1-1

1. BASIC SOIL AND ROCK CHARACTERISTICS

1.1. THE PHASE DIAGRAM

Soils are normally composed of three constituents - solid soil particles, air and water. The air and water occupy the void spaces or pores between the solid particles. In the case of saturated soils the pore fluid is made up entirely of water.

To facilitate calculations involving various amounts of the three constituents of a soil it is convenient to represent these constituents by means of a diagram, often known as a phase diagram , as illustrated in Fig.1.1. The symbols for the masses and volumes of the constituents are also shown on this figure. The mass of the air occupying the voids is ignored since it is negligible by comparison with the masses of water and solid.

A number of definitions may now be given in terms of the symbols in Fig.1.1.

M + M Bulk Density ρ = W S (1.1) VA + V W + V s (Sometimes referred to as total density ρt)

Ms Dry Density ρd = (1.2) V A + V W + Vs

MW Density of Water ρw = (1.3) VW

3 ρw is commonly taken as 1000 kg/m for convenience Volume of Voids Vv = V A + V W (1.4)

V Void Ratio e = V (1.5) VS

V e Porosity n = V = , (1.6) VV + V S 1 + e often expressed as a percentage.

VW Degree of Saturation S or S r = . (1.7) VA + V W usually expressed as a percentage. 1-2

Volume Mass air VA

water VW MW

VS solid MS

Fig.1.1 Phase diagram for a partly Saturated soil

Volume Mass

VW water MW

VS solid MS

Fig.1.2 Phase diagram for a Saturated soil

Volume Mass

air VA

3 water VW MW

0.025 m

VS solid MS 45.0 kg

Fig.1.3 1-3

Density of Solid Particles or Soil Particle Density

Ms ρs = (1.8) Vs

Specific Gravity of Solid Particles ρ G = s (1.9) ρw Water Content or Moisture Content

M w = W , (1.10) MS usually expressed as a percentage.

VA Air Voids Va = , (1.11) VA + V W + V S usually expressed as a percentage.

With a saturated soil the volume of air becomes zero as illustrated in Fig.1.2. Referring to the figure a further definition can be given.

MW + M S Saturated Density ρsat = (1.12) VW + V S

Example A soil sample having a total volume of 0.025mm 3 and total mass of 45.0 kg. has been removed from the ground. If the water content and specific gravity of the soil are 20.0% and 2.68 respectively calculate: a) the dry density of the sample, b) the degree of saturation, c) the porosity.

Referring to the phase diagram in Fig.1.3 the unknown terms M S, M W, V A, V W, VS can be calculated as follows:

MW = w x M S = 0.20M S but MW + M S = 45.0 kg ∴ 1.20M S = 45.0 ∴ M S = 37.5 kg ∴ MW = 45.0 - 37.5 = 7.5 kg 1-4

The volumes can now be calculated

MW 7.5 3 VW = = = .0075 m ρw 1000 MS 37.5 3 VS = = = 0.014 m Gρw 2.68 x 1000 3 ∴ VA = .025 - .014 - .0075 = .0035 m

With these known quantitites the three items required can now be determined:

MS a) dry density ρd = (1.2) VA + V W + V S

37.5 = 1500 kg/m 3 = .025

V b) degree of saturation S = W (1.7) VA + V W

.0075 = 0.682 or 68.2% = .0035 + .0075

V + V c) porosity n = A W VA + V W + V S

.0035 + .0075 = 0.440 or 44.0% = .025

1.2 IDENTIFICATION OF SOILS In addition to the techniques described in Geomechanics 2 for identification of the mineralogical components of soils, a number of relatively simple laboratory tests which are useful in identifying various soil types, has been developed. The presentation here will concentrate on grain size and plasticity characteristics, but reference should be made to books on soil testing for details of the testing procedures. (Bowles, 1970, Lambe, 1951, Kezdi, 1980). More sophisticated laboratory tests, which may be used for soil identification are used on occasions but these will not be discussed in this introductory presentation.

1.2.1 GRAIN SIZE DISTRIBUTION Soils are traditionally described by one or more of the names gravel, sand, silt or clay which indicate sizes of the soil particles. A number of slightly different 1-5

classification systems are in use relating size ranges to these four names but probably the most widely used is the M.I.T. system as follows: Gravel - grain size greater than 2mm Sand - 0.06 mm to 2 mm Silt - 0.002 mm to 0.06 mm Clay - grain size less than 0.002 mm

Soils often consist of mixtures of these four ranges resulting in names such as silty sand, sandy clay, etc. The distribution of grain sizes in the gravel and sand ranges is found by sieving. A sample of dry soil is passed through a nest of sieves with the coarsest sieve at the top and the finest sieve at the bottom. The mass of soil retained on each sieve is measured as shown in the sample calculation in Table 1.1. From this information a histogram may be constructed as in Fig.1.4. Because of the large range of grain sizes encountered in soils a log scale is normally used. It has been found more convenient in soil engineering practice to integrate the histogram and to present the data as a cumulative distribution curve as illustrated by curve A in Fig.1.5.

