UNIVERSITY OF HONG KONGLIBRARY

Hong Kong Collectiongift from

Hong Kong Gov't Printer

CCO PUBLICATION No. 8/90

FOUNDATION PROPERTIES OFMARBLE AND OTHER ROCKS IN

THE YUEN LONG -TUEN MUN AREA

GEOTECHNICAL CONTROL OFFICECivil Engineering Services DepartmentHong Kong

© Government of Hong Kong

First published, December, 1990 Jsl^at*^—

Prepared by :

Geotechnical Control Office,Civil Engineering Services Department,6th Floor, Empire Centre,68, Mody Road,Kowloon,Hong Kong.

This publication is available from :

Government Publications Centre,General Post Office Building,Ground Floor,Connaught Place,Hong Kong.

Overseas orders should be placed with :

Publications (Sales) Office,Information Services Department,1, Battery Path,Central,Hong Kong.

Price in Hong Kong : HK$58

Price overseas : US$10 (including surface postage)

Cheques, bank drafts or money orders must be made payable to HONG KONGGOVERNMENT

FOREWORD

The Yuen Long-Tuen Mun Eastern Corridor project involves theconstruction by the Highways Department of a 7 km-long dual two-lane trunkroad. The geology of the project area is complex and locally highlyvariable, giving rise to various concerns in relation to the design ofbridge foundations, not the least being the occurrence of buried marblecontaining cavities.

The Geotechnical Control Office has been assisting the HighwaysDepartment with this project since 1986. Construction work is now underwayand the road is scheduled for completion in 1993. Before constructioncommenced the Office undertook a feasibility study, planned and supervisedthe ground investigation and advised on the design of bridge foundations.Recommendations arising from the investigation have been presented to theHighways Department in the form of Advisory Reports.

The ground investigation included numerous deep boreholes and anextensive programme of laboratory testing of rock samples was carried out.In view of the lack of published local data on the engineering propertiesof the rock types likely to be encountered in deep foundations in thisarea, it was decided to publish the data obtained in this project alongwith an outline of the approach to the design of bored piles. This shouldserve as a useful source of information for other projects involving deepfoundations in the Yuen Long - Tuen Mun area. It should be noted that thispublication is not intended as a guide to standards of geotechnicalpractice nor is it a state of the art review.

Dr T. Y. Irfan drafted and produced the publication, with checking andediting by Mr J. B. Massey, Dr R. P. Martin and Mr Y. C. Chan. Drs A.Cipullo and P. C. Tsui assisted with the interpretation of the groundinvestigation data. Dr Cipullo also helped with the planning and executionof the laboratory testing programme. Messrs M. C. Chan and L. P. Hocarried out most of the point load tests.

(A. W. Malone)Principal Government Geotechnical Engineer

December 1990

CONTENTS

PageNo.

Title Page 1

FOREWORD 3

CONTENTS 5

1. INTRODUCTION 9

2. GEOLOGICAL SETTING 11

2.1 GENERAL GEOLOGY 11

2.2 DESCRIPTION OF THE LITHOLOGICAL UNITS 11

2.2.1 General 112.2.2 Superficial Deposits 122.2.3 Basic and Acidic Intrusions 122.2.4 Volcanic Rock Units 132.2.5 Metasedimentary Rock Unit 132.2.6 Marble Unit 13

3. GEOTECHNICAL CHARACTERIZATION OF FOUNDATION ROCKS 15

3.1 GEOMECHANICS CLASSIFICATION OF ROCK MASSES 15

3.2 WEATHERING/ALTERATION MASS AND MATERIAL CLASSIFICATION 15

3.3 WEATHERING PROFILE IN CARBONATE ROCKS 17

4. LABORATORY TESTING OF INTACT ROCK 19

4.1 TESTING METHODS 194.2 ROCK TYPES TESTED 19

5. ENGINEERING PROPERTIES OF INTACT ROCK 21

5.1 UNIAXIAL COMPRESSIVE STRENGTH (UCS) 21

5.1.1 Tuff Breccia 215.1.2 Marble 21

5.2 STRESS-STRAIN BEHAVIOUR AND ELASTIC PROPERTIES 22

5.2.1 Tuff Breccia 225.2.2 Marble 22

5.3 POINT LOAD STRENGTH (PLS) 235.3.1 Classification of Rocks in Terms of Point Load 23

Strength5.3.2 Tuff Breccia 235.3.3 Marble 245.3.4 Metasiltstones and Metasandstones 24

PageNo.

5.3.5 Basic Dykes 24

5.4 PHYSICAL INDEX PROPERTIES 25

5.4.1 Tuff Breccia 25

5.4.2 Marble 25

5.5 RELATIONSHIPS BETWEEN INDEX PROPERTIES AND 25STRENGTH PROPERTIES

5.6 CORRELATION BETWEEN POINT LOAD STRENGTH AND UNIAXIAL 26COMPRESSIVE STRENGTH

5.7 GEOMECHANICAL CLASSIFICATION OF MARBLE AND TUFF BRECCIA 26IN TERMS OF INTACT STRENGTH AND ELASTIC MODULUS

6. ROCK MASS PROPERTIES 29

6.1 GENERAL 29

6.2 WEATHERING PROFILES 29

6.2.1 Volcanic Rock Units 296.2.2 Metasedimentary Rock Unit 29

6.2.3 Marble Unit 30

6.3 DISCONTINUITIES (RQD AND FRACTURE INTENSITY) 30

7. PRELIMINARY ASSESSMENT OF BEARING CAPACITY OF FOUNDATION 33ROCKS7.1 GENERAL 33

7.2 ALLOWABLE BEARING PRESSURES FOR DEEP FOUNDATIONS IN 33THE PROJECT AREA

7.2.1 Code Values 33

7.2.2 RQD Method 34

7.2.3 Canadian Foundation Engineering Method 34

7.2.4 Settlement Calculations: Rock Mass Factors 35and Rock Mass Deformation Moduli

8. GENERAL COMMENTS ON FOUNDATIONS WITH RESPECT TO THE MARBLE UNIT 37

9. CONCLUSIONS 41

REFERENCES 43

TABLES 47LIST OF TABLES 49

TABLES 51

FIGURES 63

LIST OF FIGURES 65

FIGURES 67

PageNo.

PLATES 93

LIST OF PLATES 95

PLATES 97

00

I. INTRODUCTION

The Northwest New Territories has seen rapid construction activityfor new town development in recent years. Foundation conditions in theNorthwest New Territories are generally more varied and complex than inother urban areas of Hong Kong where only granitic and volcanic rocks areencountered. The presence of marble under a thick superficial soil coverwas reported by Siu & Wong (1985). The discovery of marble with karsticfeatures i n c l u d i n g large cavities (Pascal, 1987) led to specialinstructions being issued for foundation works within a Designated Area,i.e. that affected by marble bedrock (Lands and Works Branch TechnicalCircular No. 4/89 and Buildings Ordinance Office Practice Note 129). In1990, the Buildings Ordinance and Regulations were amended to introducenew control provisions for the area within which marble may be found,referred to as "Area Number 2 of the Scheduled Areas". In addition tomarble, which may locally contain large cavities, marble-clast bearing tuffbreccia, pyroclastic volcanic rocks, granites, granodiorite, sedimentaryand metamorphic rocks underlie the area. These are generally covered by athick layer of superficial materials consisting of fill, alluvium, debrisflow and marine deposits. The geology is further complicated by a numberof faults and dyke intrusions.

The route of the Yuen Long to Tuen Mun Eastern Corridor, a proposedtrunk road joining the two new towns (Figure 1, Plate 1), crosses this areaof complex geology. Construction of the new road will involve a number ofembankments across the alluvial plain, cut slopes through the hillsides andbridges across the stream courses and in the interchange areas.

The Geotechnical Control Office (GCO) has been assisting the HighwaysDepartment with the geotechnical aspects of the foundation and slopedesign, including the site investigation and interpretation of thefoundation conditions at a number of bridge sites at Interchanges 1, 3 and4. A laboratory testing programme involving determination of index,strength and deformation properties of the main rock units was undertakenin order to assess the properties of the foundation rocks at these bridgesites. The engineering properties of the local metamorphic rocks,particularly marble, are little known and no detailed test data have beenpublished. The main testing programme was contracted out to the Departmentof Civil and Structural Engineering of the University of Hong Kong. Thiswas supplemented by point load testing of the main rock units by technicaland professional staff of the GCO.

In view of the general geotechnical interest of the area, it wasdecided to publish this information in order to provide data on thefoundation conditions and the engineering properties of the rocks.

01

11

2. GEOLOGICAL SETTING

2.1 GENERAL GEOLOGY

Recent geological mapping by the Geological Survey of Hong Kong of thearea between Tuen Mun and Yuen Long indicates that this portion of theNorthwest New Territories is underlain by metamorphic rocks includingmarble of Carboniferous age, and by volcanic rocks and granite intrusionsof Jurassic to Cretaceous age (Langford et al, 1989; Darigo, 1989; Frost,1991) (Figure 2). Basalt dykes, probably Tertiary in age, are often foundassociated with faults. Superficial deposits (fill, alluvium, mud anddebris flow deposits), usually 5 to 20 m thick, cover the bedrock which isgenerally deeply weathered in the low-lying areas. A generalized cross-section of the strata in the Yuen Long Area is shown in Figure 3.

The Carboniferous rocks belong to the Mai Po member of the Lok Ma ChauFormation and the Yuen Long Formation of the San Tin Group (Tables 1 and2). Volcanic rocks belong to the Tuen Mun Formation of the Repulse BayGroup. The Mai Po Member consists of metasiltstones and metasandstoneswith phyllite layers, whereas the Yuen Long Formation consists of marble,dolomitic in part, interbedded with siltstones in the upper horizons.

Ground investigation carried out for the Highways Department projecthas shown that, in the southern portion of the area near Tuen Mun, theunderlying bedrock consists predominantly of alternating layers oftuffaceous siltstone and tuff breccia with marble clasts. Also present inthe southern portion of the area are predominantly andesitic volcanic rocksof the Tuen Mun Formation, Repulse Bay Volcanic Group. In the northernportion of the area, near Yuen Long, the dominant rock types aremetamorphosed sandstones and siltstones of the Mai Po Member of the Lok MaChau Formation, and marble and interbedded marble and metasiltstones of theYuen Long Formation. The hills between Tuen Mun and Yuen Long (Plate 1)are dominantly composed of fine- and fine- to medium-grained granite.Detailed (1:5 000 scale) geological maps of the area between the twotowns, known as "the Designated Area11, have been produced by theGeotechnical Control Office (see list of GCO publications at the back ofthis publication).

The broad structural geology of the Northwest New Territoriesindicates that the Carboniferous bedrock forms a wedge, bounded andcontrolled by faults, extending from Guangdong Province, and underlyingmuch of the Lo Wu - Yuen Long - Tuen Mun Plain. The regional geologicalstructure is dominated by a series of northeast-southwest trending faultsgenerally dipping northwest, with more recent cross-faults trendingnorthwest-southeast and offsetting the former. The overall regional dip ofthe foliation and bedding is towards the northwest at about 50°, but sharpvariations in the dip and dip direction are also present, which complicatethe geological succession in many areas.

2.2 DESCRIPTION OF THE LITHOLOGICAL UNITS

2.2.1 General

Examination of soil and rock samples obtained during the groundinvestigation suggests the presence of five broad lithological units.

12

These are, from the youngest to the oldest, as follows :

(a) Super f i c ia l d e p o s i t s of Late Ter t ia ry toQuaternary age, comprising al luvium, mud anddebris flow deposits, plus recent fill.

(b) In t rus ive dyke rocks of granite, rhyolite,andesite and basalt of probable Cretaceous andTertiary age (Frost, 1991).

(c) Interbedded siltstone, sandstone, marble-bearingtuff breccia and tuffs of Jurassic age (Tuen MunFormation of the Repulse Bay Volcanic Group).

(d) Interbedded metasiltstones and metasandstones ofCarboniferous age (Mai Po Member of the Lok MaChau Formation).

(e) Marble and interbedded marble and metasedimentaryrocks of Carboniferous age (Yuen Long Formation).

The weathering terms used in the following sub-sections are taken froma rock mass classification which is based on the scheme given by BSI(1981).The details of this classification are explained in Section 3.2. Thisclassification was found to be the most appropriate for the purposes of theproject.

Plates 2 to 15 illustrate the various rock units encountered in theboreholes in the project area.

2.2.2 Superficial Deposits

Fill occurs over much of the area, generally up to 3 m thick, but upto 6 m in some localities. It-generally consists of loose to medium densesilty and clayey sands, locally gravelly and cobbly. Alluvium is the mostwidespread superficial deposit overlying bedrock in both the northern andsouthern portions of the site. It often occurs as inter!ayered soft tofirm, grey or brownish grey, clayey silt, and loose to dense, light grey,coarse and occasionally fine sand. Its thickness is generally between 5 mand 15 m, but may be up to 24 m thick in areas underlain by old buriednatural drainage channels. Mudflow and debris flow deposits, which areknown to occur in the Yuen Long area above marble bedrock, were identifiedin one or two boreholes. No marine deposits were found in the boreholesinspected for the project.

2.2.3 Basic and Acidic Intrusions

Granite and rhyolite dykes were found intruding both the marble andthe sedimentary rocks in a limited number of boreholes. The dykes aretypically highly to completely weathered, with a thickness not exceeding5 m. Frost (1991) reported the presence of granite and granodiorite in anumber of deep boreholes, up to 250 m, drilled for the geological surveyof the Yuen Long area.

Dykes of basic and intermediate composition also occur as thin to

13

thick intrusions (Plate 5), often associated with faults, in the marble andmetasiltstone at Interchanges No. 3 and 4 (Figure 1). The rocks are strongand dark grey to black when fresh, and become a dense to very densegreyish green sandy silt when completely decomposed* The major basicintrusions strike northeast-southwest and dip northwest with thicknessesranging from 5 m to 15 m, following the general structural features of thearea. Thermal metamorphism has obviously occurred along the contact zonebetween the dykes and the country rock (Plate 5), particularly the whiteand grey marble subunits (Tsui & Irfan, 1990; Frost, 1991).

2.2.4 Volcanic Rock Units

A sequence of marble-bearing tuff breccia and tuffs interbedded withtuffaceous siltstone/sandstone occurs at the location of Interchange No. 1.(Figure 1). This sequence has been named the Tin Shui Wai Member of theTuen Mun Formation (Darigo, 1989). The sandstone and siltstone areweathered to a loose to very dense sandy silt and silty sand to depths of60m or more (Plate 13). The tuff breccia is strong to very strong andwidely jointed when fresh, containing 20% to 50% of subrounded to angularfragments of marble, quartzite and metasandstone embedded in a greenishgrey to grey fine-grained tuff matrix. The fine-grained tuff may alsooccur as distinct bands which are easily recognizable in the moderatelydecomposed state (Plates 10 to 13) as they do not exhibit the typicalhoneycombed relict structure of the dissolved carbonate clast-rich zones.

A sequence of tuff of andesitic composition is present locally underone of the bridge foundations in the southern portion of the site.

2.2.5 Metasedimentary Rock Unit

Interbedded metasiltstones and metasandstones of the Mai Po Member ofthe Lok Ma Chau Formation (Table 1), overlying marble of the Yuen LongFormation, occur in the northern portion of the site. This unit isgenerally completely weathered to depths of 15 to 40 m, locally to 70 m ormore. The rocks are generally grey or dark grey, strong in the fresh stateand they may show a pronounced foliation (Plates 14 and 15). Graphiticsiltstone, usually strongly foliated, is also known to occur at certainhorizons.

2.2.6 Marble Unit

The marble unit belongs to the Carboniferous Yuen Long Formation andoccurs in the northern portion of the site near Yuen Long. Boreholes haverevealed the occurrence of three major, visually recognizable, marblesubunits : white marble, grey marble, and interbedded marble and siltstone,all belonging to the Ma Tin Member (Plates 2 to 8). The former twosubunits were encountered in boreholes at Interchanges No. 3 and 4, andthe interbedded variety was encountered mainly at Interchange No. 4(Figure 1). Stratigraphically, the interbedded marble is underlain by thegrey marble subunit, which is in turn underlain by the white marblesubunit. The oldest marble, the Long Ping Member (Plate 9), was notencountered in any of the boreholes put down during the site investigationfor the project.

14

The interbedded marble and metasiltstone subunit is characterised bythe presence of white to grey, fine-grained marble beds with narrow tothickly-laminated, light greenish grey metamorphosed siltstone (Plates 4and 7). The siltstones are typically crushed and sheared, with smooth,polished and slickensided shear planes. The weathering profile isgenerally deep in this subunit, and all the weathered rock grades may bepresent (see Section 3.3). Large cavities are generally absent in theinterbedded subunit but minor solution features are present.

The grey or bluish grey marble (Plates 2 and 6) is typically strongand fine-grained, with moderately to widely-spaced joints when fresh, whilein its weathered state it generally becomes medium dense to dense, slightlyclayey and silty, fine to occasionally medium sand. The latter product,generally very thin, represents the insoluble portion of the original rock,which was probably an impure argillaceous limestone prior to metamorphism.The grey marble subunit at some of the bridge sites has been locallyaffected by granitic intrusions and contains granitic veins and silicifiedpatches (Plates 2 and 3).

