FOUNDATION DESIGNOF CAISSONS ONGRANITIC AND

VOLCANIC ROCKS

GEO REPORT No. 8

T.Y. Man & G.E. Powell

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© Hong Kong Governmentjpre-asco 22 KAY 1997

First published, November 1991 | CLASS NO.First Reprint, April 1995 '

Prepared by:

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PREFACE

In keeping with our policy of releasing information ofgeneral technical interest, we make available some of our internalreports in a series of publications termed the GEO Report series.The reports in this series, of which this is one, are selected from awide range of reports produced by the staff of the Office and ourconsultants.

Copies of GEO Reports have previously been madeavailable free of charge in limited numbers. The demand for thereports in this series has increased greatly, necessitating newarrangements for supply. In future a charge will be made to coverthe cost of printing.

The Geotechrdcal Engineering Office also publishesguidance documents and presents the results of research work ofgeneral interest in GEO Publications. These publications and theGEO Reports are disseminated through the Government'sInformation Services Department. Information on how to purchasethem is given on the last page of this report.

A. W. MalonePrincipal Government Geotechnical Engineer

April 1995

EXPLANATORY NOTE

This GEO Report consists of the following two technical review documentsprepared by the Advisory Section of the now defunct New Works Division on thesubject of caisson design in igneous rocks :

Section Title Page.No.

1 Foundation Design of Caissons on Granitic Rocks : 5A Technical ReviewT.Y. Irfan & G.E. Powell (1982)

2 Foundation Design of Caissons on Volcanic Rocks : 57A Technical ReviewT.Y. Irfan (1983)

1 FOUNDATION DESIGNOF CAISSONS ON

GRANITIC ROCKS :A TECHNICAL REVIEW

T.Y. Irfan & G.E. Powell

This report was originally produced as GCO Report No. 16/82

CONTENTS

PageNo.

Title Page 5

CONTENTS 6

1 . INTRODUCTION 8

2. ALLOWABLE BEARING STRESS 9

2.1 Building Codes 9

2.2 Empirical Correlation between RQD and Allowable Bearing 10Stress

2.3 Canadian Foundation Engineering Method 10

3. SETTLEMENT OF FOUNDATIONS ON ROCK 10

3.1 Rock Mass Modulus 11

3.1.1 Effect of Weathering on Rock Mass Modulus 11

3.1.2 Plate Loading Tests 12

4. ROCK SOCKET 13

5. DESCRIPTION OF GRANITIC ROCKS 14

5*1 Classification of Granites 14

5.2 Rock Mass Classification of Granites 15

5.2.1 Description of Weathering State of Rock 15Mass

5.2.2 Description of Weathering Grades of Rock 15Material

6. ENGINEERING PROPERTIES OF WEATHERED GRANITIC ROCKS 16

6.1 General 16

6.2 Uniaxial Compressive Strength and Elastic Properties 16

6.3 Point Load Strength 16

7. ALLOWABLE BEARING STRESSES FOR GRANITIC ROCKS 16

7.1 Allowable Bearing Stress 16

7.1.1 Building Codes 16

7.1.2 RQD and Allowable Bearing Stress 17

7.1.3 Canadian Foundation Engineering Method 17

7.2 Settlement <jy

7.3 Rock Socket 18

8. CONCLUSIONS 19

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PageNo.

9. REFERENCES 20

LIST OF TABLES 2A

LIST OF FIGURES

1. INTRODUCTION

Foundation design is based on two basic criteria; bearing capacity andsettlement. The basic problem in foundation design is the choice of anallowable bearing stress which will not exceed the safe bearing capacity ofrock and the settlement of the structure caused by deformation of the rockwill be less than the allowable settlement for the structure.

The methods commonly in use for the selection of a design bearing stressfor deep foundations on rock fall into four main categories :

(a) building codes,

(b) empirical rules,

(c) rational methods based on bearing capacity andsettlement analyses, and

(d) field load tests.

Regardless of the method used for bearing stress analysis, the allowablebearing stresses specified by the various existing Building Codes, based onlocal experience, tend to control the design. Many building codes recommenda presumptive value for the allowable bearing stress and very few relatethese values to simple quantitative rock parameters. In the case ofstructures imposing large loadings, the code values are normally conservativeand the settlements are unknown. Field load tests are expensive and very fewload tests have been carried out to determine the bearing stresses of deepfoundations, such as bored piles and hand-dug caissons, in rock.

Parameters considered in the design of pile and caisson foundations onrock, based on bearing capacity and settlement analyses, are :

(a) the strength of the intact rock material and the rockmass,

(b) the rock mass modulus,

(c) the structure of the rock mass,

(d) the construction practice,

(e) the embedment ratio for base resistance, and

(f) the socket roughness, if side resistance is takeninto account.

In the general case, the load on a deep foundation is carried partly byskin friction and partly by end bearing, in the design of rock caissons inHong Kong, skin friction is usually neglected. Evans et al (1982) statedthat "structural designs (in Hong Kong) are based on practically nofoundation yield and standard building designs have very small settlementconstraints, much smaller than would be the case in European practice; noallowance is made for skin friction11. However, it must be realized that, forthe section socketed within rock, full skin friction is mobilized after muchsmaller movements than is for end-bearing, and hence a substantially reducedportion of the total applied load is transferred to the base (Gill, 1980).

In Hong Kong, granitic rocks are of common occurrence, and an increasingnumber of heavy structures are being built on granitic rock foundations.Presumptive allowable bearing stresses of about 5 MPa have typically beenused as design values for caissons (end-bearing) in slightly weatheredgranite. Minimum RQD values of 75 percent have been specified to reach thisvalue in most works contracts.

In this report, various well-established and internationally used designmethods for pile foundations on rock have been reviewed. Allowable bearingstresses and likely settlements for granitic rock foundations have beencalculated by various methods, with particular reference to the fresh tomoderately weathered granitic rocks including granodiorites.

2. ALLOWABLE BEARING STRESS

The mechanism of bearing capacity failure of an intact rock is much moreconplex than either assumed or observed in the failure of a soil mass.Ultimate bearing capacity of rock has very little engineering significanceand the calculation of the ultimate bearing capacity is conplex. Failure maybe defined by :

qfi = 2.7 qu (Ladanyi, 1966) (1)

where qfj_ is the stress at incipient failure and qu is the unconfinedcompressive strength of the rock. Safe bearing capacity in rocksapproximates to the unconfined compressive strength after allowing a factorof safety of 3* In a case where the rock is stronger than the concrete, thebearing capacity of the rock imposes no practical limitation on thefoundations, and the allowable bearing capacity is then governed by thebearing stress at which allowable settlement occurs.

2.1 Building Codes

Many building codes specify presumptive allowable bearing stresses.However, they differ considerably in their recommendations for the same kindof rock (Table 1). A number of building codes relate the allowable bearingstress to the uniaxial compressive strength of the rock material (e.g.Uniform Building Code of America, 1964, Dallas Building Code, 1968) by thefollowing formula :

Qa * K qu (2)

where qa = allowable bearing stress,

qu s uniaxial compressive strength of the intact rock material, and

K = a factor, usually 0.2 to take account of the nature of jointingof the rock.

The values calculated by this method do not include increases allowedfor embedment into rock. The British Code (British Standards Institution,1972) and the Chicago Code (1972) allow an increase in bearing stress of 20%for every 300 mm embedment up to a maximum equal to twice the allowablebearing stress.

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2.2 Empirical Correlation between RQDand Allowable Bearing Stress

Peck et al (1974) suggested an empirical correlation between theallowable contact stress and the Rock Quality Designation, RQD (Figure 1).The RQD value is an approximate measure of the joint intensity of the rockmass, which in turn is an indicator of the rock mass compressibility. Theauthors stated that these values are based on settlement criteria and shouldnot be increased for a foundation embedded into rock.

2.3 CanadianFoundationEngineeringMethod

Allowable bearing stress is calculated by the following formula(Canadian Geotechnical Society, 1978) :

Qa = Ksp qu d (3)

where KSp is an empirical factor which depends upon spacing ofdiscontinuities and includes a factor of safety of 3 (Table 2), qu is theaverage unconfined compressive strength of rock cores and d is the depthfactor given by the formula :

Hd = 0.8 + 0.2 ~ < 2 (4)

where Hs is the depth of socket in rock having a strength equal to qu and Dis the diameter of socket.

KSp is also calculated by the following formula which takes into accountspacing of discontinuities, c, thickness of discontinuities S , and thefooting width B :

v - 3 + c/B , .Ks = - ...-•"::::::.": ...... • :::: ...... . . . . . . (5).

10 /1 + 300 <S7c

3- SETTLEMENT OF FOUNDATIONS ON ROCK

For foundations on fresh rock, settlement is so small that it is hardlyworth considering except for special structures where total and differentialsettlement must be extremely small. For large diameter caissons and piles onfresh granitic rocks, the bearing capacity of the rock is no limitation sincethe rock is always stronger than the concrete. Foundation design in freshrock is influenced by the nature and intensity of discontinuities asexplained in the previous section. In weathered rock, in addition to theseparameters, the degree and type of weathering control the design.

In order to determine an allowable bearing stress it is necessary toestimate the settlement of the foundation. Settlement in rock foundations canbe calculated by elastic analysis. For a rigid pile foundation, settlementis given by the following formula :

s -3 ~ 2m

where s = settlement,

q = uniform load per unit area,

Em = deformation modulus of the rock mass under the pile,

Is = depth reduction factor (Burland, 1970),

r = radius of pile, and

V = Poisson's ratio.

3.1 Rock Mass Modulus

Deformation modulus of the rock mass, Em, is the primary factor insettlement calculations. It is difficult to define and measure the massdeformation moduli when the rock mass is jointed and weathered, Hobbs (1975)defined a rock mas s factor , j, as the ratio of the deformation modulus of arock mass, Em> in any identifiable lithological and structural component tothat of the deformation modulus of the intact rock, E±9 comprising thecomponent :

EiMost rocks exhibit a linear relationship between the modulus of

elasticity of intact rock and the uniaxial compressive strength. Granitesare good examples of this, and it is possible within limits to estimate theintact modulus from the compressive strength.- Figure 2 shows a plot ofmodulus of elasticity against compressive strength for fresh and weatheredgranitic rocks.

3.1.1 Effect of Weathering on Rock Mass Modulus

The strength and elastic modulus of intact rock specimens aredrastically reduced with increased weathering.

The modulus ratio, Mr = Ej/qu, is only marginally affected as the rock•material weathers (Figure 2). The discontinuities have an increasinglysmaller influence on the mass modulus as the modulus of the intact rockdecreases, i.e. the j-value increases with increase in weathering (Table 3).

RQD values and fracture frequency can be related quite closely tomass/intact rock modulus ratio. Table 4, based on Deere et al (1966) andCoon and Meritt (1970), gives typical j-values associated with RQD ranges andfracture intensity.

Woodward et al (1972) in their textbook 'Drilled Pier Foundations1

suggested, the use of reduction factor, a E (Emass/Eseismic) vs RQD as anapproximate way to obtain the rock mass modulus for settlement calculations.Peck et al (1974) based their design stress values on RQD (Figure 1). Whenthis chart is used, limiting settlement f should not exceed 12.7 mm, even forlarge loaded areas'. Although it is difficult to compute settlements usingthis approach, it does provide a convenient starting point for evaluating

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foundations on rock masses.

Bieniawski d975a, 1978) correlated the reduction factor aE withGeomechanics classification Rating of the rock mass (Figure 3). The RockMass Rating (RMR) is based on six rock mass parameters including weatheredstate, RQD, strength of intact rock, and spacing and condition ofdiscontinuities. Hoek and Brown (1980) constructed the information presentedin Bieniawskifs paper to establish a relationship between in situ deformationmodulus of rock mass and rock mass class (Figure 4). Kulhawy (1978) and,Kulhawy and Goodman (1980) suggested the use of a geomechanical model toestablish equivalent rock mass properties from the individual properties ofthe rock material and the discontinuities. The rock material ischaracterized, by the elastic properties Er and Vr, while the discontinuityproperties are defined by a normal stiffness, Kn, and a shear stiffness, KS.A plot of reduction factor &%, against discontinuity spacing is shown inFigure 5. RQD values are correlated with mean discontinuity spacing inFigure 6. These two figures are combined in Figure 7 which gives the modulusreduction factor as a function of RQD for no core loss and 10% core loss,i.e. representing weak zones which cannot be recovered by conventionalcoring. To use Figure 7, RQD, Er and Kn values must be known. The RQD issimply determined by logging the rock cores, while Er °an be determined fromuniaxial compression tests on cores in the laboratory. The normal stiffnessKn can only determined from compression tests on discontinuities. Forpreliminary design purposes, where testing may not be warranted, Er and Kncan be calculated from the published data.

3.1.2 pla te Load ing Te st s

Rock mass deformation modulus or rock mass factor can be determined moreaccurately by plate load test, and settlement calculated by the formula :

S r

T = & a • (8)P P

where Sf = settlement of foundation,

Sp = settlement calculated from the plate load test,

rf = radius of the foundation,

rp = radius of the plate, and

a depends on the plate dimensions but is approximately unity.

in situ field testing can be time-consuming and expensive, and thereforeit is usually only warranted for special structures, relatively heavyloading, and unusual or particularly poor rock mass conditions includinghighly to completely weathered rocks. In the absence of plate load tests,one of the methods based on borehole RQD or fracture intensity and laboratorydeformation modulus given above can be used to determine the modulusreduction factor and the settlement under specified load conditions.

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4. ROCK SOCKET

In the case of rock caissons, load transfer through skin friction on theportion of the shaft within the overburden, i.e. residual soil and completelyweathered rock, is normally small and usually neglected. However, theportion of the caisson socketed in rock contributes significantly to loadtransfer. Studies indicate that shaft resistance values can be large and canaccount for a significant portion of the load support capacity of drilledpier and caisson foundations (Ladanyi, 1977; Pells £ Turner, 1979;Horvath et al, 1980; Williams et al, 1980; Donald et al, 1980). The resultsshow that the transfer of load into the embedding medium depends on :

(a) the ratio of moduli of concrete and the medium,

(b) the depth of embedment,

(c) the presence of seams or layers of weaker rock, and

(d) the Poisson's ratio.

Some building codes suggest increase of presumptive bearing stresseswith depth of embedment to a maximum of twice the basic value. For example,the Chicago Building Code allows the end-bearing stress to be increased by20% for every 300 mm embedment into the rock up to a maximum value of 20 MPawith a socket of 1.5 tn deep in massive, crystalline rock. The CanadianFoundation Engineering Method includes the effect of the rock socket in thecalculation of bearing stress by the following formula :

Qa =

where d is the depth factor and equal to

Hd = 0.8 + 0.2 •— < 2

(3)

U)

where Hs = depth of the socket in rock having a strength qu, and

D = diameter of the socket.

Coates (1967) suggested the use of the following formula to calculatethe average allowable bond strength (adhesion) for piers socketed into rock :

Bond strength = 0.05 f& *

where ffc s 28 day compressive strength of concrete.

(9)

The Draft Australian Piling Code recommended the use of followingformulae (Williams et al, 1980) :

fs = 0.05 qu

fb = 0.5 qu

(10)

(11)

where qu = unconfined compressive strength of rock,

fs * mobilized side resistance, and

fk s mobilized base resistance.

The choice of these values was based on both on acceptable deformationsand on safe load capacity. If so, their use in design can be assumed tosatisfy both settlement and load capacity criteria.

Rosenberg and journeaux (1976) proposed a load capacity criterion basedon an elastic solution for load distribution in a pile, using laboratory andfield strength tests. The peak side resistance was found to depend primarilyon rock strength. Figure 8 shows a correlation of measured bond strength andunconfined compressive strength for six different rock types.

Load test data on socketed piers has been collected for over 50 sites,located mainly in Australia, Canada, Britain and USA, and shaft resistanceplotted on a log-log scale against uniaxial compressive strength of rock byHorvath et al (1980) in Figure 9. Diameter of the piles ranged from 400 to1 220 mm and the embedment ratio, LS/DS> from 1 to 20. The relationship canbe closely approximated using the following equation :

Sr = b/TJ (12)

where b = 0,2 to 0.25,

Sr = shaft resistance, and

fc s controlling compressive strength, i.e. the unconfined compressivestrength of the weaker material, either concrete or rock.

As a final comment on the subject of rock roughness, it should be notedthat the roughness of the pier-socket wall interface has a significantinfluence on the magnitude of mobilized shaft resistance. However, there isvery little quantitative data available on this aspect.

Table 5 is taken from Thorne (1980) and shows the attained socketadhesions from a number of cases reported in the literature compared withunconfined compression test data from rock cores. The results indicate thatthe governing factor in strong rocks is the concrete strength. End-bearingstresses are also shown in the same table. The only failures recorded are inrocks with open or clay-filled joints at 10 mm spacing or closer. Table 6also summarizes various test data on shaft resistance.

5. DESCRIPTION OF GRANITIC ROCKS

5.1 Classification of Granites

Granites contain quartz and feldspars as essential constituents.Classification is based on 'texture and grain size, and the geologicalsubdivision into three classes (alkali granites, adamellites andgranodiorites) is on the basis of type and relative proportions of feldspars(Hatch et al, 1972).