Table 1.1 Sieve Analysis of a Sand Soil ______

Sieve Mass Retained Percent Cumulative Percent Aperture gm Retained Percent Retained Finer ______2.36 mm 2.5 2.6 2.6 97.4 1.18 mm 9.3 9.8 12.4 87.6 600 µm 25.2 26.5 38.9 61.1 300 µm 28.7 30.2 69.1 30.9 150 µm 18.1 19.0 88.1 11.9 75 µm 6.4 6.7 94.8 5.2 Pan 5.0 5.2 100.0 95.2 100.0

For soil classification purposes two parameters which can be determined from the grain-size distribution curve are often quoted. These are:

Effective Size which is the grain size corresponding to the 10 percent finer point on the curve. This can be referred to as D 10 . 1-6

Fig. 1.4 Histogram from a Sieve Analysis

Fig. 1.5 Grain size distribution curves

1-7

Uniformity Coefficient (C u) which is a measure of the uniformity of grain size in the soil and is defined as the ratio of the 60% finer size (D 60 ) to D 10 .

D60 that is Cu = (1.13) D10 For curve A in Fig.1.5 the uniformity coefficient is:

0.57 Cu = 0.14 = 4.1 which indicates a relatively uniform soil (sometimes referred to as poorly graded).

A grain size distribution curve for a soil with a uniformity coefficient larger than that for soil A in Fig.1.5 is illustrated by curve B (well graded soil) in Fig.1.5. For the silty clay soil represented by curve C in Fig.1.5 it is not possible to determine the uniformity coefficient since the effective size is unknown.

Coefficient of Cuvature (C c) is a value that can be used to identify a poorly graded soil.

2 (D30 ) Cc = (1.14) D10 .D60

A well graded soil has C c between 1 and 3 as long as C u is also greater than 4 for gravels and 6 for sands.

The finer portions of the grain size curves B and C cannot be determined by sieving since a sieve with an aperture of about 75 µm is normally the finest sieve used in this type of test. For silt and clay size soils the grain size distributions are found by means of a sedimentation procedure in which a sample of the soil is allowed to settle in water. This procedure utilizes Stokes Law which relates the size of a sphere to its fall velocity in a fluid (usually water) by means of the expression:

18000 η v D2 = (1.15) g(Gs - G w) where D is the sphere diameter in mm η is the dynamic viscosity of water in N sec/m 2 v is the fall velocity of the sphere in cm/sec. g is the gravitational acceleration in cm/sec 2. Gs is the specific gravity of the sphere solid Gw is the specific gravity of the water. 1-8

The concentration of solids in the water at a particular time after the commencement of sedimentation is found by measuring the specific gravity of the suspension with an hydrometer. Alternatively the concentration may be found by taking a small volume of suspension from a particular depth by means of a pipette. The mass of solids is determined by drying off the water.

During preparation of the suspension for a sedimentation (or hydrometer) test a deflocculating agent such as sodium hexametaphosphate or sodium silicate is customarily added to prevent the formation of soil flocs. Some clay soils behave in such a way that a variety of grain size distribution curves may be obtained depending upon the type and concentration of deflocculating agent that is used. Discussion of the recommended procedure for determining the grain size distribution of soils is given in the S.A.A. Standard AS1289.

1.2.2 SOIL PLASTICITY Changes in soil water content can produce significant changes in soil behaviour. It is not surprising therefore to find that two widely used identification tests involve observations of soil behaviour at two different water contents. In these tests water contents, known as the Atterberg Limits , at which particular soil characteristics develop are measured.

The larger water content, known as the Liquid Limit (w l) is the water content at which the soil flows in a specially made cup when subjected to a series of small blows. The liquid limit device permits the cup containing the soil in which a small groove has been cut, to be lifted and dropped a small distance. The liquid limit is the water content at which the groove closes when the soil has been subjected to 25 blows. The test is performed by counting the number of blows to close the groove at various water contents. The results are then plotted on a diagram such as Fig.1.6, from which the liquid limit may be interpolated. The liquid limit may be estimated from the results of a test at a single value of water content (w). If the number of blows for this test is n then the following expression can be used to provide an estimate of w l.

n 0.121 wl = w( 25 ) (1.16) For many Australian soils the following expression has been found to provide a better estimate of w l. n wl 0.091 = w( 25 ) (1.17) 1-9

Small laboratory cone penetrometers are increasingly being used for the measurement of liquid limit. The British (BS 1377-1975) device for example is 35mm long cone and has a 30 o tip and a mass of 80 g. The liquid limit is taken to be the water content of the soil when the penetration of this cone is 20 mm.

The smaller water content, known as the Plastic Limit (w p) is the water content at which small threads of the soil crumble when rolled to a diameter of 3mm.

Fig. 1.6 Flow curve for Liquid Limit determination

These two tests are conducted on clayey and silty soils. These tests cannot be conducted on granular soils such as sands and gravels. (See S.A.A. Standard AS1289). The typical liquid and plastic limits for some clay soils are illustrated in Table 1.2 which demonstrates the magnitude of the influence of the adsorbed cation as well as the type of clay mineral. 1-10

TABLE 1.2 Typical Atterberg Limits for some Clay Soils ______

Soil Liquid Limit (w l) Plastic Limit (w p) (%) (%) ______Sodium Kaolinite 50 30 Calcium Kaolinite 40 28 Sodium montmorillonite 700 50 Calcium montmorillonite 500 80 Sodium Illite 120 50 Calcium Illite 100 45 ______Some frequently used terms which involve the Atterberg Limits are:

Plasticity Index IP = w l - w p (1.18) and gives a measure of the range of water content over which the soil is in a plastic state. w - w Liquidity Index = p (1.19) wl - w p

wl - w Consistency Index = (1.20) wl - w p

The liquididty and consistency indices are measures of the natural water content (w) of a soil in relation to the liquid and plastic indices.