The white marble subunit (Plates 5 and 6), which is known to underliethe alluvial cover at the eastern end of Yuen Long, has only beenencountered at the Bridge No. 14 site at Interchange No. 4 and the BridgeNo. 13A site at Interchange No. 3 (Figure 1). The white marble is a fineto coarsely crystalline, moderately strong rock with very widely-spacedjoints. No soil residue is formed over this subunit because of its purecomposition, except where it has been affected by acidic or basicintrusions.

Marble adjacent to the major basic and acidic dykes is altered to arock varying in composition from a dark grey skarn-like material to marblewith chloritic veins (Plate 5) as a result of contact metamorphism andhydrothermal alteration (Tsui & Irfan, 1990). The intensity of alterationdecreases away from the contact. No mineralogical study of the effects ofcontact metamorphism of the basic dykes in the Yuen Long area has beenundertaken. It is this contact metamorphic zone which is differentiallyweathered in the otherwise fresh marble underlying some of the bridgesites, particularly at Interchange No. 3 (Plate 5). In some cases, thisaltered and weathered layer directly underlies the superficial layers,resulting in the formation of a weathering profile showing a transitionfrom completely weathered to slightly weathered and fresh marble(Figure 4).

Some small lengths of zero or very low core recovery are shown in theborehole logs in the grey and white marble, particularly near the topsurface of the bedrock. These are thought to be associated with smallsolution cavities, some of which appear to have been partly infilled withsoft to firm, light brown, clayey silt with marble fragments of gravelsize. Most of the infill material has not been recovered.

No major cavities or other solution effects around joints wereidentified in the drillholes. However, the presence of such features atgreater depths or in a thicker sequence of the pure white marble subunitcannot be discounted.

15

3. GEOTECHNICAL CHARACTERIZATION OF FOUNDATION ROCKS

3.1 GEOMECHANICS CLASSIFICATION OF ROCK MASSES

For sound foundation design, the engineering properties of the soil orrock masses must be known in order to determine the behaviour of the groundunder the imposed load. The important engineering properties of the rockmass are deformability and strength, and these depend on :

(a) the properties of intact material,

(b) the discontinuity pattern and its characteristics, and

(c) the characteristics of the weathering profile.

The intact rock properties can be determined by laboratory tests.Measurement of rock mass properties by insitu testing is generally veryexpensive, and because of variations in geological conditions, can onlyprovide data for a specific locality or a site. By classifying the rockmass into a number of broad classes or groups, each of which can beexpected to show reasonably distinctive engineering behaviour, the limitedfield test data and experience gained at one site can be applied to othersites with similar characteristics.

A number of geotechnical rock classification systems have beendevised. These take into account such factors as structure,discontinuities, details of the weathering profile, groundwater conditionsand the material properties. Some of the best known systems have beendeveloped for underground excavations (e.g. Bieniawski, 1976; Barton etal, 1974), where various rock material and mass characteristics have beengiven numerical weightings to arrive at a number of geomechanical classes.The classifications are then used to predict the rock mass deformationmoduli (Bieniawski, 1978) or stand-up times in tunnels (Bieniawski, 1976;Barton et al, 1974). The assessment of weathering has become an importantaspect of rock mass classification for engineering purposes in Hong Kong,where the rocks are deeply weathered.

In this investigation, a simplified engineering classification schemebased on lithological characteristics and mass weathering zones (Section3.2) has been used to delineate the foundation layers. Laboratory testinghas been carried out to determine the intact material properties of variousrock types, particularly those of the marble subunits and the tuff breccia.The rock mass characteristics, together with intact rock properties, havethen been used to assess the rock mass engineering properties of thevarious foundation units (Chapter 8).

3.2 WEATHERING/ALTERATION MASS AND MATERIAL CLASSIFICATION

A unified mass classification scheme broadly based on BS 5930 (BSI,1981) has been used to characterize the weathering and alteration state ofall the foundation rocks (Table 3). The application of this scheme, withmodifications as explained below, to various igneous, volcanic andsedimentary rock sequences is decribed in several GCO unpublished reportsand technical publications (e.g. Powell & Irfan, 1987 for volcanic andvolcano-sedimentary rocks; Irfan & Powell, 1985 and Choy et al, 1987 for

16

granites; Iffan, 1988 for metamorphic rocks). A brief discussion ofweathering processes and the applicability of the scheme to carbonate rocksin general, and to the marble unit in Yuen Long in particular, is given inthe next section.

The moderately weathered/altered rock mass zone has been separatedinto two sub-zones at about 10% soil content, based on Irfan & Powell(1985). For foundation purposes, a moderately weathered/altered rock massin strong rock with less than 10% soil is considered to be a favourablefoundation layer for end-bearing piles because of its high bearing capacityand low settlement properties, except for marble and other carbonate rocksaffected by dissolution. In the latter case, the bearing capacity andsettlement characteristics will depend on the size and distribution ofdissolution features and the discontinuity pattern. The foundationproblems associated with solution and discontinuity effects in solublecarbonate rocks have been discussed in detail by Sowers (1976a, 1984) andsummarized by Dearman (1981).

For description of the weathering (including solution) and alterationstate of the rock material, a uniform scheme has been used for all therocks (Table 4). Based on visual recognition of weathering and alterationeffects, three broad material classes have been identified :

(a) Fresh Rock (Grade 1)

(b) Decomposed/Disintegrated Rock (Grades 2, 3 and 4)

(c) Soil (Grades 5 and 6)

Solution has been included in the broader term of "Decomposition", ashave the effects of alteration (e.g. hydrothermal alteration). It isusually difficult to visually distinguish the effects of hydrothermalprocesses from weathering effects in hand specimens, particularly in rockswhere more recent weathering effects are superimposed on generally mucholder alteration effects. The suffix (A) in brackets can be used at theend of the decomposition term if such effects are clearly recognised, e.g.Slightly Decomposed (A) Granite.

The Decomposed/Disintegrated Rock material class has been subdividedinto three grades :

(a) Slightly (Grade 2).

Material which is partially discoloured, withslight decomposition/disintegration of mineralconstituents. Further sub-division has been made,where necessary, as follows :

(i) Rock with less than 50% discoloration (Grade21).

(ii) Rock with more than 50% discoloration (Grade211),

based on the amount of staining of the rockmaterial.

17

(b) Moderately (Grade 3).

Material which is completely discoloured, with oneor more mineral constituents showing some degreeof chemical alteration or a moderate degree ofmicrofracturing, or both.

(c) Highly (Grade 4).

Material which is completely discoloured, with oneor more mineral constituents showing a high degreeof chemical alteration to gritty aggregates or ahigh degree of microfracturing, or both.

The Soil class has been subdivided into two grades :

(a) Completely Decomposed/Disintegrated (Grade 5).

Material which still retains the parent rockfabric as a result of weathering or alteration,but which behaves like a soil in terms ofconsistency and strength.

(b) Residual Soil (Grade 6).

Material which has lost all or most of the parentfabric.

The terms "Fresh" to "Residual Soil" used to describe the weatheringgrades in Table 4 broadly correspond to the decomposition grade scheme forrock material used in Geoguide 3 (GCQ, 1988), which has been drawn upmainly with reference to granitic and volcanic rocks.

In pure carbonate rocks and evaporites, the intermediate gradesbetween Fresh Rock and Residual Soil do not usually occur or are difficultto distinguish by simple visual means unless tested in the laboratory, e.g.increase in porosity due to solution of individual mineral grains orgroups of grains or cementing material.

3.3 WEATHERING PROFILE IN CARBONATE ROCKS

A typical weathering profile developed in carbonate rocks is given inFigure 5. The characteristics of the weathering profile depend upon theimpurities present in the rock as well as the discontinuity pattern, thestructural features and environmental factors such as rainfall andtemperature. The predominant weathering process is solution. In rockscomposed of calcium carbonate (CaC03) with little or no impurities, theremay be no intermediate grades between Fresh Rock and Soil, and Fresh Rockmay be overlain by a very thin structureless soil ("Residual Soil")representing the insoluble residue of the original rock. The rock maycontain solution cavities, partly or wholly infilled, particularly alongdiscontinuities. Usually the surface of the rock is very irregular, withpinnacles and troughs of a metre to hundreds of metres across. Some verycherty or clayey carbonate rocks may develop a residual cover more than 30m thick. In some cases, particularly in very impure carbonate rocks, athick transition zone between Fresh Rock and Residual Soil may form which

18

may be very variable laterally. Moneymaker (1968) reported a transitionzone over 65 m thick beneath some dams in Kentucky, U.S.A. A truesaprolitic soil which retains structural features of the rock may alsodevelop as part of the transition zone (Deere & Patton, 1971)*

The components of the weathering profile can hence be classified interms of percentages of fresh rock, decomposed rock and soil (or void) ashas been done for other rocks (Table 3). In impure carbonate rocks allthe rock mass zones may be present, whereas in pure carbonate rocks a thinlayer of Residual Soil is usually underlain by Fresh Rock (Figure 5).

In the project area, the white and grey marble subunits of the YuenLong Formation are generally pure and only a thin (or missing) ResidualSoil layer is present, usually underlain by Fresh Rock without anytransition zones. In some cases, small cavities, partially or whollyfilled, are present below a very irregular karstic surface. All the zoneswere seen to be present where the marble has been altered by intrusions(Figure 4). In the interbedded marble and metasiltstone subunit underlyingsome of the bridge sites, a gradual transition from a structureless sandysilt (Residual Soil) to Fresh Rock occurs (Table 3, Plate 7).

19

4. LABORATORY TESTING OF INTACT ROCK

4.1 TESTING METHODS

The laboratory testing programme primarily involved determination ofstrength and deformation properties of intact rock specimens, together withsome selected index properties. Uniaxial compressive strength anddeformation properties (Young's and Secant Moduli, and Poisson's ratio)were determined on oven-dried rock cores at the Rock Mechanics Laboratoryof the University of Hong Kong in accordance with the specificationscontained in ASTM Standard D3148-80 (ASTM, 1985). The cores were cut to alength/diameter ratio of 2 to 3 and the ends were machine-lapped. Physicalindex properties for each specimen, namely saturation moisture content,saturated and dry density and porosity, were determined in accordance withISRM (1978). The core specimens tested and their locations are shown inPlates 2 to 13.

Point load testing of both core and irregular lump specimens wascarried out in accordance with ISRM (1985). For cores which were tested inuniaxial compression, immediately adjacent core pieces of the same gradewere subjected to point load tests in order to obtain a direct correlationbetween uniaxial compressive strength and point load strength for differentrock types. Point load testing was also undertaken at selected locationson weaker, weathered specimens where uniaxial strength testing was notpractical.

4.2 ROCK TYPES TESTED

The laboratory programme was limited by the financial and timeconstraints of the project. Strength testing was mainly concentrated ontwo of the three major rock units present in the project area, namely thetuff breccia unit of the Tuen Mun Formation underlying almost all thebridge sites at Interchange No. 1, near Tuen Mun, and the marble unit ofthe Yuen Long Formation underlying the bridge sites at Interchanges No. 3and 4 (Figure 1). No laboratory testing was carried out for themetasedimentary rocks of the Mai Po Formation which are found under thebridge sites at Interchange No. 4, west of Yuen Long. This was because nocores of suitable length devoid of fractures were available, and becausethe rocks were found to be completely weathered in areas where theyoverlie the marble subunits. One specimen selected for testing wasfractured during sample preparation.

Only two specimens of the basic dyke unit were tested since this rocktype is only significant in the foundations of two proposed bridges. Inaddition, these rocks are very fractured, even in the fresh state; hencethe strength of this unit was determined by point load testing of irregularsamples and core specimens of short length. This was also the case withthe metasedimentary rocks and the more intensely weathered specimens.

20

21

5. ENGINEERING PROPERTIES OF INTACT ROCK

5.1 UNIAXIAL OPPRESSIVE STRENGTH (UCS)

5.1.1 Tuff Breccia

The results of uniaxial compressive strength tests on tuff brecciaspecimens are tabulated in Table 5 and the ranges of values for eachweathering grade are shown in Table 6. A few of the specimens failedprematurely along pre-existing fractures and veins. These are marked withan asterisk in the table and are not used in the following assessment.

Fresh rock was not present in the boreholes drilled to depths between40 m and 100 m and hence was not tested. The freshest tuff brecciaspecimens tested were from the slightly discoloured rock grade (2i) andthese showed strengths of UCS = 150 to 300 MPa (i.e. very strong toextremely strong). The variation in strength reflects the variation inlithology, with the specimens from the fine tuff bands (without any marbleclasts) being generally stronger than the marble clast-bearing tuff. Thehighest strength in this investigation was however obtained on the lattervariety of almost fresh rock (Table 5). There is a gradual decrease instrength values with increased decomposition in the early stages ofweathering. However, the UCS is drastically reduced from about 150 MPa to50 MPa or lower once solution of marble clasts, and possibly CaC03bonding, results in a rock with a honeycombed texture (Plates 10 to 12).

The pure tuff bands do not show honeycombed texture and, in general,show only a gradual decrease in strength with increased weathering.However, no test results are available for more intensely-weathered tuffsfrom this investigation.

No uniaxial compressive strength testing was carried out on thesandstone and siltstone members of the Tuen Mun Formation as these rocksare too intensely weathered within the depths drilled to be suitable forthis test.

5.1.2 Marble

The results of uniaxial compressive strength tests on marble specimensfrom the various subunits are tabulated in Table 7 and the ranges of valuesfor each rock type and weathering grade are given in Table 8.

Variations in strength occur even within the same marble subunit dueto variations in texture (including porosity), grain size and proportion ofimpurities present in the rock. Both grey and white marble are strong tovery strong rocks in the fresh state, with UCS = 65 to 138 MPa and 86 to122 MPa respectively. Recently, Yiu & Tang (1990) reported a UCS range of40 to 136 MPa (except for one test result of 20 MPa) from limited tests ongrey to white marbles of the Ma Tin Member found in the Tin Shui Wai area.Marble of more weathered grades (reflected by increase in porosity) do notusually occur in these two subunits unless affected by granite or basicdyke intrusions. For example, grey marble containing thin granite veinsgave UCS = 72 to 122 MPa and 47 to 70 MPa in the case of partiallydiscoloured (and possibly slightly dissolved) and completely discolouredspecimens respectively (Table 8). The strength is significantly higher in

22

silicified marble specimens, where UCS values of 121 to 188 MPa wereobtained on fresh grey marble specimens which appeared to have beenaffected by a granitic intrusion nearby.

No fresh specimens of impure marble (termed "banded impure marble")interbedded with metasiltstone were available for testing. Specimensshowing slight effects of solution (in the form of increased porosity anddiscoloration) gave UCS of 39 to 66 MPa (i.e. moderately strong rock).

5.2 STRESS-STRAIN BEHAVIOUR AND ELASTIC PROPERTIES

5.2.1 Tuff Breccia

The results of the uniaxial stress-strain tests for tuff brecciaspecimens are given in Tables 5 and 6 in terms of tangent Young's modulus,Et, (at 50% of ultimate stress), secant modulus, Es, (at 0 to 50% ofultimate stress), and Poisson's ratio.

The two freshest tuff breccia specimens showed very high elasticmodulus values of Et = 137 and 128 6Pa. In general, pure tuff specimensgave lower modulus values, Et = 50 to 75 GPa, compared to the specimenscontaining marble clasts, Et = 62 to 137 GPa. The stress-strain curvesshow differences in behaviour (Figure 6). The marble clast-bearingspecimens generally show curvilinear and concave-upward initial portions(the type IV behaviour of Deere & Miller, 1966, see also Hendron, 1968)indicating inelastic behaviour, while those of pure tuff specimens showsteep straight line behaviour (type I behaviour). The typical stress-strain curves of Deere & Miller for various rocks in uniaxial compressionto failure are given in Figure 10.

Tangent modulus values of Et = 55 to 80 GPa were obtained for thehighly discoloured (grade 211) tuff breccia specimens. The variation in Etvalues with increased weathering, at least in the initial stages, is maskedby that due to textural and compositional variation in the tuff brecciaunit. The value drops to Et = 17 to 37 GPa once the rock is completelydiscoloured and small voids are formed as a result of solution of marbleinclusions in the rock (i.e. honeycombed texture). The secant modulusvalue correspondingly decreases with increased weathering. A relationshipEt = 1.14 Es exists between the two moduli (Figure 7).

No systematic variation is apparent in the values of Poisson's ratio,both in terms of rock type and weathering grade, with slightly discoloured(grade 2i) and highly discoloured (grade 2ii) specimens having v = 0.18 to0.54 and v = 0.22 to 0.45 respectively (Table 5). Slightly lower valuesof v = 0.11 to 0.38 were obtained for the specimens showing honeycombedtexture.

5.2.2 Marble

The results of the uniaxial stress-strain tests for marble specimensare given in Table 7 and are summarised in Table 8.

The purer white marble subunit shows a narrow band of tangent modulusvalues within the range of Et = 65 to 83 GPa, with most test values fallingaround 66 GPa. The corresponding secant modulus values at 0 to 50%

23

ultimate stress level are Es = 55 to 86 GPa. The grey marble specimensshow a wider scatter of moduli values of Et = 43 to 93 GPa and Es = 30 to83 GPa, reflecting the greater natural variation in texture and compositionof this rock. The grey marble specimens affected by granitic intrusionsgave values as high as Et = 111 GPa in the case of slightly decomposedmarble with granitic veins, and as low as Et = 33 GPa in the case ofs i l ic i f ied marble (Table 8). The impure banded marble specimens gavegenerally lower moduli values of Et = 34 to 53 GPa and Es = 22 to 56 GPa.

