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SITE CHARACTERISATIONSTUDY - PHASES 1 AND 2GEO REPORT No. 71N.P. KoorHKK82GEOTECHNICAL ENGINEERING OFFICECIVIL ENGINEERING DEPARTMENTTHE GOVERNMENT OF THE HONG KONGSPECIAL ADMINISTRATIVE REGION

SITE CHARACTERISATIONSTUDY - PHASES 1 AND 2GEO REPORT No. 71N.P. Koor{ BOOKS wssmiiBm m ORDINANCE47*-%This report was originally produced in November 1997as GEO Special Project Report No. SPR 8/97

- 2 -© The Government of the Hong Kong Special Administrative RegionFirst published, July 1999Prepared by:31B. REC. NO.te: =r - r -—^DATEREG'DCLASS NO.AUTHOR NO.Geotechnical Engineering Office,Civil Engineering Department,Civil Engineering Building,101 Princess Margaret Road,Homantin, Kowloon,Hong Kong.This publication is available from:Government Publications Centre,Ground Floor, Low Block,Queensway Government Offices,66 Queensway,Hong Kong.Overseas orders should be placed with:Publications Sales Section,Information Services Department,Room 402,4th Floor, Murray Building,Garden Road, Central,Hong Kong.Price in Hong Kong: HK$292Price overseas: US$43 (including surface postage)An additional bank charge of HK$50 or US$6.50 is required per cheque made in currenciesother than Hong Kong dollars.Cheques, bank drafts or money orders must be made payable toThe Government of the Hong Kong Special Administrative Region

- 3 -PREFACEIn keeping with our policy of releasing information whichmay be of general interest to the geotechnical profession and thepublic, we make available selected internal reports in a series ofpublications termed the GEO Report series. A charge is made tocover the cost of printing.The Geotechnical Engineering Office also publishesguidance documents as GEO Publications. These publicationsand the GEO Reports may be obtained from the Government'sInformation Services Department. Information on how topurchase these documents is given on the last page of this report.R.K.S.ChanHead, Geotechnical Engineering OfficeJuly 1999

- 4 -FOREWORDThis report presents the results of Phases 1 and 2 of the Site Characterisation Study carriedout by the GEO in response to Professor Morgenstern's recommendation (d) made in his reporton the Kwun Lung Lau landslide in 1994. The objective of the study was to determine theapplicability of non-invasive geophysical methods to the identification of some importantfeatures which affect slope and retaining wall stability in Hong Kong.The study was managed by Mr N.P.Koor. It involved him carrying out an initial literaturereview, preparing contract documents, designing and supervising the two phases of site trials,managing six contractors, and designing and supervising ground investigations at four of thetrial sites.A Working Group was established in order to obtain a consensus on the form and directionof the study from the geotechnicat community in Hong Kong, The Working Group comprisedprofessionals representing the Geotechnical Engineering Office (GEO), the Hong KongInstitution of Engineers (HKIE) and local universities. The members were Messrs R.P.Martin(GEO), Hugh H.RChoy (GEO), NJP.Koor (GEO), K.C.Yeo (GEO), A.C.O.Li (GEO), S.Parry(GEO), J.L.PHo (GEO), J.Moms (GEO), P.R.Sayer (HKIE), K.Morton (HKIE), L.S.Chan(University of Hong Hong (UHK)) and X.S.Li (Hong Kong University of Science andTechnology (HKUST)).Dr L.S.Chan of the Department of Earth Sciences of the University of Hong Kong providedvaluable advice and direction on the technical aspects of the site trials, geophysical results andinterpretations.Technical support for site supervision of the Phase 1 site trials was provided by MessrsK.C.Chan and P.C.Cheng, Technical support for site supervision of the Phase 2 field trials andsubsequent ground investigation was provided by Mr K.W.Cheung, and Engineering GeologyGraduates Ms A.Y.S.Liu, Ms W.KY.Law and Mr J.C.F.Wong. Technical support in procuringthe ground investigation was provided by Mr K.W.Cheung with professional advice and supportfrom Mr M.J.Shaw. All the Figures, Tables and Plates contained in the report were produced byMessrs K.C.Chan and P.C.Cheng. All of these contributions are gratefully acknowledged.(R.P.Martin)Chief Geotechnical Engineer/Planning

- 5 -ABSTRACTIn response to recommendation (d) contained in Volume 1 of the report on the KwunLung Lau Landslide of 23 July 1994 (Hong Kong Government, 1994), the Planning Division ofthe GEO initiated a Site Characterisation Study on the use of non-invasive geophysicaltechniques to investigate masonry walls and man-made slopes in Hong Kong. Seven noninvasivegeophysical methods have been assessed through two phases of field trials to determinetheir applicability to the identification of features which affect slope and retaining wall stabilityin Hong Kong. Selection of the seven methods was based on a literature review of internationaland local land-based geophysical practice. The selected methods were ground penetrating radar(GPR), shallow seismic reflection, spectral analysis of surface waves (SASW), resistivityimaging (RI), self potential, electromagnetic methods (EM) and thermal imaging. Two othermethods, seismic refraction and sonic method, were tested at individual sites by two contractorsbut were not stipulated in the contract requirements.The field trials were carried out by six contractors for Phase 1 and five out of the originalsix for Phase 2. The contractors were selected based on their technical expertise and track recordin geophysical investigations for civil engineering works. The participating contractors for thePhase 1 field trials were Guandong South China EGD Co. (GSC), Bachy Soletanche Group(BS), Meinhardt Works (MW), Golder Associates (HK) Ltd (GA), Fugro Geotechnical Services(HK) Ltd. (FGS) and the Institute of Geophysical and GeochemicaJ Exploration (IGGE). ThePhase 2 contractors were the same as for Phase 1 apart from Meinhardt Works who decided notto participate.The Phase 1 field trials, which tested all seven methods were made at four sitesconsisting of two pre-war masonry walls, one cut slope and one fill slope. All four sites hadsome existing ground investigation data which were provided to each of the contractors prior tothe trials for purpose of calibrating the geophysical results. Based on observations of thefieldwork and the geophysical results, the techniques were divided into three groups, as follows:Group 1. Techniques which produced some promising results andmay be applied widely to sites in Hong Kong. These areGround Penetrating Radar and Resistivity Imaging.Group 2. Techniques which are affected by environmental noiseand limited by characteristics inherent in the technique,but might be usefully applied at specific sites. These areElectromagnetic Conductivity (frequency domain) andSpectral Analysis of Surface Waves.Group 3. Techniques which did not provide any usefulinformation and do not warrant further consideration.These are High Resolution Seismic Reflection, SelfPotential, Electromagnetic Conductivity (time domain)and Thermal Imaging.

- 6 -In Phase 2 the Group 1 and 2 techniques were further tested at four new sites againconsisting of, two pre-war masonry walls, one cut slope and one fill slope. The Phase 2 sites hadno existing ground investigation data so as to allow the Working Group to assess if thegeophysical methods alone can be reliable and accurate without any pre-conceptions of the siteconditions. Preliminary interpretations were made by each of the contractors based solely on thegeophysical results. Subsequent conventional ground investigations by GEO were then carriedout at the sites and the results were given to each of the contractors for re-interpretation of theirgeophysical results.The Phase 2 trials concluded that the overall quality of the raw data and interpretationsvaried significantly with the expertise of the individual geophysics teams. Certain contractorswere able to demonstrate that a combined geophysical investigation utilising GPR and RI canlocate the back of masonry walls if they are less than 3m thick and define zones of elevatedmoisture content and voids with reasonable accuracy. Only limited success was achieved indetermining the location of corestones and the thickness of loose fill at the two slope sites.In the light of the conclusions from the field trials, it is recommended that due to theinconsistent raw data and interpretations it would not be advisable at present to let a termcontract specifically for non-invasive geophysical techniques for site characterisation in HongKong, or to require the use of such techniques in LPM studies. Also, further trials of the four orother techniques are not warranted. However, since some of the results were encouraging it isrecommended that further research work on developing GPR and RI for masonry wallinvestigations is carried out through a local University with support from GEO. The researchshould focus on ways to enhance the resolution of the two techniques and also to develop a siteand data processing methodology which would ensure more consistent results from contractors.

- 7 -CONTENTSTitle Page 1PREFACE 3FOREWORD 4ABSTRACT 5CONTENTS 71. INTRODUCTION 102. APPLICATION OF GEOPHYSICS TO SLOPES AND WALLS 112.1 Introduction 112.2 Retaining Structures in Hong Kong 122.3 Natural and Man-made Slopes 132.4 Physical Anomalies Behind Slopes or Walls 13Page3. PHASE 1 FIELD TRIALS 143.1 Introduction 143.2 Phase 1 Field Trial Sites 143.2.1 Trial Site A - Kennedy Town Police Quarters. Feature No. 1411SW-A/C2563.2.2 Trial Site B - Eliot Hall, Hong Kong University. Feature No. 1411SW-AVR7033.2.3 Trial Site C - Sir Ellis Kadoorie School. Feature No. 11SE-A/R39 153.2.4 Trial Site D - Cape Collinson Crematorium. Feature No. 1511SE-D/F193.3 Phase 1 Results 163.3.1 Introduction 163.3.2 Assessment of Results 163.3.3 Shallow Seismic Reflection (SSR) 163.3.4 Spectral Analysis of Surface Waves (SASW) 173.3.5 Resistivity Imaging (RI) 17No.

- 8 -3.3.6 Self Potential (SP) 173.3.7 Electromagnetic Methods (FDEM&TDEM) 173.3.8 Ground Penetrating Radar (GPR) 183.3.9 Thermal Imaging (11) 183.3.10 Others 18PageNo.3.4 Phase 1 Conclusions and Recommendations 194. PHASE 2 HELD TRIALS 194.1 Introduction 194.2 Phase 2 Field Trial Sites 204.2.1 Introduction 204.2.2 Trial Site E - Wall North of Stubbs Villa off Stubbs Road - 20Wall No. 11SW-D/R2084.2.3 Trial Site F - Wall adjacent to Hollywood Road Police Quarters 21Block B - Wall No. 11SW- A/R1244.2.4 Trial Site G - Cut Slope opposite to Lions Mommg Hill School,Blue Pool Road - Part of Slope No. 11SE-C/C514.2.5 Trial Site H - Fill Slope adjacent to Sze Yu House,Choi Wan Estate - Part of Fill Slope No. 11NE - A/F1254.3 Field Trials4.3.1 Introduction4.3.2 Preliminary Field Trial Results4.4 Ground Investigation4.4.1 Introduction4.4.2 Trial Site E4.4.3 Trial Site F4.4.4 Trial Site G4.4.5 Trial Site H4.5 Comparison of Preliminary Interpretation with Ground Investigation Data4.5.1 Introduction4.5.2 Trial Sites E and F4.5.3 Trial Site G212222222324242425262627272728

- 9 -4.5.4 Trial Site H 284.6 Final Interpretation 295. CONCLUSIONS AND RECOMMENDATIONS 296. REFERENCES 30LIST OF FIGURES 32LIST OF PLATES 57APPENDIX A : SHE CHARACTERISATION STUDY PROJECT BRIEF 69APPENDIX B : GEOPHYSICS LITERATURE REVIEW 77APPENDIX C : PROFILES OF CONTRACTOR AND FIELD WORK 117PROGRESSPageNo.APPENDIX D: ASSESSMENT OF PHASE 1 FIELD TRIAL RESULTS 147APPENDIX E : DETAILED ASSESSMENT OF THE PHASE 2 191PRELIMINARY FIELD TRIAL RESULTS

- 10 -1. INTRODUCTIONThe collapse of an old masonry wall in Kwun Lung Lau on Hong Kong Island in 1994was triggered by saturation of the soil behind the wall Subsequent investigations showed thatthe main cause of the landslide was defective water-carrying services which saturated the slope.The masonry wall was thinner than indicated on available records and aggravated the failure(Hong Kong Government, 1994). Recommendation (d) contained in Volume 1 of the Report onthe Kwun Lung Lau Landslide of 23 July 1994 (Hong Kong Government, 1994) stated that:"The GEO should undertake and support elsewhere in HongKong, research into improved means of site characterisationfocused on factors that affect slope stability in Hong Kong. TheWriter does not think that the development of slope warningsystems for the conditions found in Hong Kong is promising. Thecritical features are small and numerous and instability oftendevelops in an abrupt manner. However, there are a number ofnew developments in geophysics such as radar and non-contactresistivity that might be found useful in discovering subsurfacedefects and enhanced moisture zones."In response to this recommendation, the Planning Division of the GEO initiated a SiteCharacterisation Study on the use of non-invasive geophysical techniques to investigate masonrywalls and man-made slopes in Hong Kong. The project brief for the study is reproduced inAppendix A which was agreed by Prof. Morgenstern on 27 February 1995. Seven non-invasivegeophysical methods have been assessed through two phases of field trials to determine theirapplicability to the identification of features which affect slope stability in Hong Kong. Themethods were selected based on a literature review of international and local land-basedgeophysical practice. This literature review, which describes briefly the theory of each of thetechniques together with an extensive reference list, is presented in Appendix B. The seventechniques assessed were; ground penetrating radar (GPR), shallow seismic reflection (SSR),spectral analysis of surface waves (SASW), resistivity imaging (RI), self potential (SP),electromagnetic methods (EM) and thermal imaging (TI).The field trials were carried out at eight sites (Figure 1). Phase 1 field trials were made atsites with some existing ground investigation (GI) data (sites A, B, C and D) and were used as acalibration exercise to identify potentially applicable methods. Phase 2 field trials focused onfour techniques selected from Phase 1 which were tested at four sites with no existing groundinvestigation data (sites E, F, G and H). In Phase 2 preliminary interpretations were made byeach of the participating contractors based solely on the geophysical results. Subsequentconventional ground investigation by GEO was then carried out and the results were given to thecontractors for re-interpretation of their results. The techniques were assessed by comparing thepreliminary interpretations made by the contractors with the results of the ground investigations,and by taking into account the consistency of the raw data and interpretations presented by thedifferent contractors.Six contractors were selected based on their technical expertise and track record ingeophysical investigations for civil engineering works. Profiles of each of the contractors,together with the techniques and equipment tested, are presented in Appendix C. The