Plasticity Index Activity = (1.21) percent of soil finer than 2 µm

High activity is associated with high water retention capability, high compressibility, low strength, high swelling and shrinking by comparison with low activity soils. Soil with an activity within the range of 0.75 to 1.25 is considered normal. Inactive soils have values below 0.75 while active soils have values above 1.25. Some typical values of activity are: Sodium montmorillonite 6 Calcium montmorillonite 1.5 Illite 0.9 Kaolinite 0.4 A graphical plot of plasticity index against liquid limit (called a plasticity chart) is frequently used to classify fine grained soils (silts and clays) as illustrated in Fig.1.7. 1-11

The plot is divided into four regions by the two lines as shown. The group symbols in these regions are interpreted as follows:

C - clay M - silt O - organic soil H - high plasticity L - low plasticity

As an example the symbol CH means inorganic clays of high plasticity. The montmorillonites in Table 1.2 are CH soils.

The relationship between the Atterberg limits and the engineering properties of soils by means of the plasticity chart was first observed by Casagrande (1932).

Fig. 1.7 Plasticity chart for classification of fine grained soils.

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1.3 SOIL CLASSIFICATION Several soil classificaton systems are in common use, most of them being based upon grain size distributions of soils and some based upon a combination of grain size and plasticity characteristics. One widely used system is the Unified Soil Classification System which is detailed in Tables 1.3 and 1.4 and in which soils are initially sub-divided into coarse grained or fine grained on the basis of grain size. Further sub-divisions are made into various groups depending upon grain size and plasticity characteristics. The above tables which are metricated and are taken from AS1726-1975, SAA Site Investigtion Code, follow the original Unified Classification System(USBR Earth Manual) and ASTM D2487-69 except that they adopt the particle size limits given in AS1289 and other standards, viz:

Gravel 2-50mm Sand 0.06-2mm Silt and Clay < 0.06mm The system excludes the boulder and cobble fractions of the soil and classifies only the material less than 60mm in size. In the original Unified Classification System the grain sizes used corresponded to the No. 200 (74 µm) and No. 4 (4.7mm) sieves, whereas in this metricated system the grain sizes (in Tables 1.3 and 1.4) are 0.06mm and 2.0mm respectively. As 60mm, 2mm and 0.06mm sieve sizes are not normally used, the percentages passing these sizes can be obtained from a particle size distribution curve determined from a laboratory test. Alternatively, the percentages passing may be estimated in the field.

The plasticity chart (Fig.1.7) is used to classify the fine grained soils and the fines (fraction smaller than 0.06mm) that may be present in the coarse grained soils. The meanings of the letters used for the group symbols are given partly in Section 1.2.2, the remainder being given below:

G - gravel S - sand W - well graded P - poorly graded. Some typical engineering characteristics of the soil groups in Table 1.3 are listed in Table 1.5. The Unified Soil Classification System has been described in more detail by the U.S. Corps of Engineers (1953). 1-13

Example Classify the following soils according to the Unified Soil Classification System and comment briefly on their suitability for the impervious zone of an earth dam.

Soil A B C D % finer than 0.06mm 4 58 25 18 % finer than 2.0mm 40 85 70 62 Liquid Limit (%) - 55 40 35 Plastic Limit (%) - 15 20 27

Soil A is a gravel since more than half is larger than 0.06mm and more than half is larger than 2.0mm. It is a clean gravel since there are less than 5% fines (finer than 0.06mm). The grain size curve for this gravel has been estimated from the two known points in Fig.1.8. Although the uniformity coefficient C u is not known it is certainly greater than 4 and the value of C c is probably around unity - consequently the soil may be classified as GW, a well graded gravel.

Because this soil is highly permeable it would be unsuitable for the impervious zone of an earth dam.

Soil B is a fine grained soil since more than half is finer than 0.06mm. This soil plots in the CH region of the plasticity chart Fig.1.7 based on the Atterberg limits. The soil is therefore CH, a highly plastic clay.

Because this soil is very impermeable it could be suitable for the impervious core of an earth dam but only if a thin core is used becuase CH soils are low in strength by comparison with other more suitable impervious soils.

Soils C and D are sands since more than half of the material is larger than 0.06mm and more than half of the coarse fraction is smaller than 2.0mm. Because both soils contain more than 12% fines, the soils must classify as either SC or SM. From the plasticity chart soil C plots above the A line whereas soil D plots below the A line. Therefore soil C is SC, a clayey sand and soil D is SM, a silty sand.