The Poisson's ratios vary between v = 0.23 and 0.49 for the grey,white and banded marble var iet ies. No discernible differences wereobserved between these types except for the grey marble affected byintrusions, where lower values of v = 0.16 to 0.28 were obtained, forexanrple, on silicified marble specimens. The mean Poisson's ratio valuesare, respectively, 0.37, 0.30 and 0.31 for the fresh grey, white and bandedmarble subunits.

Some clear d i f ferences in stress-strain behaviour of the variousmarble types were observed in the specimens tested. While the grey marblegenerally displayed the type IV-V behaviour (i.e. plastic-elastic- plastic)the white marble showed type I behaviour (with a straight line in theinitial stages of compression) in the case of strong specimens to type IVbehaviour in the case of less strong specimens (Figure 8). The behaviourdisplayed by the impure banded marble is of type V (plastic-elastic-p last ic) , which is typical of schistose rocks, whereas the silicifiedmarble and the marble with granitic veins showed straight lines typical ofstrong igneous rocks, limestones, etc. (Figure 9).

5.3 POINT LOAD STRENGTH (PLS)

5.3.1 Classification of Rocks in Terms of Point Load Strength

Extensive point load testing was carried out on a wide spectrum ofmaterials from various weathering grades, including very weak rocks of allthe major rock units present in the project area. The mean results of thepoint load tests carried out on the specimens adjacent to core sectionstested in uniaxial compression are presented in Tables 5 and 7 for the tuffbreccia and marble units respectively, and the ranges of values for eachrock type and weathering grade are given in Tables 6 and 8. Figures 11 to13 show the mean point load strength values obtained on all specimensincluding those prepared from the remainder of the UCS samples for the tuffbreccia and various marble types. The mean results on specimens from themetasandstones and metasi Its tones of the Lok Ma Chau Formation and basicdykes are presented in Figures 13 and 14 respectively. Table 9 gives aclassification of the rock units in terms of point load strength andweathering grade of material.

5.3.2 Tuff Breccia

The grade l-2i tuff breccia is a very strong rock with PLS > 7 MPa.The fresher varieties and pure tuff bands have strengths up to 14 MPa(Tables 5 and 6). The strength is reduced with increased discoloration asa result of slight chemical alteration of tuff components (i.e. feldsparsand biotite), and possibly slight solution of marble clasts. The highlydiscoloured tuff breccia specimens (grade 2ii) have strengths in the range

24

of PLS = 4.5 to 11 MPa (Figure 11). The strength is drastically reducedwhen the rock is moderately decomposed (i.e. grade 3) and large pores areformed as a resul t of solut ion of marble c lasts . The test isinsufficiently sensitive to accurately determine the strengths of weakermaterial because of its honeycombed texture.

No testing was carried out on the tuffaceous sandstone and siltstonemember of this unit, as the weathering profile is very deep and no suitablerock specimens were available for testing.

5.3.3 Marble

The point load strengths of the fresh white and grey marble subunitsvary between PLS = 2.8 and 5.4 MPa (Figure 12, Table 8). The grey marblewhich has been affected by granitic intrusion and/or containing siliceouspatches shows a wider range of weathering than the more pure variety, withthe fresh rock having PLS > 6.5 MPa. The strength gradually drops to about3.0 MPa with increased discoloration and solution. More weathered material(i.e. grades 3 to 5), although present in the boreholes, was not tested.

The point load strength results are given separately for theinterbedded impure marble and metasiltstones of the uppermost subunit ofthe Yuen Long Formation (Figure 13). Only one test result exists for thefresh marble from this subunit since fresh rock was not encountered withinthe depths reached by the boreholes sunk in the project area. The impuremarble showing slight effects of decomposition (solution) has PLS = 1.5 to4.0 MPa. The strength reduces gradually with increasing solution of CaC03and disintegration before the rock is left as a sandy silty residue. Themetasiltstones are slightly stronger, but highly fractured, with PLS = 2.0to 5.5 MPa (Figure 13).

5.3.4 Metasiltstones and Metasandstones

The point load strength testing was limited to the moderately andhighly decomposed/disintegrated rock specimens of metasiltstone andmetasandstone from the Mai Po Formation . Fresh and slightly decomposed/disintegrated rock was not reached in any of the initial boreholescompleted until the start of the testing programme. The strongest rocktested gave PLS = 3.4 MPa for a test carried out perpendicular to thefoliation direction (Figure 13). The fresh metamorphic rock is expected tobe very strong, with PLS > 6 MPa. These rocks generally have a strongfoliation and the PLS values are likely to be smaller for tests carried outin directions other than perpendicular to the foliation planes.

5.3.5 Basic Dykes

Limited point load testing was undertaken on specimens selected fromthe thick basic dykes, particularly those present in the foundations ofBridge Nos 13 and 13A. The freshest rock specimen tested showed slighteffects of weathering in the form of slight discoloration, with PLS =9.0MPa (Figure 14). The strength is reduced significantly from about 5 MPa to0.4 MPa once the rock is corrpletely discoloured. Some specimens whichinitially appeared to be fresh were observed to be affected by weatheringand alteration when examined in detail after testing.

25

5.4 PHYSICAL INDEX PROPERTIES

5.4.1 Tuff Breccia

In the slightly discoloured and fresh states, the tuff breccia is avery dense rock having a very small saturation moisture content, is, of<0.2%, and a related effective porosity, neff, of < 0.8% (Tables 5 and 6).With increasing discoloration, these values increase to 0.4% and 1.0%respectively. Once the rock is completely discoloured, i.e. moderatelydecomposed, the values increase significantly, with is increasing to 5% ormore and neff to 12% or more, particularly in the marble-bearing brecciamember.

The variation in density with weathering is not clear at the earlystages, with the highly discoloured specimens having generally a higherdensity than the slightly discoloured specimens. This discrepancy may bedue to the limited testing carried out on the tuff breccia unit, which hasa very variable composition. The slightly to highly discoloured tuffspecimens gave generally lower dry density values (d<j = 2.70 to 2.82 Mg/m3)than those of the marble-clast bearing specimens (d(j = 2.62 to 3.03 Mg/m3).Once the rock is conpletely discoloured or affected by solution or both,the density drops significantly to d<j = 2.25 Mg/m3 or lower.

5.4.2 Marble

Fresh grey and white marble have similar saturation moisture contents(is < 0.2%), density (d<j = 2.70 to 2.85 Mg/m3) and effective porosity(neff < 0.5%). The freshest impure banded marble specimens tested gaveslightly higher saturation moisture contents (up to 0.5%) and relativelyhigh effective porosity (up to 1.4%) but similar density values (Tables 7and 8). The dry density of the grey marble affected by granitic intrusionis higher than the pure marble (d<j = 3.07 to 3.23 Mg/m3), contrary to theexpected values based on mineralogical composition of these two rocks, i.e.the specific gravity of quartz is 2.65 whereas that of calcite is 2.72.Some heavy minerals (e.g. iron-oxides) may have been introduced into themarble by the granite intrusion. Higher saturation moisture contents andeffective porosities were found in the marble specimens affected byintrusion (i.e. is = 1.5% and neff = 4.0%).

5.5 RELATIONSHIPS BETWEEN INDEX PROPERTIES AND STRENGTH PROPERTIES

For prediction purposes, and also to assess graphically the effect ofweathering on each property, selected index properties were plotted againstthe strength properties of the marble and tuff breccia units. Plots ofuniaxial compressive strength and point load strength versus saturationmoisture content, effective porosity and dry density are given in Figures15 and 16 for the tuff breccia specimens and in Figures 17 and 18 formarble specimens.

No statistical analysis of the correlations between the variousproperties has been attempted because of the limited test data.

26

5.6 CORRELATION BETMEEN POINT LOAD STRENGTH AND UNIAXIAL OPPRESSIVESTRENGTH

Point load strength has been widely used to estimate uniaxialcompressive strength of rocks in the field and laboratory (Broch &Franklin, 1972; Bieniawski, 1975; Irfan & Dearman, 1978). A figure of 24first proposed by Broch & Franklin (1972) and recommended by IAEG (1981)appears to be the most appropriate correlation factor for strong andisotropic rocks. For weaker rocks (i.e. strength less than 50 MPa) it isconsidered essential to establish a site-specific correlation factor.

No correlation factors have been determined for marble or tuffbreccia, either in Hong Kong or elsewhere. However, correlation factorshave been determined on various types of limestones. For example, Hawkins& Olver (1984) determined a factor of 26.5 for oolitic limestone ofJurassic age from England, while Carter & Sneddon (1977) obtained 26 and28.5 for Carboniferous limestones from core samples. Norbury (1984) quotedcorrelation values of 24 to 54 for crystalline limestones.

The best-fit relationships obtained in this study for the marblesubunits are UCS - 24 PLS for all specimens and UCS = 25.5 PLS forspecimens without granitic veins (Figure 19). The test results on marblespecimens significantly affected by granitic intrusions have been excluded.

For the tuff breccia unit, a significant number of failures occurredthrough pre-existing cracks or weak veins. These have been excluded fromthe calculation of the correlation factor. The best-fit relationshipobtained for the tuff breccia unit is UCS = 22.5 PLS (Figure 19).

5.7 GEOMECHANICAL CLASSIFICATION OF MARBLE AND TUFF BRECCIA IN TERMS OFINTACT STRENGTH AND ELASTIC MODULUS

Geomechanical classification of intact rock material is commonly basedon uniaxial compressive strength and the modulus of elasticity (Deere &Miller, 1966, see also Deere, 1968). The values of the compressivestrength and the modulus are plotted on a logarithmic scale to accommodatea wide range of values. Three modulus classes are delineated based on theratio of the modulus to the uniaxial compressive strength (H - High ModulusRatio, M - Average Modulus Ratio and L - Low Modulus Ratio) with the classboundaries at Et : UCS = 500 : 1 and 200 : 1.

The uniaxial compressive strengths and tangent elastic moduli ofmarble specimens determined in this study are plotted on Deere & Miller'sstrength classification chart in Figure 20. The strength envelopes ofmarble (based on limited test results) and limestone-dolomite determined byDeere & Miller (1966), and dolomite-limestone-marble given by Dearman(1981), are also shown in this figure. The range of strength and modulivalues for concrete commonly used in foundations are plotted on the graphfor comparison, i.e. UCS = 17.5 to 35 MPa and Et = 17 to 34 GPa. All theresults, with the exception of two which plot above the 1000 : 1 line, fallbetween the 1000 : 1 and 500 : 1 lines, i.e. all marble subunits have HighModulus Ratios. The uniaxial compressive strength values show a widerscatter than that determined by Deere & Miller, falling generally betweenthe Strong (S) and Very Strong (VS) classes depending on the presence ofimpurities, banding, grain size, and the effects of solution and graniticintrusion.

27

The test values for tuff breccia fall in the Average Modulus Ratioclass, with those of the pure tuff specimens plotting in the lower half ofthe class, i.e. nearer to the 200 : 1 line (Figure 21). The weatheringscale of the material is also shown in the figure. The strength valuesfall in the range of Extremely Strong (ES) for the freshest specimens toModerately Strong (MS) and even lower in the more weathered specimensshowing honeycombed solution features (Figure 21). As expected, thestrengths cover a wide range of values due to variation in mineralogy,porosity, grain size, weathering state and other fabric features which maybe present in the specimens. No comparative envelopes exist for similarrocks tested elsewhere.

COCM

29

6. ROCK MASS PROPERTIES

6.1 GENERAL

There are no rock outcrops in the project area which can be used todirectly assess the mass properties of the foundation rocks. The followingdescription of rock mass properties is based on borehole records.

The weathering profiles formed in various rocks in the project areaare very variable. This reflects the wide variation in rock type (evenwithin the same unit), the discontinuity pattern and other structuralelements of the area. In addition, the effects of contact metamorphism,hydrothermal alteration and mineralization, as related to acidic and basicintrusions prior to weathering and post-dating general metamorphism of therocks, have contributed further to the formation of complex weatheringprofiles. The rock mass conditions are locally very variable under eachbridge site, and sometimes across each pier location.

6.2 WEATHERING PROFILES

6.2.1 Volcanic Rock Units

The tuff breccia and tuffs which underlie the southern part of theroute, near Tuen Mun, are generally deeply weathered. The weatheringprofile is deepest in the upper tuffaceous sandstone-siItstone member. Thethickness of the corrpletely to highly weathered rock is generally between20 and 40 m underneath an alluvium/fill cover 5 to 12 m thick (Figure 22).Thin layers of more resistant highly/moderately decomposed rock, generallyof sandstone or tuff breccia beds, are present in the completely weatheredrock. In the moderately weathered rock mass, marble-clast bearingbands/beds are differentially weathered to honeycomb-textured rock as aresult of solution of marble clasts, whereas the pure tuff bands are moreresistant to weathering (Plates 10 to 13). The tuffaceous sandstone/siltstone beds are more intensely weathered to a clayey sandy silt to siltysand. Therefore, the moderately weathered rock mass zone may be made up oflayers of very strong tuff with intervening porous tuff breccia and/orclayey silt and sand, generally following bedding structures which appearto dip towards the northwest. This zone, which can be extremely variablein terms of rock and soil proportions and mass permeability, is up to 10 mthick before the slightly weathered tuff breccia is reached.

Honeycombed structure may not form if the tuff breccia contains a highpercentage of marble fragments, as observed in the Tin Shui Wai area(Darigo, 1989). Collapse of the rock mass may occur at an early stage inweathering due to dissolution of a large number of marble clasts.Relatively large cavities, up to a few metres in diameter, may occur if therock is made up of large fragments of marble.

6.2.2 Hetasedimentary Rock Unit

Metasedimentary rocks of the Mai Po Member (phyllites, metasandstonesand occasionally quartzites) commonly underlie the northern part of theproject area (Interchange No. 4) but also occur, overlying marble, on bothsides of the nullah at Interchange No. 3 (Figure 1). The weathering

30

profile developed over these metamorphic rocks is very s i m i l a r to thosedeveloped in metasedimentary rocks elsewhere in the Territory (e.g asdescribed by Greenway et al, 1987). A th i ck completely weathered' zoneconsisting generally of yel lowish brown (in the case of metasandstone) topurplish grey (in the case of metasiltstone and p h y l l i t e ) s i l ty sand toclayey sandy si l t , passes into a highly weathered rock cons is t ing of eithervery weak rock with l i t t le soil along d i scon t inu i t i e s or as in terveningbands of very weak to weak rock and soil (Plates 14 and 15). The totalthickness of the completely to highly weathered rock is generally 15 to30 m, but can be up to 60 m (Figure 23). Horizontal to subver t ica l zonesof less weathered material may occur depending on the bedding direct ion andother structural features. Moderately and less weathered rocks occur atdepths of over 30 m in areas where there is a th ick metasedimentarysuccession. In areas where pure m a r b l e of the Yuen Long Formationunderlies the metasedimentary rocks at shallow depths, there may be a sharptransiton from completely weathered rock (clayey silts and sands) to almostfresh marble. Slightly weathered and fresh metasandstones are very strongrocks but may show a strong strength anisotropy due to the presence of apronounced foliation (Plate 15).

6.Z.3 Marble Unit

In general, a complete weathering profi le is absent in the whi te andgrey marble subuni ts , and a t h in or absent residual soi l layer is under la inby .™rtl? ^taining solution features and cavities near its top. Freshmarble with no efforts of solution was not general ly encountered in theboreholes dr i l led for this project (up to 100 m). However, in almost a l lof the br idge sites u n d e r l a i n by marble, this s imple picture of the

r±lnh,-lSm

COrnpliCauted b* faulti"9. dyke intrusion and the* ^ *~ °f * m^ and

* and metas11tstone subuni t , a more or lesssoMion n n,™ ri h 1S 5resent (Rlate 7)- This is formed by bothsi t tonp LPH ?anSnnp h0H

S ' and So1uti°n and disintegration of calcareousD r«uMhlv h^ ,l«f S* Jhe thicknesses of the original strata have?es t ofy c^ inn nf n reat1y and the "»« structure disturbed as awe vinf JltS bV Ure

flHmarb1! beds ^d subsequent collapse of the

the marb le hal been Iff erK?^* t0.the major basic and ac^d1c d^kes 'l*^M™*y£* A^if jsr^"1" and ^droth?a:a result of var iable sn inHnn ' * -. -9, f Weatne^n9 zones are present as«wte\,t a Lee ° ' if,f ; sjr1? and secorsnion °v°^to subvprt irai laverc nf r««o i. i f",igure 4) • In such instances, verticaldept s fPlatJ fy in contr?!6^ decomPosed material can occur at greatalteration ]> St t0 marb1e whkh has ™* been affected by

6.3 DISCONTINUITIES (RQD AND FRACTURE INTENSITY)

which adefonnabillty of the rock mass Tte dilrlnf • 18-llflJa*ntly, *1!crealecan be assessed by Rock Ouarn*, n dlscp.ntln"ity state of the rock masscores, butlt should be SSid thrt'CS ««») value, detamlned ondiscontinuity roughness, openlno wnt?S<f * not *ake lnto account the

3 a pwimg, continuity or condition, or the presence

31

and nature of any infilling material (Irfan & Powell, 1985). However, RQDis useful in classifying rock masses for the selection of tunnel supportsystems and for foundations when used with other parameters (e.g. strengthof intact rock, weathering state, e tc* ) . Fracture intensity (number offractures per metre) is preferred to RQD, particularly in weathered rocks,because of inherent errors in determining the latter.