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5.2 Rock Mass Classification of Granites

Rock mass characterization for engineering purposes involves thedescription of the geological nature of the rock mass, including thepetrographic properties and details of discontinuities and structures, coupledwith an assessment of the engineering properties of the rock material.Weathering grade classification is an extremely useful tool for rockdescription. Assessment of weathering grade has become an important aspectof rock mass description for engineering purposes (Dearman, 1976). Thedistribution and grades in a weathering profile plays an important part in therecognition and assessment of uniformity of foundation condition (Knill &Jones, 1965).

Engineering geological schemes for grading rock masses have not yet beendeveloped. The best that can be achieved is a detailed semi-quantitative orquantitative description of rock material properties plus description ofdiscontinuity and weathering state. The weathering grades, backed up bydiscontinuity and strength grades, provide the best indication of rock massgrade. Rock and soil material may be described in qualitative terms. Fieldindex tests, such as Schmidt hammer and slakeability, have been usedsuccessively for the description of slope materials in Hong Kong (Hencher &Martin, 1982). Such a material description scheme may be used to define theweathered material in each foundation layer.

In a civil engineering context, assessment of foundation conditionsdepends mainly on the logging of drill cores. Percentage core recovery,recognition of weathered rock, and estimation of proportion of discoloured tofresh rock permit determination of distinctive mass weathering zones I to V.Calculation of RQD (Rock Quality Designation) has to be relied upon tocomplete the rock mass characterization.

5.2*1 Description of Weathering State of Rock Mass

Recognition of distinctive weathering grades in the rock mass may bebased on the degree of discolouration, the rock/soil ratio, and the presenceor absence of the original rock fabric. The descriptive schemes forweathering grades of rock material and rock mass recommended by BS 5930 (BSI,1981) have been used in this report.

The weathering profile in the rock mass may therefore be described interms of the distribution of the various types of weathered rock materialswithin it, and the effects that weathering has had on discontinuities.Experience with a variety of rock types, including granite, has shown that theclassification is of general application, but in some cases subdivisions ofgrades are necessary.

Variations in intensity of weathering are generally gradational, butsometimes very sharp boundaries exist between the material components in onegrade. In the former, engineering properties for each mass will berepresented by a spectrum of values; in the latter, a bimodal range ofproperties is given relating to the two distinct components of the mass grade.

5.2.2 Descriptionof Weathering GradesofRock Material

A descriptive scheme for weathering grades of rock material may be

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established on the basis of the changes associated with mechanical andchemical weathering (Table 8). Individual stages listed in Table 8 may besubdivided using qualifying terms, for example 'partially discoloured1,'wholly discoloured1 and 'slightly discoloured' to aid in description of thematerial being examined. If desired such terms may be quantified.

6. ENGINEERING PROPERTIES OF WEATHERED GRANITIC ROCKS

6.1 General

Quantitative test data used in the calculation of allowable bearingstresses and settlements of foundations on granite (Tables 9 and 10) havelargely been based on the work carried out by Irfan (1977) on a wide spectrumof weathered granites including granodiorites (Irfan & Dearman, 1978; Dearman& Irfan, 1978 a,b). Published laboratory test data on the strength anddeformation properties of granitic rocks have also been included forcomparison (Table 11). There is very little published systematic data on theengineering properties of weathered Hong Kong rocks.

6.2 Uniaxial Compressive Strength and Elastic Properties

Table 9 sets out the classification of weathered granite in terms ofuniaxial compressive strength, elastic modulus and point load strength basedon the laboratory determination of engineering properties. uniaxialcompressive strength testing was carried out in accordance with the methodsgiven in Hawkes and Mellor (1970). The tangent Young's modulus and Poisson'sratio were calculated from the third loading cycle at 50% of the ultimatestress (Deere & Miller 1966; ISRM, 1978). Lower-bound values and mean valueshave been selected as design parameters for each rock mass class (Table 10)and used in the calculation of bearing stress and settlement for pile andcaisson foundations in granites. published engineering parameters forgranites based on the data compiled by Kulhawy (1975) and, Lama and Vutukuri(1978) are given in Table 11. The values quoted in the literature aregenerally for 'fresh' granites. Rock mass deformation modulus and the effectof weathering on mass engineering properties are discussed in section 3.1.1.

6.3. Point Load Strength

Point load strength has been widely used to estimate uniaxial compressivestrength of rocks in the field and laboratory (D'Andrea et al, 1965; Broch &Franklin, 1972; Bieniawski, 1975b). Figure 10 shows the correlation ofcompressive strength with point load strength for weathered granitic rocks(Dearman et al, 1978). Reliability of the point load test has been improvedwith recognition of the size dependancy of the results (Bieniawski, 1975b) andstandardization of the method (ISRM, 1973). The test is applicable over awider range of strengths than the Schmidt hammer (Irfan & Dearman, 1978)„

7. ALLOWABLE BEARING STRESSES FOR GRANITIC ROCKS

7.1 Allowable Bearing Stress

7*1.1 Building Codes

Granites, when fresh or slightly weathered, are massive crystalline rocks

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(excluding raicrofractured granites). Presumptive allowable bearing stressspecified by many national building codes is 10 MPa (Table 1), without takinginto account the rock socket effect. Moderately weathered granite may beassumed as 'sound foliated rock' with presumptive bearing stresses around4 MPa.

Table 12 gives allowable bearing stresses calculated by using lower-boundand average uniaxial compressive strength values for each weathering grade ofrock mass and K = 0.2 as specified by some building codes. Minimum allowablebearing stress for the fresh to slightly weathered granite using this approachis over 20 MPa.

7.1.2 RQD and Allowable Bearing Stress

By using the empirical correlation between the allowable contact stressand RQD suggested by peck et al (1974), maximum, average and minimum allowablebearing stresses for various weathering grades of granite have been calculated(Table 13). The minimum allowable bearing stress for the slightly to freshgranites is over 6.5 MPa and average values are over 10 MPa. If design isbased on these values, the settlement of the caissons should not exceed12.5 mm as stated by Peck et al (1974).

7.1.3 Canadian Foundation Engineering Method

Allowable bearing stresses for the fresh to moderately weathered granitescalculated by the Canadian Foundation Engineering Method, using KSp =0.1 fora joint spacing of 300 mm, are tabulated in Table 14. Lower-bound values ofallowable bearing stress, using minimum uniaxial compressive strength ofintact rock material, is over 10 MPa for the slightly weathered to freshgranite. The rock mass is assumed to have favourable characteristics with therock surface perpendicular to the foundation and with no open discontinuities.

Ksp values have also been determined for various weathering grades andcaisson diameters of 1 to 4 m (Tables 15 and 16). A joint spacing of 300 mmand a joint thickness of 1 mm for the fresh to slightly weathered granite and5 mm for the moderately weathered granite have been adopted as the lower-boundvalues. The above relationship is valid for thickness of discontinuitiesless than 25 mm if filled with soil or rock debris. This may be the case forthe moderately weathered granite where the material around the joints mayeither be extremely weak or completely weathered to soil. The allowablebearing stress calculated by this method is much higher than the bearingstress determined assuming Ksp = 0.1 for the whole rock mass.

7.2 Settlement

Settlements have been calculated for a range of bearing stresses of 5,7.5, 10 and 15 MPa for pier and caisson foundations of 1 to 6 m diameter,using the following formula (6) given in Section 3.

Depth reduction factor of Is = 0.85 for p = 0.22 has been adopted toallow for an average embedment of the foundation into sound rock ofapproximately one diameter (Burland, 1970, Figure 12). In computing thesettlement, it is assumed that all the load is transferred to the base (i.e.end-bearing) and reduction of the load due to rock socket effect has been

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neglected for the overlying rock. This is an extremely conservativeassumption.

Mass deformation modulus for each type of foundation layer has beencomputed from lower-bound elastic modulus of intact rock in each weatheringgrade for various rock mass factors or reduction coefficients, correspondingto various RQD classes, to take into account the jointing in the rock mass(Table 10). In the final analysis of settlement for each class of rock mass,a rock mass factor of 0.8 for the fresh granite, 0.5 for the slightlyweathered granite and 0.2 for the moderately weathered granite have beenselected as design factors based on average RQD of each class of rock mass(Deere et al, 1966).

The values calculated by this method (Table 17) are the upper-boundvalues for settlement, as conservative values for rock mass factors andelastic modulus have been adopted in calculating the rock mass modulus.Effect of rock socket in reducing the end-bearing stress and settlement hasbeen ignored.

The maximum settlement computed for caisson diameters of 1 to 6 m isless than 9.5 mm for the slightly weathered granite and less than 19*1 nim forthe moderately weathered granite for a high bearing stress of 15 MPa.

In Figures 11 to 14, total settlements computed for each class ofweathered granite have been plotted against the pile diameter for various RQDclasses.

7.3 RockSocket

Shaft resistance or bond strength of piles and caissons socketed intogranitic rock have been calculated using the following formula recommended bythe Draft Australian piling Code, and also suggested by pells et al (1978) andCoates (1967) :

Shaft resistance (bond strength) = 0.05/?J . . . . . (9)

The uniaxial compressive strength of the moderately weathered to freshgranite is very much higher than the uniaxial compressive strength or theconcrete used for piles. Therefore uniaxial compressive strength of theconcrete, is taken as the controlling strength. The shaft resistance valuesfor different grades of concrete are tabulated in Table 18. The shaftresistance has also been calculated by using the following formula(Table 19) :

Shaft resistance = b >/"fJ (12)

where b = 0.20 to 0.25

A conservative approach has been adopted in the calculation of shaftresistance. Higher values of shaft resistance have been reported in theliterature for weaker rocks such as sandstones and shales (see Tables 5 and6), The roughness of the caisson-socket wall interface has not been takeninto account. The presence of narrow seams and open joints down the socketwall is advantageous as these can produce the required roughness by beingwashed out during excavation (pells et al, 1980)*

8- CONCLUSIONS

Allowable loadings for end-bearing piles on rock are traditionallyconservative. For many structures no great saving would be achieved byadopting higher allowable bearing stresses. However, for large structuresimposing heavy loadings founded on numerous deep caissons and piles,considerable saving could be achieved by increasing the allowable bearingstresses and hence reducing the number of caissons or piles.

Safe bearing capacities of 5 MPa for massive crystalline igneous rock inhard sound condition (core recovery greater than 85%) and 3 MPa for mediumhard rock (core recovery greater than 5035) have been specified by the HongKong Building (Construction) Regulations. However, allowable bearing stressesquoted in most other building codes for the same rock are much higher, usually10 MPa or more.

It is recommended that the allowable bearing stress for Hong Konggranites could be increased significantly.

Minimum allowable bearing stresses for granites have been determined byusing the following methods :

(a) Building Codes - presumptive bearing stress

(b) Building Codes - empirical factors

(c) Canadian Foundation Engineering Methods

(d) RQD method

(e) Settlement

In the calculation of allowable bearing stress for granitic rock for theabove methods (c), (d) and (e), the strength of the intact rock material, thedeformation modulus of the intact rock and rock mass, the structure of therock mass (jointing, joint spacing, RQD), the weathered state of thediscontinuities and the rock mass have been taken into consideration. Minimumallowable bearing stresses for granitic rock determined by variousconventional design methods, using conservative geotechnical parameters, areset out in Table 20.

The design parameters proposed are the upper-bound values for settlement,as conservative parameters for rock mass factor, j, and elastic modulus havebeen adopted. The effect of rock socket in reducing the end-bearing stressand settlement has also been ignored.

Rock-socketed caissons could be designed to carry their design load inside resistance plus base resistance, provided that no doubt exists regardingthe mobilization of either component. Studies indicate that shaft resistancevalues for strong rocks can be large (Horvath et al, 1980). Shaft resistanceof caissons socketed into slightly to moderately weathered granite calculatedby conservative methods using the compressive strength of concrete as theweaker material is 1 to 2 MPa depending on the type of concrete used. Theroughness of caisson-socket wall interface has not been taken into account.To date, no completely satisfactory design method for such rock sockets hasbeen published. Only recently, Williams et al (1988) suggested a designmethod based on a combination of settlement and strength criteria.

- 20 -

No laboratory or field testing has been carried out to determine theengineering properties of Hong Kong foundation rocks. Engineering parametersof granite used in this report are based on the work carried out by Irfan(1977) on a wide spectrum of weathered granitic rocks. Lower-bound valueshave been selected for each grade of rock mass. These values should beverified during construction of caissons by a field and laboratory testingprogramme.

Highly weathered granite is composed of various proportions ofdiscoloured, weakened rock material and friable soil; the distribution anddepth of this zone is variable. If caissons are to be founded in suchmaterials and in extremely fractured areas, field tests such as pressuremeter,plate loading and caisson loading tests should be carried out.

9. REFERENCES

Bieniawski, Z.T. d975a). Case Studies : prediction of rock mass behaviourby the geomechanics classification, proceedings of the SecondAustralia- New Zealand Conference on Geomechanics, Brisbane, Australia, pp 36-41.

Bieniawski, Z.T. (I975b). The point load test in geotechnica] practice.Engineering Geology, vol. 9, PP 1-11.

Bieniawski, Z.T. (1978). Determining rock mass deformability : experiencefrom case histories, international Journal of Rock Mechanics and MiningSciences and Geomechanical Abstracts, vol. 15, pp 237-247.

Broch, E. & Franklin, J.A. (1972). The point load strength test.InternationalJournalofRock Mechanics and Mining Sciences, vol. 9, PP667-697.

BSI (1972). Code of .Practice for Foundations (CP 2004). British StandardsInstitution, London.

BSI (1981). Code of Practice for Site Investigation^ BS 5930 : 1981 (FormerlyCP2001). British Standards Institution, London, 14 p.

Burland, J.D. (1970). Discussion on papers in session A. ProceedingsofConference on insitu Investigationsin Soilsand Rocks, pp 61-62, BritishGeotechnical Society.

Canadian Geotechnical Society (1978). Canadian Foundation Engineering Manual.Canadian Geotechnical Society, Ottawa.

Coates, D.F. (1967). Rock Mechanics Principles. Mines Branch Monograph 874,Department of Energy, Mines and Resources, Ottawa, Canada.

Coon, R.F. & Merritt, A.H. (1970). Predicting in situ modulus of deformationusing rock quality indexes. In situ Testingin Rock, AmericanSocietyfor Testing and Materials, STP 477, PP 154-173.

DrAndrea, D.V., Fischer, R.L. & Fogelson, D.E. (1965). Prediction ofcompressive strength of rock from other properties. U.S. Bureau of MinesRep, investigation^ No. 6702.

Dearman, W.D. (1976). Weathering classification in the characterisation of

- 21 -

rock : a revision. Bulletin of the International Association ojfEngineering Geology, No. 13, pp 123-127.

Dearman, W.R., Baynes, F.J. & Irfan, T.Y. (1978). Engineering grading ofweathered granite. Engineering Geology, vol. 12, pp 345-374.

Dearman, W.R. & Irfan, T.Y. (I978a). Classification and index properties ofweathered coarse-grained granites from South-West England, proceedingsoftheThirdInternational Congress, International Association ofEngineering Geology, Madrid, Section II, vol. 2, pp 119-130.

Dearman, W.R. & Irfan, T.Y. d978b). Assessment of the degree of weatheringin granite using petrographic and physical index tests. InternationalSymposium on Deterioration and protection of Stone Monuments. Unesco,Paris, paper 2.3/35 p . — —

Deere, D.U. & Miller, R.p. (1966). Engineering classification and indexproperties of intact rock. Report AFWL-TR-65-116, Air Force WeaponsLaboratory (WLDC), Kirtland Air Force Base, New Mexico 87117.

Deere, D.U., Hendron, A.J., Patton, F.D. & Cording, E.J. (1966). Design ofsurface and near surface construction in rock. Proceedings of the EighthSymposium of Rock Mechanics, Minnesota, American Institution of MiningEngineers, pp 237-303 (1967).

Donald, I.B., Chiu, H.K. & Sloan, S.W. (1980). Theoretical analysis of rocksocketed piles. Proceedings of the International Conference onStructural Foundationson Rock, Sydney, Australia, Balkema, pp 303-316.

Evans, G.L., McNicholl, D.P. & Leung, K.W. (1982). Testing in hand dugCaissons. proceed ings of the Seventh Southeas t Asian GeotechnicalConference, Hong Kong, vol. 1, pp 317-332.

Gill, S.A. (1980). Design and construction of rock caissons, proceedings ofthe international Conference on Structural Foundations on Rock, Sydney,Australia, Balkema, pp 241-252.

Hatch, F.H., Wells, A.K. & Wells, M.K. (1972). The petrology of Igneous Rocks(1Oth edition). London, Murby, 469 p.

Hawkes, I. & Mellor, M. (1970). Uniaxial testing in rock mechanicslaboratories. Engineering Geology, vol. 4, pp 177-285.

Hencher, S.R. & Martin, R.P. (1982). The description and classification ofweathered rocks in Hong Kong for engineering purposes, proceedings ofthe Seventh Southeast Asian Geotechnical Conference, Hong Kong, pp 125-142.

Hobbs, N.B. (1974). Factors affecting the prediction of settlement ofstructures on rock : with particular reference to the Chalk and Trias.Review paper, Session IV : Rocks, proceedings ofthe Conference onSettlement of structures, British Geotechnical Society, Pentech press,PP 579-610 (1975).

Hobbs, H.B. (1975). Foundations on Rock. Soil Mechanics, Bracknell.