Both types of soil would be suitable for the impervious core of an earth dam. 1-14

TABLE 1.3 UNIFIED SOIL CLASSIFICATION SYSTEM (from Add. No. 1 (Feb. 1978) to AS1726 - 1975)

TABLE 1.3 UNIFIED SOIL CLASSIFICATION SYSTEM (from Add. No. 1 (Feb. 1978) to AS1726 - 1975

1-15

TABLE 1.4 UNIFIED SOIL CLASSIFICATION SYSTEM (from Add. No. 1 (Feb. 1978) to AS1726 - 1975)

e

n

i

l

"

A Above"A"linewith PIbetween4and7 areborderlinecases dual requiringuseof symbols " Above"A"linewith PIbetween4and7 areborderlinecases dual requiringuseof symbols or OH MH

CH 60 60 2 2 30 30 10 10 OL 60 10 60 10 CI Liquidlimit (D ) (D ) Plasticitychart ------D xD ------D xD D ---- D or D ---- D criteria U c c U ML C = Greaterthan4 C = Between1and3 C = Greaterthan6 C = Between1and3

CL o etnalgaaineurmnsfrGW for gradationrequirements meetingall Not below Atterberglimits "A"lineorPIlessthan4 above"A" Atterberglimits linewithPIgreaterthan7 omeigl rdtorqieet o SW for gradationrequirements Notmeetingall tebrlmt below Atterberglimits "A"lineorPIlessthan4 above"A" Atterberglimits linewithPIgreaterthan7

aoaoyclassification Laboratory

CL-ML

o laboratoryclassificationoffinegrainedsoils for

%t 12% to 5% odln aerqiigueo ulsymbols dual of use requiring case Bordeline

oprnsisatequalliquidlimit Comparingsoils increase Toughnessanddrystrength withincreasingplasticityindex oeta 12% than More M C M SC SM, GC, GM,

0 10 20 30 40 50 60 70 80 90 100 esta 5% than Less

W P W SP SW, GP, GW, 0

60 50 40 30 20 10

iv ie oregandsisaecasfe sfollows as classified are soils grained coarse size) sieve

lsiiyindex Plasticity

75mm .0 than smaller (fraction fines of percentages on Depending

ve cur size grain from sand and gravel of percentages Determine

e il identification field der un given as fractions the identifying in curve size grain Use ddescription) describingsoils Informationrequiredfor ieyia ae indicatedegree name; Givetypical andcharacterofplasticity, andmaximumsizeof amount con- inwet colour coarsegrains: or any,local dition,odourif andotherpert- name, geological inentdescriptiveinformation,and inparentheses symbol undisturbedsoilsaddinfor- For stratif- mationonstructure, consistencyandundis- ication, turbedandremouldedstates, moistureanddrainageconditions Example brown:slightlyplastic: Clayeysilt, percentageoffinesand: small rootholes:firm numerousvertical anddryinplaces;loess;(ML) ieyia ae:indicateap- names: sand Givetypical proximatepercentagesof maximumsize: andgravel: surfacecondition, angularity, andhardnessofthecoarse orgeologicalname grains:local andotherpertinentdescriptive informationandsymbolin parentheses. degree undisturbedsoilsaddinfor- For mationonstratification, ofcompactness,cementation, moistureconditionsanddrain- agecharacteristics. Example: 20% Siltysand,gravelly;about particles rounded hardangulargravel 12.5mmmaximumsize; andsubangularsandgrains 15%non- coarsetofine,about lineswithlowdry plastic compactedand strength;well moistinplaces;alluvialsand; (SM) yia names Typical elgaegaes gravel- gradedgravels, Well no littleor sandmixtures, fines gravel- Poorlygradedgravels, no littleor sandmixtures, fines poorly mixtures Siltygravels, gradedgravel-sand-silt poorlygraded Clayeygravels, gravel-sand-claymixtures gravelly gradedsands, Well littleornofines sands, gravelly Poorlygradedsands, littleornofines sands, poorlygraded Siltysands, mixtures sand-silt poorlygraded Clayeysands, sand-claymixtures Inorganicsiltsandveryfinesands, clayey rockflour,siltyor finesandswithslightplasticity lowtomedium sandy Inorganicclaysof plasticity,gravellyclays, leanclays siltyclays, clays, silt- siltsandorganic Organic claysoflowplasticity micaceousor inorganicsilts, dictomaceousfinesandyor elasticsilts siltysoils, high Inorganicclaysof clays plasticity,fat mediumto claysof Organic highplasticity andotherhighlyorganicsoils Peat 1 ML OL MH CH OH Pt GW GP GM GC SW SP SM SC Group CL,CI symbols High None limit) Slight medium medium Medium Slightto Slightto nfesi classification(includingidentificationan Unifiedsoil Toughness nearplastic (consistency on high none slow slow Slow None Slowto Quickto (reaction Dilatency toshaking) Nonetovery Nonetovery high high Readilyidentifiedbycolour,odour spongyfeelandfrequentlybyfibrous texture high istics slight sievesize Noneto medium medium Slightto Slightto

crushing character-

Mediumto Mediumto Widerangeofgrainsizeandsubstantial all intermediateparticle amountsof sizes rangeof sizes Predominantlyonesizeora withsomeintermediate sizes missing identification Non-plasticfines(for seeMLbelow) procedures identificationpro- Plasticfines(for seeCLbelow) cedures Widerangeingrainsizesandsub- intermediate amountsofall stantial particlesizes rangeof sizesmissing Predominantelyonesizeora withsomeintermediate sizes identificationpro- Non-plasticfines(for seeMLbelow) cedures, identificationpro- Plasticfines(for seeCLbelow) cedures, r strength Dry Hightovery

muto fines) of amount muto fines) of amount

fines) fines)