For the present invest igat ion, the RQD values given on thecontractor 's logs have been plotted against the fracture intensity forvarious rock units and weathering zones (Figures 24 and 25). RQD valueshave been standardized to about 1.5 m core lengths, where necessary, to becompatible with the normal pract ice of determining RQD for use infoundation design. No fracture intensities were determined by thecontractor where the rock was very fractured. These were determined by6CO staff, either by counting the pieces or by measuring the average sizeof core p i eces from the good-qual i ty photographs provided. Aclassification of various foundation units in terms of RQD and fractureintensity, based on the borehole records and Figures 24 and 25, is given inTable 10.

In general, the grey and white marble subunits in the fresh state havewidely- to very widely-spaced discontinuities (i.e. 0.6 to 6 m). Thediscontinuity spacing in the interbedded marble and metasiltstone subunitdepends on the thickness of the siltstone layers, which are generally veryclosely-spaced (i.e. 0.06 to 0.2 m). Pure marble layers in this subunithave widely-spaced discontinuities. The tuffs and tuff breccia of the TuenMun Formation in the fresh to slightly weathered state have moderately- towidely-spaced discontinuities, with tuffaceous siltstone and sandstoneunits having more closely-spaced bedding planes, foliation and joints. Themetasedimentary rocks of the Mai Po Member are generally closely-bedded orfoliated with discontinuity spacings of less than 0.2 m, except inunfoliated metasandstones where these may be up to 0.6 m or larger. Inthick basic dyke intrusions, the discontinuities are generally moderately-spaced (i.e. 0.2 to 0.6 m) in the fresh to slightly weathered state. Inrocks affected by faulting and dyke intrusion, the discontinuity spacing iscloser and the rocks are more intensely weathered or altered. Thediscontinuity dip and dip directions, particularly bedding and foliationplanes, can vary widely as a result of faulting and folding. The generalstructural features of the project site have already been described inChapter 2.

CMno

33

7. PRELIMINARY ASSESSMENT OF BEARING CAPACITY OF FOUNDATION ROCKS

7.1 GENERAL

As part of the GCO involvement in the Yuen Long - Tuen Mun EasternCorridor project, the site investigation results and an outline of methodsfor preliminary assessment of bearing capacity for large-diameter boredpiles and hand-dug caisson piles were compiled in an internal report. Theapproach adopted for bearing capacity assessment is summarised in thisChapter. It should be emphasised that this is not intended to be a stateof the art review of the subject nor is it a guide to standards ofpractice.

Allowable bearing pressures for the design of deep foundations on rockcan be selected on the basis of one or more of the following :

(a) building codes,

(b) empirical rules,

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

(d) field load tests.

Bu i ld ing codes are tradit ional ly conservat ive. Theoreticalconsiderations and field test results suggest that the ultimate bearingcapacity of a rock mass is unlikely to be reduced much below the uniaxialcompressive strength of the intact rock material even if open verticaldiscontinuities are present (Poulos & Davis, 1980). The presence of largevoids below the foundation would of course be an exception to this generalrule.

The al lowable bearing pressure depends on the compressibility andstrength of the rock mass and the permissible settlement of the structure.Both the compressibility and the strength of the rock mass are related tothe strength of the intact rock, the lithology, the frequency, nature andorientation of the discontinuities, and the weathering and alterationstate. The compressibility of the intact rock is dependent on the degreeof decomposition and disintegration.

The compressibil i ty and strength of rock masses are difficult toquantify and even large scale test results on individual piles may not berepresentative of the bearing characteristics of the foundation as a vhole.

7.2 ALLOWABLE BEARING PRESSURES FOR DEEP FOUNDATIONS IN THE PROJECT AREA

7.2.1 Code Values

The "presumed bearing values11, i.e. the presumptive allowable bearingpressures specified by var ious building codes and authorities areinvariably very conservative. They also differ in their recommendationsfor the same rock. Many design codes relate the presumed bearing valuesto a geological rock classification (e.g. BSI, 1986), while others basethem on a proportion of the unconfined compressive strength of the intact

34

rock, generally 0.2 x DCS.

Table 11 gives a comparison of presumptive allowable bearing^stressesfor var ious rock types including partially weathered and intenselyfractured rocks. The broad foundation rock groupings in Table 11 have beenassigned approximate mass weathering and discont inui ty c l a s s e s inaccordance with the terms used elsewhere in this document. No specificvalues are given for marble, nor for the volcanic rocks common in HongKong. With reference to the rock types present in the project area inparticular, and the Yuen Long area in general, in the fresh or slightlyweathered state, the metasedimentary rocks of the Lok Ma Chau Formation andthe interbedded marble and metasiltstones of the Yuen Long Formation wouldbe included under the "foliated metamorphic rock" category in Table 11.The grey and white marble subunits would be included in either themetamorphic group or the sedimentary group, being similar to manylimestones of medium strength. The tuff breccia unit could be placed inany of the first three groups, depending on whether it is composed of puret u f f , m a r b l e c l a s t - b e a r i n g t u f f o r i n t e r b e d d e d tu f f a n dsandstone/siItstone. Moderately weathered rocks could be classified as thefourth category in Table 11, i.e. "badly fractured, or broken, or partiallyweathered rocks", and the highly weathered rocks would come under the fifthcategory where no stress values are specified.

7.2.2 RQD Method

Table 12 presents values of allowable contact pressure for jointedrocks on the basis of their RQD (Peck et al, 1974). The values refer toaverage RQD within a depth below the foundation level equal to the width ofthe foundation, provided that the RQD is fairly uniform. Peck et al (1974)state that the values are based on settlement criteria, with settlement notexceeding 12.5 mm.

The ranges of RQD values and the fracture intensities are given inTable 10 for each weathering grade in each rock type. These values can beused to calculate the allowable bearing stress for each foundation unit forpreliminary design purposes. However, as discussed in Section 6.3, thereare drawbacks to using RQD to assess rock quality, particularly forclosely-jointed or bedded rocks and for rocks containing thick compressiblediscontinuity fillings and voids.

7.2.3 Canadian Foundation Engineering Method

Al lowable bearing pressure for "sound rock" foundations can becalculated by using the fol lowing formula, as given in the CanadianFoundation Engineering Manual (Canadian Geotechnical Society, 1985) :

% = Ksp Qu d (1)

where qa = allowable bearing pressure on the rock,

qu = average uniaxial compressive strength (UCS) of rock core,

Ksp = 0. 1 to 0.4, an empirical coefficient depending on the jointspacing and including a factor of safety of 3,

35

d = depth factor, given by :

d = l + 0.4 -^< 3.4 ............. (2)bs

where Ls = depth (length) of the rock socket,

bs = diameter of the rock socket.

Ranges of uniaxial compressive strength that can be used for thecomputation of qa are given in Tables 6 and 8 for the rocks in the projectarea. KSp can also be calculated from the following formula :

K - 3 + c/B ............. (3)sp 10J1 + 3005/c

where c = discontinuity spacing,

8 = thickness of infilling of discontinuity,

B = foundation width.

The mean discontinuity spacings for each foundation unit are given inTable 10 and the properties of the discontinuities are discussed in Section6.3. The Canadian Foundation Engineering Manual (Canadian GeotechnicalSociety, 1985) states that the above relationship is valid for thicknessesof discontinuity less than 25 mm, if filled with soil or rock debris.While the formula may be valid for fresh to moderately weathered meta-sedimentary, igneous and volcanic rocks, and marble with no solutionfeatures, it will not be applicable to the white and grey marble subunitscontaining voids, nor to the highly and completely weathered rocks.

7.2.4 Settlement Calculations : Rock Mass Factors and Rock MassDeformation Moduli

The settlement of a rigid foundation or average settlement, S, of af lexib le foundation at the surface of a rock mass modelled as anhomogeneous elastic half -space can be calculated by the following formula :

q B ( l - ^2)

where qa = average bearing pressure on the rock,

B = width or diameter of the foundation,

v = Poisson's ratio of the rock mass,

Em = deformation modulus of the rock mass,

I = influence value, which is dependent upon the shape ofthe foundation (see, for example, BSI, 1986).

36

Solutions also exist for piles embedded in an elastic medium (e.g.Poulos & Davis, 1980).

The following approach can be used as a simple means of determiningapproximate values of the rock mass modulus.

The rock mass deformation modulus, Em, can be calculated by :

Em - J Ei (5)

where Ei is the Young's modulus of the intact rock and j is the Rock MassFactor (Hobbs, 1975). The latter reflects the effects of discontinuitieson the expected performance of the intact rock. The Rock Mass Factor canbe assessed for each structural or lithological unit from the discontinuityspacing or RQD (Table 13). If elastic properties of the intact rock havenot been determined, Ej can be calculated by :

Ei = Mr qc (6)

where Mr is the modulus ratio of intact rock (Deere & Miller, 1966) and qcis the uniaxial compressive strength of intact rock.

Table 13 gives a rock mass quality classification based on approximaterelationships between RQD, discontinuity spacing and rock mass factors.For practical purposes, BS 8004 (BSI, 1986) suggests that the value for jcan be approximated by the average discontinuity spacing in metres, if thediscontinuities are reasonably tight.

Alternatively, the rock mass deformation modulus can be assessed fromthe rock mass class. For example, Bieniawski (1978) proposed the followingformula:

Em = 1.76 RMR - 84.3 (7)

where Em is the insitu static modulus of deformation in GPa and RMR is theRock Mass Rating in accordance with the geomechanics classification ofBieniawski (1978). This formula is not applicable to rock masses ofrelatively low quality (i.e. with RMR values < 48).

For preliminary settlement analysis, mean rock mass factors that canbe used to determine rock mass moduli are given in Table 10 for each mainlithological unit. The deformation moduli, Poisson's ratios and uniaxialcompressive strengths of intact rock material are given in Tables 5 to 9for each grade of material in each rock type (tuff breccia and marble unitsonly).

37

8. GENERAL COWENTS ON FOUNDATIONS WITH RESPECT TO THE MARBLE UNIT

Foundation condit ions within the marble unit are very complex,,particularly near the top of the succession, due to :

(a) the presence of a karstic surface with extremelyvariable rockhead levels (the legacy of weatheringand e ros ion before the depos i t i on of thesuperficial deposits),

(b ) the w e a t h e r i n g s t a t e o f the rock m a s s ,particularly with regard to voids and wideneddiscontinuities formed by solution weathering inthe pure marble subunits,

(c) the p r e s e n c e of a l te rna t ing competent andincompetent beds or layers in the interbeddedsubunits formed as a result of differentialw e a t h e r i n g of marb le , impure marb le andmetasiltstone members,

(d) the presence of folding and faulting, particularlythe thrust faults bringing older strata above theyounger strata, and

(e) the dyke intrusions and associated alteration( e . g . c o n t a c t metamorph ism, hydrothermala l t e r a t i o n a n d m i n e r a l i z a t i o n ) , w i t hdifferentially weathered/altered, near-vertical tovertical zones extending to great depths in themarble and dyke rock.

The presence of voids and enlarged discontinuities, and the extremelyvariable karstic surface, are likely to be the major geotechnicalconstraints in the design of deep pile foundations on marble bedrock. Thebedrock sur face (defined as moderately weathered/altered rock mass orbetter) may vary very rapidly, particularly in the pure marble members,which contain individual pinnacles of rock up to many metres high. Therock surface underneath a residual soil or superficial soil cover may alsobe uneven at a small scale. The marble most susceptible to void formationis the pure white marble subunit. The voids generally occur near thekarstic surface in this rock and range in height from 0.1 to 2 m in theboreholes drilled in the project area. Pascal (1987) and Langford et al(1989) reported void heights of 5 to 15 m, occasionally 25 m, under YuenLong town itself. Most cavities appear to be confined to a level above -70mPD (Langford et al, 1989). It is therefore very important to ensure thatsufficient boreholes are drilled at all deep foundation sites in order toadequately invest igate the variat ion in the bedrock profile and thepresence of voids. Houghton & Wong (1990) state that cross-hole seismicsurveys can be used to define the lateral continuity of dissolutionfeatures.

Chan & Hong (1985) reported the presence of a "weak compressiblelayer11 with SPT 'N 1 values less than 5 just above the limestone bedrock inMalaysia. Sowers (1976b) also reported that the residual soil close to thecontact with limestone is much softer and sometimes "pasty11. The formation

38

of this weak compressible clayey soil layer is attributed by Sowers to thedownward percolation of water which then flows laterally across the rocksurface. Such a layer was not detected from SPTs in this investigation,but there were no undisturbed drillhole sarrples available to check for itsexistence: thus its presence cannot be precluded in the project area (andin the Yuen Long area in general). Weak and compressible clayey soils mayalso occur inside cavities and close to dyke contacts in the alteredmarble. The possible presence of these compressible pockets may need to betaken into account in foundation design, since they could lead to largedifferential settlement of individual piles or pile groups.

Other problems to be considered in the design and construction ofpiled foundations in the Yuen Long area are similar to those described bySowers (1976a) and briefly summarized by Dearman (1981). Some of theseproblems have been highlighted by Pascal (1987), McNicholl et al (1989) andHoughton & Wong (1990) in the Yuen Long and Tin Shui Wai areas. For drivenpiles, the common design and construction problems are likely to be pilebuckling, pile deflection, tip damage and uncertain support, particularlyfor piles founded on a sloping "bedrock" surface (see, for example Houghton& Wong, 1990). Uncertain or discontinuous support due to the presence ofcompressible layers or voids, sudden loss of bentonite support (duringboring) and dewatering are the likely major problems for cast-insitu piles.Another problem which often affects shallow foundations above marblebedrock is collapse or subsidence of the ground surface due to the upwardmigration of voids through the soil cover by erosion (Sowers, 1976b). Thisis aggravated by changes in the groundwater table due to seasonalvariations or dewatering. Pascal (1987) reported formation of suchcollapse features during a pumping test carried out in Yuen Long.Sinkholes and collapses may also occur when the rock roof of a cavityeventually becomes incapable of supporting its own weight. Changes in pHof the groundwater, for exanple as a result of contamination, can alsoresult in solution of marble.

The bearing capacity of unweathered marble rock masses withwidely-spaced tight discontinuities is likely to be high and thecompressibility low. Both the white and grey marble subunits are strongrocks with intact UCS values in excess of 60 MPa (Table 8), i.e. strongerthan the concrete used for pile foundations. These rocks also have veryhigh intact elastic modulus values of over 45 GPa. However, the impuremarble, which is generally found interbedded with metasiltstone of varyingthickness, can have values of UCS of less than 40 MPa and elastic modulusof less than 35 GPa in their more weathered states. Although the marbleslightly affected by granitic intrusions can have a higher strength in thefresh state than the unaltered marble, the strength reduces drasticallyonce the rock is affected by both decomposition and solution (Table 8).This type of rock was found locally in one or two boreholes. It appearsthat the marble adjacent to thick basic dykes has generally been altered toa mixture of weak rock and soil for some distance away from the dyke.

Fresh marble with a high bearing capacity is generally found only at asignificant depth, over 30 m, in the Yuen Long area. In cases where end-bearing piles are chosen as the foundation type, the marble bedrock needsto be properly investigated, with particular emphasis on the possiblepresence of cavities near the bedrock surface. Design revisions orremedial works during construction may need to be considered, since thesize and distribution of cavities cannot generally be economicallydetermined by normal site investigation techniques. Probing below the

39

founding level by coring is one means of ensuring that no opening orcompressib le filling of signif icant thickness exists below the pile.Alternatively, the defects can be treated by grouting or minipiling, or canbe al lowed for by building in a suitable degree of redundancy into arevised foundation design.

40

41

9. CONCLUSIONS

Foundation conditions in the area between Tuen Mun and Yuen Long arevaried and locally very complex. This reflects the variable geology andalteration and weathering processes. Marble is present in the northernportion of the area near Yuen Long, underlying superficial deposits orintensely weathered metasedimentary rocks, whereas the southern portion ofthe area near Tuen Mun is dominantly underlain by a marble-clast bearingtuff breccia and other tuffaceous rocks. The marble locally containscavities and generally has a very irregular karstic surface.

The complex foundation condit ions have been characterized by as imp l i f i ed g e o m e c h a n i c a l c l a s s i f i c a t i o n based on l i tho logica lcharacteristics, discontinuity properties and mass weathering/alterationclasses, primarily as determined from borehole logs. A laboratory testingprogramme was carried out to determine the intact properties of the variousrock types, particularly the marble and marble-clast bearing tuff breccia.These properties can be used as the basis for calculating the bearingcapacity and settlement of foundations by various methods.

No material weathering grades between fresh rock and residual soilstates are present in the pure marble (or at least are not recognisable inhand specimens). However, various weathered states of rock material canbe present in the very impure marble members and those subunits affected byacidic and basic intrusions.

The pure marble subunits (the white and grey marble) are strong rocksin the fresh state with uniaxial compressive strengths in excess of 65 MPaand up to 140 MPa, and elastic modulus values of over 45 GPa and up to95 GPa. The impure marble is generally weaker than the pure white andgrey marble, with specimens showing slight affects of weathering havinguniaxial strengths of 40 to 65 MPa. No fresh impure marble specimens wererecovered in the boreholes. When the rock is affected by graniticintrusions, the strength is increased, up to a value of 190 MPa.