- 11 -participating contractors for the Phase 1 field trials were; Guandong South China EGD Co.(GSC), Bachy Soletanche Group (BS), Meinhardt Works (MW), Colder Associates (HK) (GA),Fugro Geotechnical Services (HK) Ltd. (FGS) and the Institute of Geophysical and GeochemicalExploration (IGGE). Meinhardt Works voluntarily withdrew from the Phase 2 trials. Thepersonnel and equipment used in Phase 2 were essentially the same as for Phase 1.This report summarises the results of the Phase 1 and 2 field trials and makesrecommendations for further work. Sub-surface features that can affect slope or retaining wallstability in Hong Kong and potentially identifiable with geophysical methods are discussed inSection Two. The two phases of the field trials are summarised in Sections Three and Four.Conclusions and recommendations for further work are presented in Section Five.Interpretative reports on both phases have been produced by each contractor and arereferenced in Section Six and Appendix C (Section C.3). Each report describes the geophysicalmethods used, field procedures, methods of analysis and presents the contractors interpretationof the results. These reports are contained in the Geotechnical Information Unit (GIU) of theCivil Engineering Library and should be read in conjunction with this report. Groundinvestigation reports for the eight trial sites are also contained in the GIU.The interpretations contained in the contractors final reports were based on thegeophysical information obtained, the GI data supplied by GEO, and the expertise of thecontractor. The contractors were required to submit draft reports to the Working Group forcomments and an interim review. The intention of this review was not to question the accuracyof the interpretations made but to ensure that each interpretation was justified and supported inthe report. This procedure also helped to obtain a measure of the relative quality of the work ofeach contractor2. APPLICATION OF GEOPHYSICS TO SLOPES AND WALLS2.1 IntroductionGeophysical methods are most successful where there are strong contrasts in the physicalproperties between the target feature and its surroundings. The material properties frequentlyused in geophysical investigations are elasticity, electrical conductivity, density, magneticsusceptibility and electrical polarisation potential. Some of the most important features whichcan affect the stability of man-made slopes and walls are listed below and discussed in thesubsequent sections along with a description of old masonry walls in Hong Kong.(i) Geometry and structural condition of retaining structureswhich support a slope or platform.(ii) Strength and spatial disposition of the soil and rock whichform a slope or platform.(iii) Discontinuities within a slope such as faults, shear zones,joints, hydrothermally altered zones and dykes.(iv) Ground water.

- 12 -(v) Zones of enhanced moisture content within a slope or behinda retaining structure.(vi) Voids behind hard surface coverings.2.2 Retaining Structures in Hong KongTwo distinct groups of walls may be identified in Hong Kong, namely, pre-war and postwar(Jukes et al 1986). Post-war retaining structures are mainly cantilever, counterfort andgravity structures of mass or reinforced concrete construction. In general they have beendesigned and constructed in accordance with engineering principles and are not discussed furtherin this report.Pre-war walls are largely gravity structures of masonry or mass concrete construction.Records of the design of pre-war walls generally do not exist, and therefore the condition andgeometry of these walls require investigation if stability is to be determined. Shelton (1980) andChan (1996) have studied the construction and stability of pre-war masonry retaining walls inHong Kong. Chan (1996) describes three main types of masonry wall in Hong Kong, namelytied face walls, stone rubble walls and stone pitching (Figure 2).Tied face walls were normally adopted to retain cuttings and were most popular in the1840s. Typically, the front layer of blocks are well squared and bonded by thin layers oflime/sand mortar. The rear blocks in contact with the cut face are dry-packed and are tied to thefront face by headers.Stone rubble walls cover a wide range of wall types from random rubble walls to dressedblock walls with horizontal tie beams (Figure 2). However, they all have a similar coredstructure consisting of a front layer of dressed or dry-packed blocks, a rear vertical layer ofcommonly dry packed, rough slabby blocks and a core of excavated rock fill ranging in sizefrom gravel to boulders. Variations include cores stabilised with lime, tied rubble walls withrectangular granite headers and rubble walls with concrete or lime stabilised soil beams.Stone pitching is a single layer of bonded rock blocks, normally 300mm thick, laid onto aslope surface to prevent infiltration and erosion. The blocks are normally laid on a layer of nofinesconcrete or crushed rock which acts as a drainage layer (Figure 2).The three aspects of a masonry wall that are crucial to the assessment of its stability areits thickness, internal structure, and seepage conditions (Chan, 1996). Investigation techniquescommonly adopted in Hong Kong to determine the geometry of masonry walls include weepholeprobing, coring using standard concrete coring equipment or modified triple tube core barrels,and hand-excavated trial pits behind or at the toe of the wall. Weephole probing has manydrawbacks. The weepholes may not extend completely through the wall section or may becomeblocked or collapsed. The often sinuous nature of the weepholes makes probing difficult and thepotential to probe beyond the back of the wall if internal erosion around the weephole has takenplace will result in an over-estimation of wall thickness. Due to the heterogeneous nature of thebuilding materials used to construct masonry walls and their complex structure, recovery usingsingle core barrels is often very poor, rendering interpretation difficult. Hand-excavated trial pits

- 13 -are a satisfactory method of investigation but have time, cost, safety and access implicationswhich often make them unattractive during the preliminary stages of an investigation.Obstructions due to services, large rock boulders and restricted access space often limit the depthof trial pit excavation to only a few meters.Physical contrasts in density and resistivity may exist between the masonry wall and theback-fill materials behind the wall such that the interface may be identified by severalgeophysical techniques. If the wall contains voids or zones of increased moisture content thenthese areas may also produce geophysical anomalies especially in terms of electrical propertiessuch as resistivity or conductivity.2.3 Natural apd Man-iriad$ SlopesAlthough geophysical techniques cannot directly determine the in situ shear strength of aparticular soil or rock, they are potentially useful in mapping the distribution of soil or rock ofsimilar strength and stiffness between physical investigation points since these properties willmanifest themselves as variations in density and elasticity. The mapping of fill bodies is anexample where geophysics may be useful.Adversely-oriented discontinuities, including relict features in soils, may control slopestability. Such features are often difficult to locate using conventional ground investigationtechniques. Geophysical techniques are potentially suitable to detect open or infilleddiscontinuities since contrasts in conductivity and density may exist between the discontinuityand the surrounding intact rock mass. The resolution of many geophysical techniques however,is probably insufficient for detailed discontinuity mapping.Geological features which may influence the local pore pressure distribution in a slopemay also be identified using geophysical methods. Massey & Pang (1988) describe three typesof feature which can influence pore pressure distribution in a slope as follows; soil zones or rockbands having substantially different permeability from the surrounding soil, relict discontinuitiesand relatively impermeable dykes and veins, and pipes and other subsurface erosion features. Allof these features may modify electrical, elastic and density properties of the rock and soil tosome extent.2.4 Physical Anomalies Behind Slopes or WallsZones of high moisture content behind masonry walls or hard slope surface coveringsmay indicate an ongoing deterioration of the feature, for example due to a leaking water main orother water-bearing utility pipe, or preferential ground water flow along a discontinuity or nonwaterbearing utility. An increase in moisture content will affect the electrical properties of thehost medium and should therefore be identifiable with certain electrical techniques.Voids can develop behind hard slope surface covers due to internal erosion by flowingwater or settlement of loose fill. The detection of a void may indicate a leaking water mainbehind the feature, or preferential ground water flow along a discontinuity, and may be a naturalprogression from a zone of elevated moisture content (Figure 3). Voids may produce significant

- 14 -contrasts in electrical, density or elastic properties that can be detected with certain geophysicaltechniques.3. PHASE 1 FTELD TRIALS3.1 I^trodi^ctionThe Phase 1 Field Trials were made at four sites by six geophysical contractors between5 December 1995 and 12 February 1996. Selection criteria for the four sites were: (i) theexistence of good quality ground investigation data, (ii) the features were typical to Hong Kong,(iii) ease of access and, (iv) located within the urban environment. This section briefly describesthe important aspects of each site, presents a summary of the results and the recommendationsfor the Phase 2 field trials. A detailed description of each site is presented in Interim Report No.2 (Koor, 1996). The locations of the trial sites are shown in Figure 1.3.2 Phase 1 Field Trial Sites3.2.1 Trial Site A - Kennedy Town Police Quarters. Feature No. 11SW-A/C256Site A is a north-west facing M L-shaped" soil cut slope (Plate 1) with both chunam andshotcrete surface protection located between Block A and Block B at Kennedy Town PoliceQuarters (Figure 4). The slope decreases in height from about 10.8m in the north-east to about8.2m in the south and is inclined to between 50° and 60°. A Im-wide berm runs at about midheightthroughout the full length of the slope. During the trials two wet areas existed along thesouth western half of a concrete platform at the crest of the slope (Figure 4 and Plate 1). Theywere caused by outflow from drainage pipes from Block A. Seepage from weepholes throughthe shotcrete was evident on the slope below these two areas (Figure 4). A transformer room islocated at the north eastern end of Block A (Figure 4). The geophysical trials were made alongfour traverses TA01 to TA04 which were chosen to coincide with existing borehole and chunamstrips, information from which is shown on Figure 4.A total of 7 drill holes and 3 chunam strips were excavated previously at the site between23 January and 12 February 1988 under Term Contract GC/85/02 (Bachy Soletanche, 1987 a ) andbetween 18 to 19 March 1988 under Term Contract GC/85/02 (Bachy Soletanche 1987 b ). Atypical geological section through the slope is shown in Figure 5, A layer of concrete 100mm to150mm thick covers the platform at the crest of the slope. Below the concrete slab is a layer offill L5m to 5.5m thick, A reinforced concrete layer between 200mm and 700mm thick wasencountered at the base of the fill in the north-east. A wedge of colluvium up to 3.5m thickunderlies the fill in the south western half of the slope. Tuff was encountered in varying states ofweathering below the fill and colluvium.3 - 2 -2 Trial Site B - Eliot Hall. Hong Kong University. Feature No. 11SW~A/R7O3Site B is a 6.4m high vertical, 100m long, east-west trending, dressed block retainingwall with horizontal tie beams (Plate 2). It is located between May Hall and Eliot Hall at theUniversity of Hong Kong, Pok Fu Lam (Figure 6). The retaining wall has a facing of bonded,

- 15 -squared fresh to slightly decomposed tuff blocks (typically 400mm by 350mm) with three,300mm-thick horizontal concrete beams equally spaced up the wall. Clay pipe weepholes,75mm in diameter are equally spaced up the wall. The wall is supported along its length byconcrete flying buttresses spaced at about 10m. The wall supports a 7m-wide building platformfor May Hall which is covered with a concrete slab in poor condition. The geophysical trialswere made along five traverses TB01 to TB05 located to coincide with existing drillhole,corehole and trial pits, information from which is shown on Figure 6.Three vertical drillholes, three horizontal and three inclined coreholes and three trial pitswere excavated at the site between 8 and 15 September 1993 under Term Contract GE/93/06(Vibro (H.K) Ltd, 1993). As shown in Figure 7, a fill layer 3m to 4m thick overlies 2m to 4m ofcolluvium, which in turn overlies completely decomposed tuff. The core of the wall is composedof cobbles and boulders of weathered tuff. The thickness of the wall increases from about L3mat the top to between 1.6m and 2.6m at the base of the wall.3.2.3 Trial Site C - Sir Ellis Kadoorie School Feature No. 11SE-A/R39Site C is a 7.5m to 8m high sub-vertical, 31.8m long, south-west facing, dressed blockretaining wall with horizontal tie beams (Plate 3). It is located behind the Sir Ellis KadoorieSchool (Figure 8). The wall is inclined at 65° to the horizontal and is faced with bonded, square(400mm by 380mm) slightly decomposed granite blocks. Three 200mm-thick concrete tiebeams run horizontally along the wall. Drainage through the wall is provided by six levels of80mm-diameter clay pipe weepholes. A 30° vegetated slope exists above the crest of the wall. A2.5m wide passage way separates the foot of the wall from the school building. The geophysicaltrials were made along three traverses located to coincide with existing drillhole and coreholesTC01 to TC03, information from which is shown on Figure 8.Two vertical and one sub-horizontal drillhole, one sub-horizontal corehole and two trialpits were excavated at the site between 30 October to 8 November 1995 under Term ContractGE/95/06 (Bachy Soletanche, 1995 a ). A section through the retaining wall is presented on Figure9. The ground behind the retaining wall comprises about 3.5m of. fill overlying completelydecomposed granite. The wall is about 2m wide at its base, thinning to about 0.5m wide at thetop.3.2.4 Trial Site D - Cape Collinson Crematorium. Feature No. 11SE-D/F19Site D is a 16m-high north-facing, fill slope with an average inclination of 37° (Plate 4).It is located on the northern side of the Cape Collinson Crematorium (Figure 10). At the crest ofthe slope is a 80m-long, 9m to 15m wide platform covered with grass and trees (Plate 5). Thesurface of the fill slope is covered with dense vegetation of mainly shrubs and small trees. Thesurface materials at the top half of the slope consist of very loose fill with an abundance ofbroken glass. The lower part of the slope surface is composed of cobble and boulder-sizedangular fragments of rock fill. Geophysical trials were made along two traverses TD01 andTD02 (Figure 10).