(apreciable (appreciable

ltl rno or (little ltl rno or (little

fines fines

la gravels Clean

estimatedweights) sands Clean

rvl with Gravels ad with Sands 50

esta 50 than less

rae than greater

iudlimit liquid

Fieldidentificationprocedures limit liquid

it n clays and Silts

2.36mm 2.36mm

it n clays and Silts

rcini agrthan larger is fraction rcini mle than smaller is fraction

Identificationprocedureonfractionsmallerthan.425mm oeta afo coarse of half than More oeta afo coarse of half than More

Gravels Sands

otenkdeye naked the to

(Excludingparticleslargerthan75mmandbasingfractions visible particle smallest the about is size sieve .075mm The ihyrai soils Highlyorganic

05mseesize sieve .075mm 05mseesize sieve .075mm

oeta afo aeili mle than smaller is material of half than More oeta afo aeili agrthan larger is material of half than More

iegandsoils grained Fine oregandsoils grained Coarse TABLE 1.5

ENGINEERING CHARACTERISTICS OF MAJOR SOIL TYPES ______

MAJOR DIVISIONS LETTER COMPRESSIBILITY DRAINAGE VALUE FOR EMBANKMENTS PERMEABILITY COMPACTION CHARACTERISTICS & EXPANSION CHARACTERISTICS cm/sec ______GW Almost Excellent Very stable, pervious shells k > 10 -2 Good, tractor, rubber-tyred, None of dikes and dams steel wheeled roller ______GRAVEL Almost Excellent Reasonably stable, pervious k > 10 -2 Good, tractor, rubber-tyred, and GP None shells of dikes and dams steel-wheeled roller. GRAVELLY SOILS GM Very Fair to Poor Reasonably stable, not k = 10 -3 Good, with close control slight to to practically paticularly suited to shells, to 10 -6 rubber-tyred, steel wheeled COARSE slight impervious but may be used for roller. impervious cores or blankets. GRAINED SOILS GC Slight Poor to Fairly stable, may be used k = 10 -6 to Fair rubber-tyred, sheeps practically for impervious core. 10 -8 foot roller. impervious ______SW Almost Excellent Very stable, pervious k > 10 -3 Good, tractor. None sections slope protection required. ______SAND SP Almost Excellent Reasonably stable, may be k > 10 -3 Good, tractor. and None used in dike section with SANDY flat slopes. SOILS Very Fair to poor Fairly stable, not k = 10 -3 Good with close control SM slight to to practically particularly suited to shells, to 10 -6 rubber-tyred, sheeps foot slight to impervious but may be used for roller. medium impervious cores or dikes. ______SC Slight to Poor to Fairly stable, use for k = 10 -6 Fair, sheeps foot roller medium practically impervious core for flood to 10 -8 Rubber-tyred. impervious control structures. ______1-17

TABLE 1.5 (cont.)

ML Slight to Fair to Poor Poor stability, may be used k = 10 -3 Good to poor, close control SILTS medium for embankments with proper to 10 -6 essential, rubber-tyred roller control. ______and CLAYS CL Medium Practically Stable, impervious cores and k = 10 -6 Fair to good, sheeps foot roller, impervious blankets to 10 -8 rubber tyred ______

FINE wl < 50 OL Medium to Poor Not suitable for embankments k = 10 -4 Fair to poor, High to 10 -6 sheeps foot roller. ______

GRAINED MH High Fair to poor Poor stability, core of hydraulic k = 10 -4 Poor to very poor, sheeps SOILS fill dam, not desirable in to 10 -6 foot roller. rolled fill construction. ______

SILTS CH High Practically Fair stability with flat slopes k = 10 -6 Fair to poor, sheeps foot roller and impervious thin cores, blankets and dike to 10 -8 CLAYS sections. ______wl > 50 OH High Practically Not suitable for embankments k = 10 -6 Poor to very poor, sheeps foot impervious to 10 -8 roller. ______HIGHLY Pt Not used for construction Compaction not practical ORGANIC SOILS

FIG1.8

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1.4 ROCK CLASSIFICATION SYSTEMS

In discussing rock classification systems a distinction needs to be made between rock mass and rock substance. A rock mass consists of an aggregate of blocks of rock substance separated by discontinuities : structural features such as bedding planes, cleavage planes, joint planes, fissures and solution cavities. Locally, planes of structural weakness may be open and air-filled, water-filled or infilled with alteration products or materials of a nature different from that of the rock blocks. Alternatively, the rock mass may be traversed by fracture planes on either side of which the rock blocks abut tightly. The rock mass will conform to the geological structure of the area and may be affected by folding and faulting.

The blocks of rock substance lying between discontinuities or joint planes are composed of aggregates of mineral particles together with voids which may be isolated or interconnected and air- or water-filled. Additionally the rock substance may contain closed or incipient joints which are not always visible to the naked eye.