Hoek, E. & Brown, E.T. (1980). Underground Excavations in Rock. The

- 22 -

institution of Mining and Metallurgy, London 527 p.

Horvath, E.G., Trow, W.A. & Kenney, T.C. (1980). Results of tests todetermine shaft resistance of rock-socketed drilled piers, proceedingsof the International Conference on Structural FoundationsonRock,Sydney, Australia, Balkeraa, pp 349-361.

irfan, T.Y. (1977). Engineering Properties ofWeathered Granite. UnpublishedPh. D. Thesis, University of Newcastle-upon-Tyne, England, 812 p.

irfan, T.Y. & Dearman, W.R. (1978). Engineering classification and indexproperties of a weathered granite. Bulletin of the internationalAssociation of Engineering Geology, No. 17, PP 79-90.

International Society for Rock Mechanics (1973). Suggested method fordetermining point-load strength index. International Society forRockMechanics Committee on LaboratoryTests. Document 1, pp 8-12.

International society for Rock Mechanics (1978). Suggested method fordetermining the uniaxial compressive strength and deformability of rockmaterials. International Society for Rock Mechanics Committee onLaboratory Tests. international Journal of RockMechanics and MiningSciences and Geomeohanics_Abstracts, vol. 16, no. 2, pp 135-140 (1979).

Knill, J.L. & Jones, K.S. (1965). The recording and interpretation ofgeological conditions in the foundations of the Roseires, Kariba andLatiyan Dams. Geotechnique, Vol. 15, pp 94-124.

Kulhawy, F.H. (1975). Stress deformation properties of rock and rockdiscontinuities. Engineering Geology, vol. 9, pp 327-350.

Kulhawy, F.H. (1978). Geomechanical model for rock foundation settlements.journal ofGeotechnical Engineering Divisionf Proceedingsof AmericanSociety of Civil Engineers, Vol 104, No. GT2, pp 211-227.

Kulhawy, F.H. & Goodman, R.E. (1980). Design of foundations on discontinuousrock. proceedings of the International Conference on StructuralFoundations on Rock, Sydney, Australia, pp 209-220.

Ladanyi, B. (1966). Discussion on Paper by D.F. Coates and M. Gyenge on plateloading tests on rocks. American Society of Testing and Materialsf_Special Technical Publication 402.

Ladanyi, B. (1977). Discussion on friction and end bearing tests. CanadianGeotechnical journal, vol. 14, no. 1, pp 153.

Lama, P.D. & Vutukuri, v.S. (1978). Handbook on MechanicalPropertiesofRocks. Trans Tech Publications, 4 volumes.

Moye, D.G. (1955). Engineering geology for the Snowy Mountains Scheme.Journal of the Institution of Engineers. Australia, vol. 27, pp 287-298.

Peck, R.B., Hanson, W.E. & Thornburn, T.H. (1974). Foundation Engineering.(2nd edition), New York, Wiley, 514 p.

Pells, P.J.N., Douglas, D.J., Rodway, B., Thorne, C.P. & McMahon, B.K. (1978).Design loadings of foundations on shale and sandstone in the Sydney

- 23 -

region. Australian Geomechanics Journal, vol. 68, pp 31-39.

pells, P.J .N. & Rowe, R . K . & Turner, R.M. (1980). An experimentalinvestigation into side shear for socketed piles in sandstone.proceed ings of the International Conference on Structural Foundations onRock, Sydney, Australia, pp 291-302.

pells, P . J .N. & Turner, R.M. (1979) . Elastic solutions for the design andanalysis of rock socketed piles, Canadian GeoteGhnical Journal, vol. 16,pp 481-487.

Rosenburg, P. & Journeaux, N.L. (1976). Friction and end bearing tests onbedrock for high capacity socket design. Canadian^^Geotechnic^al Journal,vol. 13, PP 324-333.

Thome, C.P. (1980). The capacity of piers drilled into rock, proceedingsof theInternational Conference on Structural Foundations on Rock,Sydney, Australia, pp 223-233-

Williams, A.F. , Johnston, I.W. & Donald, I.E. (1980). The design of socketedpiles in weak rock. proceedings of the international Conference onStructural Foundations on Rock, Sydney, Australia, pp 327-3^7.

Woodward, R.J. Jr., Gardner, W.S. & Greer, D.M. (1972). Drilled pierFoundations. McGraw-Hill, New York.

LIST OF TABLES

Table Pa«e

No, No.

1 Presumptive Allowable Bearing Stress for Rock 26Specified by Various Building Codes

2 Classification of Rock Mass in Terms of 2?Discontinuities and Empirical Coefficient, KSp

3 Effect of Weathering on Rock Mass Properties 28

4 RQD Classes and Rock Mass Factors 29

5 Socket Adhesion, Unconfined Compressive Strengths 30and Achieved End-bearing Stresses of Various RockFoundations (Thome, 1980)

6 Shaft Resistance Values for Various Rock Types (from 31Horvath et al, 1980)

7 Scale of Weathering Grades of Rock Mass 31(BSI, 1981)

8 Description of Weathering Grades of Rock Material 32(BSI, 1981)

9 Engineering Properties of Granitic Rocks (based on 33Irfan, 1977; Dearman & Irfan 1978a, b; Irfan &Dearman, 1978)

10 Summary of Engineering Properties of Weathered 33Granitic Rocks Used in Calculation of AllowableBearing Stresses

11 Engineering Properties of Granites (Based on the 34data compiled by Kulhawy, 1975 andLama & Vutukuri, 1978)

12 Allowable Bearing Stresses for Weathered Granitic 34Rocks, for K=0.2

13 Allowable Bearing Stresses for Weathered Granitic 35Rocks Based on the RQD Method

1** Allowable Bearing Stresses for Weathered Granitic 35Rocks Calculated by the Canadian FoundationEngineering Method, Ksp =0.1

15 Empirical Coefficient, Ksp, for Weathered Granitic 36Rocks

16 Allowable Bearing Stresses Determined by the Canadian 36Foundation Engineering Method, Using CalculatedKSp values

- 25 -

Table PageNo. No.

17 Settlement of Granite Foundations Under Various 3?Loads

18 Shaft Resistance Values for Piles Socketed into 4gSound Rock by the Australian Piling Method(Sr = 0.05 f')*c

19 Shaft Resistance Values for Piles Socketed into 40Sound Rock by Horvath et al (1980) Formula(Sr = 0.22 /f7")c

20 Summary of Allowable Bearing Stresses Calculated 41by Various Design Methods and Proposed Design Valuesfor Granitic Rocks

- 26 -

Table 1 - Presumptive Allowable Bearing Stress for Rook Specifiedby Various Building Codes

Code

BOCA 1970

Boston 1970

Chicago 1970

Los Angeles 1970

Uniform Building Code 1970

San Fransisco 1969

National BuildingCode of USA 1967

Dallas 1968

CP 2004 1972(BSI, 1972)

New York City 1970

Hong Kong 1976

MassiveCrystallineBedrock(MPa)

10

10

10

10

0.2 q*

3-5

10

0.2 q*

10

6

5

SoundFoliatedRock

(MPa)

4

5

10

4

0.2 q*

3-5

4

0.2 q*

4

6

3

20% increase forevery 300 mmembedment intorock

Can be increasedfor embedmentinto rock

Legend :

q* Uniaxial compressive strength of intact rock.

- 27 -

Table 2 - Classification of Rock Mass in Terms of DiscontinuitySpacing and Empirical Coefficient, Ksp

Term

Very Widely Jointed

Widely Jointed

Moderately CloselyJointed

Joint Spacing(m)

3

1 - 3

0.3 - 1

K3P

0.4

0.25

0.1

- 28 -

Table 3 - Effect of Weathering on Rock Mass Properties (Hobbs, 1975)

Term Grade Rock Mass Properties

FreshandSlightlyWeathered

I

II

MDderatelyWeathered

III

HighlyWeathered

IV

CompletelyWeathered

ResidualSoil

VI

In faintly and slightly weathered rock jt is possible thatthe j-value, owing to the reduction in stiffness of thejoints as a result of penetrative weathering alone, willshow a fairly sharp decrease compared with that of thesame rock in fresh state. The intact modulus, bydefinition, is unaffected by penetrative weathering. Thesafe bearing capacity is not therefore affected by faintweathering and may be only slightly affected by slightweathering.

In moderately weathered rock the intact modulus, andstrength, can be very much lower than in the fresh rockand thus j-value will be higher than in the fresh state,unless the joints and fractures have been opened byerosion or softened by the accumulation of weatheringproducts. The intact modulus and strength can be measuredin the laboratory, and the bearing capacity assessed, inthe same way as for fresh rock. Triaxial tests may bemore appropriate than uniaxial tests, and it would beadvisable to adopt conservative values for the factor ofsafety.

In highly weathered rock difficulties will generally beencountered in obtaining undisturbed samples for testing.If samples are obtained the strength and modulus willgenerally be underestimated, frequently by large margins,even with apparently undisturbed samples. In such rockin-situ tests with either the Menard pressuremeter or theplate should be carried out to determine the bearingcapacity and settlement characteristics. The greatestdifficulties in assessing bearing capacity and settlementare likely to be encountered in highly weathered rocks, inwhich the rock fabric becomes increasingly disintegratedor increasingly more plastic.

In completely weathered rock and residual soil it may bepossible to obtain fair quality samples depending upon theparent rock type and the consistency of the product.Generally the samples will tend to be less disturbed thanwhen taken in the same rock in the highly weathered state.The bearing capacity and settlement characteristics ofrock in these extreme states can be assessed using theusual method for testing soils.

Note : In residual granitic soils the usual methods of laboratory testingmay be difficult to perform satisfactorily, or may lead to severedisturbance of the sample. As a result there are difficulties inassessing bearing capacity and settlement characteristics by theseprocedures.

. 29 -

Table 4 - RQD Classes and Rock Mass Factors (Based on Deere,et al, 1966 and Coon & Merritt, 1970)

QualityClassification

Very poor

Poor

Fair

Good

Excellent

R.Q.D

(?)

0-25

25-50

50-75

75-90

90-100

FractureFrequencyper ra

15

15-8

8-5

5-1

1

VelocityIndex,VF2/VL2

0-0.2

0.2-0.4

0.4-0.6

0.6-0.8

0.8-1.0

MassFactor,

j

0.2

0.2

0.2-0.5

0.5-0.8

0.8-1.0

Legend :

Vp Seismic velocity in the fieldVL Seismic velocity in the laboratory on cores.

- 30 -

Table 5 - Socket Adhesion, Unconfined Compressive Strengths andAchieved End-bearing Stresses of Various RockFoundations (Thorne, 1980)

REF,NO.

1A

1A

1A

14

3 -

2

U

6

6

6

5

5

5

8

9

10

11

12

12

12

12

12

n

12

13

LOCATION

WESTMEADAUSTRALIA

NEWCASTLEAUSTRALIA

BRISBANEAUSTRALIA

PERTH AUST.

SYDNEY AUST.

AUCKLANDNEW ZEALAND

BRISBANE AUS1(PLATE TEST)

NANTICOKECANADA

NANTICOKECANADA

OTTOWACANADA

CALIFORNIAU.S .A.

U . K .

U.K.

BROOKFIELDNOVA SEOFIA

CONVENTRYU . K .

MELBOURNEAUSTRALIA

SYDNEYAUSTRALIA

HALIFAXCANADA(PLATE TEST)NORTH QUEBECCANADAQUEBECCANAfAC PLATE

LABRADOR(PLATE)

CANADA

CANADA

ERARINCN.S .W.

OCR TYPE

vianamatta Shale (Shear tone*o 100 nan In otherwise f reshock)

Tighea H i l l Sandstone *

bate )

King Park Shale

Sandstone & S i l ta tor teVar i ab ly cemented

Arg l lUte

Fresh Limestone contain! 3tnmchick bi tuminous shale scant at0.6 to 1.0 m spacing

Sl igh t ly Weathered Limestone

Shale, occasional recemtnted•oisture f rac tures and "thin

lengths 75 to 250 sun

weathered Sandstone and Shale

Hard Shale Fractures 0.3 to1 . 0 m spacing

Shale (Joints <? 10 to 20 mm)

Shmle contains "frequent 'weathered zones. Disintegrateson exposure

Muds tone bands 0.6 MPa(d about1 m spacing. Fractures 1? 100mm

Moderately hard, Muditone andsandstone. Joint spacingaverage A to lOmnt many clayf i l l ed .Fisai le shale, joints 20 to

10mm th ick , 20 to AOnun spacingin ISOtwj shear cone just belowbase of pile

Steeply dipping weatheredslates core recovery BX 657.

A XT 957.

Sandstone, RQD 107.

Friable Iron formations simi-lar to weathered & Friable

Fractured & sheared andesi teshear xonts wi th soft y.reenchlor i te on surfaces BXL corerecovery 33 to 757,

H o r i z o n t a l l y bedded ihtltcore length 75 to 125 tare

Weathered f r a c t u r e d in ter -bedded sandstone & shales

CLAYSTONE

UNCONFJNEDCOMPRESSION

( Q u )MPa

3^

10 to 15

27. S

0.7 to 1 .0

18.2

55 to 125

55 to 125

55

-

8

-

0.5

8.0

20(confined

at 700 k P a )

6 to 40

30 average

-

.

-

-

10.3

20 ,7

.

2.6 to 10.85.5 average

ROCK SOCKETM A X . ATTAINED STRESSLS

A DHLS IONMPa

2 .5

2.5U )

-

1.3

3.0

-

.

-

-

3.1

1.0

1 . 2 < 2 i

0.25°

0.25 ( A

0 . 2 2 < 2

0.88(1

2 . A 8 < 3

-

-

-

-

l.l (n

1.7U )

1.0

rQu

(1)0.07

0 .2

.

.

0 , l l < » >

.

-

0.06

-

0.15

.

0.50(0.007

f * c )

0.03

O.QAA ( 1

0.08

-

,

.

.

o.n< n

. 0 6 f t )

) .08 ( l )

' 0 . 0 5 f t )

0 03f ' c )

END BEARINGMPa

28

u"

1 .6

*

50

18.8

12.7 &7.5

22

22

27. K

-

1 . 4 < 2 >

A . 2

TQU

0.83

1

-

.

1.8

22

<• • ' «>O.A U ;

K),18

>0.18

0.5

.

.17

.

3.65 ( 2 )

8.0#1}

U.8 ( 3 )

3. A

2 A . 7

26.8U )

5 . A ( 1 )

-

O . A 5

O . A O C 1 )

0.6

-

.

. -

-

.

P u l l o u t Test

t o c k e t t e d load e q u i v a l e n t to13.6 MPa end b e a r i n g a l o n e or1.3 MPa In adhes ion a lone .

LAB.SECAWMODULUS

MPa

3700

-

.

-

*

-

-

.

-

.

-

CALC, FIELDMODULUS

HPa

3000

2500

485

1250

1920

121

A50

15000

A 000

rQu

88

700

28

.

70

1AO

25 PLATETEST

170

A S

Def lec t ion toamaLto o»easure

12A

A 00

100

-

50

-

-

-

.

-

-

-

-

-

130

70 to80

2300to

3200

-

.

.

-

390

1130

17

100

-

.

.

-

38

55

F i e l d test showedh l & h creep ( 5)

f l ) F a i l u r e A t t a ined ( 2 ) Proportion o f end b e a r l n g / a d h e n s l o n e s t i m a t e d ( 3 ) Concrete sha f t f a i l e d

(A) S h a f t grooved, stress given to outside of grouv'e. f 5 ) High water I n f l o w s thought to have s o f t e n e d claystone.

Table 6 - Shaft Resistance Values for Various Rock Types(from Horvath et al, 1980)

RockType

Shale andSandstone

Limestone andChalk

Others

No.ofTests

28(50 to 16 000)

10(150 to 1000+)

2

UnconfinedCompressiveStrengthMPa(psi)

0.35 to 110(17 to 1J40+)

1 to 7+(17 to 300)

0,35 to 10.5+(50 to 1500+)

ShaftResistance

MPa(psi)

0.12 to 3+

0.12 to 2.1

0.12 to 1.1(17 to 160)

Table 7 - Scale of Weathering Grades of Rock Mass (BSI, 1981)

Term Description Grade

Fresh

SlightlyWeathered

ModeratelyWeathered

HighlyWeathered

CompletelyWeathered

ResidualSoil

No visible sign of rock material weathering;perhaps slight discoloration on majordiscontinuity surfaces.

Discoloration indicates weathering of rockmaterial and discontinuity surfaces. All therock material may be discoloured by weathering.

Less than half of the rock material is decomposedor disintegrated to a soil. Fresh or discolouredrock is present either as a continuous frameworkor as corestones.

More than half of the rock material is decomposedor disintegrated to a soil. Fresh or discolouredrock is present either as a discontinuousframework or as corestones.

All rock material is decomposed and/ordisintegrated to soil. The original massstructure is still largely intact.

All rock material is converted to soil. The massstructure and material fabric are destroyed.There is a large change in volume, but the soilhas not been significantly transported.

II

III

IV

VI

- 32 -

Table 8 - Description of Weathering Grades of Rock Material (BSI, 1981)

Term Description

Fresh

Discoloured

Decomposed

Disintegrated

No visible sign of weathering of the rock material.

The colour of the original fresh rock material is changedand is evidence of weathering. The degree of change fromthe original colour should be indicated. If the colourchange is confined to particular mineral constituentsthis should be mentioned.