- 16 -A total of 4 drillholes and 15 trial pits have been excavated previously. Six trial pits tobetween 1.3m and 2.2m below ground level were excavated by on 11 and 12 May 1987 underContract 197 of 1985 (Gammon (Hong Kong) Ltd., 1987). Four drillholes to between 7.58m and12.3m and 9 trial pits to between 13m and 3.2m deep were excavated between 18 Novemberand 2 December 1995 under Term Contract GE/95/06 (Bachy Soletanche, 1995 ). The locationof existing ground investigation points are shown in Figure 10. A geological section is presentedin Figure 11. The fill attains a maximum thickness of 5.7m. It thins down-slope to 1m to 1.5m atdrill holes DH3 and DH4 and was absent in trial pit TP3. The fill is generally described as graveland cobbles of weak to moderately strong angular tuff. Down slope the colluvium appears to beabout lm thick in trial pits TP1 5 TP2 and TP3. The colluvium is underlain by moderately toslightly decomposed tuff.3.3 Phase 1 Results3.3.1 IntroductionThe Phase 1 field work was observed full time by personnel from Planning Division(GEO). Details of the contractors, including joint venture partners and key personnel,equipment, and breakdown of site works progress, are contained in Appendix C.All of the contractors experienced difficulty working on the fill slope at Site D due to theloose surface materials and the abundance of glass fragments in the fill on the upper portion.Prior to the commencement of the fieldtrials all visible glass fragments were removed. Howeversome buried glass fragments worked to the surface as the contractors moved about the slope,imposing some hazard to the field work. Therefore surveys were only carried out from woodenwalkways erected either side of the traverse from where they could be done in safety (Plate 4).Most contractors also found that the bamboo scaffolding erected for wall access tended tointerfere with the deployment of the large low-frequency GPR and EM antennas. In hindsight itwould have been better to provide moveable ladders rather than a fixed access.3.3.2 Assessment of ResultsThe assessment was based on field and environmental constraints, limitations intrinsic tothe method, degree of subjectivity in interpretation, and consistency of results among contractorsin comparison with the geotechnical information. The detailed assessment of each of thegeophysical methods tested is presented in Appendix D. Sections 3.3.3 to 3.3.10 summarise themain results from the Phase 1 fieldtrials.3.3.3 Shallow Seismic Reflection fSSR)The high-resolution seismic reflection method is relatively simple and quick to carry outin the field and has good penetration depth Sophisticated data processing is required tomanipulate the raw data. Interpretation appears subjective, resulting in inconsistent results.Ground roll, seismic refraction events, environmental noise and back scatter are the majorlimitations of the method. No useful data were obtained by any of the contractors using this

- 17 -method. The feasibility of using the reflection method for site characterisation in Hong Kong isdoubtful Further trials were not warranted.33.4 Spectral Analysis of Surface Waves (SASW)The SASW method was not adversely affected by noise during the site trials but depth ofpenetration and consistency of results was significantly reduced by site constraints, complexground conditions and voids below surface slabs. The depth of penetration was good wherespace permitted and resolution of 0.1m was achieved. There are some ambiguities andinconsistencies in the interpretations, especially with regard to the masonry wall traverses. Theusefiilness of the S ASW method to determine wall thickness was limited and this aspect was notpursued specifically in Phase 2. However, the technique has an advantage over many othergeophysical techniques because it measures shear wave velocity which can be related directly togeotechnical parameters. The technique was therefore tested further in Phase 2.3.3.5 Resistivity Imaging (RT)Generally consistent results were obtained despite the use of different electrodeconfigurations and equipment. The RI method is quick and only limited data processing isrequired to produce an apparent resistivity pseudosection. Further modelling is required toproduce true resistivity versus depth profiles. Along short traverses, the depth of penetration islimited to about 2m and data for the end portions of the traverse are difficult to obtain. Themethod can also be affected by the presence of metallic objects and electrical installations.Where a sufficiently long traverse allows, the technique has had some success in determiningelevated moisture zones and the geometry of retaining walls. This method was tested further inPhase 2.3.3.6 Self Potential (SP)The method has severe limitations due to the interference of metallic objects and hardsurface covering which prevent direct contact with the soil. None of the contractors managed toproduce any useful interpretations. Further trials of this technique were not warranted.3.3.7 Electromagnetic Methods (FDEM & TDEM)The frequency-domain electromagnetic (FDEM) method is quick and easy to apply andsurveys can be made by a single geophysicist Its major limitation is the large anomalies causedby surface and near-surface metallic objects. Surveys are made on a grid to produce isoconductivitymaps. None of the contractors produced any useful interpretations. However, atsites free from metallic interference, the method may still be useful as a quick reconnaissancetool to identify shallow conductivity contrasts such as air-filled voids. Further trials of thismethod were therefore made in Phase 2.

- 18 -The time-domain electromagnetic (TDEM) method using small coincident loop coilconfigurations is quick and requires one to two personnel to cany out a traverse. It has a goodpenetration range but the resolution is dependent on the sampling rate. The results suggest thatthe resolution was inadequate for the top 5m of the profile. The technique is also severelyaffected by near-surface metallic objects which produce large anomalies. No useful informationwas obtained by either of the contractors that practised the method in the field trials. Use of thismethod for site characterisation purposes in Hong Kong is not recommended unless thetechnology can be developed to allow higher resolution in the top 5m to 10m.33.8 Ground Penetrating Radar fGPR)Ground penetrating radar (GPR) surveys at all four sites could be made by two personnelin a few hours. The equipment is light and robust, especially the SIR 2 and pulseEKKO 1000systems. Large, low-frequency antennas were however difficult to manoeuvre along sub-verticaland vertical traverses by one person. Investigation depths of 10m were reported using the100MHz antenna. Resolution to 50mm was achieved with the 9Q0MHz and IGHz antennas. Themost significant noise resulted from surface metallic objects along the traverse, although airwave interference to the 100MHz antenna was noted at Site C by GA. The electromagnetic wavevelocity used by the contractors varied by as much as 50%. Uncertainty in determination of wavevelocity is the most significant limitation to the method since it affects the depth-to-reflectorcalculations. GPR produced some reasonably accurate images of concrete slab thickness, voidsbelow slabs, utilities and the thickness of retaining walls. The success of the technique doeshowever appear to be contractor-dependent. Better results were obtained when the contractorscarried out pre-data acquisition calibration. Different processing software used by differentcontractors, however, have produced highly variable radargrams for the same traverses. Thistechnique was tested further in Phase 2.33.9 Thermal Imaging (TI)The method is quick and easy to carry out by one person. Limited processing is required.There are constraints of time, location and weather which limit its applicability. The results fromBS and GA were ambiguous and not consistent. Further trials of this technique were notwarranted.33.10 OthersSeismic refraction was carried out by GA at all of the sites (see Appendix C). Thetechnique was successful at Site D along TD01 where a simple two-layer case was modelled.The results identified the top of weathered tuff within lm but could not differentiate between filland colluvium. The method is useful only when the sub-surface layers are relatively uniform andsub-parallel to the surface. In view of the generally non-uniform ground conditions in slopes andretaining walls in Hong Kong, further trials were not warranted.

- 19 -The sonic method in the form of PUNDIT testing of masonry blocks and concrete slabswas performed by BS. Seismic velocities were determined for some of the materials tested butotherwise this method was of little use and was not considered further.3.4 Phase 1 Conclusions and Recommendation^(a) Phase 1 field trials were successfully completed between 5 December 1995 and 12February 1996. The importance of selecting a competent contractor to carry out non-invasiveengineering geophysical surveys was demonstrated.(b) The results obtained by different contractors in some cases differed even when thesame equipment was used.(c) Based on observations of the fieldwork and the results, the geophysical techniqueswere divided into the three groups, with Groups 1 and 2 being tested further in Phase 2:Group 1. Techniques which produced some promising results andmay be applied widely to sites in Hong Kong. These areGround Penetrating Radar and Resistivity Imaging.Group 2. Techniques which could be severely affected by noiseand limited by characteristics inherent in the technique,but might be usefully applied at specific sites. These areElectromagnetic Conductivity (frequency domain) andSpectral Analysis of Surface Waves.Group 3. Techniques which did not provide any usefulinformation and did not warrant further consideration inthe Site Characterisation Study. These are HighResolution Seismic Reflection, Self Potential,Electromagnetic Conductivity (time domain) andThermal Imaging methods.4. PHASE 2 FIELD TRIALS4.1 IntroductionThe Phase 2 Field Trials were carried out by the five contractors at four sites between 1October and 1 November 1996. Preliminary interpretative reports based on the geophysicalresults were submitted to GEO in late November 1996. Each contractor then gave a presentationof their results to GEO in early December 1996. Ground investigation (GI) carried out under theGEO term contract at the four sites commenced on 11 December 1996 and was completed on 11January 1997. Factual reports on the GI were received in GEO on 4 February 1997 and weresubmitted to each of the geophysical contractors. Final interpretative reports based on the GIresults were submitted by all five contractors by June 1997. This section of the report brieflydescribes each site, presents the results of the preliminary interpretations and briefly describesthe GI results. Section 5.5 describes the comparisons between the preliminary interpretations and

- 20 -the GI data, final interpretations and conclusions made. Details of each of the contractors'personnel, techniques and equipment used are shown in Appendix C.4.2 Phase 2 Field Trial Sites4.2.1 IntroductionThe initial criterion for selection of the Phase 2 sites was that they should be currently inthe Landslide Preventive Measures (LPM) work programme with the GI planned for December1996. This was desirable for the following reasons: the geophysical results could be integratedinto the proposed ground investigation, a high density of GI points would be possible,topographic plans of the sites would be available and land matters and access would be easier toresolve. In the event, due to logistical reasons only one of the trial sites (Site G) was a pre-GILPM site. Two masonry walls, one cut slope and one loose fill slope were finally selected. Thetwo walls and the cut slope had no existing GI data. The fill slope (Site H) was included in theLPM 1995/96 Programme and had been investigated by Ove Arup and Partners underAgreement No. CE 45/94. Existing GI data therefore existed for the fill slope but were notreleased to the contractors prior to the geophysical field trials.4,2.2 Trial Site E - Wall North of Stubbs Villa off Stubbs Road - Wall No. 11SW-D/R208Site E is a 62m long dressed block masonry wall which reduces in height from llm inthe east to 0m in the west and is inclined at about 80° (Plate 6). It forms part of the retaining walland cut slope complex which supports the building platform for Stubbs Villa located to the southof the wall (Figure 12). At the toe and crest of the wall is a 3.5m to 4m wide ramp whichaccesses Stubbs Road to the east. The masonry wall facing is composed of bonded, square (450by 450mm), slightly decomposed granite blocks. The mortar bonding between each block was inpoor condition at the time of the trials, showing signs of spalling, erosion and weathering, andwas friable in places.The masonry wall has three, 300mm thick horizontal concrete tie beams at +38.2 lmPD,+41.12mPD and 444.24mPD. The upper and lower tie beams are pinched out by the top and toeof the wall (Figure 12). Two rows of clay pipe weepholes with an internal diameter of 85mmand an outside diameter of 100mm are located in between the tie beams (Figure 12). Probingshows that the weepholes are generally about 4m deep in the eastern half of the wall with a fewanomalous depths of 5m and above (Figure 12). The weephole depths reduce westwards to about3.3m and then 2.5m in the central portion of the wall. The weephole depths then increase furtherwest to greater than 5m close to the low end of the wall. Some of the weepholes showedevidence of persistent seepage such as algal growth around the hole and the build-up of calcitedeposits below the mouth (Figure 12).Several large trees grow at the top and part-way up the face, with aerial root systemscovering large sections of the wall A lOOmm-diameter Towngas pipe runs vertically up the faceof the wall and several manhole covers were located on the ramps (Figure 12).