Rock classification systems, many of which were developed to assist in assessing rock mass behaviour in tunnelling, are used to:

(a) Divide a particular rock mass into zones of similar behaviour; (b) Provide a basis for understanding the characteristics of each zone; (c) Yield quantitative or semi-quantitative data for engineering design; (d) Provide a common basis for communication. Examples of widely used classification systems, a few of which are described in more detail on the following pages, are: 1. Rock loads acting on tunnel supports (Terzaghi, U.S.A., 1946) 2. Stand-up time of unsupported tunnels (Lauffer, Austria, 1958) 3. Degrees of weathering of rock substance (Moye, Australia, 1958) 4. Rock Quality Designation, RQD (Deere, U.S.A., 1964) 5. Description of Rock Properties for Foundation Purposes (ASCE, 1972) 6. Rock Structure Rating, RSR (Wickham, U.S.A., 1972) 7. Geomechanics Classification, or Rock Mass Rating, RMR (Bieniawski, South Africa, 1973) 8. Rock Mass Quality, Q (Barton, Norway, 1974) 9. Uniaxial compressive strength (International Society for Rock Mechanics, 1979) 10. Basic Geotechnical Description (I.S.R.M., 1981). 1-20

1.4.1 Rock Substance Weathering

The Moye classification was originally developed for the granitic rocks of the Snowy Mountains area. In spite of some deficiencies it is now generally applied to most rocks. FR Fresh: no visible sign of weathering. FRST Fresh, with Limonite Stained Joints : weathering limited to the surfaces of major discontinuities. SW Slightly Weathered: penetrative weathering developed on open discontinuity surfaces, but only slight weathering of rock substance. MW Moderately Weathered: weathering extends throughout the rock mass, but the rock substance is not friable. HW Highly Weathered: weathering extends throughout the rock mass, and the rock substance is partly friable. CW Completely Weathered: the rock is wholly decomposed and in a friable condition, but the rock texture and structure are preserved. RS Residual Soil: a soil material with the original texture, structure and mineralogy of the rock completely destroyed.

A slightly different classification system (MDB) was developed by McMahon, Douglas and Burgess. In contrast to the Moye system, the MDB system does not assume that a progressive loss of strength always occurs as an effect of increased weathering.

1.4.2 Rock Quality Designation (RQD) This is an index based on modified core recovery, from diamond drilling with double tube core barrels, of at least NX size (54 mm diameter). Only the sound pieces of core, 100mm or more in length, are considered.

RQD is expressed as the percentage of the total length drilled that is recovered in lengths of at least 100mm.

RQD 91 - 100 Excellent 76 - 90 Good 51 - 75 Fair 25 - 50 Poor 0 - 24 Very Poor 1-21

1.4.3 The Geomechanics Classification (RMR System)

This engineering classification of rock masses uses the following parameters, which can be obtained from bore cores, or measured in the field: Uniaxial Compressive Strength of Rock Substance Rock Quality Designation (RQD) Spacing of Discontinuities Condition of Discontinuities Groundwater Conditions Orientation of discontinuities

From the RMR value which is obtained by adding the five ratings in Table 1.6 and adjusting the total in accordance with Table 1.7, the probable stand-up time for a given diameter tunnel in the described rock mass can be estimated and the method of excavation can be recommended. The effective deformation modulus (E M) of foundation rock can also be deduced from its RMR:

EM = 2(RMR) - 100 GPa (1.22) for RMR greater than 50, and X EM = 10 GPa (1.23) where X = (RMR - 10)/40 for RMR less than 50

1-22

TABLE 1.6 - RMR - Classification Parameters and their Ratings

Parameter Ranges of Values 1 Strength Point-load For this low range- of intact strength >10 MPa 4-10 MPa 2-4 MPa 1-2 MPa uniaxial comp test is rock index preferred material Uniaxial 5-25 1-5 <1 compressive >250 MPa 100-250 MPa 50-100 MPa 25-50 MPa MPa MPa MPa strength Rating 15 12 7 4 2 1 0 2 Drill core quality RQD 90-100% 75-90% 50-75% 25-50% < 25%

Rating 20 17 13 8 3 3 Spacing of >2 m 0.6-2 m 200-600mm 60-200mm <60mm discontinuities

Rating 20 15 10 8 5 Lightly 4 Very rough Lightly rough Slickensided rough surface.Not surfaces. Or Gorge<5 surfaces. Soft gorge >5 mm Condition of continuous.N Seperation<1 mm thick Or o Seperation< thick Or Seperation > discontinuities mm. Slightly Seperation separation.Un 1mm. 5 mm continuous weathered 1-5 mm weathered Highlyweath walls continuous rock ered walls Rating 30 25 20 10 0 Ground < 10 10-25 25-125 5 Inflow per 10m None >125 liters/min water tunnel length liters/min liters/min liters/min Ratio (Joint water pressure/major 0 0.0-0.1 0.0-0.2 0.2-0.5 > 0.5 principal stress) Completely General Damp Wet Dripping Flowing conditions dry Rating 15 10 7 4 0

TABLE 1.7 RMR - RATING ADJUSTMENT FOR DISCONTINUITY ORIENTATIONS ______

Strike and dip Very Favourable Fair Unfavourable Very orientations of joints favourable unfavourable Tunnels 0 -2 -5 -10 -12 Ratings Foundations 0 -2 -7 -15 -25 Slopes 0 -5 -25 -50 -60

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TABLE 1.8 RMR - ROCK MASS CLASSES DETERMINED FROM TOTAL RATINGS ______

Rating 100 <−− 81 80 <−− 61 60 <−− 41 40 <−−21 < 20 Class No I II III IV V Description Very good rock Good rock Fair rock Poor rock Very poor rock

TABLE 1.9 RMR - MEANING OF ROCK MASS CLASSES

Fig. 1.9 Use of RMR to estimate Stand-up Time

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1.4.4 Rock Mass Quality (Q) The six parameters chosen to describe the rock mass quality Q are as follows:

RQD = rock quality designation Jn = joint set number Jr = joint roughness number Ja = joint alteration number Jw = joint water reduction factor SRF = stress reduction factor.