The rock is weathered to the condition of a soil in whichthe original material fabric is still intact, but some orall of the mineral grains are decomposed.

The rock is weathered to the condition of a soil in whichthe original material fabric is still intact. The rockis friable, but the mineral grains are not decomposed.

Note : The stages of weathering described above may be sub-divided usingqualifying terms, for example, fpartially discoloured1, fwhollydiscoloured', and 'slightly discoloured1, as will aid thedescription of the material being examined. These descriptivequalifying terms may be quantified if necessary.

- 33 -

Table 9 - Engineering Properties of Granitic Rocks (Based on Irfan,1977; Dear-man & Irfan, 1978 a, b; Irfan & Dearman, 1978)

MassWeatheringGrade

I Fresh

II SlightlyWeathered

III ModeratelyWeathered

MaterialWeatheringGrade

Fresh

PartiallyDiscoloured

CompletelyDiscoloured

Weakened

UniaxialCompressiveStrength,ucss*(MPa)

> 150

120 - 150

100 - 150

50 - 100

PointLoadStrength,PLSS*(MPa)

> 6

5 - 6

4 - 6

2 - 4

TangentYoung f sModulus,Et(GPa)

60 - 80

40 - 60

30 - 50

15 - 30

Pois son'sRatio

0.18

to

0.38

& * Saturated condition

Table 10 - Summary of Engineering Properties of Weathered GraniticRocks Used in the Calculation of Allowable Bearing Stresses

MassWeatheringGrade

Fresh

SlightlyWeathered

ModeratelyWeathered

Uniaxial CompressiveStrengthMean

UCS(MPa)

175

125

75

Lower Bound,UCS(MPa)

150

100

50

Tanget Young'sModulusLower Bound,

Et(GPa)

60

30

15

Rock MassFactorLower Bound,

j

0.8

0.5

0.2

RockMassModulus

(GPa)

48

15

3

Masai'sRatio

0.22

0.22

0.22

Table 11 - Engineering Properties of Granites (Based on the data compiledby Kulhawy, 1975, and Lama & Vutukuri, 1978)

Rock Type

Granite (mainlyfresh)

Granite (mainlyfresh)

Granite (slightlyaltered-weathered )

UniaxialCompressiveStrength

(MPa)

120 to 300very fewless than120

110 to 325very fewless than100

55 to 90

Modulus ofElasticity

(GPa)

50 to 75very fewless than50

55 to 75very fewless than55

8 to 45

Poisson1 sRatio

0.18 to0.27

0.14 to0.39

0.10 to

Reference

Lama &Vutukuri, 1978

Kulhawy, 1975

Kulhawy, 1975

Table 12 - Allowable Bearing Stresses for Weathered Granitic Rocks,for K = 0.2

MassWeatheringGrade

I Fresh

II SlightlyWeathered

III ModeratelyWeathered

Uniaxial Compressive StrengthUCS-min

(MPa)

150

100

50

. UCS-av(MPa)

175

125

75

Allowable Bearing Stressqa-min(MPa)

30

20

10

qa-av(MPa)

35

25

15

- 35 -

Table 13 - Allowable Bearing Stresses for Weathered Granitic RocksBased on the RQD Method

MassWeatheringGrade

Fresh

SlightlyWeathered

ModeratelyWeathered

R.Q.D.(1>

75-100usually 90

50*90

50-75

Allowable Bearing Stress, qa(MPa)

min

12

6.5

6,5

av.

20

12

10

max

30

20

12

Note : (1) RQD values are from Dearman et al, 1978.

Table 14 - Allowable Bearing Stresses for Weathered Granitic RocksCalculated by the Canadian Foundation Engineering Method,K = 0.1

MassWeatheringGrade

I Fresh

II SlightlyWeathered

III ModeratelyWeathered

Uniaxial Compressive Strength

UCS-min(MPa)

150

100

50

UCS-av(MPa)

175

125

75

Allowable Bearing Stress

qa-min(MPa)

15

10

5

qa-av(MPa)

17.5

12.5

7.5

- 36 -

Table 15 - Empirical Coefficient, Ksp, for Weathered Granitic Rocks

MassWeatheringGrade

I

II

III

Fresh

SlightlyWeathered

ModeratelyWeathered

KspPile Diameter (m)

1 2 3 4

0.23 0.22 0,22 0.22

0.23 0.22 0.22 0.22

0.13 0.13 0.13 0.12

Table 16 - Allowable Bearing Stresses Determined by the CanadianFoundation Engineering Method, Using Calculated KspValues

MassWeatheringGrade

I Fresh

II SlightlyWeathered

III ModeratelyWeathered

Uniaxial Compressive Strength

UCS-min(MPa)

150

100

50

UCS-av(MPa)

175

125

75

W1'

0.23

0.23

0.13

A]]owab2e Bearing Stress

qa-min(MPa)

34.5

23.0

6.5

qa-av(MPa)

40.3

28.8

9.8

Note : (1 ) Assuming embedment of the pile into sound rock forapproximately one diameter

Table 17 - Settlement of Granite Foundations Under Various Loads (Sheet 1 of 3)

Fresh Granite Ei = 60 GPa

Pile Radius (m)

Bearing Stress

(MPa)

Reduction Coeff.XJ

Settlement (mm)

Reduction Coeff.,ZJ

Settlement (mm)

Reduction Coeff.*J

Settlement (mm)

0.5

5 7.5 10 15

0.8

0.07 0.10 0.13 0.20

0.5

0.11 0.16 0.21 0.32

0.2

0.26 0.40 0.53 0.79

1

5 7.5 10 15

0.8

0.13 0.20 0.26 0.40

0.5

0.21 0.32 0.42 0.63

0.2

0.53 0.79 1.06 1.59

2

5 7.5 10 15

0.8

0.26 0.40 0.53 0.79

0.5

0.42 0.63 0.85 1.27

0.2

1.06 1.59 2.12 3.18

3

5 7.5 10 15

0.8

0.40 0.60 0.79 1.19

0.5

0.63 0.95 1.27 1.91

0.2

1.59 2.38 3.18 4.76

I

uo

Table 17 - Settlement of Granite Foundations Under Various Loads (Sheet 2 of 3)

Slightly Weathered Granite Ei = 30 GPa

Pile Radius (m)

Bearing Stress(MPa)

Reduction Coeff.,Ij

Settlement (mm)

Reduction Coeff.,*J

Settlement (mm)

Red uc t ion Coe f f . ,IJ

Settlement (mm)

0.5

5 7.5 10 5

0.8

0.13 0.20 0.26 0.40

0.5

0.22 0.32 0.42 0.64

0.2

0.52 0.80 1.06 1.58

1

5 7.5 10 15

0.8

0.26 0.40 0.52 0.80

0.5

0.44 0.64 0.84 1.28

0.2

1.04 1.60 2.12 3.16

2

5 7.5 10 15

0.8

0.52 0.80 1.04 1.60

0.5

0.88 1.28 1.68 2.56

0.2

2.08 3.20 4.24 6.32

3

5 7.5 10 15

0.8

0.78 1.20 1.56 2.40

0.5

1.32 1.92 2.52 3.84

0.2

3.12 4.80 6.36 9.48

U)00

Table 17 - Settlement of Granite Foundations Under Various Loads (Sheet 3 of 3)

Moderately Weathered Granite Ei = 15 GPa

Pile Radius (m)

Bearing Stress(MPa)

Reduction Coeff.,ZJ

Settlement (mm)

Reduction Coeff.,Ij

Settlement (mm)

Reduction Coeff.,Jj

Settlement (mm)

0.5

5 7.5 10 15

0.8

0.26 0.40 0.53 0.79

0.5

0.42 0.64 0.85 1.27

0.2

1.06 1.59 2.12 3.18

1

5 7.5 10 15

0.8

0.53 0.79 1.06 1.59

0.5

0.85 1.27 1.69 2.54

0.2

2.12 3.18 4.23 6.35

2

5 7.5 10 15

0.8

1.06 1.59 2.12 3.18

0.5

1.69 2.54 3.39 5.08

0.2

4.23 6.35 8.47 12.7

3

5 7.5 10 15

0.8

1.59 2.38 3.18 4.76

0.5

2.54 3.81 5.08 7.62

0.2

6.35 9.53 12.7 19.05

Table 18 - Shaft Resistance Values for piles Socketed intoSound Rock by the Australian piling Method(Sr = 0.05 f<O*

ConcreteGrade

20

30

40

UniaxialCompressiveStrength

(MPa)

20

30

40

ShaftResistance,

(MPa)

1.0

1.5

2.0

Legend

Uniaxial compressive strength of the weaker material,concrete in this case

Table 19 - Shaft Resistance Values for piles Socketed into SoundRock by Horvath et al (1980) Formula (Sr = 0*22

ConcreteGrade

20

30

40

UniaxialCompressiveStrength,

fc(MPa)

20

30

40

ShaftResistance ,

sr(MPa)

1.0

1.2

1.4

Table 20 - Summary of Allowable Bearing Stresses Calculated by Various Design Methods andProposed Design Values for Granitic Rocks

Rock Type

FreshGranite

SlightlyWeatheredGranite

ModeratelyWeatheredGranite

Allowable Bearing Stress (MPa)

BuildingCodes

K = 0,2q-min q-av

30 35

20 25

10 15

Canadian FoundationEngineering Method

Ksp = 0.1q-min q-av

15 17.5

10 12.5

5 7.5

Kspq-min q-av

34.3 40.3

23.0 28.8

6.5 9.8

RQDMethod

q-av

20

12

6.5

ProposedDesignValue

q-min

15

10

5(D

Note : Up to 10 per cent by volume of completely decomposed or disintegrated soil is permitted.

1

-tr

~ 42 -

LIST OF FIGURES

Figure Paee

No. No-

1 Allowable Contact Pressure on Jointed Rock 43(After Peck, Hanson & Thornburn, 1974)

2 Classification of Weathered Granites in Terms of 44Strength and Young's Modulus (Dearman & Irfan, 1978)

3 Reduction Factor Versus Rock Mass Rating 45(Bieniawski, 1975a)

4 Relationship between Insitu Deformation Modulus 46and Rock Mass Rating (Bieniawski, 1978)

5 Modulus Reduction Factor versus Discontinuity 47Spacing (Kulhawy, 1978)

6 RQD versus Number of Discontinuities (Kulhawy, 1978) 48

7 Modulus Reduction Factor versus RQD (Kulhawy, 1978) 48

8 Bond Strength versus Unconfined Compressive Strength 49(Rosenberg & Journeaux, 1976)

9 Shaft Resistance versus Unconfined Compressive 50Strength (Horvath & Kenney, 1978)

10 Relationship between Point Load Strength and 51Compressive Strength for Weathered Granite(Irfan & Dearman, 1978, Figure 3b)

11 Settlement versus Foundation (Pile) Radius for 52Fresh to Moderately Weathered Granites(Bearing Stress = 5 MPa)

12 Settlement versus Foundation (Pile) Radius for 53Fresh to Moderately Weathered Granites(Bearing Stress =7.5 MPa)

13 Settlement versus Foundation (Pile) Radius for 54Fresh to Moderately Weathered Granites(Bearing Stress = 10 MPa)

1^ Settlement of versus Foundation (Pile) Radius Fresh 55to Moderately Weathered Granites (BearingStress = 15 MPa)

Allowable Contact Pressure on Jointed Rock. qa ( tsf )

1

I

cfr O

cr*"0 i—•fl> (DoV? O* o

§ a>fft oCo c^o

*•*

03

D- c

or oC D

CJ <L<* O

M-

oo

UJ

t

<MN/m 2

X

CM

E

16 r

8 -

uT4

cncDO

1 -

0.5 -

0.25L

BHIGH

STRENGTH

CMEDIUMSTRENGTH

DLOW

STRENGTHVERY HIGH

STRENGTHVERY LOW STRENGTH

o Hingston Down

• Dartmoor

Bodnin Moor

Peterhead

Lee Moor

Granite family of- Deere & Miller (1966)

7.5

103

12.5 25 50 100 200 400 MN/m2

Compressive Strength ( MPa )

Figure 2 - Classification of Weathered Granites in Terms of Strengthand Young's Modulus (Dearman & Irfan, 1978)

LOCALITIES :

S3 Orange Fish Tunnel

OOlcpsloot Bridge

Nevada Test Site

Dworshak Darn

K a r iba Powerhouse

0.1

20 30 40 50 60 70 80Geomechanics Classification Rating

90 100

Figure 3 - Reduction Factor Versus Rock Mass Rating(Bieniawski, 1975a)

1.080

70

I 6 0o

503

~Oo

§

|5*£o

30

20

10

NGI Classification

POOR FAIR GOOD VERYGOOD

EXTREMELYGOOD ,

EXCPT.GOOD

10 100 1*00 1000

50 60

FAIR

70_L

80

GOOD

90J_

100

VERY GOOD

CSIR Classification

Figure H - Relationship between Insitu Deformation Modulusand Rock Mass Rating (Bieniawski, 1978)

5020 10Discontinuities Per 15 m Run

5 4 3 2

Q3 0.6 09Discontinuity Spacing, S ( m

.2 1.5

Figure 5 - Modulus Reduction Factor versus DiscontinuitySpacing (Kulhawy, 1978)

100

10 20 30 40 50 60

Discontinuities Per 1 5 m Run

Figure 6 - RQD versus Number of Discontinuities (Kulhawy, 1978)

20 40 60

RQD (%)

80 100

Figure 7 - Modulus Reduction Factor versus RQD (Kulhawy, 1978)

- J»9 -

10000

in-1000

31cr

_C

cnc

CO

CD>I/)toCDL_CL£oo•oCD£

«4—

C

8 100c

10i y I I I M

10 100Measured Bond Value ( ps i )

1000

Figure 8 - Bond Strength versus Unconfined Compressive Strength(Rosenberg & Journeaux, 1976)

- 50 -

100Compressive Strength, f^ (MPa)

Figure 9 - Shaft Resistance versus Unconfined CompressiveStrength (Horvath & Kenney, 1978)

- 51 -

10

UCSS = 24xPLS s

GO_ia.

0 100UCSS ( M N / m 2 }

200

Figure 10 - Relationship between Point Load Strength andCompressive Strength for Weathered Granite(Irfan & Dearman, 1978, Figure 3b)

Bearing Stress = 5 MPa

20

15

eE

0;

ohoa;

CO

FreshGranite

RQD

Slightly WeatheredGranite

Moderately WeatheredGranite

1 2Foundation Radius

1 2Foundation Radius m

1 2Foundation Radius

Figure 11 - Settlement versus Foundation (Pile) Radius for Fresh to Moderately WeatheredGranites (Bearing Stress = 5 MPa)

Total Settlement ( m m_*

en o 01ISJo

C

CD

a Let"1 CD») cf3 cfH. ̂rt* (DCD 5CO (D

03 CD

H- CO

W CO

CO ^cf O"3 CCD 3co aco CD

cfIf H-

o•O D•U1 ^-N

TJS H-Tl H1

CD CD

aH-CO

a>COD*

aa>

CD(-4^J

cfcr<D

CLQ

D

o

OCDCLO

6"

0Q.C

T I

oo3^iiH+>ro

CO

to"IT*-»•

O *<"

i ^—• c»

** I

CD

Q12.

CO

OO)

I!

In2

DO

2:oa.

— ̂Q

P

*-*•rra>—ia>CL

OO

Total Settlementen o

mm,cn

T

O

(ftC

CD

Lx)

I

tf

cr 0)CD gW CD

03CD <0) CD

H. 03D C09 03

CXI ^1ct O-5 CCD D0) Q,03 CD

IIOa

CD

0)CL

cCO

Hi)

o

CD0)

TlOC

Q

5

Oa.

5

OcDQLQ

5'D

DQ.

r. </»ff ̂

CO

PO

H?to

o

1

sro>

CDCDD

(D

00

rS

u

2

Q.CD-3

CDt_i

*<J

CD

CDQ.

OcDQ.O

O*

Q9-cU)

CO

CDO

ocun>S

0 ST

1 ̂.̂' ^

r* mP*»-̂IT

roOL

enuio o

a

- trS -

Total Settlementan o

mm,en

I

CD

Cf 0>CD 3Ca CD

^CO O

<5i -s03

03 CC* 03

CD ^to oCO C

it CLCD

CD

03

C

CD0)

oca.a

30QQ.,

c" |SJ -

a.ao"3

OQ.

in

o

Q5

CD

Da

00

<a"zr*-*•

O *<"

§ 3-

ITre>

OJ0)Q

CO

en

0a

OexCD

CDt~j

«<-

CD

CDCu

•noc

2.o'

Qa.

\\ \\ \\(DO tn o

- 57 -

2 FOUNDATION DESIGNOF CAISSONS ON

VOLCANIC ROCKS :A TECHNICAL REVIEW

T.Y. Irfan

This report was originally produced as GCO Report No. 13/83

- 58 -

CONTENTS

PageNo.