On the strength versus modulus chart, all the marble types plot in theHigh Modulus Ratio class. The stress-strain behaviour of the intact rockis variable, depending on the rock type, presence of impurities,foliation/bedding and other characteristics.

The relationships between the uniaxial compressive strength, UCS, andthe point load strength, PLS, determined for the marble are UCS = 24 PLSfor all specimens and UCS = 25.5 PLS for specimens not affected byintrusions (i.e. without granitic veins).

The tuff breccia is a very strong to extremely strong rock in theslightly decomposed to fresh state, with uniaxial strength in excess of150 MPa and elastic modulus of over 50 GPa. The strength and moduli valuesvary according to the different lithologies. The pure tuff bands arestronger than those containing marble clasts. There is a gradual decreaseof strength and moduli with decomposit ion in the early stages ofweathering. The strength and moduli are drastically reduced in the tuffbreccia once the solution of marble clasts produces a honeycombed texture.

The stress-strain behaviour of the tuff breccia is also affected bythe lithology. The pure tuff specimens show elastic behaviour, whereas the

42

marble-clast bearing specimens display a plastic-elastic-plastic behaviour.These rocks have Average Modulus Ratios. No comparative stress-strengthenvelopes exist for similar rocks elsewhere.

The relationship between the uniaxial compressive strength and thepoint load strength determined for the tuff breccia is UCS = 22.5 PLS.

The UCS/PLS correlation factors determined in this investigation forthe marble and tuff breccia units are similar to the va lue of 24recommended by many researchers for isotropic rocks.

No correlations have been attempted between the index and strengthproperties of the rocks because of limited test results. Except for pointload strength, no strength and deformation properties were determined forthe metasedimentary rocks and the dyke intrusions present in the projectarea, since no suitable cores were available for testing.

A preliminary assessment of the bearing capacity of the foundationrocks has been carried out and various material and mass parameters thatcan be used to calculate bearing capacity and settlement by a number ofmethods have been presented. These are summarised in Tables 5 to 10.

A number of problems to be considered in the design and constructionof foundations on marble in the Yuen Long area have been outlined. Forpiles founded on marble bedrock, the irregular nature of the karsticsurface and the possible presence of cavities are two important factorsthat deserve careful attention during detailed ground investigation.Consideration may need to be given to design revisions and remedial worksduring construction, since the size and distribution of cavities cannotgenerally be economically determined by normal investigation techniques.

43

REFERENCES

ASTM (1985). Standard test method for elastic moduli of intact rock corespecimens in uniaxial compression. Test Designation D 3148-80. 1985Annual Book of ASTM Standards, American Society for Testing andMaterials, Philadelphia, vol. 04.08. pp 519-525.

Barton, N., Lien, R. & Lunde, J. (1974). Engineering classification ofrock masses for the design of tunnel support. Rock Mechanics, vol. 6,pp 189-236.

Bieniawski, Z.T. (1975). The point load test in geotechnical practice.Engineering Geology, vol. 9, pp 1-11.

Bieniawski, Z.T. (1976). Rock mass classification in rock engineering.Proceedings of the Symposium on Exploration for Rock Engineering,Johannesburg, pp 97-106.

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

Broch, E. & Franklin, J.A. (1972). The point load strength test.International Journal of Rock Mechanics and Mining Sciences, vol. 9,pp 667-697.

BSI (1981). Code of Practice for Site Investigations, BS5930; 1981(Formerly CP 2001). British Standards Institution, London, 147 p.

BSI (1986). British Standard Code of Practice for Foundations, BS 8004:1986 (Formerly CP 2004). British Standards Institution, London,149 p.

Canadian Geotechnical Society (1985). Canadian Foundation EngineeringManual. Second Edition. Canadian Geotechnical Society, Ottawa, 456p.

Carter, P.G. & Sneddon, M. (1977). Comparison of Schmidt hammer, pointload and unconfined compression tests in Carboniferous Strata.Proceedings of the Conference on Rock Engineering, Newcastle, U.K. pp197-210.

Chan, S.F. & Hong, L.P. (1985). Pile foundations in limestone areas ofMalaysia. Proceedings of the Eighth Southeast Asian GeotechnicalConference, Kuala Lumpur, pp 4.17-4.28.

Choy, H.H., Earle, Q.C., Irfan, T.Y. & Burnett, A.D. (1987). Studies forthe extension of a major urban quarry in Hong Kong. Planning andEngineering Geology, (edited by M.G. Culshaw, F.G. Bell, J.C. Cripps &M. Q'haraK Geological Society Engineering Geology Special PublicationNo. 4, London, pp 367-377.

Coon, R.F. & Merritt, A.H. (1970). Predicting insitu modulus ofdeformation using rock quality indexes. In Situ Testing in Rock,American Society for Testing and Materials, Special TechnicalPublication No. 477, pp 154 73:

44

Darigo, N.J. (1989). A volcanic breccia in the buried karst of Hong Kong.Proceedings of the Third Multidisciplinary Conference on Sinkholes andthe Engineering and Environmental Impacts of Karst, Florida, pp225-2321

Dearman, W.R. (1981). Engineering properties of carbonate rocks. (GeneralReport). Proceedings of the Symposium on Engineering Geology Problemsof Construction on Soluble Rocks, Istanbul. Published in Bulletin oTtFuTlnternational Association of Engineering Geology, No. 24, pp 3-17.

Deere, D.U. (1968). Geological considerat ions. Rock Mechanics inEngineering Practice, (edited by K.G. Stagg & O.C. Zienkiewicz), JohnWiley, New York, Chapter 1, pp 1-20.

Deere, D.U. & Miller, R.P. (1966). Engineering Classification and IndexProperties for Intact Rock. Report AFWL-TR-65-116, Air Force WeaponsLaboratory (WLDC), Kirtland Air Force Base, New Mexico, 273 p.

Deere, D.U., Merritt, A.H. & Coon, R.F. (1969). Engineering Classificationof In Situ Rock. Report AFWL-67-144, Air Force Systems Command,Kirtland Air Base, New Mexico.

Deere, D.U. & Patton, F.D. (1971). Slope stability in residual soils.Proceedings of the Fourth Panamerican Conference on Soil Mechanics andFoundation Engineering,San J u a n , P u e r t o R i c o , A m e r i c a n S o c i e t y o ?Civil Engineers, pp 87-170.

Frost, D.V. (1989). Palaeokarst of Yuen Long, northwest New Territories,Hong Kong. Proceedings^ of the Third Multidisciplinary Conference onSinkholes and the Engineering and Environmental Impacts of Karst,Florida, pp 239-246.

Frost , D . V . (1991). Geology of the Yuen Long Designated Area.Geotechnical Control Office, Hong Kong, (Hong Kong Geological SurveyMemoir no. 7), (in press).

GCO (1988). Guide to Rock and Soil Descr ipt ions (Geoguide 3 ) .Geotechnical Control Office, Hong Kong, 189 p.

Greenway, D.R. , Powell, G.E. & Irfan, T.Y. (1987). A case history ofslope design in complex weathered low grade metamorphic rock.Geotechnical Engineering, vol. 18, pp 145-166.

Hawkins, A.B. & Olver, J.A.G. (1984). Point load tests. Correlationfactors and contractual use, an example from the Corallian atWeymouth. Site Investigation Practice ; Assessing BS 5930, (edited byA.B. Hawkins) , Geological Society , Engineering Geology SpecialPublication No. 2B 1986. London, pp 269-271.

Hendron, A.J. Jr. (1968) Mechanical properties of rock. Rock Mechanics inEngineering Practice, (edited by K.G. Stagg & O.C. Zienkiewicz). JohnWiley, New York, Chapter 2, pp 21-53.

Hobbs, N.B. (1975). Factors affecting the prediction of settlement ofstructures on rock : with particular reference to the Chalk and Trias.(Review Paper). Proceedings of the Conference on Settlement ofStructures. Pentech Press, London, pp 529-610.

45

Hong Kong Government (1985). Buildings Ordinance (and BuildingRegulations). Laws of Hong Kong, Chapter 123, revised edition 1985,Hong Kong Government Printer, 387 p. (Amended from time to time).

Houghton, D.A. & Wong, C.M. (1990). Implications of the karst marble atYuen Long for foundation investigation and design. Hong KongEngineer, vol. 18, no. 6, pp 19-27.

IAEG (1981). Rock and soil description for engineering geological mapping.Report by the IAEG Commission on Engineering Geological Mapping.Bulletin of the International Association of Engineering Geology, no.24, pp 235-274.

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.

Irfan, T.Y. & Powell, G.E. (1985). Engineering geological investigationsfor pile foundations on a deeply weathered granitic rock in Hong Kong.Bulletin of the International Association of Engineering Geology, no.32, pp 67-80.

Irfan, T.Y. (1988). Rock Weatherability Tests on Metamorphic Rocks fromSeung Ma Lei Yue. GCO Advisory Report, ADR 8/88, Geotechnical ControlOffice, Hong Kong, 40 p. plus plates (Unpublished).

ISRM (1978). Suggested methods for determining water content, porosity,density, absorption and related properties and swelling and slake-durability index properties. International Society for Rock MechanicsCommittee on Laboratory Tests. International Journal of RockMechanics and Mining Sciences and Geomechanics Abstracts, vol. 16, no.2, pp 141-156.

ISRM (1985). Suggested method for determining point load strength.International Society for Rock Mechanics Commission^ on TestingMethods. International Journal of Rock Mechanics and Mining Sciencesand Geomechanics Abstracts, vol. 22, no. 2, pp 51-60.

Langford, R.L., Lai, K.W., Arthurton, R.S. & Shaw, R. (1989). Geology ofthe Western New Territories, Geotechnical Control Office, Hong Kong,140 p. (Hong Kong Geological Survey Memoir No. 3).

McNicholl, D.P., Yiu, M., Mak, L.M., Clover, A.M. & Ho, H.Y.S. (1989).Piled foundation in Tin Shui Wai Area 5, Yuen Long marble area, HongKong. Proceedings of the Second International Conference onFoundations and Tunnels V London, pp 181-193.

Moneymaker, B.C. (1968). Reservoir leakage in limestone terranes.Proceedings of the Symposium on Reservoir Leakage and GroundwaterControl . Association of Engineering Geologists, Seattle.

NAVFAC (1982).DepartmentWashington,

Design Manualof the

D.C., 244Navy,

P-

7.2 -Naval

FoundationsFaci T i t l es

and Earth Structures,Engineering Command,

Norbury, D.R. (1984). The point load test. Site Investigation Practice :Assessing BS 5930, (edited by A.B. Hawkins) , Geological SocietyEngineering Geology Special Publication No. 2, 1986, pp 325-329.

46

Pascal, D. (1987). Cavernous ground in Yuen Long, Hong Kong. GeotechnicalEngineering, vol. 18, pp 205-221.

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

Poulos, H.G. & Davis, E.H. (1980). Pile Foundation Analysis and Design.John Wiley, 397 p.

Powell, G.E. & Irfan, T.Y. (1987). Geotechnical design for a controlledtip in Hong Kong. Planning and Engineering Geology, (edited by M.G.Culshaw, F.G. Bell, J.C. Cripps & M. O'Hara), Geological SocietyEngineering Geology Special Publication No. 4, London, pp 517-523.

Siu, K.L. & Wong, K.M. (1985). Concealed marble at Yuen Long. Proceedingsof Conference on Geological Aspects of Site Investigation, GeologicalSociety of Hong Kong, Bulletin No. 2, pp 75-88.

Sowers, G.F. (1976a). Foundation bearing in weathered rock. RockEngineering for Foundations and Slopes. American Society of CivilEngineers, New York, vol. 2, pp 32-42.

Sowers, G.F. (1976b). Settlement in terranes of well-indurated limestone.In Analysis and Design of BuildirEnvo Publishing Co., pp 701-725.In Analysis and Design of BuildingFoundations, (edited by H.Y. Fang),

]BT

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

Sowers, G.F. (1984). Correction and protection in limestone terrane.Proceedings of the First Multidisciplinary Conference onSinkholes,Orlando, Florida, pp 373-378.

Tsui, P.C. & Irfan, T.Y. (1990). Complex site geology in marble bedrock,Southwest Yuen Long, Hong Kong. Karst Geology in Hong Kong, (editedby R.L. Langford, R. Shaw & A. Hansen), Geological Society of HongKong, Bulletin No. 4, (in press).

Yiu, M. & Tang, K.H. (1990), Case study of pile construction problems infaulted marble bedrock in Tin Shui Wai Area 5, Hong Kong. Proceed ingsof the Conference on Deep Foundation Practice, Singapore, (in press).

47

TABLES

48

49

LIST OF TABLES

Table PageNo. No.

1 Geological Succession in the Western New Territories 51(Langford et al, 1989)

2 Lithostratigraphy of the Carboniferous San Tin 52Group

3 Unified Mass Weathering/Alteration Classification 53Scheme for All Rocks in the Tuen Mun -Yuen Long Area

4 Unified Material Weathering Classification Scheme 54for All Rocks in the Tuen Mun - Yuen Long Area

5 Laboratory Test Results for Tuff Breccia 55

6 Ranges of Laboratory Test Values for Tuff Breccia 56

7 Laboratory Test Results for Marble 57

8 Ranges of Laboratory Test Values for Marble 58

9 Classification of Rock Units in Terms of Point 59Load Strength Values (MPa)

10 Classification of Rock Units in Terms of RQD, 60Fracture Intensity and Rock Mass Factor

11 Presumptive Allowable Bearing Stress (MPa) for 61Rock Specified by Various Building Codes andAuthorities

12 RQD and Allowable Contact Pressure on Jointed Rock 62(Peck et al, 1974)

13 Rock Mass Quality Classification Based on 62Rock Mass Factor, Discontinuity Spacing andRQD (Based on Deere et al, 1969; Coon & Merritt,1970 and Hobbs, 1975)

50

51

Table 1 - Geological Succession in the Western New Territories(Langford et al, 1989)

Superficial Deposits (Onshore)Age

QUATERNARY Molocene

Holoceneand

Pleistocene

Pleistocene

Genetic Classification

Fill; sanitary fillAlluvium

Beach depositsRaised beach depositsDebris flow depositsTalus (rockfall deposits)

Terraced alluviumDebris flow deposits

Principal Materials

Clay, silt, sand and gravel

SandSandSilt and sand wilth cobbles and bouldtrsBoulders

Clay, silt, sand and gravelSilt and sand with cobbles and boulders

Superficial Deposits (Offshore)Age

QUATERNARY Holocene

Pleistocene

Named Divisions

Hang Hau FormationMarine Sand

Chek Lap Kok Formation

Principal Materials

Mainly mudSand

Clay, silt, sand and gravel

Solid RocksAge

MESOZOIC UpperCretaceous

UpperJurassic

PALAEOZOIC Carboniferous

Named Rock Divisions

Kat 0 Formation

Repulse Tai Mo Shan FormationBay Ap Lei Chau FormationVolcanic Shing Mun FormationGroup

Ngau Liu MemberShek Lung Kung MemberYim Tin Tsai FormationTuen Mun FormationTsing Shan Formation

San Tin Lok Ma Chau FormationGroup Yuen Long Formation

Principal Rock Types

Sedimentary breccia

Coarse ash crystal tuffFine ash crystal tuffLithic and crystal tuff, tuff- brecciaand tuffite

Ash crystal tuffCrystal tuff and tuff- brecciaCoarse ash crystal tuffMeta-andesite lavaSandstone and conglomerate

Metasandstone and metasiltstoneMarble

Major Intrusive Rocks

MESOZOIC UpperJurassie-LowerCretaceous

Fine-grained graniteFine to medium -grained graniteMedium -grained graniteCoarse-grained graniteGranodiorite and Dacite

Minor Intrusive Rocks

TERTIARY Palaeocene

MESOZOIC UpperJurassic -LowerCretaceous

AndesiteBasalt and GabbroLamprophyre

Feldsparphyric RhyoliteQuartzphyric RhyoliteAplite and Fine-grained granitePegmatite

52

Table 2 - Lithostratigraphy of the Carboniferous San Tin Group

Lithology

SanTinGroup

Lok Ma ChauFormation

Yuen LongFormation

TaiShekMoMember

Mai PoMember

Ma TinMember

LongPingMember

White to yellowish-grey, metamorphosedfine - to medium- grained sandstone,quartzite and conglomerate, with thinlayers of phyllite

Pale- to dark-grey, metamorphosed fine-grained sandstone, siltstone andcarbonaceous siltstone, with thinlayers of phyllite and graphite schist

Interbedded marble and siltstone, withthin layers of graphite schist

White to grey, fine - t o coarse-grainedmarble, partly dolomitic, with thinlayers of phyllite

Grey to dark grey marble, withdisrupted bedding planes and laminae ,siliceous horizons

Thickness(m)

> inn

> snn

> 70

> 250

> 300

Table 3 - Unified Mass Weathering/Alteration Classification Scheme for All Rocks in the Tuen Mun - Yuen Long Area

Weathering/Alteration Stateof Rock Mass

Marble Unit(Yuen Long Formation)

Volcanic Rock Units[Tuen Mun Formation)

Metasedimentary Rocks(Lok Ma Chau Formation)

MinorIntrusions

MajorIntrusions

BroadClass

MassZoneDescriptor

MassZone .Symbol

Recognition WhiteMarble

GreyMarble

nterbeddedGarble andMetasiltstone

TuffBreccia

TuffaceousSiltstone/ TuffSandstone

Metasandstone,Metasiltstone,Phyllite andQuartzite

Basalt/Rhyolite

Granite,Grano-diorite

FreshRock

Fresh WI 100% rock v/see Note 11

Weathered/AlteredRock

Sapro-lite

SlightlyWeathered/Altered

ModeratelyWeathered/Altered

HighlyWeathered/Altered

WII

WHIi

Wlllii

WIV

100% rock(withdiscoloration)

>90% rock

50-90% rock

0 - 50 % rock

X(seeNote 2)

v/(seeNote 3

X(seeNote 4)

X(seeNote 2)

(seeNote 3

X(seeNote 41

S/

(seeNote 6}

(seeNote 7)

v/(seeNote 7)

v7

N/ N/

Soil

CompletelyWeathered/AlteredResidualSoil

WV

WVI

100% soilwith structure/texture

100 % soilwithout structure/texture

X(seeNote 5

X(seeNote 5

v7

(seeNote 6}

\/(seeNote 6}

v/ v"

v/

01CO

Legend

Present Not generally present ( see notes Suffix A is used if rock mass is altered

Notes : (1) For thick pure marble beds the weathering profile is similar to that of the white and grey marble. Fresh rock not reached at depthsup to 100m drilled.