- 21 -4.23 Trial Site F - Wall adjacent to Hollywood Road Police Quarters Block B - Wall No,11SW-A/R124Site F is a vertical 41m long tied rubble masonry wall between 3.5m and 5m high(Plate 7) located north east of the Hollywood Road Police Quarters Block B (Figure 13). At thebase of the wall is a playground and basket-ball court at a level of about +38.60mPD. A 5mwideconcrete covered platform at about +43.70mPD separates the wall from the quartersbuilding. A masonry stair case links the playground to the platform (Figure 13). The change inheight of the wall from 5m to 3.5m coincides with a reduction in the level at the top of the wallto 442.15mPD. The wall facing consists of irregular blocks of slightly decomposed granite andtuff. The individual blocks vary in length between 1m and 2m and are generally 0.5m to 0.75mwide. At certain levels in the wall there appear to be header blocks spaced horizontally at about1.5m which are more regular in shape and size at about 400mm square and are mostly composedof granite (Plate 8). These are probably long rectangular blocks which tie the wall together in asemi-systematic pattern as described by Chan (1996). The facing blocks are bonded with cementmortar which was in poor condition at the time of the trials and was seen to be missing in places,revealing voids within the wall.The wall has two levels of weepholes in the higher part (Figure 13). The weepholes arecomposed of clay pipe with an internal diameter of 85mm and a outside diameter of 100mm.The depths from weephole probing are shown on Figure 13 and range between 1.5m and 2.15m.The weepholes are inclined at about 17° to the horizontal. Several trees were growing along thetop of the wall and in one place the root system has lifted the granite coping (Figure 13). Alongthe outer edge of the coping is a 3m high chain link fence. A series of manholes are equallyspaced along the 5m wide platform at the top of the wall.4.2.4 Trial Site G - Cut Slope opposite to Lions Morning Hill School, Blue Pool Road - Part ofSlope No. 11SRC/C51Site G is a north-east facing, 20m high, 55° road-side cut soil slope (Plate 9) adjacent toBlue Pool Road (Figure 14). The slope is 40m wide at road level and has two 1.2m wide bermsat +144mPD and +149.5mPD. Blue Pool Road falls from south east to north west from about+140.6mPD to +136.1mPD along the length of the slope. The slope is covered with chunamwhich at the time of the trials was cracked and spalled in several places. Prior to the field trialsthe site had vegetation growing through the chunam mostly at the south eastern end. In thespalled areas the exposed slope forming material was extremely weak, medium-pinkish brown,coarse-grained completely decomposed granite. The slope is bounded to the south by a vegetatednatural slope. Surface drainage is provided by a series of 300mm U-channels along the toe andon each berm which feed into 300mm and 450mm wide stepped channel running along the northwestern boundary of the slope. A 250mm-wide inclined drainage channel with weepholes drainsinto the catch-pit at the base of the slope at the north-western end. A Towngas utility box islocated at the north western end of the slope on the first berm and a series of pipes run down theslope from the box into the pavement at the toe (Figure 14). A metallic pipe filled with concreteprotrudes from the lower slope at the south-eastern end (Figure 14). Further north-west of thepipe is a rock outcrop of moderately decomposed granite which protrudes through the chunam.

- 22 -4.2.5 Trial Site H - Fill Slope adjacent to Sze Yn House. Choi Wan Estate - Part of Fill SlopeNo. 11NE-A/F125Site H is situated in the north part of Choi Wan Estate, Kowloon. It is bounded by a smallplayground with a small carpark to the east, Clear Water Bay Road to the south, St. JosephPrimary School and a small shed to the west, and slope 11NE-A/F79 to the north (Figure 15).The slope has a maximum height of 7m, is 31m long and inclined at 26° (Plate 10). Prior to thefield trials the slope was thickly vegetated with trees and small shrubs. A metal fence runs alongthe crest of the slope separating it from the playground. A 900mm-wide concrete drainagechannel runs along the toe the slope and is covered by a concrete and cast iron grating over itsfull length. A 250mm U-channel is located at the crest of the slope. A twin 1650mm-diameterculvert and a 450mm diameter sewer pipe passes the slope to the east and are located about 6mto 7m below ground level (Figure 15).The slope was previously registered as slope 11NE-A/F125 for which there are two Stage1 Study Reports prepared in April 1993 and October 1994. Both reports characterise the featureas high consequence and further studies were required.The slope was investigated by Ove Arup and Partners under LPM Contract No. GE/96/05in August 1995. The results of the investigation are contained in the Stage 3 Study ReportS3R14/96 (Ove Arup and Partners, 1996). The ground investigation was carried out under GEOTerm Contract GE/93/1L It comprised two vertical boreholes, four trial pits and four GCOprobe holes. In situ density tests were also carried out in the trial pits to determine the fielddensity of the fill. The locations of the investigation points are shown on Figure 15 and theresults are contained in the contractors report (Bachy Soletanche, 1995 C ). The in situ density testsand laboratory compaction results indicate that the fill is generally loose, with the degree ofcompaction ranging between 49% to 83% with an average of 71%. The geology at the site isdescribed in Section 4.4 together with the more recent GI information.4.3 Field Trials4.3.1 IntroductionBased on the results and recommendations from the Phase 1 fieldtrials, GPR, RI, FDEMand SASW were evaluated further at the four sites described above. GPR and RI were tested atall four sites, FDEM at the two slope sites and SASW at the fill slope only. In order to allowcomparisons to be made between the contractors, predetermined traverses were selected at eachsite for testing the geophysical methods. The traverses are shown on Figures 12 to 15 inclusive.Extra traverse made by each of the contractors are described in their Final Interpretative Reports(see Section 6.).This Section summarises the conclusions from the preliminary Phase 2 field trial resultsbased on the suitability of each technique in terms of consistency of results, resolution, depth ofpenetration and the effects of noise. Typical radargrams, resistivity sections, iso-conductivitymaps and shear wave velocity profiles are presented and discussed in Appendix E, whichsupport the conclusions made in this section. Only selected results which best illustrate theconclusions are presented in Appendix E. For a full set of results the reader should consult thecontractors final interpretative reports.

- 23 -The GEO provided access at each sites. At the two wall sites, bamboo scaffolding waserected at 0.75m from the wall face to allow easy passage of the large GPR antennas up anddown the walls. At the cut slope, bamboo scaffolding was also used but major structuralelements had to be laid directly onto the slope surface to ensure stability. Although the grid was0.75m from the slope surface, the elements on the slope surface were a major obstacle to thesmooth running of the GPR antennas, especially for horizontal traverses. Vegetation growing outfrom the chunam was also removed prior to the trials. At the fill slope, vegetation clearance wasmade to provide a relatively un-obstructed slope surface apart from two groups of trees (Figure15). No other access was provided at the fill slope.The field trials were attended full time by GEO staff so that observations and recordscould be made of the works completed each day, the different methodologies and equipmentused, and any difficulties experienced by each contractor.4.3.2 Preliminary Field Trial ResultsBased on the results of the Preliminary Interpretative Reports the following conclusionswere made:(a) Many of the GPR radargrams produced by differentcontractors appeared not to show the same information.(b) The 100MHz GPR antenna appeared to be affected by airwave interference which limited its usefulness.(c) The 500MHz GPR antenna has a maximum two way traveltime of 50ns which effectively limits its penetration to amaximum depth of approximately 2.5m (based on a bulkelectromagnetic wave velocity of 0.1 m/ns).(d) Some of the contractors interpreted gain controlled artefactson the radargrams as reflectors.(e) The general forms of the inverted RI sections produced byeach contractor were generally consistent, but the details ofthese sections were variable. Such variations were due tosome extent to the different contouring packages used,(f) Several anomalies observed on the iso-conductivity maps forSites G and H were caused by surface metal artefacts such asthe Towngas pipes at Site G and the cast iron toe drainagegully at Site H.(g) Different processing methodologies were used by the threecontractors who presented SASW results in the PreliminaryInterpretative Report. Consequently no consistent results wereobtained for this method.

- 24 -4.4 Ground Investigation4,4.1 introductionGround investigations were carried out by Enpack (Hong Kong) Limited under ContractNo. GE/95/03. Full time site supervision of the GI was made by professional and trainee staff ofGEO. The ground investigation design was based on the contractors' preliminary interpretationsso that identified anomalies could be investigated. The investigation techniques used at each sitewere horizontal drillholes and trial pits at sites E and F, chunam strips and horizontal coreholesat site G and trial pits at site H. To ensure high quality core was recovered from the horizontaldrillholes, triple tube HMLC core barrels were used in conjunction with an air-foam flushingmedium. Generally good quality core was obtained with core recovery greater than 90% beingachieved.4.4.2 Trial Site EFour horizontal drillholes, one vertical drillhole and two trial pits were excavated at thesite at locations shown on Figure 12. Details of the drillhole and trial pit logs and core and trialpit photographs can be found in the contractors report (Enpack, 1997 a ) and are therefore notrepeated in this report.Interpreted cross-sections through the masonry wall based on the ground investigationdata are presented on Figures 16 and 17. The section lines coincide with the two predeterminedvertical wall traverses TE01 and TE02 (Figure 12) and are discussed below.The wall height at Section "IE - IE" is 9.5m. The wall is 0.95m wide at the top asexposed in TPE2. At about +45mPD the wall increases in thickness to 3.8m and to about 4.1mat +38.5mPD (Figure 16). Two lines of mass concrete haunching exposed in TPE2 coincide withservice manhole covers and appear to be sitting on-top of the wall. The granite foundation forthe upper retaining wall was also exposed in TPE2 and appears to sit directly on the wall,however this was not confirmed on site due to lack of space for excavation between the servicehaunching and the foundation blocks. The back face of the wall is approximately vertical, theincrease in thickness due to the inclination of the front face of the wall. The wall thickness of 4mestimated from the weephole probing agrees well with the GI results.The wall is composed of slightly decomposed cobbles and boulders of granite bondedtogether with an orangish brown to brown medium sand mortar. Some of the block interfaceshave an orangish brown weathering rind up to 5mm thick. The vertical drillhole (DHE1)encountered four layers of mass concrete within the wall. The upper three coincide with thehorizontal tie beams. The lower layer is 400mm thick and sits directly on completelydecomposed granite and is interpreted to be the wall foundation (Figure 16).The top and bottom tie beams appear to have been constructed perpendicular to the frontface of the wall and hence slope back into the wall, whilst the middle beam dips out of the wallat a shallow angle. At +43.4mPD a fragment of a weephole was encountered in drillhole DHE1-.This suggests that the weepholes at this level are inclined at about 20° to the horizontal dippingout of the wall. This does not agree with the probing results which indicated that the weepholes

- 25 -were essentially horizontal. This disparity could be due to the weephole fragment beingdisplaced within the core-run during the drilling or extraction process.The wall height at Section "2E - 2E" is 5.3m. The top of the wall is 0.68m wide asexposed in trial pit TPEL The wall section at "2E - 2E" is more complex than at "IE - IE" andappears to be a composite structure with the retaining wall above (Figure 17). The interpretationis that the wall is about 2.1m thick at about +42.0mPD and increases to about 2.5m thick at thetoe. The back face is approximately vertical, the increase in thickness being due to theinclination of the front face. The wall is composed of slightly decomposed cobble and bouldersof granite bonded together with a reddish brown and pinkish brown sand mortar. Behind theback face is a layer of fill which ranged from a sandy coarse angular gravel of strong granite indrillhole HDHE1 to a soft brown very sandy clay in drillhole HDHE2. This fill layer ranges inthickness between 0.8m and 1.5m. Behind the filled zone another layer of granite boulders andcobbles bonded together with pinkish brown mortar was encountered in both the drillholes. Thislayer is between 1.9m to 2.4m thick and is assumed to be part of the foundation of the upperwall The back face of the foundation is vertical, behind which is a 0.9m thick fill layercomposed of orange brown and pinkish brown mottled orange and white slightly clayey sand.Behind the fill, both drillholes encountered completely decomposed granite. The weepholeprobing confirm the composite nature of this section of the wall. Weepholes adjacent to thesection line are either 2.5m deep, i.e. extend to the back of the masonry wall, or are greater than5m deep and presumably extend through the masonry wall and the upper wall foundation anddrain ground water from behind the foundation.4.4.3 Trial Site FFour horizontal drillholes and two trial pits were excavated at locations shown on Figure13. Details of the drillhole and trial pit logs and core and trial pit photographs can be found inthe contractors report (Enpack, 1997 b ).An interpreted cross-section and horizontal section through the masonry wall ("IF - IF'and "2F - 2F") are presented on Figures 18 and 19 respectively. The section lines coincide withthe two predetermined vertical wall traverses TF01 and TF02 (Figure 13) and are discussedbelow.At section "Fl - Fl" the wall is 2.2m thick at the top as exposed in trial pit TPF1 andincreases in thickness to 3.15m. at about +4.5mPD. A stepped profile to the wall has beenassumed but a gradual increase in thickness of the wall below +41.5mPD could also be possibleas indicated by the double-dotted line on Figure 18. The upper part of the wall has a 0.2m thickfacing of dark grey fresh tuff. Behind the facing the wall is composed of grey honeycombedmass concrete, the aggregate consisting of strong angular granite gravel (drillhole HDHF2). Thelower part of the wall has a 0.4m thick facing of dark grey fresh tuff. Behind the facing is 0.22mof grey mass concrete, the rest of the wall being composed of cobbles and boulders of tuff andgranite at different grades of weathering. The matrix between the cobbles and boulders generallyconsists of silty fine to coarse sand (drillhole HDHF4), Both trial pits encountered an old drygranite sewer running parallel to the wall, see Figure 18 & 19. Orangish brown mass concreteencountered in drillhole HDHF2 has been interpreted as the mass concrete foundation to thesewer (Figure 18).