Title Page 57

CONTENTS 58

1. INTRODUCTION 59

2. DESCRIPTION AND CLASSIFICATION OF VOLCANIC ROCKS 60

2.1 General 60

2.2 Geological Description of Volcanic Rocks in Hong Kong 60

2.3 Scale of Weathering Grades in the Rock Mass 61

3. ENGINEERING PROPERTIES OF VOLCANIC ROCKS 61

3.1 General 61

3.1.1 Hong Kong Data 62

3.2 Classification of Hong Kong Volcanic Rocks in Terms 52of Strength and Deformation Properties

4. ALLOWABLE BEARING STRESSES AND SETTLEMENTS FOR FOUNDATIONS 62ON VOLCANIC ROCKS

4.1 Allowable Bearing Stress and Settlement 62

4.2 Calculation of Allowable Bearing Stress 63

4.2.1 Building Codes 63

4.2.2 RQD and Allowable Bearing Stress 64

4.2.3 Canadian Foundation Engineering Methods 64

4.2.4 Settlement 55

4.3 Rock Socket 55

5. CONCLUSIONS ^

6. REFERENCES gy

LIST OF TABLES |0

LIST OF FIGURES 83

- 59 -

1. INTRODUCTION

Design allowable bearing stress for deep foundations on rock can beselected on the basis of any of four different procedures: building codes,empirical rules, rational methods based on bearing capacity and settlementanalysis and field load tests.

Building codes are traditionally conservative and in many structureslittle financial gain would be achieved by adopting higher allowable stresses.However, in the case of structures imposing large loadings such as bridges,dams, multistorey buildings, considerable saving could be achieved byincreasing the allowable bearing stresses based on rational methods of bearingcapacity and settlement analysis. Theoretical considerations and field testresults suggest that the ultimate bearing capacity of the rock mass isunlikely to be reduced much below the uniaxial compressive strength of theintact rock, even if open vertical joints are present. In most cases wherethe rock is stronger than the concrete, the allowable bearing stress isgoverned by the bearing stress at which allowable settlement occurs.

To evaluate the allowable bearing stress and settlement of foundationson discontinuous rock, the rock mass must be characterized. Characterizationof rock masses for foundation analysis and design can only be done with a fullappreciation and understanding of the role of the geologic factors involved(Kulhawy & Goodman, 1980). Some of the factors that are considered in thecharacterization of rock masses for foundations are:

(a) rock type,(b) discontinuities (orientation, spacing, continuity,

openness, infilling),(c) structure of the rock mass,(d) rock material properties (strength, deformation

modulus),(e) weathering and alteration,(f) groundwater,(g) durability,(h) in situ stresses, and(i) geometry of imposed structure in relation to

the geological structure.

Volcanic deposits usually give rise to extremely variable foundationconditions due to wide variations in strength, durability and permeability.Generally, the older volcanic rocks do not present many problems infoundation engineering unless they are weathered. Hong Kong volcanic rocksare geologically very old deposits; ash and lava deposits have been weldedtogether, hardened under great pressures, slightly metamorphosed andtransformed into very strong rocks with strengths in excess of 150 MPa in thefresh state. However, these rocks have been weathered extensively bydominantly chemical processes under Hong Kong's sub-tropical climate over avery long period of time. Weathering significantly reduces the strength anddeformation properties of the rock.

In this report, allowable bearing stresses and settlements of thecaisson foundations on weathered Hong Kong volcanic rocks have been computed,with particular reference to the fresh to moderately weathered rock massgrades, by various well-established and widely used foundation designmethods. The volcanic rocks have also been characterized in terms of massand material properties for the purposes of foundation analysis and design.

- 60 -

Detailed discussion of various methods of calculation of allowablebearing stresses and settlement and the effect of weathering on the rock massproperties have been given in "Foundation Design of Caissons on GraniticRocks: A Technical Review" (Irfan & Powell, 1982).

2. DESCRIPTION AND CLASSIFICATION OF VOLCANIC ROCKS

2.1 General

The engineering behaviour of rock masses is controlled by the mass andmaterial properties of the rock. Therefore, rock mass characterization forengineering purposes involves the description of the geological nature of therock mass, including the petrographic properties and details ofdiscontinuities and structure, coupled with an assessment of the engineeringproperties of the rock material such as strength and deformation modulus. Adetailed semiquantitative or quantitative description of rock materialproperties supplemented by description of discontinuities and weatheringstate provides one of the best engineering geological schemes for gradingrock masses which then can be used in the preliminary design of foundations.

2.2 Geological Description of Volcanic Rocks in Hong Kong

Volcanic rocks of Hong Kong are grouped under the Repulse Bay Formationby Allen and Stephens (1971). The Repulse Bay Formation consists of asuccession of tuffs, agglomerates, ignimbrites and mainly acid lavasdeposited subaerially with several intercalated units of sedimentary rocks.These rocks have been taken to a few kilometres within the crust, hardened,folded, faulted and slightly metamorphosed by a granitic batholith.

The volcanics have been subdivided on the basis of major lithotypes intothe following classes :

(1) Undifferentiated volcanic rocks RB

(2) Sedimentary rocks and water-laidVolcani-clastic rocks RB

(3) Acid lavas RBv

(4) Mainly banded acid lavas, some weldedtuffs

(5) Coarse tuffs

(6) Agglomerates R-*lbag

(7) Dominantly pyroclastic rocks withsome lavas

The pyroclastics and lavas are similar in composition to granites. Theterm pyroclastic is used for rocks formed by all mechanisms of dispersal ofdebris extruded from a volcano which are distinct from lava flows andexplosive pyroclastic erupts (Allen & Stephens, 1971). The common names usedfor pyroclastic rocks are : fine tuff, coarse tuff, lapilli tuff, tuffbreccia, pyroclastic breccia and agglomerate.

- 61

The volcanic rocks of the Repulse Bay Formation are well-jointed.Generally three or more sets of joints occur giving the rock mass a blocky-tabular structure. Joint spacing commonly ranges from 200 to 600 mm(moderately jointed, ISRM 1978) but in the vicinity of fault and shear zonesa joint spacing of 20 -200 mm is more common. Coarse tuffs may have widely-spaced joints, 600 - 2 000 mm, and may produce corestones when weathered.

Weathering is generally shallow in the volcanics with an average depthin the order of 10 metres except along the fault and shear zones and also incertain kinds of tuffs and sedimentary rocks where it may extend much deeper,to depths of 40 m or more. The depth of weathering may vary considerablyover short distances due to the variations in grain size, mineral content,jointing pattern and hydrological conditions. The change from fresh volcanicto completely weathered volcanic is generally gradual and corestones arerare.

2.3 Scale of Weathering Grades in the Hock Mass

Rock can weather by chemical decomposition or by physicaldisintegration. Generally both mechanical and chemical effects occurtogether, but one or the other may be dominant depending on the climaticregion during active weathering. In Hong Kong, rocks are weathered to greatdepths by dominantly chemical processes (decomposition) under a humid sub-tropical climate over a long period of time.

A scale of weathering grade in a rock mass may be erected on therelative intensity of decomposition and disintegration. The scale ofweathering grade used in this report is the one recommended by BS 5930 (BSI,1981) (Tables 1 and 2). This scheme, unlike earlier schemes, does not takeaccount of changes either in rock strength or whether or not discontinuitiesare open as these are distinct aspects of the rock mass which are dealt withwhen the rock mass is described fully. The scheme is based on the visualrecognition of the degree of discolouration, the proportion of rockdecomposed and/or disintegrated to soil and the presence or absence of theoriginal rock fabric. The rock mass grade can then be based on theweathering grade supplemented by determination of discontinuity and materialstrength grades. This in turn can be used to estimate the modulus ofdeformation of the rock mass.

3* ENGINEERING PROPERTIES OF VOLCANIC ROCKS

3.1 General

There is very little published data on the engineering properties of thefresh and weathered volcanic rocks of the Repulse Bay Formation. Publishedlaboratory test data compiled by Lama and Vutukuri (1978) on the strength anddeformation properties of volcanic rocks are given in Table 3* Figure 1 isan engineering classification of the volcanics such as dacite, andesite andrhyolite in terms of Young's modulus and uniaxial compressive strength.

Most of published test data on strength and deformation properties ofvolcanics are from relatively recent tuff deposits of USA and Japan with verylow densities of 1.6 to 2.0 mg/m3 and strengths of 3 to 40 MPa.

- 62 -

3.1.1 Hong Kong Data

Repulse Bay Volcanics are much older in age. The have been compressedunder great pressures and iretamorphosed to sorre degree with densities inexcess of 2.5 Mg/m3 and strengths of 100 MPa or more in the fresh state.Available test data compiled from various Public Works Department (P.W.D.)projects on the strength and deformation properties of the Repulse Bayvolcanic rocks is tabulated in Table 4. The validity of some of the testresults are questionable, particularly in the case of fresh volcanics where.very low compressive strength and tangent Young's modulus values areobtained. Failures through the discontinuities nay have been included inthese results and the testing method is unlikely to have rr.et the ISRMstandards.

3.2 Classification of Hong Kong Volcanic Rocks in Terms of Strength andDeformation Properties

Tables 5 and 6 set out the classification of weathered Hong Kong volcanicrocks in terms of rraterial properties such as the uniaxial compressivestrength and the tangent Young's modulus and the rock mass properties such asthe joint intensity and the RQD. The corresponding rock mass factors, (Hobbs,197*0 given in Table 6 is based on Deere et al (1966), and Coon and Merritt(1970).

In Hong Kong, volcanic rocks are closely to moderately jointed, and havelower than usual RQD's, usually in the range of 50-75? when fresh.

The mass deformation modulus to be used in the settlement analysis hasbeen calculated for each rock mass class from the following formula :

E

where j is the rock mass factor,Ej is the deformation modulus of the intact rocks, andEm is the deformation modulus of the rock mass

Lower-bound and mean values of uniaxial compressive strength and tangentYoung's modulus have been selected as the design parameters (Table 7) for eachrock mass class (foundation layer) and used in the calculation of bearingstresses and settlements of the pile and caisson foundations on volcanicro ck s.

The rock mass modulus and the effect of weathering on mass engineeringproperties are further discussed elsewrhere (Irfan & Powell, 1982).

4* ALLOWABLE BEARING STRESSES AND SETTLEMENTS FOR FOUNDATIONS ON VOLCANICROCKS ' '

^•1 Allowable Bearing Stress and Settlement

Theoretical considerations suggest that the ulti irate bearing capacity ofrock is unlikely to be reduced much below the uniaxial compressive strengthof the intact rock, even if open vertical joints are present (Poulos & Davis,

- 63 -

1980). On the basis of available data, an allowable bearing stress in theorder of 0.3 X unconfined uniaxial compressive strength would appear to bequite conservative for all rocks except swelling shales. Reference to thetheoretical solutions show that such values generally include a factor ofsafety of at least 3 in fractured or closely-jointed rocks and 12 or more forintact rocks. Thorne (1980) recorded end-bearing stresses of 0.3 to 4 xuniaxial compressive strength in actual field tests carried out in differentrock types and in most cases no failure occurred (Table 8).

In a case where the rock is stronger than the concrete, the bearingcapacity of the rock imposes no practical limitation on the foundation and theallowable bearing capacity is then governed by the bearing stress at whichallowable settlement occurs.

There are various ways of determining allowable bearing stress offoundations on rock. In this review, the allowable bearing stresses for HongKong volcanic rocks are determined by using the following methods :

(i) Building codes - presumptive bearing stress- empirical bearing stress

(ii) RQD method

(iii) Canadian Foundation Engineering Methods

(iv) Settlement

A brief description of these methods is given in Irfan and Powell(1982).

4.2 Calculation of Allowable Bearing Stress

4,2.1 Building Codes

Presumptive allowable bearing stresses specified by various buildingcodes and authorities differ in their recommendation for the same kind ofrock (Table 9). No specific values are given in these codes for volcanicsexcept that the rocks are classified in general terms such as massivecrystalline rocks in sound condition, foliated metamorphic rocks in soundcondition, sedimentary rocks, shattered rocks, weathered rocks, etc.

Widely- to very widely-jointed (joint spacing of 600 mm or greater),fresh to slightly weathered volcanics can be considered as massivecrystalline rocks with presumptive bearing stresses of 5 to 10.7 MPa. Freshvolcanics with medium-spaced joints (joint spacing of 200 to 600 mm) can beconsidered as "foliated rock in sound condition" or stronger sedimentary rockwith presumptive bearing stresses of 2 to 6 MPa. When the rock is closelyjointed or highly fractured, or moderately to highly weathered, then thepresumptive allowable bearing stresses specified range between 0.5 and 3 MPa,but are generally in the range of 1 to 1.5 MPa.

Uniform Building Code (1964) and Dallas Code (1968) relate the allowablebearing stress to the uniaxial compressive strength of the intact rockmaterial by the following formula :

Allowable bearing stress = K x Uniaxial compressive strength of core

Table 10 gives allowable bearing stresses calculated for Hong Kong volcanicrocks by using lower-bound and average uniaxial compressive strength valuesand K = 0.2 as specified by these codes for each grade of rock rrass.

4,2*2 RQD and Allowable Bearing Stress

Allowable bearing stress of volcanic rocks calculated for a range of RQDvalues usin£ the empirical correlation between the allowable contact stressand RQD suggested by Peck et al (197*0 are tabulated in Table 11. Theallowable bearing stress for the fresh to slightly weathered volcanic rocksdetermined by this method is over 6,5 MPa even for an RQD value as low as50%. In the moderately weathered volcanics with very low RQDfs this valuemay reduce to 1 MPa. If design is based on these values settlement of thecaisson foundations is not expected to exceed 12.5 mm (Peck et al, 1974).

4.2.3 Canadian Foundation Engineering Method

Allowable bearing stresses of Hong Kong volcanic rocks have also beencalculated by using the following formula (Canadian Geotechnical Society,1978):

where qa is the allowable bearing stress,qu is the average uniaxial compressive strength of rock cores,KSp is an empirical coefficient depending on the discontinuity spacing

and including a factor of safety of 3, andd is the depth factor and equal to :

d = 0.8 + s 4 2

where Hs is the depth of socket, andD is the diameter of the socket.

In the calculation of Kspf a joint spacing of 300 mm and joint thicknessof 1 mm for fresh to slightly weathered rocks and 5 mm (or less than 25 mmif filled with soil or rock debris) for moderately weathered rocks, have beenadopted. In moderately weathered volcanic rocks the material around thejoints may be extremely weak or completely weathered to soil. In theweathering grade classification, moderately weathered rock rray contain up to50? decomposed or disintegrated material (BSI, 1981). For the purposes ofthis study the cut-off point is taken at W% soil within the zone ofmoderately weathered rock. This approximately corresponds to 25 mm ofdecomposed or disintegrated material along the joints in the weathered rockmass. For very closely-jointed rocks or for rocks weathered to higherdegrees or where the rock is of very low strength, in situ pressuremetertests are recommended.

Minimum allowable bearing stresses calculated by the Canadian FoundationEngineering method is over 10 MPa for the fresh to slightly weatheredvolcanic rocks (Table 12). For moderately weathered volcanic rocks, theallowable bearing stress ranges from 1.3 to 3.5 MPa depending on the strength

- 65 -

of intact rock.

4.2.4 Settlement

Settlement in rock foundations can be calculated by elastic analysis,from pressurerreter test results or from plate load tests. If deforrration orsettlement is the limiting criterion of a structure imposed on a rock massthe deformation modulus of the rock mass is the prime controlling factor indefining this settlement. Therefore, the determination of the rock massmodulus is an important part of the investigation, design and constructionprocess. A large number of in situ pressuremeter tests must be carried outto assess the variabil i ty of elastic modulus of the rock irass and the effectof discontinuities on the mass elastic modulus. In situ plate load tests canbe used to assess the settlement, but the results depend on the plate size,tests are expensive and di f f icul t to carry out properly, and results arefrequently variable.

In the absence of in situ test data settlements can be computed byelastic theory from the properties determined in the laboratory and anempirical rock mass factor (or reduction factor) to take into account thejointec state of the rock mass using the following formula :

s -s -- ZF-m

where s is the settlement,q is the uniform load per unit area,Em is the deformation modulus of the rock mass under the pile,Is is the depth reduction factor,r is the radius of pile, andV is the Poissonfs ratio.

Various empirical and semi -empirical methods of estimating rock massmodulus have been suggested in the literature (Coon & Merritt, 1970;Woodward, et al, 1972; Bieniawski, 1975; Hobbs, 1974; Kulhawy & Goodman 1980;Thorne, 1980). In the present investigation, the rock mass moduli have beencomputed from the lower-bound and average elastic moduli of the intactvolcanic rock in each foundation layer, using various rock mass factorscorresponding to a range of RQD classes and joint intensities as discussed inSection 3.2.

Table 13 gives the maximum and average computed settlements of caissonfoundations on weathered volcanic rocks under different bearing stresses. Adepth reduction factor of Is = 0.85 for v = 0.25 has been adopted to allowfor an average embedment of the foundation by approximately one diameter(Burland, 1970).

In computing the settlement, it is assumed that all the load istransferred to the base and the reduction of the load due to the rock socketeffect has been neglected for the overlying rock. Elastic shortening of theconcrete shaft of caisson is not included in these calculations. For hand-dug caissons a considerable proportion of the load is expected to be taken upby side friction. In addition, for rock-socketed piles lateral dilation ofthe caisson into the socket my take the majority of the remaining load, andrelatively little load will be transferred to the base. These latter two

- 66 -

relatively little load wi l l be transferred to the base. These latter twomechanisms could be expected to reduce settlements of the caisson.

Settlement nay also result from the presence of debris at the bottom ofa caisson excavation and a careful inspection is therefore necessary toeliminate this possibility.

