rec., Vol. 144, No. 21, pp. 38-39, May requirements for power rollers for em• 25, 1950. bankment construction (see Table 27). 9. H. Allen, et al. Report of Com• Granular-Base Compaction. A sum• mittee on Warping of Concrete Pavements, mary of specifications for pneumatic- Proc. Highway Research Board, Vol. 25, tire rollers is given in Table 28, "Cur• pp. 199-250, 1945. rent State Highway Standard Specification 10. Soil Classification Method AASHO Requirements for Pneumatic Tire Rollers M 145-49. ... for Compaction of Base Courses." 11. Current Road Problems No. 8-R, Smooth-Wheel Power Rollers. A sum• Thickness of Flexible Pavements, High• mary of "Current State Highway Stand• way Research Board, November, 1949. ard Specifications for Smooth Wheel 12. Aaron, H., Spencer, W. T., and Power Rollers" is given in Table 28. Marshall, H. E., Research on the Con• struction of Embankments, Public Roads, REFERENCES Vol. 24, No. 1, pp. 1-26, July, August, September, 1944. 1. Corps of Engineers, Soil Com• 13. Williams, F. H. P., and Maclean, paction Investigation, Report No. 1 Com• D. J. The Compaction of Soil, Road Re• paction Study on Clayey Sand. Tech. search Technical Paper No. 17, Depart• Memo. No. 3-271, Waterways Experiment ment of Scientific and Industrial Re• Station, Vicksburg, Mississippi, April, search, Road Research Laboratory, 1949. (London), 1950. 2. Corps of Engineers, Soil Compac• 14. Corps of Engineers, Soil Compac- 77

tion Investigation, Report No. 1, Com• and Control Procedures Used in Con• paction Studies on Clayey Sands. Tech. struction of Embankments. Public Roads, Memo. No. 3-271, Waterways E;q)eri- Vol. 22, No. 12, page 271, February ment Station, April, 1949. 1942. 15. Corps of Engineers, Soil Compac• 26. The apparatus is described in tion Investigation, Report No. 2, Com• Public Roads, Vol. 22, No. 12, p. 277, paction Studies on Silty Clay. Tech. February 1942. Memo. No. 3-271, Waterways Experi• 27. Bouyoucos, G. J., The Alcohol ment Station, July 1949. Method for Determimng the Water Con• 16. Hicks, L. D. , Observations of tent of Soils. Soil Scientist, Vol. 32, Moisture Contents and Densities of Soil pp. 173-179, 1931. Type Base Courses and Their Subgrades, 28. ' Bonar, A. J. , A Rapid Method Proceedings, Highway Research Board, for Determining the Moisture Content of Vol. 28, pp. 422-432, 1948. Soils. Texas Engineering E}q)eriment 17. Pumping of Concrete Pavements Station, Research Report No. 9, Col• in Kansas, Highway Research Board Re• lege Station Texas, September, 1949. search Report No. ID, 1946 Supplement, 29. Shea, J. E., Novel Type Volu• Special Papers on the Pumping Action of meter, Highway Research Abstracts, Concrete Pavements, 1946. Vol. 20, No. 3, pp. 4-5, March, 1950. 18. Kersten, M. S., Survey of Sub- 30. Woods, K. B. and Litehiser, R. R. grade Moisture Conditions, Proceedings, Soil Mechanics Applied to Highway Engi• H.R.B. Vol. 24, pp. 497-512, 1944. neering in Ohio. Ohio State University 19. Kersten, M. S., Subgrade Mois• Engineering Experiment Station, Bulletin ture Conditions Beneath Airport Pave• No. 99, July 1938. ments, Proceedings, Highway Research 31. Wyoming Highway Department, Board, Vol. 25, pp. 450-463, 1945. Soils Manual, 1949. 20. Allen, H., Report of Committee 32. Shockley, W. G. Correction of Unit on Warping of Concrete Pavements, Pro• Weight and Moisture Content for Soils Con- ceedings, Highway Research Board, Vol. taimngGravel Sizes. Corps of Engineers, 25, pp. 199-250, 1945. Waterways Experiment Station, Soils Di• 21. Allen, H., Report of Committee vision, Emb. and Found. Branch, Techni• on Maintenance of Joints in Concrete cal Data Sheet No. 2, June 16, 1948. Pavements as Related to the Pumping 33. Reagel, F. V. Standard Density of Action of the Slabs, Proceedings, Highway Bases. Missouri Highway Department, Research Board, Vol. 25, pp. 180-189, Department of Materials, Division of Ge• 1945. ology and Soils, Instruction Circular 1950- 22. TurnbuU, W. J. , Johnson, S. J., 2, June 12, 1950. and Maxwell, A. A. Factors Influencing 34. Communicationto Committee Chair• Compaction of Soils, Highway Research man L. D. Hicks, December 4, 1951. Board Bulletin No. 23, 1949. 35. F. C. Walker and W. G. Holtz, 23. Williams, F. H. P. and Maclean, "Comparison Between Laboratory Test D. J. The Compaction of Soil, Road Re• Results and Behavior of Completed Em• search Technical Paper No. 17, Depart• bankments and Foundations" presented at ment of Scientific andlndustrial Research, 1950 Spring Meeting of the American Road Research Laboratory, London, 1950. Society of Civil Engineers, Los Angeles, 24. TurnbuU, W. J. andMcFadden, G., California, April 26-29, 1950. Proceed• Field Compaction Tests, Proc. of Second ings, Separate No. 108. International Conference on Soil Mechanics 36. Summary of Requirements for and Foundation Engineering. Vol. 5, Backfilling of Trenches, Pipe Culverts and pp. 235-239, June 1948. Sewers. Highway Research Correlation 25. Allen, H., Classification of Soils Service Circular 71, July 1949. 78