These parameters are combined in pairs and are found to be crude measures of: 1. relative block size (RQD/J n) 2. inter-block shear strength (J r/J a) ( ≅ tan φ) 3. active stress (J w/SRF) The overall quality Q is equal to the product of the three pairs:

Q = (RQD/J n) . (J r/J a) . (J w/SRF) (1.24)

Thus, the following rock mass would be most favourable for tunnel stability: high RQD-value, small number of joint sets, appreciable joint roughness, minimal joint alteration of filling, minimal water inflow, and favourable stress levels. From a large number of case histories an approximate relationship has been developed between Q and RMR.

RMR = 9 ln(Q) + 44 (1.25)

Ratings for the six parameters are given in Tables 1.10 - 1.15.

TABLE 1.10 ROCK QUALITY DESIGNATION (RQD)

See section 1.4.2. Where RQD is reported or measured as ≤ 10, (including 0) a nominal value of 10 is used to evaluate Q in equation (2.23). RQD intervals of 5, i.e. 100, 95, 90 etc. are sufficiently accurate. 1-25

TABLE 1.11 JOINT SET NUMBER (J n) ______

A. Massive, no or few joints 0.5-1.0 B. One joint set 2 C. One joint set plus random 3 D. Two joint sets 4 E. Two joint sets plus random 6 F. Three joint sets 9 G. Three joint sets plus random 12 H. Four or more joint sets, random, heavily jointed, "sugar-cube" etc. 15 J. Crushed rock, earthlike 20

Note: (i) For intersections use (3.0 x J n) (ii) For portals use (2.0 x J n)

TABLE 1.12 JOINT ROUGHNESS NUMBER (J r) ______

(a) Rock wall contact and (b) Rock wall contact before 10 cm shear

A. Discontinuous joints 4 B. Rough or irregular, undulating 3 C. Smooth, undulating 2 D. Slickensided, undulating 1.5 E. Rough or irregular, planar 1.5 F. Smooth, planar 1.0 G. Slickensided, planar 0.5

Note: (i) Descriptions refer to small scale features and intermediate scale features, in that order. (c) No rock wall contact when sheared

H. Zone containing clay minerals thick enough to prevent rock wall contact 1.0 J. Sandy, gravelly or crushed zone thick enough to prevent rock wall contact 1.0

Note: (ii) Add 1.0 if the mean spacing of the relevant joint set is greater than 3m. (iii) J r = 0.5 can be used for planar slickensided joints having lineations, provided the lineations are orientated for minimum strength. 1-26

TABLE 1.13 JOINT ALTERATION NUMBER (J a) ______(J a) (φr) (a) Rock wall contact (approx) A. Tightly healed, hard, non-softening, impermeable filling i.e. quartz or epidote 0.75 (-) B. Unaltered joint walls, surface staining only 1.0 (25-35 o) C. Slightly altered joint walls. Non-softening mineral coatings, sandy particles, clay-free disintegrated rock etc. 2.0 (25-30 o) D. Silty-, or sandy-clay coatings, small clay fraction (non-soft) 3.0 (20-25 o) E. Softening or low friction clay mineral coatings, i.e. kaolinite or mica. Also chlorite, talc, gypsum, graphite etc., and small quantities of swelling clays. 4.0 ( 8-16 o)

(b) Rock wall contact before 10 cm shear F. Sandy particles, clay-free disintegrated rock etc. 4.0 (25-30 o) G. Strongly over-consolidated non- softening clay mineral fillings (continuous, but <5mm thickness) 6.0 (16-24 o) H. Medium or low over-consolidation, softening clay, mineral fillings (continuous but <5mm thickness) 8.0 (12-16 o) J. Swelling -clay fillings, i.e. montmorillonite (continuous, but <5mm thickness). Value of J a depends on percent of swelling clay-size particles, and access to water etc. 8-12 ( 6-12 o)

(c) No rock wall contact when sheared K, Zones or bands, of disintegrated L, or crushed rock and clay (see M. G,H,J for description of 6,8 clay condition) or 8-12 ( 6-24 o) N. Zones or bands of silty- or sandy- clay, small clay fraction (non- softening) 5.0 ( - ) O, Thick, continuous zones or P, bands of clay (see G,H,J for 10,13, R. description of clay condition) or 13-20 ( 6-24 o) 1-27

TABLE 1.14 JOINT WATER REDUCTION FACTOR (J w) ______(J w) Approx. water pres. (kg/cm 2) A. Dry excavations or minor inflow i.e. <5 1/min. locally 1.0 < 1 B. Medium inflow or pressure, occasional outwash of joint fillings 0.66 1-2.5 C. Large inflow or high pressure in competent rock with unfilled joints 0.5 2.5-10 D. Large inflow or high pressure, considerable outwash of joint fillings 0.33 2.5-10 E. Except ionally high inflow or water pressure at blasting, decaying with time 0.2-0.1 >10 F. Exceptionally high inflow or water pressure continuing without noticeable decay 0.1-0.05 >10

Note: (i) Factors C to F are crude estimates. Increase J w if drainage measures are installed. (ii) Special problems caused by ice formation are not considered. 1-28