Figure 2 shows the range of maximum expected values of settlementagainst allowable bearing stress for a caisson diameter of 2 IT in variousfoundation layers. The maximum settlement for caisson diameters of 1 to 4 mis less than 12.5 mm in fresh to slightly weathered volcanics for a highbearing stress of 15 MPa, even in highly jointed rock mass with average RQDof 50$ or joint intensity of 5-8 joints per netre (Table 13).

In moderately weathered volcanics settlement wil l depend on the degreeof weathering of the rock material, the amount of decomposed or disintegratedsoil along discontinuities, the defornation modulus of the rock and thejointing in the rock mass. Allowable bearing stresses of up to 3 MPa willnot lead to any excessive settlements in these rocks except in highlyfractured zones.

Higher bearing stresses my be used in moderately weathered rock masseswith high strengths anc favourable joint orientation and spacing. Higherallowable bearing stresses should be based on detailed laboratory and fieldinvestigations to determine the nass and material properties of the rock.

4.3 Rock Socket

In the case of foundations on rock, the portion of the caisson socketedin rock contributes significantly to load transfer. Studies indicate thatshaft resistance values can be large and can account for a significantportion of the load support capacity of drilled pier and caisson foundations(Ladanyi, 1977; Pells & Turner, 1979; Horvath et alf 1980; Williams et al,1980; Donald et al, 1980).

Shaft resistance values of caisson foundations socketed into rockcalculated by the Draft Australian Piling Code (Pells et al, 1978) and Coates(1967) formulae using the compressive strength of the concrete as thecontrolling strength are in the region of 1 to 2 MPa depending on the type ofconcrete used. Higier shaft resistance values have been reported in theliterature for weaker rocks such as sandstone and shales (Horvath et al,1980; Thorne, 1980, and Table 8). Further discussion of the effect of rocksockets and the calculation of shaft resistance are given in Irfan and Powell(1982).

If the caissons are to be founded in rocks weathered to higher degreesor in extremely fractured zones, detailed laboratory and field investigationshould be undertaken to determine the mass and material properties of therock.

For hand-dug caissons a considerable proportion of the load will betaken by side friction on the shaft of the caisson. In rock-socketedcaissons, side friction coupled with the lateral dilatation of the pile intothe socket will lead to reduced load being transferred to the base, and hencereduced s ettlements.

- 67 -

There is relatively very little local data on the engineering propertiesof Hong Kong volcanic rocks. Engineering parameters of volcanic rocks usedin this report are based on liirited Hong Kong data, published resultselsewhere in the world and the author's own experience. Further testing willgreatly assist to advance the state of the art in volcanics.

Where preliminary design is based solely on borehole data, theimportance of accurate and detailed logging of boreholes, particularly inareas where variable rock conditions are likely to be encountered, by aqualified engineering geologist must be emphasized. During construction, therock in caisson excavations should be visually inspected and described byexperienced personnel to verify the rode conditions assuired in the structuralfoundation design. In situ techniques such as Schmidt hammer, core drillingand percussion air drilling can be used to provide quantitative evidence ofin situ rock conditions (Irfan & Powell, 1983)*

5. CONCLUSIONS

The current local practice of using a presumptive stress of 5 MPa forfresh to slightly weathered volcanic rocks is overconservative. Considerablesaving could be achieved in the case of structures imposing large loadings byincreasing the allowable bearing stress based on engineering geologicalcharacterization of the rock mass and rational methods of bearing capacityand settlement analysis.

Variable foundation conditions exist in Hong Kong volcanic rocks due todifferences in mode of origin, weathering and structure.

Allowable bearing stresses for Hong Kong volcanic rocks have beendetermined by various conventional design rrethods available, usingconservative geotechnical parameters. Settlement of volcanic rockfoundations under various end-bearing stresses have also been calculated(Table 13). Settlement predictions by this methods are upper-bound values,as conservative parairjeters for elastic modulus have been adopted and theeffect of the rock socket in reducing the end-bearing stress and settlementhas been ignored,

A range of bearing stresses may be used for caisson foundations in theRepulse Bay Volcanics depending on the rode mass properties existing at aparticular site. Figure 2 gives the expected range of maximum settlements invarious volcanic rock foundations for a 2 m diameter caisson under differentbearing stresses.

In fresh to sli^itly weathered volcanics an allowable bearing stress of10 MPa wi l l produce settleinents of less than 12.5 mm, according to elastictheory. In moderately weathered volcanics end-bearing stresses of up to3 MPa could be used without carrying out in situ testing. These allowablebearing stresses are lower-bound values, and if required for a particularproject, hi$ier values nay be justified when sound design procedures are usedwith rock BBSS properties obtained on a site specific basis.

6. REFERENCES

Allen, P. M. & Stephens, E . A. (1971). Report on the Geological Survey ofHong Kong. Government Printer, Hong Kong, 116 p, plus 2 naps.

- 68 -

Bieniawski, Z. T. (1975). Case studies : prediction of rock rrass behaviourby the geomechanics classification. Proceeding of the Second Australia~ New Zealand Conference on Geomechanics, Brisbane, Australia, pp 36-41.

British Standards Institution (1972). Code of Practice for Foundations(CP 2004). British Standards Institution, London, 158 p.

British Standards Institution (1981). Code of Practice for SiteInvestigations (BS 5930 : 1981). British Standards Institution, London,147 p.

Bur land, J. D. (1970). Discussion on papers in session A. Proceedings ofthe Conference on In situ Investigations in Soils and Rocks, BritishGeotechnical Society, pp 61-62.

Canadian Geotechnical Society (1978). Canadian Foundation EngineeringManual. Canadian Geotechnical Society, Ottawa.

Coates, D. F. (1967). Rock Mechanics Principles. Mines Branch Monograph874, Department of Energy, Mines and Resources, Ottawa, Canada.

Coon, R. F. & Merritt, A. H. (1970). Predicting in situ modulus ofdeformation using rock quality indexes. In situ Testing in Rock,African Society for Testing and Materials, STP 477, pp. 154-123.

Deere, D. U. & Miller, R. P. (1966) . Engineering classification and indexproperties of intact rock. Report AFWL~TR*-65-116, Air Force WeaponsLaboratory (WLDC), Kirtland Air Force Base, New Mexico.

Deere, D. U . , Hendron, A. J., Patton, F. D. & Cording, E. J. (1966) . Designof surface and near surface construction in rock. Proceedings of theEighth Symposium of Rock Mechanics, Minnesota, American Institution ofMining Engineers, pp .237-303 (1967).

Donald, I. B., Chiu, H . K . & Sloan, S. W. (1980). Theoretical analysis ofrock socketed piles. Proceedings of the International Conference onStructural Foundations on Rock, Sydney, Australia, Balkena, pp* 303-316.

Hobbs, N. B* (1974) . Factors affecting the prediction of settlement ofstructures on rock : with particular reference to the Chalk and Trias.Review paper, Session IV : Rocks. Conference on Settlement ofStructures, British Geotechnical Society, Pentech Press, pp. 579-610(1975).

Horvath, R. G., Trow, W. A. & Kenney, T. C. (1980). Results of tests todetermine shaft resistance of rock-socketed drilled piers. Proceedingsof the Conference on Structural Foundations on Rock, Sydney, Australia,Balkena, pp. 349-361.

International Society for Rock Mechanics (1978). Suggested methods for thequantitative description of discontinuities in rock trasses.International Society for Rock Mechanics Commission on Standardizationof Laboratory and Field Tests. International Journal of Rock Mechanicsand Mining Sciences and Geomechanics Abstracts, v o l " 1 5 ] No"! 57PP* 319-368. — .

- 69 -

Irfan, T. Y. & Powell, G. E. (1982). Foundation Design of Caissons onGrani t ic Rocks ; A Technical Review, New Works Advisory Report, NewWorks Divis ion, Geotechnical Control Off ice ( U n p u b l i s h e d ) , p.

Irfan, T. Y. & Powell, G. E. (1983) . Recommendations For Veri f icat ion ofFounding Depth of Caissons on Rock, New Territories Trunk Road to LamKam Road Item N H 4 ( 1 1 ) . New Works Advisory Report, New Works Division,Geotechnical Control Off ice (unpubl ished) , 19 p.

Ku lhawy , F. H. & Goodman, R. E. (1980) , Design of foundations ondiscontinuous rock. Proceedings of the International Conference onStructural Foundations on Rock, Sydney, Austral ia , pp. 209*220,

Ladanyi, B. (1977) . Discussion on friction and end bearing tests. CanadianGeotechnical Journal, vol. 14, No. 1, p. 153.

Lama, P. D, & Vutukuri , V. S. (1978). H a n d b o o k o n Mechanical Properties ofRocks. Volume II : Testing Techniques and Results, Trans TechPublications, 481 p.

NAVFAC (1971) . Design Manual 7.1 - Soil Mechanics, Foundations, and EarthStructures. Department of the Navy Facilities Engineering Command,Washington , D. C,

Poulos, H. G. & Davis, E. H. (1980), Pile Foundation Analysis and Design.W i l e y , 397 p.

Peck, R. B., Hanson, W. E. & Thornburn, T. H, (197*0. Foundation Engineering.(Second edi t ion) , Wi l ey , New York, 514 p.

Pells, P .J .N. & Turner, R. M. (1979) . Elastic solutions for the design andanalysis of rock socketed piles. Canadian Geotechnical Journal, vol. 16,pp. M81-487.

Pells, P.J .N. , Douglas, D.J., Rodway, B., Thorne, C. P. & McMahon, B. K.(1978). Design loadings of foundations on shale sandstone in the Sydneyregion. Australian Geomechanics Journal, vol. 68, pp. 31-39.

Sowers, G. F. (1979). Introductory Soil Mechanics and Foundations.Geotechnical Engineering. (Fourth edition). Collier-Macmillan, 621 p.

Thorne, G. P. (1980). The capacity of piers drilled into rock. Proceedingsof the International Conference on Structural Foundations on Rock,Sydney, Austral ia , pp. 223*233.

U. S. Bureau of Reclamation (1965). Design of Small Dams. U. S. Bureau ofReclamation, Washington, D. C.

Williams, A. F., Johnston, I. W. & Donald, I. B. (1980). The design ofsocketed piles in weak rock. Proceedings of the International Conferenceon Structural Foundations on Rock, Sydney, Austral ia, pp. 327-347.

Woodward, F. J. Jr., Gardner, W. S. & Greer, D. M. (1972). Drilled PierFoundations. McGraw-Hill, New York.

~ 70 -

LIST OF TABLES

Table PageNo. Mo.

1 Scale of Weathering Grades of Rock Mass 71

2 Description of Weathering Grades of Rock Material 72

3 Laboratory Mechanical Properties of Volcanic Rocks 73(Lama & Vutukuri, 1978)

4 Engineering Properties of Hong Kong Volcanic Rocks 75

5 Classification of Volcanic Rock Materials in 76Terms of Strength and Deformation Modulus

6 Rock Mass Properties of Volcanic Rocks 76

7 Summary of Engineering Properties of 77Volcanic Rocks Used in the Calculation ofAllowable Bearing Stresses

8 Socket Adhesion and Uniaxial Compressive Strengths 78and Achieved End-Bearing Stresses of Various RockFoundations (Thorne, 1980)

9 Presumptive Allowable Bearing Stresses for Rock 79Specified by Various Building Codes andAuthorities

10 Allowable Bearing Stresses for Volcanic Rocks 80Determined by Building Codes, K = 0.2

11 Allowable Bearing Stressses for Volcanic Rocks 80Based on the RQD Method

12 Allowable Bearing Stresses Determined by the 81Canadian Foundation Engineering Method UsingCalculated Ksp Values for Pile Diameters ofOver 300 mm

13 Settlement of Volcanic Rock Foundations under 82Various Foundation Loads (End-Bearing)

- 71 -

Table 1 - Scale of Weathering Grades of Rock Mass

Term Description Grade

Fresh

SlightlyWeathered

ModeratelyWeathered

HighlyWeathered

CompletelyWeathered

ResidualSoil

No visible sign of rock mterial weathering;perhaps slight discoloration on najordiscontinuity surfaces.

Discoloration indicates weathering of rocknaterial and discontinuity surfaces. Al the rocknaterial nay be discoloured by weathering.

Less than half of the rock material is decomposedor disintegrated to a soil. Fresh or discolouredrock is present either as a continuous frameworkor as corestones.

More than half of the rock material is decomposedor disintegrated to a soil. Fresh or discolouredrock is present either as a discontinuousframework or as corestones.

All rock naterial is decomposed and/ordisintegrated to soil. The original massstructure is still largely intact.

All rock material is converted to soil. The nassstructure and material fabric are destroyed.There is a large change in volume, but the soilhas not been significantly transported.

II

III

IV

VI

- 72 -

Table 2 - Description of Weathering Grades of Rock Mater ia l

Term Description

Fresh

Discoloured

Decomposed

Disintegrated

No visible sign of weathering of the rock material.

The colour of the original fresh rock material is changedand is evidence of weathering. The degree of change fromthe original colour should be indicated. If the colourchange is confined to particular mineral constituentsthis should be mentioned.

The rock is weathered to the condition of a soil in whichthe original material fabric is still intact, but some orall of the mineral grains are decomposed.

The rock is weathered to the condition of a soil in whichthe original material fabric is still intact. The rockis friable, but the mineral grains are not decomposed.

Note : The stages of weathering described above may be sub-divided usingqualifying terms, for example, Tpartially discolouredf, fwhollydiscoloured1, and 'slightly discoloured1, as will aid thedescription of the material being examined. These descriptivequalifying terms may be quantified if necessary.

- 73 -

Table 3 - Laboratory Mechanical Properties of Volcanic Rocks(Lama & Vutukuri, 1978) (Sheet 1 of 2)

Rock

Tart

Tuff

Tuff

Location* Density,Description 0{g>'cmJ)

USA, McDowell -Dam. Ariz., iithictuff, fg, altered,salt matrixUSA.AECNe- -vada test site, la-ptlli t u f f , glasswith volcanicconstituentsMexico, 1 .9Soledad Dam 2.2USA, Green Pe- -tersDamUSA, Green Pe- -ters DamUSA.AECNe- -vada test siteJapan, Seikan 2.19TunnelJapan, Seikan 2.36Tunnel, tuff-brecciaJapan, Shimane 2.4Nuclear PlantJapan, Shimane 2.4Nuclear PlantJapan -Japan, Aorehi

Japan, Aoishi 1.91Japan, Aoishi -Canada. Macleod -MineCanada, Macleod -MineCanada, Macleod -MineCanada, Macleod -Mine

USSR, gcosyncli- 2.49nes + brecciasHungary,rhyolite.

* 1 2.08

* 2 2,08

Canada, Kirk- 2.78land, Ont.

US A. Howard 1.45Prairie Dam,Ore., JithicUS A, Oak Spring 1.6Formation. Ncv.,beddedUSA, Oak Spring -Formation, Ncv.,beddedUSA, Oak Spring -Formation, Ncv.,beddedUSA.Nev., 2.2weldedUSA.Nev., 2.39weldedCanada, Noranda 2.74Mines, Ont.. silt-cified

Modulus Modulus Poisson'sof Elasticity, of Rigidity, Ratio,E(GPa) G(GPa) u

1.38 -

9.71* - 0.10*

1.7"2.7*

7.4 0.19

7.0 0.20

3.72 - 0.19

_

-

3.0 - 0.2

2.0 - 0.2

7.14

68.0

76.070.063.43 - 0.24

74.5 - 0.25

61.4 - 0.26

71.7 - 0.28

22.7 - 0.13

_

_

86.87* 32.41*

1.38 - 0.11

4.2* 2.1"

4,9 0.17 O O H

7.6 34 0.11

10.2* 4.1-

3.65 - 0.19

81.5* 37.7" 0.07*

Compressivt Tensile RemarksStrength, Strength,ct(MPa) oi(MPa)

15.86 - gram » 1-2mm

- - variable poresize

- - seismicfield

23.0 - c « 7.0,0 = 24°

22.0 - c = 7.7,0= 19°

11.31 1.17

21.9 2.2

28.6 3.9

c = 0.4,0 = 30°c = 0.3,0 = 35°

34.7

33.8 4.31 sandy

36.0 4.31 sandy34.2 4.45 sandy_

-

-

-

p = 8.3I

9.4 - p * 30.0w« 16.5

9.8 - p - 30.0w=« 16.5

289.58 - p*1.5

3.65 - p « 42.9

p = 37.0

tension

- compression

p=14.0

11.3 1-17 p-19.8

-

Reference

B RANDOM, 1974

YOUASH. 1 s»70

ULLAO, 19^4ULLAO, 19«S4CORNS&ME m

CoRNS&NesBrrr 1967

STOWE&AINSWORTH,1968MOCHIDA, 1974

MOCHIDA, 1974

KlTAHARAe laj,1974

KlTAHAR A «t al, 1974

YAMAGUCHI, 1968YAMAGUCMI, 1953

YAMAGUCHJ, 1968YAMACUCHl,l968

HERGET, 1973

HERGET, 1973

HERGET, 1973

HERGET, 1973

BELIJCOV, 19$7

MARTOS, 1965

MARTOS,t9SS

WwDES, 1949

USBR.I9S3

ROBERTSON(Unpublished)

ROBERTSON(Unpublished)

ROBERTSON(Unpublished)

ROBERTSON(Unpublished)S TO WE, 1969

BIRCH A BANCROFT,1939

Table 3 - Laboratory Mechanical Properties of Volcanic Rocks(Lama & Vutukuri, 1978) (Sheet 2 of 2)

Rock

Rhyoiite

Dtcite

Ignimbritc

Location & Density,Description p(g/cm j)

USA.AECNe- 1.92vada test site, redto red yellow—.yellow 2,0— , red & yellow 1 .60

USA,NTS~E 1.61Tunnel, porous,cemented

Canada, Lake-shore

Canada, HelenMine, vertical

Japan, Scilcan 2.42Tunnel

Japan, Taguchi -

S. Africa, Pango- 2.67lapoost Dam

USSR, geosyncli- 2.62nes, porphyntes

New Zealand, 1.83-MaraetaiDam 2.16

wet

dry -

Modulus Modulusof Elasticity, of Rigidity,E(GPa) G(GPa)

345

15.66.34

5.03

76.53 3103

82.74

-

26.0

.41.0

.