( 2 J Generally not present in pure marble unless altered/veined by intrusions and mineralization.(3) Up to 50% dissolved voids may be partially or completely filled with clay residue.(4 ) Generally not present due to collapse of mass structure in advanced stages of solution.(5 ) Very thin or missing in pure marble.( S ) Metasiltstone beds may be structurally disturbed due to solution of purer marble beds in Zone WV, Significant volume reduction in

Zone WVI if largely composed of marble beds.( 7 J May contain small voids due to solution of marble clasts.

Table 4 - Unified Material Weathering Classification Scheme for All Rocks in the Tuen Mun - Yuen Long Area

Weathering/AlterationState of Rock Material

BroadClass

- .GradeDescriptorK

Material.®rad«Symbol

Marble Unit(Yuen Long Formation)

WhiteMarble

GreyMarble

Interbedded

ImpureMarble

Meta-Siltstone

MarbleAffected byIntrusions

Volcanic Rock Units(Tuen Mun Formation)

TuffBreccia(Marble-ClastBearing}

TuffTuffaceousSiltstone/Sandstone

Metasedimetary Rocks(LokMa Chau Formation)

Metasandstone/Metasiltstone,Phyllite andQuartzite

Minorntrusions

Basalt/Rhyolite

Majorntrusions

Granite,Grano -diorite

BroadlyEquivalent

DecompositionGrades

(GCQ, 1988)

Fresh Rock Fresh v/ v/ v/ v/

Decomposed /DisintegratedRock(WeatheredRock}

Slightly A

Decomposed /Disintegrated

ModeratelyDecomposed/Disintegrated

HighlyDecomposed/Disintegrated

X(seeNote 1}

X(seeNote i)

X

X(seeNote 1)

X(seeNote !}

X

v/(seeNote 3}

v/(seeNote 3}

v/(seeNote 3}

V

v/

v/

v/

v/

s/

v/(seeNote 4 }

v/(seeNote 4)

/

y

v/ v/

v/

/

v/

s/

1!

Hi

IV

en

CompletelyDecomposed/Disintegrated

ResidualSoil

J(seeNote 2}

v/(seeNote 2}

v/(seeNote 3)

v/

v/

v/

v/

x/

v/

v/

v/

v/

x/

v/

v/ v/

v/ VI

Legend

X

A

PresentNot generally present (see notes}The term"Decomposition " includes both solution and chemical alteration of mineral constituents. Suffix {A} is used if rock is altered.Slightly decomposed rock may be subdivided into slightly discoloured (less than 50% staining of rock material, Grade 2i) and highly discoloured(more than 50% staining of rock material, Grade 2ii}, Moderately decomposed rock, except marble, is generally wholly discoloured.

Notes : (1) In pure carbonate rocks intermediate grades between fresh rock and residual soil do not usually occur or are difficult to distinguish by simplevisual means unless tested in the laboratory (i.e. increase in porosity due to solution}.

(2) Generally not present unless impure, formed of insoluble residue.(31 Not present in purer marble members.(4) May be porous due to solution of marble clasts.{ 5 } Rock material may show various degrees of disintegration {microfracturing, etc.} with little or no chemical alteration, particularly in

technically disturbed rocks.

Table 5 - Laboratory Test Results for Tuff Breccia

RockType

TuffBreccia

TuffBreccia(honey-combed

SampleNo.

CTB11CTB 2CTB 3CTB 12CTB13CTB 14CTB 15CTB 9CTB 10CTB18CTB 20

CTB 4CTB 5CTB 1CTB 6CTB 7CTB 8CTB 17CTB19CTB 16CTB22

CTB24CTB25CTB27CTB23CTB26CTB21

BoreholeNo.

BD 8ADT 1DT 7BD 8ABD 9BBD 9BBD 9BBD 3BD 3BD11BD20

DT 7DT 7DT 1BD 1BD 1BD 2BD11BD12BD11BDU

BD 1BD 9BBD 9BBD 1BD 9BBD U

DepthCm)

25.627.816.825.833.834.634.838.940.332,632.9

17.619.726.536.141,231.832.330.831.231. 5

38.223.824.733,024.127.6

WeatheringGrade

(see Table 4}

2i2i2i2i2i2i2i2i

2(2i2i

2u

2n2n2n

2ii2 f f2ii2n2ii

2ii

333333

SaturationMoistureContent

CVo)

0.20.10.10.30.20.10,20.20.10.20.0

0.30.30.30.20.30.20.20.40.10.1

1.41.52.02.85.32.6

SaturatedDensity(Mg/m3)

2.842.792.832.852.702.712.722.842.732.702.65

2.982.893.032.972.942.972.722 622.722.90

2.652.702.592.542.372.56

DryDensity(Mg/m3)

2.842.782.822.842.692 702.712.842.732.702.65

2.982.893.022.972.942.972.712.612.722.90

2.622.662.542.472.252.49

EffectivePorosity

(%>)

0 50.30.30.80.50.30.50.50.30.50.0

0.80.70.80.50.70.50.51.00.30.3

3.64.05.27 0

12.06.6

UniaxialCompressive

Strength(MPa)

296.4281.7

246.0224.3217.2210.1

185.2149 7

90.0 •*•102.2 *127.7 #

193.2

193.2173.8170.0156.6119.6 *

71.3 *56.6 *84.2 *

139.2

152.6147.6

69.4

68.6

26.1

22.1

Modulus of Elasticity

Tangentat 50% crult

(GPa)

136 6128.275.763.251.750.050 061.778.9n.d.73.7

76 769.275.080.359.775.054.7nd59.776,9

31.937.432.829.717.0n.d.

Secantat 0 - 50% crult

(GPa)

805

106.7

74. 160.6

47.6

49.6

52.0

44.0

72.6

n.d.

74.3

66.6

61 573.6

82.5

45.0

63.6

45.7

nd.56 974.8

27.1

29.3

28.2

26.4

17.9

n.d.

Poisson'sRatio

05360.3740.2700 2100 3230 2320.4680 2840. 184

nd0.203

0 2200.2310 2420.2500.2790 4750.219

n.d.0 3060.279

0.3830 2710.1800.1190.108n.d.

PointLoad.

Strength1 '(MPa)

11 9

13 011 19 9

11.3

10 2

9.27 2

If. 9

7 78.8

8 3

8.06 98 77 38 45.96.15 45 6

5.2n.d2.62.41.70.8

Remarks

Tuff Band

Tuff BandTuff BandTuff Band

Tuff Band

Tuff Band

Tuff Band

Tuff Band

Tuff Band

Legend :

n.d. Not determined * Failed prematurely along pre-existing crack /vein

Note : 1) Average of 5 to 15 results on specimens adjacent to core section tested in umaxial compression.

enen

Table 6 - Ranges of Laboratory Test Values for Tuff Breccia

RockType

TuffBreccia

WeatheringGrade

(see Table 4

1

2i

2ii

2

3

4

SaturationMoistureContent

(V.)

n.d.

0.0 - 0.3(0.0 -0,2)

0.1 - 0.4

0.0 - 0.4

1.4 - 5.3

n.d.

SaturatedDensity(Mg/m3)

n.d.

2.65-2.85(2.65-2.83)

2.62 -3.03

2 .62-3 .03

2.37-2.70

n.d.

DryDensity(Mg/m3)

n.d.

2.65- 2.84(2.65- 2.82)

2.61 - 3.02

2.61 - 3.02

2.25- 2.66

n.d.

EffectivePorosity

(*M

n.d.

0.0 - 0.5(0.0 - 0.3)

0.3 - 1.0

0.0 - 1.0

3.6 -12.0

n.d.

UniaxialCompressive

Strength(MPa)

n.d.

150-296(185-246)

139-193

139-296

22- 152

n.d.

Modulus of Elasticity

Tangentat 50% auit

(GPa)

n.d.

50-137(50 - 76)

55- 80

50 -137

17 - 37

n.d.

Secantat 0-50% cruu

(GPa)

n.d.

44-107( 50 - 74)

45 - 83

44-107

1 8 - 2 9

n.d.

Poisson'sRatio

n.d.

0.18 - 0.54

0.22 - 0.48

0.18 -0 .54

0.11 - 0.38

n.d.

PointLoad

Strength(MPa)

n.d.

7.2 - 13.0(8.8 -11.1)

5.4 - 8.7

5.4 - 13.0

0.8- 5.2

n.d.

Remarks

Variabietithotogy withtuff bands andmarble -ctastrich layers

Honeycombedtexture whenrich in marbleclasts

Legend ;

n.d. Not determined

Note : Numbers in brackets are for pure tuff members,

Table 7 - Laboratory Test Results for Marble

RockType

GreyMarble

WhiteMarble

BandedImpureMarble

SiticifiedGreyMarble

SampleNo.

M21M22M23M 9M 8M10Mil

M 6M 3M 5M 4

M 1M 2M 7

M18M19M20M24M25

M27M28M29M26

M15M16M14M12M13M17

BoreholeNo.

BD50BD54BD54BD47BD47BD47BD47

BD47BD47BD47B047

BD47BD47BD47

BD50BD50BD50BOSSBD55

BD53BD53BD53BD53

BD40BD40BD40BD40BD40BD40

DepthCm)

55.4

44.845.2

59.756.559.964,6

48.939.6

47.545.4

34.5

34.749.2

51.952.053.347.3

48.2

70.8

73.274.330,7

57.559.950.6

49.750.260.1

WeatheringGrade

(see Table 4}

2222

333

!11\\

2222

111222

iSaturationMoistureContent

(*/*)

0.10.10.10.10.10.20.1

0.20.30.20.5

t.21.31.1

0.10.0.0.0.

0.20.50.30.1

0.10.30.20.60.71.3

SaturatedDensity{Mg/m3}

2.702.812.85

2.712.712.692.71

3.102.872.982.81

2.60

2.933.08

2.762.752.792.702.68

2.71

2.792.802.74

3.093.243.11

3.103.233.17

DryDensity(Mg/m3)

2.702.812.852.71

2.702.69

2.71

3.092.862.982.80

2.57

2.893.05

2.762.742.782.69

2.68

2.702.772.802.74

3.093.233.11

3.083.213.13

EffectivePorosity

(%)

0.20.20.30.30.30.50.3

0.71.00.51.3

3.13.83.3

0.20.20.40.30.4

0.41.40.80.4

0.21.00.72.02.24.0

UniaxialCompressive

Strength(MPaJ

125.6137.5111.989.1

81.264.674.0

122.4120.783.272.0

47.3

70.058.4 *

90.5121.5115.187.986.3

64.0

51.465.638.5

188.2145.7121.072.9 *60.9 #52.9 #

Modulus of Elasticity

Tangentat 50% crult

(GPa)

69.893.078.1

52.150.052.243.5

1 1 1 . 166.782.146.5

46.5

53.771.4

64.966.783.364.566.7

46.0

33.733.953.3

103.890.985.1

70.087.938.0

Secantat 0-50% cru|t

(GPa}

69.882.868.240.539.443.129.4

117.765.881.635.4

46.4

53.668.7

56.665.385.954.956.8

28.022.3

24.955.8

112.0101.293.8

62.898.232.7

Poisson'sRatio

0.3130.4880.3830.3750.3000.2540.466

0.2030.2780.3360.346

0.2170.2080.100

0.2860.2920.2580.3230.347

0.2300.416

n.d.0.293

0.2740.2270.1600.240

n.d.

0.170

PointLoad,

Strength11

(MPa)

4.04.64.33.63.43.43.1

6.14.84.14.6

n.d.

n.d.n.d.

4.15.15.42.63.4

1.72.02.7n.d.

6.87.56.66.16.6n.d.

Remarks

Withgraniticveins

Withgraniticveins

Legend :

n.d. Not determined •*• Failed prematurely along pre-existing crack /vein

Note : 1 ) Average of 5 to 15 results on specimens adjacent to core section tested in uniaxial compression.

Table 8 - Ranges of Laboratory Test Values for Marble

RockType

GreyMarble

WhiteMarble

BandedImpureMarble

SHicifiedGarbleIGreyMarble)

WeatheringGrade

(see Table 4

1

2

3

Range 1-3

1

2

1

2

SaturationMoistureContent

(Vo)

0.0- 0,2

0.2 - 0.5

1.1 - 1.3

0.0 - 1.3

0.0 - 0.1

0,1 - 0.5

0.1 - 0.3

0.6 - 1.3

SaturatedDensity(Mg/m3)

2.69 - 2.85

2.81 - 3.10

2.60 -3.08

2.60 -3.10

2.68 -2.79

2.71 - 2.80

3.09 - 3.24

3.10 -3.23

DryDensityCMg/m3)

2.69 - 2.85

2.80 - 3.09

2.57- 3.05

2.57 - 3.09

2.68 - 2.78

2.70 - 2.80

3.09 - 3.23

3.08 - 3.21

EffectivePorosity

{•/.)

0.2 - 0.5

0.7 - 1.3

3.1 - 3.8

0.2 - 3.8

0.2 - 0.4

0.4 - 1.4

0.2 - 1.0

2.0 - 4.0

UniaxialCompressive

Strength(MPa)

65 -138

72-122

47 - 70

47-138

86 -122

39 - 66

121 -188

53* 73*

Modulus of Elasticity

Tangentat 50% cruu

CGPa)

44- 93

46-111

47- 71

44 -111

65- 83

34- 53

85 -104

38- 88

Secantat 0 - 50% cruit

{GPa)

29- 83

35-118

46 - 69

29 -118

55 - 86

22 - 56

94-112

33 - 98

Poisson'sRatio

0.31 - 0.49

0.20 - 0.35

0.10 - 0.22

0.10 - 0.49

0.26 - 0.35

0.23 - 0.42

0.16 - 0.27

0.17 - 0.24

PointLoad

Strength(MPa)

3.1 - 4.6

4.1 - 6.1

n.d.

3.1 - 6.1

2.8 - 5.4

1.7 - 2.7

6.6 - 7.5

6.1 - 6.6

No. ofTests

onCores

7

4

3

14

5

3

3

3

Remarks

With granitic veins

With granitic veins

Limited occurrencein project area

Generally impureand interbeddedwith metastltstones

Limited occurrence

Legend :

n.d. Not determined * Failed prematurely along pre-existing crack /vein

CO

Table 9 - Classification of Rock Units in Terms of Point Load Strength Values (MPa)

ftock Type

Basic Dykes

Mai PoFormation

Yuen LongFormation

Tuen MunFormation

Basalt

Metasiltstone andMetasandstone

Banded Impure Marble

Metasiltstone

Grey Marble

Grey Marble (Silicified/with granitic veins)

White Marble

Tuff Breccia

Material Weathering Grade

Fresh

1

( Over 8.0)

( Over 5.5 )

( Over 4.0 )

{ Over 5.5 )

5.5 - 3.0

9.5 (?) - 6.5

6r\ o rt.0 - 3.0

( Over 8.0 )

SlightlyDecomposed /Disintegrated

2 i 2 ii

9.0 - 4.0

(Over 3. 5 )

4.0 - 1.5

5.5I?) - 2.0

7.0 - 3.5

14.0-7.0 11-4.5

ModeratelyDecomposed /Disintegrated

3

5.0 - 0.3

3.5 - 0.3

2.0 - 0.3

2.5 - 0.3

n M^4" fiorsQFfitIMOt yCntrrUi

(4.0 - 0.3)

Not pi

7.0 - 0.3

HighlyDecomposed /Disintegrated

4

Less than 0.5

Less than 0.5

Less than 0.5

Less than 0.5

1\/ r\ t* o * f* f\ 4*iy prcoKriii

Less than 0.5

esent

Less than 0.5

CompletelyDecomposed /Disintegrated

5

Not determined

Not determined

Not determined

Not determined

Not determined

Not determined

Note : Numbers in brackets are based on limited test results or tests on more weathered samples.