Appendix

MANUFACTURERS' SPECIFICATIONS

The 1951-52 survey of current practice includes data on current state highway and federal specifications for various types and sizes of compacting equipment. In order to present more nearly complete data on compacting equipment, manufacturers who were known producers of such equipment were contacted by letter requesting equip• ment specifications. Tables A through E include data received in reply to those requests. The list of manufacturers is not complete but is sufficiently inclusive to indicate the ranges m types and sizes of equipment and may be of value in preparation of spec• ifications for compacting equipment. The data are presented in the tables following. TABLE A

MANUFACTURERS SPECIFICATIONS FOR PNEUMATIC TIRE ROLLERS

Groos operating weight Load per wheel (b) Range of ground Rolling Inflation pressure Manufacturer Type width Tire site fin) pressure Empty Loaded (a) Empty Loaded (Lb per fin) (p.s 1 ) in of roller (Tons) (Pounds) (Tons) rPounds) (Pounds) (Pounds) width

Tampo Manufactunng Co, 5-azle, 9-wbeel 60 7 to X IS 30-36 1 4 2,750 6 03 18,000 305 2,000 47-325 San Antonio, Teiaa 7-axle, 13-wheel 84 7 90 X 15 30-35 1 8 3,700 12 6 26,000 308 2,000 47-325 Wm Bros Boiler Manufactur• 2-aile, 7-wheel 46 7 SO X 16 (4-ply) 1 1,080 7 14,000 283 2,000 43-304 Use of 6-ply tires tncmsea ing Co, Minneapolis, Mum 2-axle. 9-wheel 60 7 SO X 15 (4-ply) 1 3 2,690 0 18,000 284 2,000 43-300 capacities 15% Maxi• 2-axle , 13-wheel 84 7 50 X 15 (4-ply) 1 8 3,600 13 26,000 277 2,000 43-310 mum overloaii cacocity Single axle, 4-wbeel 106 18 X 24 (24-ply) 50-00 10 20,200 35 70,000 5,050 17,500 189-660 7, 9 ood 13 tons Maxi• Single axle, 4-wheel 106 13 X 24 (24-ply) 60-90 12 22,600 50 100,000 5,650 25,000 220-042 mum load for 1 to 5 mph rolling 6, 8 and 11 tons Maximum speed 5 mph M J Dunn Company, St 3-axle , 5-wheel 72 to 78 17 I 16 2 4 000 5-14 10,000 800 800 63-373 With calcium chloride in Paul, Minn 28,000 6,600 tires add 2,fiOO lbs Southwest Welding i Mfg 6 Independently sprung 90 1100x20 80 3 6 7,290 15 30,000 1,812 7,900 81-333 Company, Albambra, Calif whecb 4 independently sprung 80 14 00 X 20 80 6 25 10,500 25 50,000 2,629 12,600 131-029 wheels 4 independently sprung 118 18 00 x 24 00 15 30,000 60 100,000 7,500 29,000 2S4-847 wheels 4 independently sprung 126 2100 x 24- 80 IS 7 31,600 70 140,000 7,875 35,000 238-1111 wheels 4 independently sprung 140 24 00 X 32 90 24 48,000 100 200,000 12,000 S0,000 343-1428 wheels 4 independently sprung 184 30 00 x 33 160 45 90,000 200 400,000 22,600 100,000 489-2174 wheeb