- 26 -Figure 19 shows the different wall thickness at different elevations. At +40mPD the wallranges between 3.15m to 33m thick along the 5m high section and reduces to 1.5m thick at the3m high section. The wall at this level appears to be composed of cobble and boulder sized rockblocks of tuff and granite at varying grades of decomposition. The backfill behind the wall atthis level is variable, ranging from a stiff reddish brown silt clay at drillhole HDHF1 to mixturesof gravel and soft clay a drillhole HDHF3 (Figure 18). The wall is about 2.1m thick at+41.5mPD along the 5m high section.Weephole probing at the site prior to the ground investigation indicated that the wall was2m thick in the area of the weepholes which corresponds well with the GI data (drillholeHDHF2).4.4.4 Trial Site GFour horizontal coreholes and four chunam strips were excavated at the locations shownon Figure 14. Details of the corehole and chunam strip logs and core photographs can be foundin the contractors' report (Enpack, 1997°).The chunam stripping and horizontal coreholes indicate that the cut slope is veryhomogeneous being composed almost entirely of extremely weak to very weak, reddish pinkishbrown, mottled black and white completely to highly decomposed, medium grained granite withclosely-to medium-spaced, smooth planar extremely narrow kaolin-and manganese infilledjoints (Plate 11). The western end of the lower slope is composed of a dense brown clayey siltysand fill with angular gravel Some zones of less weathered granite were noted especially alongthe lower part of the slope adjacent to the protruding corestone (Plate 12). Quartz veins up to30mm thick were also encountered (Plate 13). The slope above the upper berm is composedmostly of residual soil with zones of less weathered granite.4.4.5 Trial Site HFive trial pits were excavated at the locations shown on Figure 15. Details of the groundinvestigation including trial pit logs and photographs can be found in the contractors' report.A cross-section ("Hl-Hl") through the slope is shown on Figure 20. The fill is about8.3m thick at the crest of the slope and decreases to about lm thick at the toe. The fill overliescompletely decomposed granite. Generally the top lm to 2m of fill is a dense sand with angularrock, concrete and brick fragments up to boulder size. Below this fine-grained layer the fillbecomes loose and extremely variable with layers of tuff boulders, fence posts, chain link mesh,sand and soft to firm clay. Trial pits TPH1 to TPH1C all encountered mass or reinforcedconcrete at about +27mPD (Figure 20). In trial pit TPH1B the concrete layer was horizontal andappeared to be the remains of a floor slab. The ground water level measured in standpipepiezometers installed in drillholes VBH-1 and VBH-2 and as encountered in trial pit TPH2 wasat+24mPD.

- 27 -4.5 Comparison Of Preliminary Interpretation with Ground Investigation Data4.5.1 IntroductionFigures 21 to 23 summarise the preliminary interpretations made by each contractor at allfour sites and compares them with the preferred interpretations based on the GI data. Each figureis discussed in turn. A detailed assessment of the preliminary field trial interpretations withaccompanying results can be found in Appendix E.4.5.2 Trial Sites E and FSummary information for the two masonry wall sites is presented on Figure 21. The wallgeometry determined from the GI is presented along the left hand side of the figure.GSC and IGGE both interpreted the wall along traverse TE01 to be stepped, withincreases in wall thickness coinciding with each tie beam. This model appears to be based on apreconceived idea of what the wall should look like rather than from information obtained fromthe geophysical results. As shown in Appendix E, some of the boundaries between differentgeological or man-made materials have been determined from poor-quality data. GA suggestedthat the wall is 3m thick and that the back face is parallel to the front of the wall. The three zonesidentified by GA were not identifiable from the GI results. Also, the zones of enhanced moistureidentified by GA mainly from the RI results could not be confirmed from the GI (see AppendixE). FGS's interpretation suggested that the wall is only lm thick and shows some reflectors at2m, 6m and 9m in from the wall face. Most of these reflectors have been interpreted from GPRdata and are likely to be gain-controlled artefacts rather than true reflectors (see Appendix E). BSpresented data in the form of different zones of reflection coefficient and continuous reflectorsbased only on the GPR results with no interpretation of the wall geometry. The wall thicknesswas estimated to be 4m from the weephole probing. This is more accurate than any of thepreliminary geophysical interpretations and agrees well with the GI data.GSC assumed a stepped profile for the section along TE02 with the wall being 4m thickat the base, stepping to 2m thick above the tie beam. IGGE interpreted the wall as having a fairlyconstant thickness of 2m at the base, thinning to about 1.5m at the top. This agrees fairly wellwith the interpreted thickness of the wall from the GI information; however the composite natureof the structure was not identified. GA's interpretation the wall as being a constant 3m thick andcomposed of three zones does not agree with the GI data. FGS and BS's interpretations forTEO2 are similar to TE01. Weephole probing adjacent to TE02 gave variable results, with someweepholes being about 2.5m deep whilst others are greater than 5m deep. For this sectionweephole probing did not yield any better estimates of wall thickness than the geophysics.At Site F none of the contractors picked up the increase in base thickness of the wallfrom 2.1m to 3.2m at TF01 (Figure 21). GSC interpreted the wall as being 2m thick with fillbehind whilst IGGE suggested that the wall was lm thick with fill behind. GA interpreted thewall as 2m thick with a zone of decreased void content in the upper 3m. This zone of decrease invoids coincides well with the area of wall composed of mass concrete rather than boulders andcobbles of partially weathered rock (see Appendix E). The zone of stronger reflections in GA'sinterpretation also appears to coincide with the base of the dry sewer foundation. Both FGS andBS marked various reflectors without attaching any interpretation. For this interpretation, an

- 28 -estimate of wall thickness from weephole probing would have been as good as any of thegeophysical interpretations; however some of the interpretations did provide informationregarding the spatial distribution of voids within the wall which obviously could not bedetermined from weephole probing or conventional GI alone. Along the lower part of the wallthe GI confirmed the interpretations made by GA, BS, IGGE and GSC that the wall reduced inthickness to about 1.5m (Figure 19).In summary, the preliminary interpretations made by each of the contractors at the twowall sites are inconsistent, with interpreted wall thickness ranging from lm to 4m for TE01, 1mto 4m for TE02 and lm to 2m for TF03. At Site E the results from weephole probing todetermine wall thickness were better than or at least as good as the geophysics. At Site F theresults from weephole probing to determine wall thickness were as good as the geophysics butthe geophysics provided more information regarding the spatial distribution of voids within thewall.453 Trial Site GInterpretations from GPR radargrams constructed from data obtained using 500MHzantennas along TG03 at Site G are presented in the top three diagrams on Figure 22. A singlereflector parallel to the slope surface at 12ns is presented by IGGE. BS also present a singlereflector parallel to the slope surface at 9ns. They also show a series of discrete reflectors whichare interpreted as less weathered corestones within the weathered rock mass. GA also presentdiscrete reflectors interpreted as corestones, and possibly discontinuities. The location and depth(two-way travel time) of the discrete reflectors presented by BS and GA are not coincident.Interpretations made from radargrams produced using 100MHz and 35MHz antennas by GSCand FGS respectively are presented on the bottom two diagrams on Figure 21. It should be notedthat the two-way travel time axis is increased to 200ns for the 100MHz and 300ns for the35MHz antenna. Three reflectors parallel to the slope surface have been interpreted by GSCfrom the 100MHz data. The reflectors at 120ns and 200ns are both considered to be artefacts inthe data and not true reflectors. FGS present anomalous zones, discrete deep reflectors and acontinuous shallow reflector, all of which are considered to be artefacts in the data and not truereflectors.It is apparent from the data presented above that reflectors within the weathered rockmass identified on radargrams by each of the contractors at Site G are not consistent. It isconsidered that some of the contractors have interpreted artefacts as true reflectors.4.5.4 Trial Site HPreliminary interpretations made by each contractor along traverse THO1 are comparedto the GI information on Figure 23.. GSC, IGGE, GA and BS all show a boundary parallel to theslope surface at about lm, interpreted as the interface between fill and the underlying geology.However, from the GI data it appears that the interface is probably the boundary between densesand fill and underlying loose fill below. The zone of "no GPR penetration" identified by GAcoincides approximately with the large concrete boulder identified within the fill during the GI.

- 29 -4.6 Final InterpretationFinal interpretative reports based on the preliminary geophysical results and the GIinformation have been produced by all five contractors (Bachy Soletanche, 1997, FugroGeotechnical Services (HK) Ltd., 1997, Guandong South China EGTD, 1997, Institute ofGeophysical and Geochemical Exploration, 1997 and Golder Associates Inc., 1997). Eachcontractor was able to refine his preliminary interpretation to a certain extent. However, it isconsidered that no additional major conclusions (over and above those made from thepreliminary interpretative reports) into the usefulness of these methods for site characterisationin Hong Kong was gained from the final reports.5. CONCLUSIONS AND RECOMMENDATIONSThe main conclusions from Phases 1 and 2 of the Site Characterisation Study are:i) The overall quality of the raw data and interpretations variedsignificantly according to the expertise of the individualgeophysics teams.ii) Certain contractors were able to demonstrate that acombination of ground penetrating radar and resistivityimaging can determine the back of masonry walls if less than3m thick and locate zones of elevated moisture content andvoids with reasonable accuracy.iii) Limited success was achieved in determining the location ofcorestones and the thickness of loose fill at the two Phase 2slope sites.It is recommended that:(a) Due to the inconsistent raw data and interpretations it wouldnot be advisable at present to let a term contract specificallyfor non-invasive geophysical techniques for the determinationof masonry wall thickness in Hong Kong, or to require the useof such techniques in LPM studies of walls.(b) Further trials at present of the four selected methods (namelyground penetrating radar, resistivity imaging, electromagneticconductivity and spectral analysis of surface waves) or othergeophysical methods are not warranted.(c) Since some of the results were encouraging it isrecommended that further research on developing GPR andRI for masonry wall investigations is carried out through alocal university with support from GEO. The research workshould focus on ways to enhance the resolution of the two

- 30 -techniques and also to develop a site and data processingmethodology which would ensure more consistent resultsfrom different contractors. Also, local expertise in the twomethods could be developed in this way.6. REFERENCESBachy Soletanche (1987 a ) E.D.D. Term Contract No. GC/85/02 - Works Order No.PW7/2/13.176. Site Investigation - LPM Programme - Slope No, 11SW-A/C256Kennedy Town Police Quarters.Bachy Soletanche (1987 b ) EJD.D. Term Contract No. GC/85/02 - Works Order No.PW7/2/19.111. Site Investigation - LPM Programme - Slope No, 11SW-A/C105Kennedy Town Police Quarters.Bachy Soletanche (1995 a ) Contract No. GE/95/06 - W.O.No.GE/95/06.4 - Feature No. 11SE-AR39 & .11SE-A/C136, Happy Valley, So Kon Po. Ground Investigation FactualField work Report.Bachy Soletanche (1995 b ) Contract No. GE/95/06 - W.O.No.GE/95/06.21 - AgreementNo.CE9/95 -Feature No. 11SE-D/F19. Chai Wan Ground Investigation FactualFieldwork Report.Bachy Soletanche Ltd. (1995°). Ground Investigation Factual Fieldwork Report - Final Report.Contract No. GE/93/11, W.O. No. GE/93/11SA.100, Feature No. 11NE-A/F125, ChoiWan Estate.Bachy Soletanche Ltd (1997) Site Characterisation Study Phase n Field Trials EngineeringGeophysical Methods Final ReportChan, Y.C. (1996). Study of Old Masonry Retaining Walls in Hong Kong. GEO Report No.31,225p.Enpack (1997 a ). Ground Investigation Final Field Work Report, Contract No. GE/95/03, WorksOrder No. GE/95/03.68, Site Characterisation Study Geophysical Field Trials - Phase 2,Wall North of Stubbs Villa, off Stubbs Road.Enpack (1997 b ). Ground Investigation Final Field Work Report, Contract No. GE/95/03, WorksOrder No. GE/95/03.68A, Site Characterisation Study Geophysical Field Trials - Phase 2,Wall near to Police Quarters Block B, Hollywood Road.Enpack (1997 C ). Ground Investigation Final Field Work Report 3 Contract No. GE/95/03, WorksOrder No. GE/95/03.68C, Site Characterisation Study Geophysical Field Trials - Phase 2,Cut Slope Opposite to Lions Morninghill School.