01

Table 10 - Classification of Rock Units in Terms of RQD, Fracture Intensity and Rock Mass Factor

LithologicalUnit

TuffBreccia ofTuen MunFormation

White andGreyMarble ofYuen LongFormation

InterbeddedImpureMarble andMetasiltstone ofYuen LongFormation

Metasiltstone andMetasandstonesof Mai PoMember

Basic Dykes

Mass Weathering Zone

FreshSlightly WeatheredModerately WeatheredHighly Weathered

Fresh / SlightlyWeatheredModerately Weathered

{ Dissolved )Highly Weathered( Dissolved )

FreshSlightly WeatheredModerately WeatheredHighly Weathered

FreshSlightly WeatheredModerately WeatheredHighly Weathered

Fresh to HighlyWeathered

FractureIntensity,per m

0 5 - 31 - 53 - 1 5Over 10

0 2 - 3

1 - 7

1 - 121 - 122 - 1 5Over 12

3 - 1 53 - 1 58 - 2 5Over 15

RQD(%)

90 - 10075 - 10020 - 800 - 25

80 - 100

30 - 100

Less than 50

50 - 10050 - 100

10 - 900 - 50

10 - 10010 - 1000 - 500 - 10

Rock MassFactor (2)

0 8 - 1 00 5 - 1 00 2 - 0 6Less than 0 2

0 8 - 1 0

( see Note 1 )

( see Note 1 )

0 3 - 1 00 2 - 1 00 2 - 0 6

Less than 0 2

0 3 - 0 80 2 - 0 8

Less than 02Less than 0 2

Limited occurrence in project area

Remarks

Not present at depths drilled

May contain small solution featuresif marble-clast bearing

May contain up to 50 % by volumesolution features {may be filled)Not generally present

Not encountered at depths drilledRQD and fracture intensity depend onthe thickness of metasiltstone layers,usually marble layers have higherRQD, may be structurally disturbedif significant solution is present inpure marble layers

Very closely spaced foliation planes,higher values for non-foliated rocks

Notes (1 ) Rock mass factors may not be applicable if the rock contains voids or thick compressible layers(2) See Table 13

01CD

Table 11 - Presumptive Allowable Bearing Stress (MPa) for Rock Specified by Various Building Codes and Authorities

Reference

NAYFAC, USA 1982

CanadianGeotechnicalSociety 1985

National BuildingCode, USA 1967

Uniform BuildingCode, USA 1964

Los Angeles 1970

British StandardsInstitution,BS8004 1986

US Bureau ofReclamation 1965

Dallas 1968

New York City 1970

Building ConstructionRegulations,Hong Kong* 1985

Sowers 1979

Weathering/AlterationState

DiscontinuitySpacing

Massive CrystallineRocks in

Sound Condition(Granite, Basalt, Gneiss)

6 - 1 0

10

10

0.2 qu

1.0

10

10.7

0.2 qu

6

5

>10 IRQD = 90%1

FoliatedMetamorphfc Rocksin Sound Condition

(Slate, Schist]

3 - 4

3

4

0.2 qu

0.4

3

3.8

0.2 qu

6

SedimentaryRocks in

Sound Condition

1.5 -2.5

1 -4

1.5

0.2 qu

0.3

2 - 4

0.2 qu

2 -4

1 - 3

1.5-4 IRQD=5Q%I

Fresh to Slightly Weathered

Widely to Very Widely Medium to Closely Closely to Medium

Badly Fractured Rocksor Broken Rocks, orPartially Weathered

Rocks exceptArgillaceous Rocks

0.8 - 1.2

1.0

0.2 qu

To be assessedafter inspection

1.1

0.2 qu

0.8

0.5-1.2 ISPT>50)

ModeratelyWeathered

Cfosely toVery Closely

Heavily Shatteredor

Weathered Rocks

To be assessed byexamination insitu

To be assessedafter inspection

To be assessedafter inspection

Highly to CompletelyWeathered

Very Closely

Remarks

Increase by 10% foreach 300mm embedment

Earthquake area

May need alterationupwards or downwards

Increase by 1/3 if thefoundation isrelatively dry

Increase by 10% foreach 300mm embedment

Legend .

qu Uniaxiat compressive strength (UCS) of intact rock sample•*• Building Construction Regulations (Hong Kong Government, 1985). these are currently under revision

cr»

62

Table 12 - RQD and Allowable Contact Pressure on Jointed Rock(Peck et al, 1974)

RQD(%)

100

90

75

50

25

0

qa(MPa )

30

20

13

7

3

1

Note : If tabulated value of qa exceeds unconfined compressive strength qu

of intact samples of the rock, take qa = qu.

Table 13 - Rock Mass Quality Classification Based on Rock Mass Factor,Discontinuity Spacing and RQD (Based on Deere et al, 1969;Coon & Merritt, 1970 and Hobbs, 1975)

Rock Mass QualityClassification

Very poor

Poor

Fair

Good

Excellent

RQD(%)

0 - 25

25 - 50

50 - 75

75 - 90

9 0 - 1 0 0

DiscontinuitySpacing, per m

Over 15

15 - 8

8 - 5

5 - 1

Less than 1

Rock MassFactor, j

Less than 0.2

Less than 0.2

0.2 - 0.5

0.5 - 0.8

0.8 - 1.0

63

FIGURES

64

65

LIST OF FIGURE

Figure page

No

1 Location Plan of the Yuen Long to Tuen Mun 67Eastern Corridor

2 Geological Map of Part of Designated Area 68(Darigo, 1989)

3 Generalized Section of the Strata in the Yuen Long 69Area (Frost, 1989)

4 Complex Foundation Conditions in Marble Intruded by 70Dykes at Interchange No. 3

5 A Typical Weathering Profile in Carbonate Rocks 71(Deere & Patton, 1971 and Dearman, 1981)

6 Stress-Strain Behaviour of Tuff Breccia 72

7 Relationship Between Tangent Young's Modulus 73and Secant Modulus for Tuff Breccia

8 Stress-Strain Behaviour of Pure Marble 74

9 Stress-Strain Behaviour of Banded Impure Marble 75and Marble Affected by Intrusions

10 Typical Stress-Strain Curves for Rock in Uniaxial 76Compression to Failure (Based on Deere &Miller, 1966)

11 Ranges of Point Load Strength Values for Tuff 77Breccia

12 Ranges of Point Load Strength Values for White 78and Grey Marble

13 Ranges of Point Load Strength Values for Banded 79Impure Marble and MetasiItstone (Yuen LongFormation), and Metasandstone and MetasiUstone(Lok Ma Chau Formation)

14 Ranges of Point Load Strength Values for Basalt 80

15 Relationships Between Index Properties and 81Uniaxial Compressive Strength for Tuff Breccia

16 Relationships Between Index Properties and Point 82Load Strength for Tuff Breccia

17 Relationships Between Index Properties and Uniaxial 83Compressive Strength for Marble

66

Figure PageNo. No.

18 Relationships Between Index Properties and Point 84Load Strength for Marble

19 Relationships Between Uniaxial Compressive 85Strength and Point Load Strength for Marble andTuff Breccia

20 Engineering Classification of Marble in Terms of 86Elastic Modulus and Uniaxial Compressive Strength

21 Engineering Clasification of Tuff Breccia 87in Terms of Elastic Modulus and UniaxialCompressive Strength

22 Weathering Profile in Volcanic Rock Units 88at Interchange No. 1

23 Weathering Profile in Metasedimentary Rocks 89at Interchange No. 4,

24 Fracture Intensity Versus RQD for Tuff Breccia 90(Tuen Mun Formation) and Metasedimentary Rocks(Lok Ma Chau Formation)

25 Fracture Intensity Versus RQD for Grey and White 91Marble and Interbedded Marble and MetasiltstoneSubunits (Yuen Long Formation)

Figure 1 - Location Plan of the Yuen Long to Tuen Mun Eastern Corridor

68

EXPLANATION

SEDIMENTARY AND VOLCANIC ROCKS

£ §

Undivided

Tin Shui WaiMember

0*5 I Mai PoS E I Member

Yutn LongFormation

Tuff, tuffite

Interbeddedtuffite andmarble -bearingbreccia

Metasiltstone

Marble

YUEN•LONG

Jurassic-Cretaceous

SYMBOLS :

IGNEOUS ROCKS

Granite

Fault

Thrust fault

Geological boundary

Town or place nameLAMTEI

GENERALISED CROSS-SECTION A-B

0 1km

Scale

Figure 2 - Geological Map of Part of Designated Area (Darigo, 1989}

69

Debris flow-ir Marine sediments Alluvial deposits

East

Lok Ma~10hChau

Formation Debris,"-:^ v v v

V V V

V V V V

V V V V _

V V V V V

V V V V -

V V V

v Volcanics v -v v v v v v

Dyke v v ~v v v v v

v v v v v "v v v v v

v v v vv v V V

V V

V V V

Granite andGranodiorite_ Formation

YuenFormation

-100

Figure 3 - Generalized Section of the Strata in the Yuen Long Area(Frost, 1989)

70

Bridge

Nullah

Q0.£

0)

01

50Distance

100

Bridge

Sketch Plan

Legend

Marble ( M l

Marble altered by intrusion

Marble and metasiltstone

Basic dyke

F i l l

O Void

Acidic dyke

j Borehole

Void infilled

Weathering zone boundary

Lithological boundary

Lithological boundary(inferred)

WI-W1ZI Mass weathering zone

Figure 4 - Complex Foundation Conditions in Marble Intrudedby Dykes at Interchange Ho. 3

71

Limestone outcrop

WEATHERING ZONES

Pedological horizons

Zones WV and WVIif impure

Zones Will and WIV

Open cavities

Infilled cavities, may be soft clay(Weathered insitu or transported from upper horizons

Figure 5 - A Typical Weathering Profile in Carbonate Rocks(Deere & Patton, 1971 and Dearman, 1981)

72

300r

0.5 1.0 1.5 2.0

Axial Strain ( x i O ~ 3 )

2.5

(a) MARBLE-CLAST BEARING TUFF BRECCIA

200r

Axial Strain (xlO"3)

(b) FINE ASH TUFF MEMBER OF TUFF BRECCIA

Figure 6 - Stress-Strain Behaviour of Tuff Breccia

73

20 40 60 80 100

Secant Modulus of Elasticity, Es (GPa)

120

TUFF BRECCIA

Legend: Weathering Grade

a 2i

Figure 7 - Relationship Between Tangent Young's Modulus and SecantModulus for Tuff Breccia

74

200r

Axial Strain ( x l Q ~

(a) GREY MARBLE

o 150QL

t/)100

a>M 50&QJt_QL

OO

05 10Axial Strain

15r,-3|

20

(b) WHITE MARBLE

Figure 8 - Stress-Strain Behaviour of Pure Marble

75

o 150Q.

100encu

cut-Q.£oo

50-

0 05 10 15 20Axial Strain (x lO" 3 )

(a) BANDED IMPURE MARBLE

25

200 r

05 10A x i a l Strain xlO"

(b) GREY MARBLE WITH GRANITIC VEINS/SILICIFIED MARBLE

Figure 9 - Stress-Strain Behaviour of Banded Impure Marbleand Marble Affected by Intrusions

76

Stra in , e

( a ) Type I: Elastic

10

SANDSTONE

Strain, e

(c) Type III: Plastic-Elastic

co

SCHIST

Strain , e

(e) Type V: Plastic-Elastic-Plastic

a>co

Stra in , e

| b ) Type I I : Elastic-Plastic

cul_co

MARBLE

Strain . 6

I d ) Type IV: Plastic-Elastic-Plastic

in2!CO

ROCKSALT

Strain , e

I f ) Type VI : Elastic-Plastic-Creep

Figure 10 - Typical Stress-Strain Curves for Rock in U n i a x i a l Compressionto Fai lure (Based on Deere & M i l l e r , 1966}

I * *

_J I

"T

I

3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 U 1 5 1 6 1 7

Point Load Strength (MPa)

TUFF BRECCIA

Legend :Average of 5 to 15 results on specimens adjacent tocore sections tested in uniaxial compression

Average of 5 to 15 results on core specimens

Figure 11 - Ranges of Point Load Strength Values for Tuff Breccia

OlE_ S 2~ 0.ftj *-

Mat

Mat

eria

l W

eath

erin

g G

rade

W

eath

en

—

K>

O

>

*-

^

2 to 5 not present

& © © © © «•

3 1 2 3 4 5 6 7 8 9 1 0Point Load Strength ( MPa )

(a) WHITE MARBLE

4 to 5 not present

? With granitic veins /silicified ?I j

Not present unless impure

I * ® 4<$<l> *i With granitic veins / silicifi

Not generally present unless impure

. , I* * * ! Grev*Mart>le*

ed @ *

j With granitic veins / silicified j

i i , » _, ..0 1 2 3 4 5 6 7 8 9 1 0

Point Load Strength (MPa)

fb) GREY MARBLE

Legend :

© Average of 5 to IS results on specimens adjacent tocore sections tested in uniaxial compression

4 Average of 5 to 15 results on core specimens

00

Figure 12 - Ranges of Point Load Strength Values for White and Grey Marble

79

Wea

ther

ing

Gra

de

Mat

eria

Gra

deW

eath

erin

gM

ate

-M & S

M

^4 + ® + ©

~sT

j i—LT"j_

0 1 2 3 4 5 6

Point Load Strength ( MPa )

(a) INTERBEDDED IMPURE MARBLE AND METASILTSTONE

Not tested

•TNot tested

Point Load Strength (MPa)

(b) METASANDSTONE AND METASILTSTONE {MAI PO FORMATION)

Legend :

S Metasiltstone M Marble

Figure 13 - Ranges of Point Load Strength Values for Banded Impure Marbleand MetasiItstone (Yuen Long Formation), and Metasandstoneand Metasiltstone (Lok Ma Chau Formation)

•01

TO0*-» lo 4

C7>

u_01

JC.•*•* 1

2£TEjS 2

2

\

: ?i4 4 4 ^ 4+ 444 4 4 4 4 44 4 4 4 4 7

1 1? 4* 4 * © 4

. |

1 i

I

1

? Not testedii

i i i i i t i 1 — j — i4 5 6 7

Point Load Strength (MPa)

BASALT

ooCD

10 1t

Legend ;® Average of 5 to 15 results on specimens adjacent to

core sections tested in uniaxial compressionAverage of 5 to 15 results on core specimens

Figure 14 - Ranges of Point Load Strength Values for Basalt

„ 6

i 5

8 <*a:-2 3'o

c 20

1 1•*-*

oV)

0

12

_ 10

^ 8

O c

£ 6

o» 4

|LU 2

0

3.2

3.0

| 2-.

A -2> 2'6A *J/|

CA ^ O /A Q 2M

a 2.2

i i «<f t^icP0 at a S i 20

r*

9 m

o a OT aT Q

A T T T

A A

-

1 i 1 f 1 1 I

50 100 150 200 250 300 350 0 50 100 150 200 250 300 350Uniaxial Compressive Strength (MPa} Uniaxial Compressive Strength (MPa)

- A

-

A A

A

AA

50 100 150 200 250 300 350

Legend : Weathering Grade

• 1

o 2i• 2iiA 3

o 4 ( not tested )T Tuff bands

Uniaxial Compressive Strength ( MPa)

00

Figure 15 - Relationships Between Index Properties and Uniaxial Compressive Strength for Tuff Breccia

~£ 6

"•—

| 5-«—

8 *QJt_

-*•* <3

'5Z 2Co

l rfo 13."ot/}

3.2

A

_ 3.0CO

Ea, 2.8IE.

A 2 2.6A '&

A Q 2.4A >s

Q 2.2

•A "' H0 °iD J ft D ,

-

. "• vD ° 0 °r a

• « a DT °TDTaT

AT «T

AA A

-

A

t i i i i i i

0 2 4 6 8 10 12 U '"o 2 4 6 8 10 12 14Point Load Strength (MPa] Point Load Strength (MPa)

12

~ 10oN

>s 8

O

o 6GL

> /

uD 2

A

A

Legend : Weathering Grade

A * ^

2i

3

4 (not tested)T Tuff bands

0 2 4 6 8 10 12 14Point Load Strength (MPa)

COro

Figure 16 - Relationships Between Index Properties and Point Load Strength for Tuff Breccia

_ 3

-»-*

o 20 Z

Q;u.

-*->

6

co•~oD

-4-*

O

3.2

_ 3.0en

echS

A» ^ 2.8U)Cd?

D Og *— '

a ag >,D» Dg Dg (-.

D j * •**£ ( »« *» » j j Q 2 fi

0 50 100 150 200Uniaxial Compressive Strength ( MPa)

6

*""o

—±r ^o0a.<u» 2u

£:tU

•

2 4

r

A

Ag Og

s**s

.>

^ * 9

So*a • *s'

' * . S

S • » ^^' • •/ s *

s/

Ag

'

1 1 1 I

0 50 100 150 200Uniaxial Compressive Strength (MPa)

As

AgAsi Legend: Weathering Grade

• 1 White and Grey Marble)/ — Marble • 1

\^ / a 2 Banded Impure Marble andDX

Npg/ Marble with granitic veins)v o x. a

a9 A 3

o x*4^.4J?w "^"?"<rr"^*** ° Marble with granitic veins1 *" n*""^"*"* ••• ^HB ^ 1 |

0 50 100 150 200Uniaxial Compressive Strength (MPa)

OD

Figure 17 - Relationships Between Index Properties and Uniaxial Corrpressive Strength for Marble

Effective Porosity (%) Saturation Moisture Content (%)

~J.

cCO

001

^02.ct-o"

IT

TO*

CDTO5fCDn>

HH13CLn>X

""O

3"S-sri-

OD*

§0.