1.7-6.72.34-7.7

Poisson'sRatio,u

0.24

0090 15

0.21

023

0.27

-

„

0.22

0.15-0.30»

-

CompressiveStrength,Oc(MPa)

9.65

35.322.3

24 1

262.92

155.13

85.4

-

112.5

_

7.74-33.8

13.8-46.9

TensileStrength,o«(MPa)

-

--

1 45

105.49

17.31

5.6

-

.-

0.86-2.65(R)

0.89-3.5(R)

Remarks Reference

w » 193 CORDING, 1967

w » i ? . 5 CORDING, 1967w = = 4 . 6 CORDING, 1967

MILLER, 1965

MORRISON, 1970

MORRISON, 1970

MOCHIDA, 1974

l iDActal , 1960

p » 6.06 PHELINES, 1967

p = 3.06 BELIKOV, 1967

p* 6.4-1 5.6 JAMES, 1955

JAMES, 1955

JAMES, 1955

- 75 -

Table 4 - Engineering Properties of Hong Kong Volcanic Rocks

Rock Type

Lapilli Tuf ftl

IT

»

TI

"II

II

II

tl

ti

11

II

Medium toCoarse Tuff

iinnn»n»»nn»"

Pyroclastic"""11

Lava TuffPyroclastic

iiLapilli Tuff

nCoarse TuffTuff

Description' ̂

MDVSDVFSDVMDVSDVFFFMDVFSDVSDV

SDVSDVSDVSDV/MDVSDVSDVFFMDVSDVFFF

SDV/FSDVSDV/FSDVMDVSDVMDV/SDVMDVMDVSDVMDVSDV

Uniaxia l Modulus Density,Compressive ofStrength, Elast ici ty,

UCS C d( M P a ) I G P a ) ( M g / m 3 )

2*J 4.5 2,5467 15.8 2.6970 14.2 2.7271 18.0 2.7257 11.3 2.7056 11.8 2.7379 14.8 2.7684 18.7 2.7745 12.8 2.73^Q\ 2) 0, . i (2) 2.6581 23.8 2.7194 20.6 2.6981 22.0 2.69

126 24.4 2.6970 27.7 2.679 ( 2 ) 7 . 0< 2 > 2.68

55 6.0 2.6287 19.5 2.6998 27.8 2.67

140 19.3 2.7068 15.7 2.7139 16.2 2.6428 (2) 11. 6 < 2 > 2.67

111 18.4 2.67168 21.7 2.70144 25.0 2.70

146 79.0 2.75198 59.0 2.65109 20.4 2.71155 3U8 2.7125 25.5 2.6866 18.0 2.7251 1.7 2.7539 9.5 2.63

123 15.4 2,69112 25.0 2,72166 40.0 2.74142 69.0 2.69

Locality

Tsing Yin

ii

»«

M

II

»

»

II

It

Lantaun"

Ma WanTt

»'

»

II

•'

»

II

«

II

11

»

tl

New TerritoriesIT

If

"

»

II

Tl

11

»

II

n

"

Reference

PWD ContractNo. 512 of1980

Lantau FixedCrossingProject,Phase II(Mott, Hay& Anderson,1981)

%

FutureIncrease ofWater Supplyfrom China -Stage I -WesternAqueducts(CharlesHaswell &Partners, 1983)

Notes : ( 1 ) Material description : F - fresh volcanic, S D V - sl iphtly decomposed volcanic,MDV - moderately decomposed volcanic.

(2) Failure through joint (?)

- 76 -

Table 5 « Classification of Weathered Volcanic Rock Materials in Termsof Strength and Deformation Modulus

MassWeatheringGrade

FreshVolcanics(1)

SlightlyWeatheredVolcanics

ModeratelyWeatheredVolcanics

UniaxialCompressiveStrength,UCS(MPa)

75 to 200

50 to 150

12.5 to 75

TangentYoung TsModulus,

Et(GPa)

25 to 75

15 to 50

5 to 25

Poisson 'sRatio,V

0.09

to

0.28

Note : (1 ) These ranges cover a wide spectrum of volcanic rocks in Hong Kong*

Table 6 - Rock Mass Properties of Volcanic Rocks

MassWeatheringGrade

FreshVolcanics

SlightlyWeatheredVolcanics

ModeratelyWeatheredVolcanics

JointFrequencyper DI

11 - 55 - 8

11 - 55 - 8

5 - 88 - 15

> 15

RQD

1%)

9 0 - 1 0 075 - 9050 - 75

90 - 10075 - 9050 - 75

50 - 7525 - 500 - 2 5

Rock MassFactor,

j

0.8 - 1.00.5 - 0.80.2 - 0.5

0.8 - 1.00.5 - 0.80.2 - 0.5

0.20.10.1

Table 7 - Sumrrary of Engineering Properties of Volcanic Rocks Used in the Calculationof Allowable Bearing Stresses

MassWeatheringGrade

Fresh

SlightlyWeathered

ModeratelyWeathered

UniaxialCompressiveStrength,

UCS

Mean Lowerbound

( M P a ) (MPa)

125 75

100 50

35 12.5

TangentYoung'sModulus j

Et

Mean Lowerbound

{GPa) (GPa)

40 25

25 15

12.5 5

RockMassFactor,

j

Lowerbound

0.80.5

0.80.50.2

0.20.1

RockMassModulus,

Em

Mean Lowerbound

{ GPa ) ( GPa )

32 2020 12.5

20 1212.5 7.55 3

2.5 1.01.25 0.5

Poisson'sRatio,V

0.25

0.25

0.25

- 78 -

Table 8 - Socket Adhesion and Uniaxial Compressive Strengthsand Achieved End-Bearing Stresses of Various RockFoundations (Thorne, 1980)

REF,»0.

14

14

14

14

3

2

4

6

6

6

5

5

5

a

9

10

11

12

12

12

12

12

12

12

13

LOCATION

WEST MEADAUSTRALIA

NEWCASTLEAUSTRALIA

BRISBANEAUSTRALIA

PERTH AUST.

SYDNEY AUST.

AUCKLANDNEW ZEALAND

BRISBANE AUS1(PLATE TEST)

NANTICOKECANADA

NANTICOKECANADA

OTTOWACANADA

CALIFORNIAU.S.A.

U . K .

U.K.

BROOKFIELDNOVA SEOFIA

CONVENTRYU.K.

MELBOURNEAUSTRALIA

SYDNEYAUSTRALIA

HALIFAXCANADA(PLATE TEST)NORTH QUEBECCANADAQUEBECCANADA(PtATE)

LABRADOR(PLATE)

CANADA

CANADA

ERARINCN.S .W.

ROCK TYPE

Uianarnatt* Shale (Shear zone*

rock)

Tighes H i l l Sands tone

T u f f (75«» c lay team jus t belowbase)

Kinfl park Shale

Sandstone, f r e i h defec t f r ee

Sandstone d S t l t s toneVar iab ly cemented

A r g i l l l t e

Fr*ah Limes tone con ta ins 3mmthick b i tuminous shale seams at0.6 to 1.0 m spacing

S l igh t ly Wea the red Limestoneshale seam as above

Shale, occasional recemented•olsture f r ac tu re s and "thin«ud" seams. In t ac t corelengths 75 to 250 aim

Hard Shale Fractures 0.3 to1.0 re spacing

Shale (Joints {? 10 to 20 mm)

weathered ronei .Disintegrateson exposure „_ *

Mudatone bands 0.6 MPa^ about1 m spacing. Fractures (? 100mmor closer spacing.Modera te ly hard, Muditone andtandstone. Joint spacingaverage 4 to lOxnca many clayf i l l e d .Pistil* shale , joints 20 to

10mm th i ck , 20 to 40rnoj spacingin IJOraen shear tone just belovbase of pi le

S teep ly d ipp ing weathered

A XT 957.

Friable Iron formations sirai-

•andstone .f r a c t u r e d & sheared andesi teshear zones w i t h soft greench lo r i t e on surfaces BXL corerecovery, 33 to 75%

H o r i z o n t a l l y bedded shalecore length 75 to 125 mm

Weathered f r a c t u r e d in te r -bedded sandi tone 4 shales

CLAYSTONE

UNCONFJNEDCOMPRESSION

( Q u )MPa

34

10 to 15

15 to 20

27 .5

0.7 to 1.0

18.2

55 to 125

55 to 125

55

-

8

-

0.5

B,0

20(confined

at 700 U f a )

6 to 40

30 average

-

-

.

-

10,3

20.7

„

2.6 to 10.85.5 average

ROCK SOCKETM A X . ATTAINED STRESSES

A D H E S I O NMP*

2 . 5

2 .5 U )

.

1.3

3.0

-

.

-

-

3.1

1.0

1 , 2 < 2 )

0.25 (1

0 .25 ( A

0 . 2 2 < 2

0.8fl ( n

2 .48< 3

-

-

-

.

l.l (n

1.7 ( 1 )

1.0

fQu

(1)0.07

0 . 2

-

.

o . n < > )-

-

O.Of)

-

0.15

-

0.500.007f ' c )

0.03

0.044a

0.08

-

-

-

.

o.n (n

, 0 6 f t )

).08U )

0 . 0 5 f f c )

0 .03 f ' c )

END BEARINGMPa

28

u"

1 .6

.

50

18.8

1 2 . 7 &7 . 5

22

22

_>7 .H

-

1.4 ( 2 )

4.2

•kju

0.83

1

-

.

1.8

22

0 7 ( 1 )

o l ( n

X5.18

>0.18

0.5

-

.17

.

I ' u J l o u t Test

3 .65 ( 2 )

S.orf"

21.8 ( 3 >

3.4

24.7

26.8 ( 1 )

5 . 4 < 1 5

-

0.45

0.40 C 1 )

0.6

-

.

. -

-

-

LAB.SECANTMODULUS

MPa

3700

-

-

.

-

-

-

-

.

-

.

CALC. F I E L DMODULUS

MPa

3000

?500

485

1250

1920

121

450

15000

4000

^}u

88

700

28

-

70

140

25 PLATETEST

170

45

Def l ec t ion town allto measure

124

400

100

-

50

.

Rock s t r e n g t h probablyconservat ive

-

„

-

-

-

-

.

-

Pul lou t Test

locke t t ed load equ iva len t to13.6 MPa en<t b e a r i n g a lone or1.3 MPa In adhesion d l o n e .

130

70 to80

2300to

3200

*

.

-

.

390

1130

17

100

-

.

-

•

38

55

F i e l d tes t showedh igh creep < 5)

(1 ) F a i l u r e A t t a i n e d (2 ) Proportion of end bea r lng /adhe t i s ion e s t i m a t e d f 3 ) Concrete s h a f t f a i l e d

< 4 > S h a f t f c roov«d , a t re t i given to ou t t lde o f grouve. f 5 ) High w a t e r I n f l o w s thought t o have t o f t e n e d c l a y s t o n e .

Table 9 - Presumptive Allowable Bearing Stresses (MPa) for Rock Specified by Various Building Codes and Authorities

^ •̂s. Foundation

Reference^x.

NAVFAC, USA 1971

Canadian 1978GeotechnicalSociety

EOCA 1 968

National BuildingCode, USA 1967

Uniform BuildingCode of USA 1964

Los Angeles 1965

CP 200H 1972(BSI, 1972)

US Bureau ofReclamation 1965

Dallas 1968

New York City 1970

Hong Kong 1976

Sowers 1 979

Massive crystallinerock in soundcondition (granite,basalt, gneiss)

6 to 10

10

10

10

0.2qu

1.0

10

10,7

0.2qu

6

5

> 10 (RQD = 90*)

Foliated metaoorphicrocks in soundcondition (slate,schist)

3 to 4

3

if

4

0,2qu

O.H

3

3.8

0.2qu

6

Sedimentary rocksin sound condition

1.5 to 2.5

1 to %

2.5 to 4

1.5

0,2qu

0.3

2 to 4

0.2qu

2 to 4

1 to 3

1. 5 to (RQD = 50$)

Badly fracturedrocks, or brokenrocks, or partiallyweathered rocksexcept argillaceousrocks

0.8 to 1.2

to be assessed byexamination in situ

1,0

0.2qu

1.1

0.2qu

0.8

0.5 - 1.2 (N > 50)

Heavily shatteredor weathered rocks

to be assessedafter inspection

to be assessedafter inspection

Notes

Increase by 10%for each 300 mmembedment

Earthquake area

may needalteration upwardsor downwards

Increase by 1/3if foundationrelatively dry

Increase by 10$for each 300 mmembedment

Legend : qu = uniaxial compressive strength of intact rock sampleN = SPT N -value

- 80 -

Table 10 - Allowable Bearing Stresses for Volcanic Rocks Determined byBuilding Codes, K = 0.2

MassWeatheringGrade

FreshVolcanics

SlightlyWeatheredVolcanics

ModeratelyWeatheredVolcanics

Uniaxial Compressive StrengthUCS-min

( M P a )

75

50

12.5

UCS-av( M P a )

125

100

35

Allowable Bearing Stressqa-min

( M P a )

15

10

2.5

qa-av( M P a )

25

20

7

Table 11 - Allowable Bearing Stresses for Volcanic Rocks Based on theRQD(1) Method

Rock

Type

FreshVolcanics

SlightlyWeatheredVolcanics

ModeratelyWeatheredVolcanics

RQD

(?)

75 - 10075 - 9050 - 75

90 - 10075 - 9050 - 75

50 - 7525 - 500-25

AllowableBearing Stress,

<Ja( MPa)

20126.5

20126.5

6.53.01.0

Notes : (1) RQD for use from this table should be the average within a depthbelow foundation level equal to the width of foundation, providedthe RQD is fairly uniform within that depth.

(2) These values should not be increased for embedment intorock.

(3) If the design is based on these values, the settlementof foundation is not expected to exceed 12.5 mm, evenfor large loaded areas.

- 81 -

Table 12 - Allowable Bearing Stresses Determined by the Canadian FoundationEngineering Method Using Calculated Ksp Values for Pile Diametersof over 300 mm

MassWeatheringGrade

FreshVolcanics

SlightlyWeatheredVolcanics

ModeratelyWeatheredVolcanics(S)

UniaxialCompressiveStrength

UCS-min UCS-av( MPa ) ( MPa )

75 125

50 100

12.5 35

Ksp

0.23

0.23

0.1C

AllowableBearingStress

qa-min qa-av( M P a ) ( M P a )

17.3 28.8

11.5 23

1.3 3.5

Notes : ( 1 ) Assuming embedment of the pile into sound rock for approximatelyone diameter,

(2) Joint spacing > 300 mm, and( 3 ) Joints filled with up to 25 mm of decomposed or disintegrated

material .

- 82 -

Table 13 » Settlement of Volcanic Rock Foundations underVarious Foundation Loads (End-Bearing)

Fresh Volcanic r = 0 . 2 5 I s = 0 . 8 5 = 25 GPa

Radius (m)

Searing Stress (MPa }

Reduction jCoefficient

Settlement

(mm)

ReductionCoefficient

Settlement

(mm)

ReductionCoefficient

Settlement

( mm )

max.

av.

j

max.av.

J

max.

av.

0.5

5 7.5 10 15

0,8

0.16

0.10

0.25

0,16

0.63

0.39

0.23

0.15

0.

0.38

0.23

0,

0.94

0.59

0.31

0.20

5

0.50

0.31

2

1.25

0.78

0.47

0.29

0.75

0.47

1.88

1.17

5

0.31

0.20

0.50

0.31

1.25

0.78

7,5

0

0.47

0.29

0

0.75

0.47

0

1.88

1.17

1

10 15

.8

0.63

0.39

.5

1.00

0.63

.2

2.50

1.56

0.94

0.59

1.50

0.94

3.76

2.35

5

0.63

0.39

1.00

0.63

2.50

1,56

2

7,5

0.

0.9*1

0.59

0.

1.50

0.94

0.

3.76

2.35

10

8

1.25

0.78

5

2.00

1.25

2

5.01

3.13

15

1.88

1.17

3.00

1.88

7.51

4.69

3

5

0.94

0.59

1.50

0.94

3.76

2.35

7.5

0

1.41

0.88

10 15

.8

1.88

1.17

0.5

2.25

1.41

0.2

5.63

3.52

3.00

1.88

7.51

4.69

2.82

1.76

4.51

2.82

11.27

7.04

Slightly Weathered Volcanic I? 8 0.35 I = 0 . 8 5 = 15 GPa Ei s 25 GPa

Radius ( m )

Bearing Stress ( M P a )

Reduction jCoefficient

Settlement

( m m )

max*

av.