- 31 -Enpack (1997 d ). Ground Investigation Final Field Work Report. Contract No. GE/95/03, WorksOrder No. GE/95/03.68C, Site Characterisation Study Geophysical Field Trials - Phase 2,Fill Slope adjacent to Sze Yu House Choi Wan Estate.Fugro Geotechnical Services (HK) Ltd. (1997). Final Interpretative Report Site CharacterisationStudy Non-invasive Engineering Geophysical Field Trials Phase H. 4 vols.Gammon (Hong Kong) Limited (1987) Job No.258 - Hong Kong Housing Authority - ContractNo. 197 of 1985 - Site Formation and Associated Works for Chai Wan "C Trial Pitsnear Cape Collinson Crematorium. Final Site Investigation Report. Dated May 1987.Golder Associates Inc. (1997) Final Interpretative Report to Government Engineering Office ofHong Kong Site Characterisation Study Non-invasive Field Trials Phase II Field TrialsHong Kong.Guandong South China EGTDC (1997) Site Characterisation Study Phase 2 Field TrialsEngineering Geophysical Methods Final Interpretative Report of GPR, SASW and RI onSite "E", "F\ "G" and "H".Hong Kong Government (1994). Report on the Kwun Lung Lau Landslide of 23 July 1994.Geotechnical Engineering Office, Civil Engineering Department, 2 volumes.Institute of Geophysical and Geochemical Exploration (1997). Site Characterisation Study Phase2 Field Trials Engineering Geophysical Methods Civil Engineering DepartmentGovernment of Hong Kong Final Interpretative Report on Engineering GeophysicalMethods.Jukes, A.W., Wong, C. and Ifran, T.Y. (1986). Stage 1 Studies Procedures Manual for RetainingWalls, Administrative Report AR 4/86. Geotechnical Control Office, Hong Kong, p 54.Koor, N.P. (1996) A Review of Non-Invasive Engineering Geophysical Techniques for SiteCharacterisation in Hong Kong. Interim Report No.L Planning Division, GeotechnicalEngineering Office, Civil Engineering Department, Hong Kong Government, p 36.Massey J.B., and Pang P.L.R. (1988) Stability of slopes and excavations in tropical soils(General Report). Proceedings of the Second International Conference on Geomechanicsin Tropical Soils. Singapore, vol 2, pp551-570.Ove Arup and Partners (1996). Slope 11NE-A/F125 Choi Wan Estate. Stage 3 Study ReportS3R14/96, Geotechnical Engineering Office, 13pp, 9 Figures, 2 Plates, 7 Appendices and3 Drawings.Shelton, J.C. (1980). Report on Study of Old Masonry Retaining Walls. GCO Internal Report, p26.Vibro (H.K.) Limited (1993) Ground Investigation Report by Vihro (RK) Limited - ContractNo. GE/93/06 - Works Order No. GCM2/A2/4~93.11 - Slope No. 11SW-A/7O3 - EliotHalL Universitv Drive.

- 32 -TIST OF FIGURESFigureNo.PageNo -1 Site Characterisation Study Phases 1 and 2 Field Trial Sites 342 Typical Forms of Construction of Masonry Walls 35[Adapted from Jukes et al (1986) and Chan (1996)]3 Sketch Showing the Slow Deterioration of a Slope due to 36Leaking Water Main4 Trial Site A - Plan 375 Trial Site A - Section TA01 386 Trial Site B-Plan 397 Trial Site B - Section TB01 408 Trial Site C - Plan 419 Trial Site C - Section TC01 4210 Trial Site D - Plan 4311 Trial Site D - Section TD02 4412 Trial Site E - Plan and Elevation 4513 Trial Site F - Plan and Elevation 4614 Trial Site G - Site Plan 4715 Trial Site H - Plan 4816 Trial Site E - Section "IE - IE" 4917 Trial Site E-Section "2E-2E" 5018 Trial Site F - Section "IF - IF" 5119 Trial Site F - Horizontal Section through Masonry Wall at 52Hollywood Road Police Quarters20 Trial Site H-Section "1H-1H" 53

- 33 -FigureNo.PageNo.21 Comparison of Masonry Wall Interpretations made at Sites E 54and F with only Geophysical Information22 Comparison of GPR Interpretations for Traverse TG03 5523 Comparison of Interpretations for Traverse THOl 56

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- 57 -LIST OF PLATRSPlateNo.PageNo.1 Trial Site A - View looking south west at shotcreted section 58of slope. Note zones of seepage from weepholes adjacentto the access ladder.2 Trial Site B - View looking west at dressed masonry wall 59with horizontal tie beams picked out in white.3 Trial Site C - View looking north west along dressed 60masonry wall.4 Trial Site D - View looking north east down slope along 60traverse TD02. Note access ladders either side of traverse.5 Trial Site D - View looking north east along traverse TD01 61located on the fill platform at the top of the slope.6 Trial Site E - View looking east towards Stubbs Road from 61the lower end of the dressed masonry wall.7 Trial Site F - View from playground of tied random rubble 62wall.8 Trial Site F - Granite headers in tied masonry wall. 639 Trial Site G - View of cut slope looking south east. Note 64single corestone protruding from slope face close to whitemotor car.10 Trial Site H - View looking south east at fill slope. 6511 Highly decomposed granite with kaolin and manganese in-filled 66joints exposed in chunam strip CSG4 at Site G.12 Corestone of moderately decomposed granite exposed along 67chunam strip CSG1 at Site G.13 Thin quartz vein within completely decomposed granite 68along chunam strip CSG1 at Site G.

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- 69 -APPENDIX ASITE CHARACTERISATION STUDYPROJECT BRIEF

- 70 -CONTENTSCONTENTS 70A.1 OBJECTIVE 71A.2 BACKGROUND 71A.3 CURRENT METHODS OF CHARACTERISING SLOPES AND WALLS 71A.4 EXISTING INVESTIGATION METHODS USED IN HONG KONG AND 72POSSIBLE IMPROVEMENTSA.5 POSSIBLE NEW METHODS 73A.6 PROCUREMENT OPTIONS 74A.7 INFORMATION SOURCES 74A.8 PRELIMINARY THOUGHTS ON FIELD TRIALS 75A.9 PROJECT MANAGEMENT 75A. 10 RESOURCES 76A. 11 OUTLINE PROGRAMME 76PageNo.A.12 REFERENCES 76

- 71 -A.I OBJECTIVETo assess the capability of new investigation methods, or enhanced existing methods,in order to obtain better information on the geometry of old retaining walls and groundconditions behind slopes and walls.A.2 BACKGROUNDOne of the recommendations in Volume 1 of the Report on the Kwun Lung LauLandslide of 23 July 1994 (Hong Kong Government, 1994) was :"The GEO should undertake and support elsewhere in HongKong research into improved means of site characterisationfocused on the factors that affect slope instability in Hong Kong.The Writer does not think that the development of slope warningsystems for the conditions found in Hong Kong is promising.The critical features are small and numerous and instability oftendevelops in an abrupt manner. However, there are a number ofnew developments in geophysics such as radar and non-contactresistivity that might be found useful in discovering subsurfacedefects and enhanced moisture zones."The opinion on slope warning systems given above is supported. It is not proposed toconsider such methods further.Research should be aimed at identifying improvements to existing ground investigationtechniques used in Hong Kong and the testing of newly-developed techniques. There are twomain areas of application, viz. (a) improved means of assessing the geometry of retainingwalls and related structures (e.g. hard slope surfaces, masonry and other facings) and (b) betterunderstanding of ground conditions behind slopes and walls, with emphasis on how theground may deteriorate with time through sub-surface erosion, weathering, saturation orvolume change.Given the large numbers of old slopes and walls in Hong Kong, and the difficultground access in many cases, new or improved existing investigation methods should ideallybe quick to apply and easily transportable. Indirect non-contact and non-intrusive methodsbased on remote measurements or soundings are the most attractive; however any results fromsuch methods should be readily interpretable by non-specialist geotechnical engineers.A3 CURRENT METHODS OF CHARACTERISING ST ,O?ES AND WALLS"Site characterisation" for the purpose of this project is interpreted as meaning all thework done in investigating, describing and classifying the condition of retaining walls and theground behind slopes and walls. The traditional means of characterising sites in Hong Kongis well established in Geoguides 2 and 3 (GCO, 1987; 1988). It usually consists of four mainsteps:

- 72 -(a) Desk study, including aerial photograph interpretation,inspection of old maps, plans, drawings and existing recordsof ground investigations on the site or adjacent sites.(b) Site inspection/reconnaissance, involving a walkover of thesite and its surroundings and gathering information onrelevant surface features.(c) Ground investigation, including some or all of geologicalmapping, geophysical survey, drilling or boring, trial pitting,sampling, in situ testing and laboratory testing.(d) Reporting, to cover preparation of field reports, maps, plans,and borehole logs, interpretation of data obtained andpreparation of final site investigation report.In the context of the KLL landslide, where there were no obvious signs of surfacedistress prior to failure, and other recommendations in the KLL Landslide Report whichaddress integration of information from surrounding sites, it is not proposed to undertakeresearch for this project under (a) and (b) above. Research should be devoted to methods ofground investigation (item (c) above). Following on from Section 2 above, it is proposed thatthe research be concentrated on geophysical survey methods, but other methods may also beexamined.A.4 EXISTING INVESTIGATION METHODS USED IN HONG KONG AND POSSIBLEIMPROVEMENTSOne of the main difficulties in the investigation of old masonry walls is to determinethe wall thickness. The conventional methods used in Hong Kong and their weaknesses are:. Method . • Weaknesses(a) Approved building plans, records(b) Probing weepholes(c) Coring through wall(d) Horizontal drillingSome have been found to be unreliableWeepholes often blocked by rabbish ordebrisPoor sample recovered due to single tubedrillingExpensive, and mobilisation difficultIn view of the demonstrated unreliability of some approved building plans, research isneeded into ways of improving the other techniques.The usual practice of weephole probing should be--reviewed. Initial ideas forimprovement are to require weepholes to be cleared of debris and rubbish before probing, and

- 73 -to take a driven sample at the end of some holes to ensure they are cleared and to determinethe geological materials behind the wall. In the longer term, other improvements might befeasible through liaison with ground investigation equipment manufacturers, such as :(a) developing remote-control downhole viewers to examine theinsides of weepholes,(b) improving core recovery technique in coreholes, and(c) reducing the rig size for drilling short horizontal holesthrough masonry walls in Hong Kong's congestedconditions.A.5 POSSIBLE NEW METHODSWhile conventional drilling and other field test techniques are well-established in HongKong, engineering geophysical methods are not commonly used for investigation of slopesand retaining structures. At present, seismic refraction is the only popular on-landgeophysical method. Ground radar, cross-hole seismic tomography, electromagnetictomography and well-logging techniques have been tested in a few projects but with limitedsuccess and little reporting in the technical literature.The application of modern engineering geophysics to Hong Kong conditions should befurther explored. In view of rapid recent developments in geophysical equipment, datalogging and limits of resolution, a detailed literature review is warranted as the first step.The next stage is likely to be field trials of some non-contact methods aimed at rapidcoverage of whole slopes and structures, with a view to identifying anomalies such as voids,zones of increased moisture and materials of relatively low strength or stiffness. Based on aninitial literature review and discussions, the following techniques are likely to be worthpursuing:(a) Ground radar.This provides a record of continuous electromagneticsubsurface probing. The technique may be useful indetecting cavities, identifying buried services andgroundwater tables, and determining the thickness ofretaining walls. Initial trials carried out in GEO in 1991-2were generally unsuccessful in identifying variations in soiland rock materials. Further trials are warranted.(b) Relative ground resistivity survey.This is a rapidly-applied non-contact technique based oncurrent induction using portable equipment. It has beenfound effective elsewhere in detecting cavities, groundwaterand subsurface profiles.

- 74 -Other techniques which may warrant further study and possibly trials are time domainreflectometry (TDR) and spectral analysis of surface waves (SASW). Consideration will alsobe given to density and magnetic methods, and to relatively new insertion techniques, such asthe seismic cone penetration test, although the initial view is that such methods are likely to beless attractive due to difficult access, variable penetrability of decomposed igneous rocks andcolluvium, etc.One of the important findings in the Kwun Lung Lau failure investigation was thepresence of groundwater flow pathways into the landslide site. Research into the use oftracing methods to identify groundwater flow lines will also be considered.A.6 PROCUREMENT OPTIONSThe main options are :(a) In-house research by GEO using existing groundinvestigation and geophysical term contractors and/or otherspecialist contractors by invitation.(b) Funded external research by a local consultant or tertiaryinstitution employing their own contractors, with overallmanagement by GEO.The project cannot be specified precisely at the outset. The research is best done inseveral phases, involving field trials of techniques with a review of findings before proceedingto the next phase.Option (a) is preferable in order to preserve flexibility, but option (b) may be moreexpedient if adequate GEO professional staff resources are not identified. Both options willbe fully explored.A.7 INFORMATION SOURCESA full review of previous trials of novel investigation techniques carried out in HongKong by or on behalf of GEO will be conducted and a written summary provided. Initialsuggestions for other literature to be reviewed are as follows : Geological Society EngineeringGroup Working Party (1988), Proceedings of the Annual Symposia on the Application ofGeophysics to Engineering & Environmental Problems (SAGEEP 1-6, 1989-1994),Proceedings of the Waterloo Conference on Ground Penetrating Radar (GPR 1994) andWoods (1994).'

- 75 -A.8 PRELIMINARY THOUGHTS ON FIELD TRTAT SAn initial phase of field trials should be set up in two stages :(a) The first stage should be on sites where a detailed, highqualityground investigation (GI) has already been carriedout. The GI results will form the basis for correlation withnon-contact geophysical survey results. Contractors will begiven access to the existing GI records. This will assist themin calibrating their equipment and appreciating local groundconditions.(b) The second stage will involve trials carried out as properlycontrolledresearch experiments using "class A" predictionwherever practicable, i.e. the contractor undertaking thenon-contact survey, and any other party assisting ininterpretation of the results, should have no prior knowledgeof ground conditions behind the structure or slope underinvestigation. This may be difficult to achieve in practice,but could be feasible if suitable sites with minimal previousinvestigation records can be identified. In this situation theGEO would arrange independent conventional GI, forcorrelation with the results of non-contact methods, eitherconcurrently or shortly after the work done by thegeophysical contractor. Alternatively, sites alreadyinvestigated by detailed conventional GI would be used butthe results would not be made available to the geophysicalcontractor.An additional option to be considered, although more complicated and timeconsuming,is to modify an existing site by deliberately forming anomalies such as voids andweak zones near the surface of the slope or structure and then reinstate the surface prior togeophysical survey. Minor site formation works by another contractor will be required. Thismay prove difficult to arrange in respect of lands matters and safety aspects.Further phases of fieldwork would only be contemplated if the first phase producespromising results.A.9 PROJECT MANAGEMENTOverall management of the project will be through a small working party chaired byGGE/Development, with representatives from the Planning Division, Special Projects andMaterials Divisions of GEO. CGE/Planning is the proposed project manager.