TABLE 1.15 STRESS REDUCTION FACTOR (SRF) ______

(a) Weakness zones intersecting excavation, which may cause loosening of rock mass when tunnel is excavated

A. Multiple occurrences of weakness zones containing clay or chemically disintegrated rock, very loose surrounding rock (any depth) 10 B. Single weakness zones containing clay or chemically disintegrated rock (depth of excavation ≤ 50m) 5 C. Single weakness zones containing clay or chemically disintegrated rock (depth of excavation >50m) 2.5 D. Multiple shear zones in competent rock (clay-free), loose surrounding rock (any depth) 7.5 E. Single shear zones in competent rock (clay-free) (depth of excavation ≤ 50m) 5.0 F. Single shear zones in competent rock (clay-free) (depth of excavation > 50m) 2.5 G. Loose open joints, heavily jointed or "sugar cube" etc. (any depth) 5.0

Note: (i) Reduce these values of SRF by 25-50% if the relevant shear zones only influence but do not intersect the excavation.

(b) Competent rock, rock stress problems σc/σ1 σt/σ1 (SRF) H. Low stress, near surface >200 >13 2.5 J. Medium stress 200-10 13-0.66 1.0 K. High stress, very tight structure (usually favourable to stability, may be unfavourable for wall stability) 10-5 0.66-.33 0.5-2 L. Mild rock burst (massive rock) 5-2.5 0.33-.16 5-10 M. Heavy rock burst (massive rock) < 2.5 <0.16 10-20

Note: (ii) For strongly anisotropic virgin stress field (if measured): when 5 ≤ σ 1/σ3 ≤ 10, reduce σc and σt to 0.8 σc and 0.8 σt. When σ1/σ3 > 10, reduce σc and σt to 0.6 σc and 0.6 σt, where: σc = unconfined compression strength, and σt = tensile strength (point load) and σ1 and σ3 are the major and minor principal stresses. (iii) Few case records available where depth of crown below surface is less than span width. Suggest SRF increase from 2.5 to 5 for such cases (see H).

(c) Squeezing rock plastic flow of incompetent rock under the influence of high rock pressure N. Mild squeezing rock pressure 5-10 O. Heavy squeezing rock pressure 10-20

(d) Swelling rock chemical swelling activity depending on presence of water P. Mild swelling rock pressure 5-10 R. Heavy swelling rock pressure 10-15

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Additional notes relating to use of Tables 1.10-1.15:

1. When borecore is unavailable, RQD can be estimated from the number of joints per unit volume, in which the number of joints per metre for each joint set are added. A simple relation can be used to convert this number to RQD for the case of clay-free rock masses: RQD = 115 - 3.3 J v (approx.) where 3 Jv = total number of joints per m (RQD = 100 for J v < 4.5) 2. The parameter J n representing the number of joint sets will often be affected by foliation, schistosity, slatey cleavage or bedding etc. If strongly developed these parallel "joints" should obviously be counted as a complete joint set. However, if there are few "joints" visible, or only occasional breaks in bore core due to these features, then it will be more appropriate to count them as "random joints" when evaluating J n in Table 1.11. 3. The parameters J r and J a (representing shear strength) should be relevant to the weakest significant joint set or clay filled discontinuity in the given zone. However, if the joint set or discontinuity with the minimum value of (J r/J a) is favourably oriented for stability, then a second, less favourably orientated joint set or discontinuity may sometimes be of more significance, and its higher value of (J r/J a ) should be used when evaluating Q from equation (1.24). The value of (J r/J a) should in fact relate to the surface most likely to allow failure to initiate.

REFERENCES Bieniawski, Z.T. - "Engineering classification of jointed rock masses". Trans. S. Afr. Inst. Civ. Engrs, Vol. 15, No. 12, 1973, pp 335-344. Bowles, J.E. - "Engineering Properties of Soils and their Measurement". McGraw-Hill Book Company, 187 p., 1970. Casagrande, A. - "Research on the Atterberg Limits of Soils", Public Roads, 13, pp 121- 136, 1932. Deere, D.V. - "Technical description of rock cores for engineering purposes. Rock Mechanics and Engineering Geology, Vol. 1, No. 1, 1964, pp 17-22. I.S.R.M. Commission on Classification of Rocks and Rock Masses - "Basic Geotechnical Description of Rock Masses". Int. J. Rock Mech. Min.Sci, Vol. 18, 1981, pp 85-110. Kezdi, A. - "Handbook of Soil Mechanics", Vol. 2, Soil Testing, Elsevier Scientific Publishing Company, 258 p., 1980. Lambe, T.W. - "Soil Testing for Engineers", John Wiley & Sons, 165 pp. 1951. 1-30

Moye, D.G. - "Engineering geology for the Snowy Mountains Scheme". J.I.E. Aust., Vol. 27, 1955, pp 281-299. Moye, D.G. - "Engineering Geology Manual". Snowy Mountains Hydroelectric Authority, 1958. Standards Association of Australia - "Method of Testing Soils for Engineering Purposes", Australian Standard AS1289. U.S. Corps of Engineers, Waterways Experiment Station - "Unified Soil Classification System", Tech. Memo. 3-357, 1953. Wickham, G.E, Tiedemann, H.R. & Skinner, E.H. - "Support determinations based on geologic predictions", Rapid Excavation & Tunneling Conference, Chicago 1972, pp 43-64.

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