Willamette Iron and Steel Co, 2 oscilhting axles, 4- 114 ic) 18 00 X 24 (24-ply) Not 13 5 27,000 50 100,000 6,750 29,000 60-220 Portland, Qreg wheel Specified

Supercompactors, Inc, Sacra• 2-axle (dual oscillating 174 30 00 x 33 (60-ply) 30-150 40 80,000 200 400,000 20,000 100,000 460-2299 mento, Cahf 4-wheel box) 2-axle tdual oscillatuig, 112 21 00 1 25 (44-ply) 30-150 18 36,000 100 200,000 9,000 29,000 322-1785 4-wheel box) Single box, eccentric 04 I6 00 x 21 (36-ply) 30-150 9 5 19,000 60 120,000 4,500 30,000 202-1277 axle, 4-wheel. Single box, eccentric 8S 16 00 i21(36-ply) 30-150 7 5 15,000 60 120,000 45,000 30,000 175-1412 axle, 4-wheel

W E Grace Mfg Co, Dallas, 3-axle 66 Front 7 S > 10 1,120 1,120 Tcias Open body type Drive 0 X 24 4,460 1,116 Self-propelled 11-whecl Rear 7 S i IS 6,920 087 roller 3-aile (d) eg Front 7 S X 10 Total 11,500 Tank body type Drive 0 X 24 Self-propelled ll-wbeel Rear 7 S i IS ' • • 'Approximately same as roller 1 • for open body type Shovel Supply Co, Dallas, 2-axle (e). oecillating 16 I 21 or 18 X 24 12 29 24,500 50 100,000 6,12S 29,000 In two modeb —one for Texas. 4-wbeel sand ballast, the other for cast iron blocks 2-axle dual osclUatms, - 30 X 33 (60-ply) 150 38 5 77,000 200 400,000 19,250 100,000 Cast iron ballast blocks 4-wbeel box Iowa Mfg Co, Cedar Rapids, I -axle, 2-wheel 48 24 00 X 33 (3e-ply) 40-100 IS 0 30,000 30 60,000 7,500 15,000 (Variable from static to Iowa 1-axle, 2-wheel dual 48 12 00 x 20 (l4-ply) 40-100 6 3 12,500 12 5 25,000 6,250 12,500 ) maximum vibrator in- put)

(a) Loaded weioht is product of rolling width and maximum ground pressure in pounds per inch of roller width (b) Load per wneel ts gross weight divided by number of wheeb (e) Computed by editor from spacing of IS-inch tires (d) Tank body has capacity of 1,000 galloos and may be equipped with spray bar (e) Furnished xa two modeb Model RT 100 for cast iron ballast Model RT lOOS for sand ballast 00 o

TABLE B

MANUFACTURERS SPECIFICATIONS FOR TAMPING (SHEEPSFOOT) TYPE ROLLERS

Dimensions of drums Data on tamping feet Weights Ob) Contact pressure (p,81) *

Tamping Manufacturer Model and type area Number Loaded Loaded Number Length i Diam• No per of Length of feet Loaded with Loaded with (in ) eter 2 drum3 each of foot on Empty with wet Empty with wet (in ) foot (h) ground * water sand water sand (sq in )

American Steel Works, KansasCity, Mo MS 48, Single 1 48 40 112 55 4 3,220 4,805 6.436 146 222 203 MS 60. Single 1 60 40 140 59 5 3,610 6,000 8.372 131 221 304 MS 72, Single 1 72 40 168 55 6 4,040 7,285 10.283 123 221 311 MD 96, Oscillating 2 40 112 55 8 6,100 0,724 13.242 141 221 301 MD 120, Oscillating 2 60 40 140 59 10 7,100 12,160 16,815 129 221 306 MT 144, Oscillating 3 48 40 112 59 12 10,000 14,800 10,048 151 224 302 AS 48, Single 1 48 60 90 7 3 4,100 8,300 12,076 105 306 979 AS 66, PinKlp 1 66 60 120 7 \ 4 5,460 11,060 16,072 195 395 574 AD 96, Oscillating 2 48 60 00 7 6 8,000 16,380 24,000 100 390 671 AD 132, Oscillating 2 66 60 120 7 8 10,640 21,840 31,864 100 390 560