- 76 -A.1G RESOURCESThe preliminary estimate for professional staff resources is 6 man-months of GE inputspread over the full study period, assisted by a TO(G) for an equivalent period. SGE/EG willoversee the day-to-day running of the project. Regular liaison with Materials Division staff onemployment of contractors is anticipated.Approval will be sought to fund the research from existing GEO R&D funds under theCapital Account, or from the Landslip Preventive Measures Block Vote. If existing fundscannot be identified, a request will be made to the Finance Branch for new funds. The finalexpenditure will depend on the scope of field trials attempted. $2-3M should be sufficient forthe first phase.A.11 OITTLINE PROGRAMMEIt is estimated the project will be completed within 12-18 months. The literaturereview will be carried out within the first two months. Consultant selection, if required, wouldneed a minimum of three months. The time for site selection and arranging the first fieldtrials, including resolving lands/access matters, will be of a similar order.A.12 REFERENCESGeological Society Engineering Group Party (1988). Engineering Geophysics. QuarterlyJournal of Engineering Geology. Vol. 21, pp 207-271.GPR (1994). Proceedings of the Fifth International Conference on Ground Penetrating Rady.Waterloo, Canada, June 1994.Hong Kong Government (1994). Report on the Kwun Lung Lau Landslide of 23 July,,,.1994.Geotechnical Engineering Office, Civil Engineering Department, 2 volumes.SAGEEP 1-6 (1989-1994). Proceedings of the Symposia on the Application of Geophysics toEngineering and Environmental Problems. Organised by the Environmental andEngineering Geophysical Society (EEGS), Denver, Colorado, USA.Woods, R.D. (Editor) (1994). Geophysical Characterisation of Sitfts. Volume prepared byISSMFE Technical Committee 10 for Xm ICSMFE, 1994, New Delhi, India, 14ip.

- 77 -APPENDIX BGEOPHYSICS LITERATURE REVIEW

- 78 -CONTENTSPageNo.CONTENTS78B.I LAND-BASED ENGINEERING GEOPHYSICS PRACTICE IN 80HONG KONGB.I.I GeneralB.1.2 Seismic Refraction 80B.I.3 Cross-Hole Seismic Survey 80B.I.4 Gravity Surveys 81B.I.5 Resistivity Survey 81B. 1.6 Previous Engineering Geophysics Trials by GEO 81B. 1.6.1 Ground Penetrating Radar 81B. 1.6.2 Geophysical Borehole Logging Trial 82B. 1.63 Thermography 82B. 1.6.4 Seismic Survey of Wall Thickness 83B. 1.6.5 Magnetometer and Gravity Survey Trials 83B.2 INTERNATIONAL ENGINEERING GEOPHYSICS PRACTICE 83B.2.1 Introduction 83B.2.2 The Seismic Method 84B.2.2.1 Shallow Seismic Reflection 84B.2.2.2 Seismic Refraction Method 84B.2.2.3 Surface Wave Methods 84B.2.3 Electrical 85B.2.3.1 Electrical Resistivity Surveying 85B.2.3.2 Self Potential Method 86B.2.4 ElectromagneticB.2.4.1 Introduction 86B.2.4.2 Frequency-Domain Electromagnetics 87B..2.4.3 Time-Domain Electromagnetics 88B.2.5 Ground Penetrating Radar (GPR)B.2.5.1 Introduction80ggggoc

- 79 -B.2.5.2 Case Histories 89B.2.5.3 Applications in Hong Kong 89B.3 CONCLUSIONS 90B.4 RECOMMENDATIONS 90B.5 REFERENCES 91B.5.1 References Cited in the Text 91B.5.2 Other References Reviewed 96LIST OF TABLES 104LIST OF FIGURES 110PageNo.

- 80 -B.I T ,AND-RASED ENGINEERING GEOPHYSICa^EACIICEJN HONG KONGB.I.IGeneralA summary of all land-based geophysics made for the Geotechnical Engineering Office(GEO) since 1987 is presented in Table BL This list broadly represents engineering geophysicspractice in Hong Kong in both the private and public sectors. Electronic and GeophysicalServices (EGS) has been the GEO term geophysical contractor exclusively since 1987, apartfrom a brief period in 1993 when the term contract was awarded to Geoteam (HK) Ltd but waslater novated to EGS.The land-based techniques carried out for GEO have generally been limited to seismicrefraction, gravity and resistivity surveys. Seismic tomography has been attempted at two sites inHong Kong. Information obtained from the EGS data base, which extends back to 1973indicates that pre-1987 land geophysics for both public and private clients was limited to seismicsurveys. This is similar to the practice up to the early 1980s described by Ridley-Thomas (1982).Several trials of the more modern invasive and non-invasive techniques such as groundpenetrating radar (GPR), geophysical borehole logging, thermography, seismic reflection,magnetometer and gravity surveys have been made by GEO over the past few years (see SectionB.I.6.).B.1.2 Seismic RefractionSeismic refraction surveys in Hong Kong are generally made to assist in selection anddevelopment of land borrow areas. The depth of weathering and P-wave velocity are the mainsite characteristics for which seismic refraction has been utilised. Twelve, and more recently 24channel seismographs are used for data acquisition. The most commonly-used energy source is a8kg sledge hammer and plate; however, from 1991 onwards explosives have been used. In wetground conditions a Buffalo gun is used as the energy source.Unsatisfactory results due to low signal to noise ratios are common in Hong Kong. Thisis mainly due to environmental noise and the low energy source. This problem has beenovercome by the use of explosives as the energy source and carrying out the surveys at nightwhen the environmental noise is low. Another limitation is the complex weathering profilewhich commonly exists in Hong Kong. This makes interpretation of the refraction data difficultif a simple, planar, non-dipping, layer cake model with linearly-increasing velocity with depth isassumed in the analysis. The simple intercept-time methods of analysis generally used are notvalid in such complex geological situations.B.I.3 Cross-Hole Seismic SurveyCross-hole seismic investigations have been made at two sites in Hong Kong forengineering purposes. They were used in an attempt to delineate fault or shear zones at the TsingMa Bridge tunnel anchorage's and to map caverns within buried marble below a housingdevelopment site in Ma On Shan, Area 90.

- 81 -Acoustic P-wave velocity measurements were made between three boreholes usingEG&G ES 2401, 24-channel seismographs, 24-element hydrophone streamers and a BOLT 2000psi borehole airgun at the Tsing Ma Bridge anchor site. Tomographic construction was made onthe p-wave velocity data using a Perkin Elmer 3212 and a ICC DRS 6000 mini main-framecomputer. Poor results were obtained due to low signal to noise ratios (blamed mainly on highenvironmental noise despite the surveys being done at night) and poor grouting of the plasticliners into the boreholes. To overcome the environmental noise problem, the seismographs werefitted with variable high cut, low cut and notch filters so that the gain of the individual tracescould be increased or decreased. The results were still less than satisfactory.A cross-hole seismic survey was made in 118 borehole pairs at the Ma On Shan housingproject using the same equipment as at the Tsing Ma Bridge anchor site. The survey was alsocarried out at night. Several low velocity zones were detected, and were interpreted as cavitieswithin the marble which would tend to cause dispersion, attenuation and delay to the P-waves.The low velocity zones were not investigated using physical techniques; therefore the accuracyof the seismic survey could not be verified.B.I.4 Gravity SurveysGravity surveys have been carried out for the Hong Kong Geological Survey of the GEOwith the aim to produce a Bouguer Anomaly Map of Hong Kong. The final survey was carriedout by EGS in conjunction with the British Geological Survey (BGS) in 1990-91. Evans (1990)reports that four new gravity base stations were established in Hong Kong by BGS for theregional gravity survey.B.1.5 Resistivity SurveySimple applications of resistivity surveys to determine the soil corrosivity have beenmade in connection with water supply pipelines. The Wenner electrode configuration isgenerally used with stainless steel electrodes.B.I.6 Previous Engineering Geophysics Trials by GEOB.1.6.1 Ground Penetrating RadarA ground penetrating radar (GPR) trial was made in August and September 1991. Theobjective was to determine the effectiveness of GPR in Hong Kong in the detection ofcorestones, weathering interfaces to 20m, retaining wall thickness and location of services. Thetrial was made by EGS who sub-contracted the works to a Canadian geophysical companymulti-VTEW Geoservices Incorporated. The GPR used was the pulseEKKOTV Radar of Sensors& Software (Canada) using 50,100 and 200MHz antennas.Nine sites were surveyed. The general conclusions were that the maximum penetrationobtainable, regardless of frequency of the antennas, was about 10m, The location of corestoneswithin a slope could be postulated, however their presence was not confirmed by subsequentphysical exploration. Two reinforced concrete walls were tested but the determination of wall

- 82 -thickness was not successful, It should be noted that reinforcement bars can completely attenuateelectromagnetic waves, thus resulting in no reflections beyond the bars embedded in theconcrete. The GPR had limited success in locating near-surface utilities, including water-bearingpipes.A GPR demonstration was made for GEO in December 1994 by Forest EngineeringGeophysics Exploration Co., in conjunction with the Chinese Academy of Geoexploration, at anLPM site being investigated by the Design Division of GEO. The purpose of the test was todetermine the thickness of a thin masonry retaining wall (feature no. 8SW-C/R1) behind avillage house in Sai Kung. The radar equipment used in the demonstration was the SIR Systems10A manufactured by Geophysics Survey System Inc. A 500MHz antenna was used in both thepulse and continuous profiling mode. Five vertical and two horizontal traverses were made at thesite. The thickness of the retaining wall in question was determined to be between 0.35m and0.50m thick using GPR. This correlated well with corehole information.B.l.6.2 Geophysical Borehole Logging TrialA trial was made in December 1989 in the Yuen Long Scheduled Area of Hong Kong toevaluate whether geophysical borehole logging techniques could help in the interpretation of thecomplex geology which consists of marble, meta-sediments and metamorphosed volcanic rockintruded by granites. EGS carried out the trial for the Geotechnical Control Office using an EG& G Mount Sopris Model H logging system. Three techniques were used, namely naturalgamma, self potential and single point resistivity, all housed in a single probe. The naturalgamma technique measures the natural radioactivity of the rock mass and is traditionally used inoil exploration to determine the percentage shale content. As the probe measures naturalradiation it can be used in cased boreholes. The self potential and single-point resistivitymethods measure the natural potential resistivity between the logging tool and an electrode at theground surface. Self potential is sensitive to fluid flow that produces electrical currents in theground and hence can be used to detect open fissures or permeable zones. Resistivity is sensitiveto changes in moisture content and clay content and can be used to detect permeable zones, rockquality and formation fluid.Twenty boreholes were logged; however no additional information, other than that whichcould be gained from the borehole logs themselves, was obtained from the trials*B.l.6.3 ThermographyA thermography demonstration was made by Materials Laboratory for the DesignDivision of GEO in September and October 1993. The objective was to demonstrate whetherthermography would be able to detect voids and ground water behind hard slope surfacecoverings in Hong Kong. There is no report on the trials, however notes from a meeting todiscuss the trials indicate that the technique was unsuccessful Two slopes (one a cut slope andone a fill slope) and one wall were investigated. The main points of the note state that thetechnique did not work on the vegetated fill slope and there was insufficient space available infront of the wall to obtain a clear thermographic image of the feature. Thermographic images of

- 83 -a cut slope were successfully made in Siu Sai Wan. "Hot" and "cold" areas were identified butno interpretation was made because no physical data were available.B. 1.6.4 Seismic Survey of WallShelton (1980) and Chan (1982) (see Section 6.) both refer to a field demonstration of aseismic method for the determination of wall thickness made by Integrity Testing Services. Theseismic reflection method was used but was unsuccessful due to the seismic velocity variation inthe different wall components not being accurately quantified.B.l.6.5 Magnetometer and Gravity Survey TrialsBoth magnetic and gravity trial surveys have been made in Yuen Long in an attempt tomap the shallow cavitous marble subcrop. Between 1987 and 1989 a large number ofmagnetometer measurements were made in the Yuen Long Industrial Estate (Langford, 1990).The instrument used was the Geometries Unimag Proton procession magnetometer. The surveydid not show a correlation between a negative anomaly and the presence of marble at depth.Significant sources of error were the unquantifiable anomalies related to the fill platform andmore importantly the influence of steel H-pile foundations in the area. Collar et al (1990)conducted a detailed trial gravity anomaly survey of the Yuen Long area. They had some limitedsuccess in correlating gravity anomalies with the approximate extent of the buried marbleformation.B.2 INTERNATIONAL ENGINEERING GEOPHYSICS PRACTICEB.2.1 IntroductionThis Section summarises a review of the available literature in Hong Kong on noninvasiveengineering geophysics and its applicability in identifying the features described in themain body of the report in Section 2. Geophysical methods identified as not being applicable tothe project, such as induced polarisation, gravity and magnetic methods, are not discussedfurther. Each geophysical method is discussed separately, beginning with a brief explanation ofthe theory, followed by selected case histories and comments on the applicability of the methodin identifying instability indicators.Papers and articles concerning engineering geophysics are contained in a wide variety ofEnglish language publications, ranging from journals such as Geoexploration and GeophysicalProspecting to Geotechnique and the Quarterly Journal of Engineering Geology, However, sincethe late 1980s the Society of Engineering and Mineral Exploration Geophysics (SEMEG), nowknown as the Environmental and Engineering Geophysical Society (EEGS) has been sponsoringan annual Symposium on the Application of Geophysics to Engineering and EnvironmentalProblems (SAGEEP), which has published many useful papers in their proceedings. Generaltexts by Dobrin & Savit (1988) and Griffiths & King (1983) describe the theory and generalapplication of geophysical prospecting, the latter being directed towards geologists andengineers. Another valuable source of information is the collection of papers edited by Ward(1990) focusing on theory and practice in geotechnical and environmental geophysics.