Reduction JCoefficient

Settlement

( m m )

max.

av.

Reduction JCoefficient

Settlement( m m )

max.av.

0.5

5 7.5 10 15

0.8

0.26

0.160.39

0.23

0.52

0.31

0.78

0.42

0.5

0.42

0,25

0.63

0.38

0.83

0.50

1.25

0.75

0.2

1 .04

0.63

1.560,94

2.091.25

3.131.88

1

5 7.5 10 15

0.8

0.52

0.31

0.78

0.47

1,04

0.63

1.56

0.94

0.5

0.83

0.50

1.25

0.75

1.67

1.00

2.50

1.50

0.2

2.091.25

3.131.88

4.172.50

6.263.76

2

5 7.5 10 15

0.8

1,04

0.63

1.56

0.94

2.09

1.25

3.131.88

0.5

1.67

1.00

2.50

1.50

3.34

2.00

5,01

3.00

0.2

4.172.50

6.263.76

8.345.01

12.527.51

3

5 7.5 10 15

0.8

1.56

0.94

2.35

1.11

3.13

1.884.69

2.82

0.5

2.50

1.50

3.76

2.25

5.01

3.007.51

4.51

0,2

6.263.76

9.395.63

12,527.51

18.7811.27

Moderately Weathered Volcanic V = 0.25 I s 0.85 Ei^ = 5-rnin GPa Ei^ = 12.5 GPa

Radius (m)

Bearing Stress (MPa)

ReductionCoefficient

Settlement

(mm)

ReductionCoefficient

Settlement

(mm)

ReductionCoefficient

Settlement

(mm)

ReductionCoefficient

Settlement

(mm)

J

max*

av.

J

max.

av.

J

max.

av.

J

max.

av*

0.5

1

0.16

0.06

0.25

0.10

0.63

0.25

1.25

0.50

3

0

0,47

0.19

0

0.75

0.30

0

1.88

0.75

0

3.76

1.50

5

.8

0.78

0.31

5

1.25

0.50

.2

3.13

1.25

,1

6.26

2.50

7.5

1.17

0.47

1.88

0.75

4.69

l.b8

9.39

3.76

1

1

0.31

0.13

3

0

0.94

0.38

0

0.50

0.20

1.25

0,50

1.50

0.60

0

3.76

1.50

5

.8

1.56

0.63

.5

2.50

1.00

.2

6.26

2.50

7.5

2.35

0.94

3.76

1.50

9.39

3.76

0.1

2.50

1.00

7.51

3.00

12.52

5.01

18.78

7.51

2

1

0.36

0.25

3

0

1.88

0.75

0

1.00

0.40

2.50

1.00

5.01

2.00

3.001.20

0

7.51

3.00

0

15.02

6.01

5

8

3.13

1.25

5

5.01

2.00

2

12.52

5.01

1

25.0310.01

7.5

4.69

1.88

7.51

3.00

18.78

7.51

37.5515.02

3

1

0.94

0.38

3

0

2.82

1.13

5

.8

4.69

1.88

7.5

7.04

2.82

0.5

1.50

0.60

3.76

1.50

7.51

3.00

4.51

1.80

0.2

11.27

4.51

0

22.539.01

7.51

3.00

18.78

7.51

11.27

4.51

28.16

11.27

.1

37.5515.02

56.3322.53

- 83 -

LIST OF FIGURES

Figure PageNo. No.

1 Engineering Classification for Intact Rock- 84Basalt and Other Flow Rocks (Deere & Miller, 1966)

2 Maximum Settlement Versus Allowable Bearing Stress 85for a Caisson Diameter of 2 m

«*•«•

CM

1O

•»•— *

16

8

4uT(riD

~U

1 2

1?

1 ,

0-5

0-25

*b

C

1 ^

20

15

~ 1098765

4

3

2

OJ0-8

-0-70-60-5

0-4KIMIIMI

0-3

4 8 16 3 2 (Ib/in2xl03)

EVery lowstrength

• BasaltO Art/H^xif ft f\rv\\t

75 % of po

-

o

<C^ O /— ^ ° //

^ \/-^$/ #/ ,<f*

" S o c^"

''• /:

DLow

strength

» and rhyoints

/

/^x

S*

cMediumstrength

ht<*

Y*> o

jj#x°

8High

strength

/

o

'

i i

AVery highstrength/'-f&*\

1 i 1

2 3 4 5 6 78910 20 20 4050 6(i l l i i i i

75 125 250 500 1000 2OOO 40CX

Uniaxial Compressive Strength, cr.

0(kg/cm2}

Legend :

Et = tangent modulus at 50% ultimate strength.

Classify rock as AM, BH, BL, etc.

Figure 1 - Engineering Classification for Intact Rock-Basalt and Other Flow Rocks (Deere & Miller, 1966)

- 85 -

ee

4 ,-

ou

OJCO

Xo

FRESH VOLCANIC

j=0.2

JsO.8

I10

I15

Allowable Bearing Stress ( M P a )

8-

"iE 6-1

Ecu

CDCO

Xo

SLIGHTLY WEATHERED VOLCANIC

j= 0.2

j = 0.8

i10

i15

Allowable Bearing Stress (MPa)

20-

18-

16-

— 14-

E

MODERATELY WEATHERED VOLCANIC

c

— 12-

10-

8-

6-

4-

>* j=0.5

0 5 10 15

Allowable Bearing Stress (MPa)

j = Rock mass factor

C Refer to Tables 6 & 13 )

Figure 2 - Maximum Settlement Versus Allowable Bearing Stressfor a Caisson Diameter of 2 m

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Skin Friction on Piles at the New Public Works Central GEO Report HK$97Laboratory, by J. Premchitt, I. Gray & K.K.S. Ho No. 38 (US$16.5)(1994), 158 p. (Reprinted, 1995).

Bibliography on the Geology and Geotechnical GEO Report HK$118Engineering of Hong Kong to May 1994, by E.W. Brand No. 39 (US$19)(1994), 202 p. (Reprinted, 1995).

Hydraulic Fill Performance in Hong Kong, by C.K. Shen& K.M. Lee (1995), under preparation.

Mineralogy and Fabric Characterization and Classificationof Weathered Granitic Rocks in Hong Kong, by T.Y.Irfan (1995), under preparation.

Performance of Horizontal Drains in Hong Kong, by R.P.Martin, K.L. Siu & J. Premchitt (1995), underpreparation.

Hong Kong Rainfall and Landslides in 1993, by W.L.Chan (1995), under preparation.

General Report on Landslips on 5 November 1993 atMan-made Features in Lantau, by H.N. Wong & K.K.S.Ho (1995), under preparation.

Gravity Retaining Walls Subject to Seismic Loading, byY.S, Au~Yeung & K.K.S. Ho (1995), under preparation.

Direct Shear and Triaxial Testing of a Hong Kong Soilunder Saturated and Unsaturated Conditions, by J.K.M.Gan & D.G. Fredlund (1995), under preparation.

Stability of Submarine Slopes, by N.C. Evans (1995),under preparation.

Strength Development of High PFA Content Concrete, byW.C. Leung & W.L. Tse (1995), under preparation.

AAR Potential of Volcanic Rocks from Anderson RoadQuarries, by W.C. Leung, W.L. Tse, C.S. Mok & S.T.Gilbert (1995), under preparation.

Geotechnical Area Studies Programme - Hong Kong andKowloon (1987), 170 p. plus 4 maps.

Geotechnical Area Studies Programme - Central NewTerritories (1987), 165 p. plus 4 maps.

Geotechnical Area Studies Programme - West NewTerritories (1987), 155 p. plus 4 maps.

Geotechnical Area Studies Programme - North West NewTerritories (1987), 120 p. plus 3 maps.

•Geotechnical Area Studies Programme - North NewTerritories (1988), 134 p. plus 3 maps.

GEO ReportNo. 40

GEO ReportNo. 41

GEO ReportNo. 42

GEO ReportNo. 43

GEO ReportNo. 44

GEO ReportNo. 45

GEO ReportNo. 46

GEO ReportNo. 47

GEO ReportNo. 48

,GEO ReportNo. 49

GASP I

GASP II

GASP III

GASP IV

GASPV

HK$240(US$40)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

Geotechnical Area Studies Programme - North Lantau(1988), 124 p. plus 3 maps.

Geotechnical Area Studies Programme - Clear Water Bay(1988), 144 p. plus 4 maps.

Geotechnical Area Studies Programme - North East NewTerritories (1988), 144 p. plus 4 maps.

Geotechnical Area Studies Programme - East NewTerritories (1988), 141 p. plus 4 maps.

Geotechnical Area Studies Programme - Islands (1988),142 p. plus 4 maps.

Geotechnical Area Studies Programme - South Lantau(1988), 148 p. plus 4 maps.

Geotechnical Area Studies Programme - Territory of HongKong (1989), 346 p. plus 14 maps.

Geology of Sha Tin, by R. Addison (1986), 85 p.

Geology of Hong Kong Island and Kowloon, by PJ.Strange & R. Shaw (1986), 134 p.

Geology of the Western New Territories, by R.L.Langford, K.W. Lai, R.S. Arthurton & R. Shaw (1989),140 p.

Geology of Sai Kung and' Clear Water Bay by P.J.Strange, R. Shaw & R. Addison (1990), 111 p.

Geology of the North Eastern New Territories, underpreparation.

Geology of Lantau, under preparation.

Geology of Yuen Long by D.V. Frost (1992), 69 p.

Geology of Chek Lap Kok by R.L. Langford (1994), 61p.

San Tin : Solid and Superficial Geology (1:20 000 map)(1989), 1 map.

GASP VI

GASP VII

GASP VIII

GASP IX

GASPX

GASP XI

GASP XII

GeologicalMemoir No. 1

GeologicalMemoir No. 2

GeologicalMemoir No. 3

GeologicalMemoir No. 4

GeologicalMemoir No. 5

GeologicalMemoir No. 6

Sheet ReportNo. 1

Sheet ReportNo. 2

Map HGM 20,Sheet 2

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$150(US$25)

HK$50(US$9)

HK$78(US$12.5)

HK$97(US$17)

HK$87(US$13)

Free

Free

HK$45

Sheung Shui : Solid and Superficial Geology (1:20 000map) (1992), 1 map.

Kat O Chau : Solid and Superficial Geology (1:20 000map) (1993), 1 map.

Tsing Shan (Castle Peak) : Solid and Superficial Geology(1:20 000 map) (1988), 1 map.

Yuen Long : Solid and Superficial Geology (1:20000map) (1988), 1 map.

Sha Tin : Solid and Superficial Geology (1:20 000 map)(1986), 1 map.

Sai Kung Peninsula : Solid and Superficial Geology(1:20 000 map) (1989), 1 map.

Tung Chung : Solid and Superficial Geology (1:20 000map) (1994), 1 map.

Silver Mine Bay : Solid and Superficial Geology (1:20 000map) (1992), 1 map.

Hong Kong and Kowloon : Solid and Superficial Geology(1:20 000 map) (1986), 1 map.

Clear Water Bay : Solid and Superficial Geology(1:20 000 map) (1989), 1 map.

Shek Pik : Solid and Superficial Geology (1:20 000 map),under preparation.

Cheung Chau : Solid and Superficial Geology (1:20 000map), under preparation.

Hong Kong South and Lamma Island : Solid andSuperficial Geology (1:20 000 map) (1987), 1 map.

Waglan Island : Solid and Superficial Geology (1:20 000map) (1989), 1 map.

Map HGM 20,Sheet 3

Map HGM 20,Sheet 4

Map HGM 20,Sheet 5

Map HGM 20,Sheet 6

Map HGM 20,Sheet 7

Map HGM 20,Sheet 8

Map HGM 20,Sheet 9

Map HGM 20,Sheet 10

Map HGM 20,Sheet 11

Map HGM 20,Sheet 12

Map HGM 20,Sheet 13

Map HGM 20,Sheet 14

Map HGM 20,Sheet 15 •

Map HGM 20,Sheet 16

San Tin : Solid Geology (1 : 20 000 map) (1994), 1 map. Map HGM20S

HK$45

HK$45

HK$45

HK$45

HK$45

HK$45

HK$45

HK$45

HK$45

HK$45

Lo Wu : Superficial Geology (1:5000 map) (1990),1 map.

Lo Wu : Solid Geology (1:5 000 map) (1990), 1 map.

Map HGP 5A,Sheet 2-NE-D

Map HGP 5B,Sheet 2-NE-D

HK$45

HK$45

HK$45

HK$30

HK$30

Mai Po : Superficial Geology (1:5 000 map) (1990), Map HOP 5A, HK$301 map. Sheet 2-SE-A

Mai Po : Solid Geology (1:5 000 map) (1990), 1 map. Map HOP 5B, HK$30Sheet 2-SE-A

Lok Ma Chau : Superficial Geology (1:5000 map) Map HGP 5A, HK$30(1990), 1 map. Sheet 2-SE-B

Lok Ma Chau : Solid Geology (1:5 000 map) (1990), Map HGP 5B, HK$301 map. Sheet 2-SE-B

Deep Bay : Superficial Geology (1:5 000 map) (1989), Map HGP 5A, HK$301 map. Sheet 2-SW-C

Deep Bay : Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B, HK$30Sheet 2-SW-C

Shan Pui : Superficial Geology (1:5 000 map) (1989), Map HGP 5A, HK$301 map. Sheet 2-SW-D

Shan Pui : Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B, HK$30Sheet 2-SW-D

Man Kam To : Superficial Geology (1:5 000 map) (1990), Map HGP 5A, HK$301 map. Sheet 3-NW-C

Man Kam To : Solid Geology (1:5 000 map) (1990), Map HGP 5B, HK$301 map. Sheet 3-NW-C

Tin Shui Wai: Superficial Geology (1:5 000 map) (1989), Map HGP 5A, HK$301 map. ' Sheet 6-NW-A

Tin Shui Wai : Solid Geology (1:5 000 map) (1989), Map HGP 5B, HK$301 map. Sheet 6-NW-A

Yuen Long : Superficial Geology (1:5 000 map) (1989), Map HGP 5A, HK$301 map. . Sheet 6-NW-B

Yuen Long : Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B, HK$30Sheet 6-NW-B

Hung Shui Kiu : Superficial Geology (1:5000 map) Map HGP 5A, HK$30(1989), 1 map. Sheet 6-NW-C

Hung Shui Kiu : Solid Geology (1:5 000 map) (1989), 1 Map HGP 5B, HK$30map. Sheet 6-NW-C

Muk Kiu Tau : Superficial Geology (1:5 000 map) (1990), Map HGP 5A, HK$301 map. Sheet 6-NW-D

Muk Kiu Tau : Solid Geology (1:5000 map) (1990), Map HGP 5B, HK$301 map. Sheet 6-NW-D

Chek Lap Kok : Solid and Superficial Geology (1:5 000 Map HGP 5, HK$30map) (1993), 1 map. Sheet 9-NE-C/D

Yam O Wan : Solid and Superficial Geology (1:5 000 Map HGP 5, HK$30map) (1995), 1 map. Sheet 10-NW-B

Siu Ho : Solid and Superficial Geology (1:5 000 map) Map HGP 5, HK$30(1994), 1 map. Sheet 10-NW-C

Ma Wan : Solid and Superficial Geology (1:5 000 map) Map HGP 5, HK$30(1994), 1 map. Sheet 10-NE-A

Tsing Yi : Solid & Superfical Geology (1:5 000 map) Map HGP 5, HK$30(1995), 1 map. Sheet 10-NE-B/D

Pa Tau Kwu : Solid and Superficial Geology (1:5 000 Map HGP 5, HK$30map) (1994), 1 map. Sheet 10-NE-C

ORDERING INFORMATION IS GIVEN ON THE NEXT PAGE

Copies of GEO publications (except Sheet Reports, 1:5 000 maps and other reports which arefree of charge) may be ordered by writing to :

Publications (Sales) Office,Information Services Department,28th Floor, Siu On Centre,188 Lockhart Road, Wan Chai,Hong Kong.

The Information Services Department will issue an invoice upon receipt of a wr** ^

In Hong Kong, publications may be directly purchased from :

Government Publications Centre,Ground Floor, Low Block,Queens way Government Offices,66 Queens way,Hong Kong.

Requests for copies of Geological Survey Sheet Reports and other reports which aiv free ofcharge should be directed to :

Chief Geotechnical Engineer/Special Projects,Geotechnical Engineering Office,Civil Engineering Department,Civil Engineering Building,101 Princess Margaret Road,Homantin, Kowloon,Hong Kong.

1:5 000 maps may be purchased from

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All prices given in this List are for information only and may be changed without notice.The US$ prices shown are for overseas orders and are inclusive of surface postage toanywhere in the world. An additional bank charge of HK$50 or US$6.50 is required percheque made in currencies other than Hong Kong dollars. Cheques, bank drafts or m* ayorders must be made payable to HONG KONG GOVERNMENT.

This book is due for return or renewal on the date shownunless previously recalled. Fines may be incurred for latereturn.

DATE DUE

. -DEC. 2UGO

-5t JUL 1999

LB 624.15 165Irfan, T. Y.Foundation design of caissonson granitic and volcanic rocksHong Kong : GeotechnicalEngineering Office, CivilEngineering Department, 1991.