American Steel Worb, Kansas City, Mo *> B3 48, Non-oscilbting 1 48 54 72 7 3 3,750 7,060 10,050 170 336 470 84 48, Non-oscillating 1 48 54 72 7 4 3,750 7,060 10,050 134 252 359 B4 66, Non-nscillating 1 66 54 06 7 4 5,160 8,470 11,460 184 303 410 B6 96. Oscillating 2 48 54 72 7 6 7,000 13,670 10,800 166 325 470 B8 96. Oscillating 2 48 94 72 7 8 7,000 13,670 10,800 125 244 393 B8 132. Oscillating 2 66 54 06 7 8 9,820 16,440 22,420 176 284 401 CS 79, Non-oscillating 1 79 73 136 8 18 4 9,700 111,605 28,015 303 619 004 CD 158, Oscillating 2 79 73 136 8 18 8 19,300 30,209 57,725 302 614 002

Slusser-McLeon Scrapfr Company, Sidney, Ohio Single 1 48 40 112 6 4 3,000 4,036 6.870 125 205 286 Oscillating 2 48 40 112 6 ? 8 6,000 0,870 13.740 125 205 286 Oscillating 3 48 40 112 6 12 0,000 14.809 20,610 125 206 286

Tampo Manufacturing Company, San Antonio, HI, One-drum 1 48 40 112 « 4 3,200 6.134 132 212 Teias H2. Two-drum 2 48 40 112 6 8 6,300 10,168 132 212 501. One-drum 1 60 60 120 6 4 7,200 12,317 16,876 300 912 703 502, Two-drum 2 60 60 120 6 8 14,400 24,634 33,762 300 912 703 501R. One-drum 1 72 60 120 7 8 4 8,400 13.617 18,076 300 483 649 502R. Two-drum 2 72 60 120 7 8 8 16,800 27.034 36,152 300 483 649 Wm Bras Boiler and Manufacturing Company. Ml fi

R G LeTourneau, Inc, Peoru, III XI, Single I 48 4IV6 88 54 8 4 3,610 5,606 7.610 167 260 353 X2, Oscilhiting 2 48 4H4 88 54 8 8 6,590 10,583 14,500 152 245 337 X3, Oscillatmg 3 48 41% 88 54 8 12 9.570 15,560 21,570 147 240 333 X4, Oscillating 4 43 4114 88 54 8 16 12.550 20,537 28.550 145 240 330 120. Tournapacker Oscillating 2 60 60 120 7 07 814 4 17,700 29,360 40.070' 626 1.035 1.420

McCoy Company, Denver, Colo USUD 65. Oscillating 2 60 72 138 6 to 9 8<4 or 914 4 23,500 36,959 50,500 USUD 66, Oscillating 2 72 72 168 6 to 9 8<4 or e>4 4 26.700 43.186 60,342 USHD 55, Oscillating 2 60 eo 120 6 or 7 8!4 4 15.000 25.075 35,312 535-625 890-1.040 1120-1308

Baker Manufacturmg Company, SprmgficM, III B SF S96, Oscillating 1 48 40 96 5 75 7 4 3,210 5.100 6,100 139 221 266 PF D96, Oscillaling 2 48 40 96 6 76 7 4 6.570 10.040 12 040 143 225 263 SF TS6, Oscillating 3 48 40 96 5 75 7 4 9.860 15.600 18 500 141 233 268

Bucynu-ErieCompany. South Milwaukee, Wia a TOO, Oscillating 2 48 40 112 6 7 8 e.225 9.825 11.825 135 210 250

W E GraceManufaetunngCo, Dallas, Texas' RSX 112, Oscillating 2 48 40 112 65 714 8 e,20O 140 224 310 TX 96, Oscillating 2 42 40 96 55 714 4 5.700 130 200 270 X 112, Single 1 48 40 112 55 714 4 3.200 144 228 314 RPX 10«,t)Bcillating 2 48 40 104 55 714 4 7.200 163 248 332 LXX 95, Oscillating 2 48 60 95 7 8 (•) 12.400 230 375 500 LX5XI20, Oscillating 2 eo 60 120 7 8 P) 14,250 259 455 652 LX6X136, Oscillatmg 2 72 60 130 7 8 (•) 16.250 286 525 765