5"

gCL

00c-h-S

S

1J-«jCT

fD

-QO5* *°

p.oDCL

(LA

S **D

UD

ZT

— „

*OTLJ**"**

oo

o- a

^ a

*•t»*

1*• o

«*

*

ao

-

d > D • •

3£ CO N) -* -*

I"?7" I0> o gl ~

3E O"

^7" CL 33E. ^"

^ 3" 3 oR TJ "j— • ^ ^ x;

0 § "> »D JS.< ^ 31 O2. o'q 5.5 < cr ^1/1 o> 5- .«-

D(/> Q"""""* U

Q.

O

5' ^

p.ooQ.

GO ^"-1Cty3

tQ

31

^T-.

i -o»— •

00

I 1 1

0D

O

S *0

"?°* a

a *

*

a

_

Dry Density (Mg/m3)K> K) ro co co^ en bo o N>

o

r"CO

3 T3a. o5- ho

<£ J—

2 oD_ Oiyf\>

5' ^ ^D

Q ^

D ^Q- .a>

~u o^D

c»

- 1 1 1 •

\\

D \

D\

\ ^

\ •'-• ^V • . \

\ 0. \

\ s x•\ \N S\ S

\ "\\

—

85

oa.

CO

a.

.c*-*

0>i—

•4—»

CO

O 0o 2

coOL

UCS = 24 PLS (including marble with granitic veins)UCS = 25.5 PLS (shown)

U

£ 12

w 10a.

£ 8

c 2-oQ.

25 50 75 100 125 150Uniaxial Compressive Strength, UCS (MPa)

(a) MARBLE

UCS = 22.5PLS (excluding failures through pre-existingcracks and veins ) a

*T

175

25 50 75 100 125 150 175 200 225 250 275 300Uniaxial Compressive Strength, UCS (MPa)

(b) TUFF BRECCIA

Legend ; Weathering Grade

1

o 2i

Ao

Failure through pre-existing crackin uniaxial compression

Pure tuff specimens

Marble with granitic veins

( not tested

Figure 19 - Relationships Between Uniaxial Compressive Strength and PointLoad Strength for Marble and Tuff Breccia

86

Approximate Point Load Strength (MPa)025 0 5 1 2 A 8

i Strength' class

r-MarbleDeere & Miller1966

Dolomite, LimestoneMarble & MarlstoneDearman 1981

LimestoneDeere & Miller1966

10 30 100Untaxial Compressive Strength (MPa!

300 1000

Legend

Fresh marble ( 1 )Slightly decomposed marble with slight effects of solution and/ordiscolouration (2)Moderately decomposed impure marble (3)Marble with granitic veinsSilicified marble

Figure 20 - Engineering Classification of Marble in Terms of ElasticModulus and Uniaxial Compressive Strength

87

Approximate Point Load Strength (MPa)0.25 0 . 5 1 2 4 8 1

10 30 100Uniaxial Compressive Strength t MPa

300 1000

Legend : Weathering Grade

1 (not tested)° 2i

Ao £ ( not tested )

Pure tuff bands

Note : Failures through pre-existing cracks and veins are excluded.

Figure 21 - Engineering Classification of Tuff Breccia in Terms of ElasticModulus and Uniaxial Compressive Strength

Bridge

oo_£

o>o>

10 r

0

-10

-20

-30

- A O

:wiK r _ A A- —* A A A A -

- A A A A A A :A A A A A A A A AA A A A A A A A A _A A..A A A A A A A..

A A V A A A A A A VA A A A A A A

A A A A A A A AA A A A A A A A A A i

A A V A A V A A A A AA A A A A A A A A A4 t

A A A A A A A A A A V A A A A A A

I

50 100Distance (m)

1500000

Legend

Tuffaceous Siltstone/Sandstonewith thin tuff breccia

JTM (?)

Sandstone layer

Tuff breccia (marble-clast bearing)

Granite

Fine Ash Tuff [ JTM (?)

T Borehole

— Weathering zone boundary

Lithologicai boundary

WI-W2I Mass weathering zone

t......E Fault (probable)

Figure 22 - Weathering Profile in Volcanic Rock Units at Interchange No. 1

89

Bridge

Q

CD

10

0

-10

2°

-30

- A O

-50

-60U •

Distance ( m )

Legend

Metasiltstone

MetasandstoneCmp

T Borehole

_«__ Weathering zone boundary

Lithological boundary

WI-W2I Mass weathering zone

Note : Exact orientation and thickness of beds not known (sketch only) .

Figure 23 - Weathering Profile in Metasedimentary Rocksat Interchange No. 4

90

25

;

20

E »•4.

Q.

x 15

***w>c

c10

8?3

"oo :L_

u.5

Highly Weathered

* \v \ Moderately Weathered? \ p-c 0

SX Fresh tox ss^ o Slightly M

£ o X O X X • "«

*<oo x x^ X X

Xi x X ^^^- NX X XX] ox Xi X X ^^^ X X

>r% x xj x ^^^ XiH • **"**»««»Xi *

< x*,x^^ x' x x "**'*.* '%<*^L x X • Xj X Xi ^^i

X ^***^ X X # ^T^^^^

Xj ^-^ ^ XX'

CT-1** **"*•«•«»,

0 10 20 30 40 50 60 70 80Rock Quality Designation, RQD {%)

(a) TUFF BRECCIA

_ *x \ Fresh to Slightly Weathered25

)

20^•

£

t !a.

15•»>>.t!c

£ 10

3

Og_

UL5

r -*• \< s

x\J xx x, Moderately Weathered

1 x> • ^x

x . \* V

XjX • \

\ f • Xj \

\ x Xi * xx ix

sXj • * • ^VS ^x,

XX Xi X \N% x xi xi \

- v x j • Xi x^^x-r xiX. x'* * --^^« ^-^ •

^-^i xT ""^-^r^

1 1 1 1 1 1 J 1

0 10 20 30 40 50 60 70 80Rock Quality Designation, RQD {%)

( b) METASEDIMENTARY ROCKS

Legend ;

• Fresh to slightly weathered o HighlyXi Moderately weathered ( i<1Q% soil)

Veathered, — — jfek.

• i"*"**""**•«*, * *

x 7"^-^

90 100

: |P.

1

""•""** — *. ^

90 100

weathered

Note : RQD values are standardized to 1.5m core lengths.

Figure 24 - Fracture Intensity Versus RQD for Tuff Breccia (Tuen MunFormation) and Metasedimentary Rocks (Lok Ma Chau Formation)

91

Q

pent

ens

o

Fra 01

J.

Marble with Solution Effects( Will - WIV )

Fresh Marble(WI)

A Q Qa 91

a aa

a

^^^jj^ A ,"*"&5p* .,

a n A "*A p Q A A

^0 __ A

10 20 30 40 50 60 70 80Rock Quality Designation, RQD (%)

( a ) GREY AND WHITE MARBLE

90 100

o

te tn

actu

re *

XmXXs

t i

Moderately Weathered

Slightly Weathered( W I I )

Fresh

?-«-

X

X xm•m

•mXm X,Xm

Xm Xm XXm

X% X

%xm Xm

•m *m

i iXm

t f

10 20 30 40 50 60 70 80

Rock Quality Designation, RQD (%)

( b ) INTERBEDDED MARBLE AND METASILTSTONE

90 100

Legend ;

m

Fresh marbleFresh/Slightly weatheredMarble

a Marble with solution effectsx Moderately weathered

Metasiltstone

Note : RQD values are standardized to 1.5m core lengths.

Figure 25 - Fracture Intensity Versus RQD for Grey and White Marble andInterbedded Marble and Metasiltstone Subunits(Yuen Long Formation)

92

93

PLATES

94

95

LIST OF PLATES

Plate Page

No- No.

1 Oblique Aerial Photograph Showing the Northwest 97New Territories and the Proposed Yuen Long toTuen Mun Eastern Corridor

2 Grey Marble with Granitic Veins 98(Yuen Long Formation)

3 Grey Marble (Yuen Long Formation) 99

4 Impure Marble Interbedded with Phyllite, and Grey 100Marble (Uppermost Part of the Ma Tin Member,Yuen Long Formation)

5 White Marble Altered by Basalt Dyke Intrusion 101

6 White and Grey Marble (Ma Tin Member, Yuen Long 102Formation)

7 Banded Impure Marble with Metasiltstone (Uppermost 103Part of the Ma Tin Member, Yuen Long Formation)

8 Silicified Grey Marble 104

9 Dark Grey to Black Marble (Long Ping Member, 105Yuen Long Formation)

10 Tuff Breccia with Marble Clasts (Tuen Mun Formation) 106

11 Tuff Breccia with Marble Clasts (Tuen Mun Formation) 107

12 Tuff Breccia with Marble Clasts (Tuen Mun Formation) 108

13 Sandstone, Siltstone and Tuff Breccia (Tuen Mun 109Formation)

14 Metasandstone and Metasiltstone 110(Lok Ma Chau Formation)

15 Metasandstone and Metasiltstone 111(Lok Ma Chau Formation)

96

112

113

GEOTECHNICAL CONTROL OFFICE PUBLICATIONS

Geoguide 1

Geoguide 2

Geoguide 3

Geospec 1

Geospec 2

1/84

2/84

3/84

4/84

5/84

6/84

1/85

2/85

1/88

Geotechnical Manual for Slopes (1984),295 p.

Guide to Retaining Wall Design (1982),154 p.

Guide to Site Investigation (1987),365 p.

Guide to Rock and Soil Descriptions(1988), 189 p.

Model Specif icat ion for PrestressedGround Anchors (1989), 168 p.

Model Specif ication for ReinforcedFill Structures (1989), 140 p.

Mid-levels Study : Report on Geology,Hydrology and Soil Properties (1982),265 p. plus 54 drgs.

Prediction of Soil Suction for Slopesin Hong Kong, by M.G. Anderson (1984),243 p.

(Superseded by Publication No. 1/85)

(Superseded by Geospec 1)

Review of Superficial Deposits andW e a t h e r i n g in Hong Kong, by J.D.Bennett (1984), 51 p.

Review of Hong Kong Stratigraphy, byJ.D. Bennett (1984), 86 p.

Review of Tectonic History, Structureand Metamorphism of Hong Kong, by J.D.Bennett (1984), 63 p.

(Superseded by Publication No. 1/88)

Groundwater Lowering by HorizontalDra ins , by D.J. Cra ig & I. Gray(1985), 123 p.

B ib l iography on the Geology andGeotechnical Engineering of Hong Kongto December 1987, by E.W. Brand (1988),150 p.

HK$50 (US$9.50)

HK$45 (US$9)

HK$83 (US$13)

HK$40 (US$9)

HK$25 (US$5.50)

HK$25 (US$5.50)

HK$200 (US$34)

HK$50 (US$9)

HK$40 (US$8)

HK$25 (US$5.50)

HK$20 (US$5)

HK$74 (US$12)

HK$35 (US$7)

114

1/90

2/90

GASP I

GASP II

GASP III

GASP IV

GASP V

GASP VI

GASP VII

GASP VIII

GASP IX

GASP X

GASP XI

GASP XII

GeologicalMemoir No. 1

R e v i e w of D e s i g n Methods forExcavations (1990), 192 p.

Foundation Properties of Marble andOther Rocks in the Yuen Long - Tuen MunArea (1990), 117 p.

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

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

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

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

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

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

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

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

Geotechnical Area Studies Programme-East New Territories (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 4maps.

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

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

HK$30

HK$58

(US$6.50)

(US$10)

HK$240 (US$40)

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$150 (US$25)

HK$150

HK$150

(US$25)

(US$25)

HK$150 (US$25)

HK$50 (US$9)

115

G e o l o g icalMemoir No. 2

G e o l o g i c a lMemoir No. 3

G e o l o g icalMemoir No. 4

G e o l o g i ca lMemoir No. 5

G e o l o g icalMemoir No. 6

Map HGM 20,Sheet 2

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

G e o l o g y of HongKowloon, by P.J.(1986), 134 p.

Kong Is land andStrange & R. Shaw

G e o l o g y o f t h e W e s t e r n N e wTerr i tor ies, by R.L. Langford, K.W.Lai, R.S. Arthurton & R. Shaw (1989),140 p.

Geology of Sai Kung and Clear WaterBay by P.J. Strange, R. Shaw & R.Addison (1990), in press.

Geo logy of the North Eastern NewTerritories, in preparation.

Geology of Lantau, in preparation.

San Tin : So l id and Supe r f i c i a lGeology (1:20 000 map) (1989), 1 map.

HK$78 (US$12.50)

HK$97 (US$17)

HK$87 (US$13)

HK$20 (US$3.50)

Sheung Shui :G e o l o g y (1preparation.

Kat 0 Chau :G e o l o g y (1preparation.

Solid and2 0 0 0 0

Solid and: 2 0 0 0 0

Superficialm a p ) , in

Superficialm a p ) , in

Tsing Shan (CastleSuperf ic ial Geology(1988), 1 map.

Peak) : Solid and HK$20 (US$3.50)(1:20 000 map)

Y u e n Long : Solid and Superf icialGeology (1:20 000 map) (1988), 1 map.

Sha Tin : So l id and S u p e r f i c i a lGeology (1:20 000 map) (1986), 1 map.

Sai K u n g P e n i n s u l a : So l id andSuperf ic ia l Geology (1:20 000 map)(1989), 1 map.

Tung Chung : sol id and SuperficialGeology (1:20 000 map), in preparation.

HK$20

HK$20

HK$20

(US$3.50)

(US$3.50)

(US$3.50)

S i l v e r M i n e Bay :Superficial Geology (1:20preparation.

S o l i d and000 map), in

Hong Kong and Kowloon : Solid and HK$20 (US$3.50)Superf ic ia l Geology (1:20 000 map)(1986), 1 map.

116

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

Map HGP 5,Sheet 6-NW-B

Map HGP 5A,Sheet 2-NE-D

Map HGP 5B,Sheet 2-NE-D

Map HGP 5A,Sheet 2-SE-A

Map HGP 5B,Sheet 2-SE-B

Map HGP 5A,Sheet 2-SW-C

Map HGP 5B,Sheet 2-SW-C

Map HGP 5A,Sheet 2-SW-D

Map HGP 5B,Sheet 2-SW-D

Map HGP 5A,Sheet 3-NW-C

Map HGP 5B,Sheet 3-NW-C

Map HGP 5A,Sheet 6-NW-A

C l e a r W a t e r Bay : S o l i d andSuperficial Geology (1:20 000 map)(1989), 1 map.

Shek Pik : Sol id and Superf ic ia lG e o l o g y ( 1 : 2 0 0 0 0 m a p ) , i npreparation.

Cheung Chau : Solid and SuperficialG e o 1 o g y ( 1 : 2 0 0 0 0 m a p ) , i npreparation.

Hong Kong South and Lamma Island :Solid and Superficial Geology (1:20000 map) (1987), 1 map.

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

Yuen Long : Marble in the DesignatedArea Northwest New Territories (1:5 000map) (1988), 1 map.

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

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

Mai Po : Superficial Geology (1:5 000map) (1990), 1 map.

Mai Po : Solid Geology (1:5 000 map)(1990), 1 map.

Deep Bay : Superficial Geology (1:5 000map) (1989), 1 map.

Deep Bay : Solid Geology (1:5 000 map)(1989), 1 map.

Shan Pui : Superficial Geology (1:5 000map) (1989), 1 map.

Shan Pui : Solid Geology (1:5 000 map)(1989), 1 map.

Man Kam To : Superf icial Geology(1:5 000 map) (1990), 1 map.

Man Kam To : Solid Geology (1:5 000map) (1990), 1 map.

Tin Shui Wai : Superficial Geology(1:5 000 map) (1989), 1 map.

HK$20 (US$3.50)

HK$20 (US$3.50)

HK$20

Free

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

HK$10

(US$3.50)

117

Map HGP 5B,Sheet 6-NW-A

Map HGP 5A,Sheet 6-NW-BMap HGP 5B,Sheet 6-NW-B

Map HGP 5A,Sheet 6-NW-C

Map HGP 5B,Sheet 6-NW-C

Map HGP 5A,Sheet 6-NW-D

Map HGP 5B,Sheet 6-NW-D

Tin Shui Wai : Solid Geology (1:5 000 HK$10map) (1989), 1 map.

Y u e n Long : Super f i c ia l Geo logy HK$10(1:5 000 map) (1989), 1 map.Yuen Long : Solid Geology (1:5 000 map) HK$10(1989), 1 map.

Hung Shui Kiu : Superficial Geology HK$10(1:5 000 map) (1989), 1 map.

Hung Shui Kiu : Solid Geology (1:5 000 HK$10map) (1989), 1 map.

Muk Kiu Tau : Superficial Geology HK$10(1:5 000 map) (1990), 1 map.

Muk Kiu Tau : Solid Geology (1:5 000 HK$10map) (1990), 1 map.

US$ prices shown above are for overseas orders and are inclusive ofsurface postage to anywhere in the world.

ORDERING INFORMATION IS GIVEN ON THE REVERSE SIDE OF THE TITLE PAGE.

This book Is due for return or renewal on th-3

shown unless previously recalled,, Fines may aeincurred for late return.

DATE DUE

XDSD7DSSQ

LB 552 F77

Foundation properties ofmarble and other rocks

1990.

[LB] 552 F77

XDSD70220