Shovel Supply Co, Dallas, Teiaa Ferguson 112, Oscillatmg 2 48 40 112 55 7 8 6.340 10.200 150 242 Gebhard 22, Oscillating 2 72 60 144 625 8 8 425 685 Oebhard 22, Oscillatmg 2 60 eo 120 55 714 8 14.200 25.920 320 590 Model 112W. Oscillatmg 2 48 40 112 55 7 8 8.020 11.880 180 270 327 Model 112W-48, Oscillatinfi 2 48 48 112 55 8 8 9.700 15,280 21.190 220 347 481 Model 2. Reclamation OsAting 2 60 60 120 706 10 4 28.500 37,860 47.400 1.010 1.340 1.678

1 Length of each drum ' Diameter without feet > Number of feet shown here is standard Manufacturers provide more or fewer feet as may \» specified Most manufacturers are prepared to furnish specml shapes and sues if desired ' Number in one row times number of drums per unit » Based on one row of feet m contact with ground • Manufacturer! computations ' Loaded with water and boxes loaded with sand » Data from Powers Road and Street Cata• logue. 1960-61 • Not closer than II in , not farther than 13 m e e disgonally 3 ft for each 2 sq ft of drum area TABLE C 00

MANUFACTURERS SPECIFICATIONS FOR STANDARD WEIGHT 3-WHEEL POWER ROLLERS

Dimensions of rolls Roller com• Transmission speeds pression Guide roll Drive roll (Lb per bn in ) Roll Weight overlap Overall rolling width Manufacturer Model Type group (in each (inches) Gmde side) (tons) Diam Width Dmro Width Drive Low Int 3 4 High roU (m) (m) (io) (m) roU

Gallon Iron Works and Manufacturing Com• Warrior 3-wheel 6 1 4 2 9 6 0 36 41 55 18 98 224 m 70 with 18" rolls pany, Gallon, Ohio Warrior 3-wheel 7 1 2 2 5 4 3 38 41 60 18 114 261 3>A 70 with 18' rolls 20-in width rear raUs avaibible Warrior 3-wheel 8 1 2 2 5 4 3 38 41 60 13 130 298 3!4 70 with 18'rolls 20-m width rear rolls available Chief 3-wheel 10 2 0 5 0 44 44 69 20 152 336 4 76 with 20" rolls 22- and 24-in width rear rolls available Chief 3-whcel 12 2 9 5 0 44 44 69 20 182 403 4 76 with 20' rolls 22- and 24-in width rear rolls available Trench 3-wheel 8% 3 6 60 20 Hubcr Manufacturing Company, Marion, 3-wheel 5 1 7 3 4 34 37 52 18 97 217 3 67 with 18' rolls Ohio 3-wheel 6 1 7 3 4 34 37 52 18 97 239 3 67 with 18' rolb

3-whecl 8 3 0 4 0 5 2 40 40 60 18 134 308 2V4 71 with ir rolls

3-wheel 10 2 0 4 0 5 2 44 43 69 20 148 348 4 76 with 20' rolls 24-in width rear rolls available 3-wheel 12 2 0 4 0 6 2 44 43 69 20 187 416 4 76 with 20" rolls 24-in width rear rolb available W A Hiddell Corp, Bucyrus, Ohio 10G64 3-wheel 10 1 OS 3 20 5 38 44 42 68 20 168 364 4 74 with 20' rolls

12G 54 3-wheel 12 1 oe 3 20 5 38 44 42 68 20 193 405 4 74 with 20* rolb

Auatm-Westem Company, Aurora, III Cadet 3-whecl e 1 31 3 59 5 88 36V2 37 52 18 loe 230 3-5/8 66% with 18* rolls Weights for gasoline motor powered rol- er for 6-, 7-, 8-, 10 and 12-ton rollers Cadet 3-wheel 7 1 31 3 59 6 88 36 37 52 18 124 271 3-6/8 66% with ir rolls

Cadet 3-wbeel 8 I 36 3 70 e 04 37 37 54 18 136 314 3-5/8 66% with 18" rolls Special (8-ton) avail• able with 22-tn wheeb Autocrat 3-wheel 10 1 1 3 0 4 9 43 45 63 20 168 330 fA 22- and 24-in rear rolb avaibble Autocrat 3-wheel 12 1 1 3 0 4 9 43 45 68 Vi 20 105 387 4% 22- and 24-in rear rolls available i 1 TABLE D MANUFACTURERS SPECIFICATIONS FOR VARIABLE WEIGHT 3-WHEEL POWER ROLLERS

Dimensions of rolls Transmission speeds Roller compression (Miles per hour) (Lb per lin in ) Roll over- Weight Up Overall rothog width Type group On (inches) (tons) 00 Dum Width Dum Width Mai. each High Reverae (m) (in) (in) (in) Mai with side) with wet water sand

Buffalo - Springfield VM-18 3-wheel 5- 7 6 2 Same 64 With 16* ralb 18 u width rear rolls available Roller Co, Sprmg- field, Ohio VM-10 3-wbeel 6- 8 5 2 Same 68 with 18* rolls 20 m width rear rolls available

VM-21 3-wheel 7- 10 3 6 6 2 Same 68 with 18* rolls 20 and 22 in width rear rolls available VM-24 3-wheel 8- 11 3 e 6 2 Same 68 with 18- rolls 20, 22, and 24 tn width rear rolb available 3-wheel VM-31C 10-1214 3 9 9 0 Same 76 with 20* roUs 23 and 24 m width rear roUs available 3-wheel 12-15 6 0 Same VM-32C 3 6 76 with 20* rolls 23 and 24 in width rear rolb available

00 00

MANUFACTURERS SPECIFICATIONS FOR VARIABLE WEIGHT TANDEM POWER ROLLERS (Does not include 3-axle type)

Transmission speeds (Miles per hour) Dimensions of rolb Roller Compression—fLb per lln in )

Weight Type group Guide roll Drive roll Guide roll • (tomi) High Moi Mai Dmm Width Diam Width with with (in ) (in ) (in ) (in ) water sand

Gabon Iron Works and Man• Tandem 3-6 I 5 34 30 66 171 ufacturing Company, Tandem 5-8 1 5 34 40 108 144 130 207 Cialion, Ohio Tandcni 8-12 223 465 48 178 184 282 Tandem 10-14 223 465 48 206 217 317

Buifalo-Spriiiglicld. Spritig- KT-7 Tandem 3-5 159 3 02 30 Geld, Ohio 2 12 404 KT-I6C Heavy duty tandem 5- 8 I 75 35 50 40 63 140 KT-17C Heavy duty tandem 6- 9 I 75 35 50 40 63 151 233 KT-240 Heavy duty tandem 8-12 I 75 35 50 48 00 185 285 KT-25C Hravy duty tandem 10-14 I 7^ 35 50 48 60 240 340 VT-48 Heavy duty tandem 15-21 135 2 75 4 I 51'1 71% 330 505

Clyde Iron Works, Duluth, 21 Tandem 1-IU l;pto- 2 14 20 26 47 2| 67 6| Minn 80 Tandem 3-4 I'p lo- 2 44 36 107 156

Huber Manuructurtng Coni- Tandem 3- 4 26 44 44 64 112 171 patiy, Marion, Ohio Tandem 4- 5 20 44 44 64 68 150 198 Tandem 5- 8 195 3 62 52 97 135 125 203 Tandem 8-10 1 95 3 62 52 111 147 209 266 Tandem 8-12 29 57 114 173 3 207 4| 298 6 Tandem 10-14 57 185 240

Littleford Bros, Cincinnati, 185 Van- Tandem 4-6 100 Ohio Packer

Esaick Manufacturing Com• Tandem 114-2 1-1 8 2 8-3 4 2614 110 pany, Los Angeles. Calif 30O Tandem 2- 3 l-l 2 2 2-4 I 110 148 400 Tandem 3- 4 1-2 114-4 105 160 50O Tandem 1-3 2 1 5-6 36 156 Tandem m-i 23 42 50 136 5-8 Austin-Western ComiKiny, Tandem 5-8 I 0/2 26 2 26/4 63 145 Weights are for gaso- \iirora. 111 8 1014 I 0/2 20 2 20/4 63 242 I in e -powered modeb TaniiK) Mfg Co, Kan An• tonio, Texas

* Where compression for guide roll is not given it was not shown by manufacturer The Highway Research Board is organized under the auspices of the Division of Engineering and Industrial Research of the Na• tional Research Council to pro• vide a clearinghouse for highway research activities and informa• tion. The National Research Council is the operating agency of the National Academy of Sciences, a private organization of eminent American scientists chartered in 1863 (under a spe• cial act of Congress) to "investi• gate, examine, experiment, and report on any subject of science or art."