- 84 -The reference list in Section B3 is split into references cited in the text and others whichhave been reviewed as part of the project but not cited.B.2.2 The Seismic MethodB.2.2.1 Shallow Seismic ReflectionSeismic reflection methods exploit subsurface acoustic impedance contrasts which reflectbody waves back to geophones located at the surface (Figure Bl). Acoustic impedance is theproduct of related parameters, seismic velocity and density.Non-invasive, high-resolution seismic reflection is mostly used to identify interfacesbetween soft or loose sediments and underlying consolidated soil or bedrock. In such geologicalconditions the impedance contrast is large and therefore the reflected p-wave energy is high.Miller et al (1990) describe a case history where seismic reflection was successful in imaging analluvial bedrock interface as shallow as 4m below the ground surface. The standard commondepth point (CDP) method (Figure Bl(a)) was used with an air rifle as the energy source. Thisproduced a repeatable high frequency wave for CDP stacking. The use of an air rifle as theenergy source also reduces the amount of ground roll and air wave noise. Long spikedgeophones helped improve ground coupling in areas of dry, loose, rocky ground.Pullan & Hunter (1990) describe the Optimum Offset Technique (Figure Bl(b)) ofshallow seismic reflection and illustrate its usefulness with three case histories where bed rockwas delineated below saturated sediments. They note that the high frequencies required for highresolution are preferentially attenuated, especially if the surface layers are dry and coarse grainedand that high resolution seismics are best suited to bedrock mapping where bedrock is overlainby fine-grained saturated soils. They also note that even if small amounts of gas are present inthe near surface sediments, seismic signals are subject to extreme attenuation. This could besignificant in partly-saturated soils in Hong Kong.High resolution seismic reflection may be successful in mapping fill bodies. Althoughenvironmental noise may be a problem, the use of CDP, stacking and other modem methods ofanalysis may allow the method to be utilised in certain circumstances in Hong Kong.B.12.2 Seismic Refraction MethodAs noted in Section Bl, the refraction method (Figure B2) is used in Hong Kong todetermine bedrock depth and form with variable success. Its use in identifying instabilityindicators other than mapping simple stratigraphy is considered limited.B.2.2.3 Surface Wave MethodsThere are two main surface wave methods in use, depending on the energy source.Impact sources, such as a hammer or a drop weight, produce a transient impulse, while vibratorsproduce continuous waves. The choice of source affects the details of the way in which fielddata is acquired and processed. The data from impact sources is processed using the Spectral

- 85 -Analysis of Surface Waves (SASW). The vibrator source data is processed using the ContinuousWave Method (CWM) (Matthews et al in press*). Stokoe et al (1994) describe the fundamentalsof SASW and Matthews et al (in press b ) describe in detail the CWM.Surface wave methods have been extensively used as a non-destructive test to determinethe shear stiffness and thickness of concrete pavements. An annotated bibliography by Hiltumen& Gucunski (1990) contains over 40 references on SASW, most of which are concerned withconcrete pavement measurements; however, case histories where the method has been used tomonitor the effectiveness of ground improvement and in liquefaction studies are also included.With advancement in the understanding of small strain stiffness of soil and rock, surface wavemethods have been used to determine ground stiffness profiles for use in geotechnical design.This is because the strain associated with a seismic wave propagating through soil or rock is inthe order of about 0.001% (Matthews et al in press b ), which is comparable with the strainsmeasured around excavations and below foundations. Al-Shayea et al (1994) suggest that thereshould be further development of the SASW method for the purpose of locating voids. Theypresent research in which the dispersion curve showed marked differences for free field lines andlines over voided areas.Although no case histories have been found which relate directly to features associatedwith slope instability in Hong Kong, the determination of stiffness-depth profiles using surfaceseismic methods could be useful if the profiles can be correlated with typical weathering gradesof local granitic and volcanic rock found in Hong Kong. SASW may also be useful indetermining the thickness of masonry retaining walls.B.2.3 ElectricalB.2.3.1 Electrical Resistivity SurveyingWard (1990) describes the fundamentals of resistivity surveying, data acquisition andprocessing, including detailed discussion of the pros and cons of various electrodeconfigurations (Figure B3). He also describes case histories where the resistivity method hasbeen used to detect unfilled and filled cavities in limestone, where a marked resistivity high wasassociated with an air-filled void and resistivity lows associated with clay-filled voids.Resistivity image profiling utilises the dipole-dipole electrode configuration (Figure B4)which produces a 2D apparent resistivity pseudo section. The pseudo section is then inverted toproduce the final resistivity section. Hiromasa & Hideki (1990) present a case study of a rockinvestigation in which resistivity imaging was used to characterise the ground along a proposedtunnel route. The technique was used to identify faults, fracture zones and altered zones along a1600m long survey line. The depth of investigation was about 300m in weathered and freshgranite. Zones of different resistivity values were identified and related to weathering grade andalteration of the granite rock mass. With the aid of air photo interpretation, the locations ofmajor faults, shear zones and altered zones were identified.Northmore & Jackson (1995) successfully used a British Geological Survey-designedresistivity imaging system (RESCAN) to monitor moisture migration in a soil embankment inKenya to obtain an understanding of the mechanisms which trigger landslides and seriouscracking in the embankments.

- 86 -Resistivity methods may be useful in mapping fault or shear zones, zones of elevatedmoisture content and possible voids. The method has a distinct disadvantage over otherelectromagnetic methods as it requires insertion of electrodes into the ground, but has themarked advantage of being able to produce a 2-D resistivity section of the site.B.2.3.2 Self Potential MethodThe self-potential (SP) is based on surface measurement of natural differences in electricpotential resulting from subsurface electrochemical reactions. SP anomalies are generated bysubsurface currents in the earth. SP investigations have been used to help locate and delineatethe sources responsible for the production of such flows. As the method offers relatively rapidfield data acquisition and the ability to respond directly to flows of interest, it is a cost effectivereconnaissance investigation method prior to more intensive studies (Corwin, 1990).SP surveys are conducted by measuring the potential difference in the ground using a pairof non-polarising electrodes and a high-impedance voltmeter. Corwin (1990) recommends thefixed-base configuration which uses a stationary electrode and a moving measuring electrode.The advantage of the fixed base configuration over the gradient configuration (which utilisestwo electrodes and a connecting wire of fixed length equal to the separation betweenmeasurement stations) is that errors associated with the gradient configuration such as soilcontact effects, electrode polarisation and time varying potentials, are not cumulative.For engineering purposes the SP method is used almost exclusively to study of groundwater movement. Corwin (1990) cites many examples of SP investigations of dam seepage.Geological features such as faults, shear zones and major discontinuities, which tend to formpreferential paths for water flows, have also been identified using the SP method.SP data are qualitative and are often severely affected by spatial factors and errors causedby large time-varying potentials such as those generated by corrosion or telluric currents. Inengineering applications the severity of these effects is compounded by relatively low SPanomaly levels and high artificial noise sources in urban areas (Corwin, 1990).The SP method may be useful in Hong Kong to detect water flow associated with leakingservices, if the problems associated with noise can be overcome.B.2.4 EleetromagneticB .2.4.1 IntroductionElectromagnetic methods are used to determine ground conductivity by measuring theresponse of the ground to induced electromagnetic fields. The advantage over conventionalresistivity methods is that they are non-invasive and measurements are relatively quick and easyto make. Measurements can be either made in the frequency domain or the time domain, whichhave different applications. Comprehensive reviews of electromagnetic methods and theirapplications to environmental and engineering problems are given by Nobes (1994) and McNeill

- 87 -B.2.4.2 Frequency-Domain ElectromagneticsFrequency-domain electromagnetic measurements are primarily used for profiling todetect and map lateral changes in conductivity. A typical conductivity meter such as the GeonicsEM-31 (McDowell, 1981) consists of transmitting and receiving coils located at the ends of a4m-long boom. Surveys are carried out by one person taking readings of direct conductivity on aset of parallel traverses or a grid of stations. McDowell (1981) notes that the orientation of theboom relative to the traverse direction depends on the nature of the target, also that the readingsare a measure of the conductivity of the ground between the ends of the boom and could varywith boom orientation where lateral inhomogeneity exists. The basic principle of the equipmentis to pass an alternating current of a certain frequency through a transmitter coil which inducescircular eddy current loops into the earth. The magnetic field at the surface, as measured by thereceiving coil, is the combination of the secondary field created by the induced current loops andthe primary field. Normally, there is both a difference in direction and phase between theprimary and secondary fields. The magnitude of the magnetic generated in one of these eddyloops is proportional to the value of the current within the loop, which inturn is directlyproportional to the terrain conductivity. The second component is the in-phase component, theratio of the secondary to primary magnetic field measured in parts per thousand of the primaryfield. This component is useful because it is very sensitive to metallic objects.From a number of case histories McDowell (1981) compares three types ofelectromagnetic devices: the terrain conductivity meter, conventional resistivity meter and thefluxgate magnetic field gradiometer. He notes that use of the conductivity meter such as theGeonics EM-31 is quick and inexpensive as compared with conventional resistivitymeasurements. At two sites where resistivity and magnetic surveys were impossible due toconcrete and metal surface cover, the electromagnetic survey was relatively unaffected.Conductivity surveys have been successful in locating sand lenses in clays, mine shafts,backfilled basements and cess pits.Anon (1988) describe several applications of the frequency-domain electromagneticmethod. Where low resistivity bedrock is overlain by clay-rich soils, the depth to bedrock can bemapped because conductivity can be crudely related to clay thickness. They note thatmeasurements made with the Geonics EM34 and EM31 compared very closely with the resultsobtained with conventional resistivity profiling. There is little reason to consider resistivityprofiling , therefore , if ground conductivity surveys can be carried out with approximately thesame depth of penetration. Faults and shear zones can be located owing to the different electricalproperties within such zones as compared with the surrounding rock (normally conductivityhighs due to deep weathering), or of one rock being faulted against another. Ground conductivityprofiling methods are commonly used in Africa to locate water-bearing shear zones in basementareas for water supply. The location of either air-filled (conductivity lows) or clay-filled(conductivity highs) voids is more cost effective than resistivity profiling for depths in the rangeof(3mto30m.Electromagnetic profiling can be considered as a favourable means of investigation inHong Kong since it is truly non-invasive, quick and relatively inexpensive. It is potentiallyuseful for mapping high moisture content zones, voids and altered shear zones or weathereddykes.

B.2.4.3 Time-Domain FJecfromagnetfesTime-domain electromagnetics (TDEM) involves measuring the electrical conductivityof soil and rock by inducing pulsating currents in the ground with a large transmitter coil andthen monitoring the decay of the secondary eddy current between the pulses with a separatereceiver coil (Figure 5B(a & b)). TDEM is primarily used to the determine depth and thicknessof soil and rock layers (Frischnecht & Raab, 1984).Nelson & Haigh (1990) describe a case history where TDEM was used in conjunctionwith high resolution seismic methods to delineate the location of sinkholes in lateritic terrain.Whiteley (1983) describes a joint TDEM and resistivity sounding to locate bedrock and toresolve a thin saline layer above bedrock. The TDEM gave a better estimate of bedrock depthwhilst joint inversion of both methods gave accurate estimates of the saline layer and depth tobedrock. Hoekstra & Blohn (1990) describe a case history where two thin basalt flows wereidentified using shallow TDEM surveys. Changes in resistivity profile correlated well with theinterface between the two basalt flows and the underlying tuff.Time Domain Electromagnetics has possible applications in Hong Kong in thedetermination of stratigraphy as different weathering grades in either granite or volcanic rockscontain different clay contents. It rnay also be possible to use TDEM to determine high moisturezones and ground water table conditions and, to a lesser extent, altered zones and embedded claylenses.B.2.5 Ground Penetrating Radar (QPR)B.2.5.1 IntroductionDue to its popularity and growing importance a separate section has been devoted to GPRinstead of including it as a sub-section under B.2.4. Ground Penetrating Radar uses the principleof reflected electromagnetic waves to locate buried objects (Figure B6). The basic principles andtheory of GPR are given in many technical papers, notably Daniels (1989) and Daniels &Roberts (1994). Over the past five years GPR has improved significantly mainly due to advancesin electronic signal processing. Data acquisition and analysis have taken advantage of powerful,quick and portable computers. Since GPR and seismic survey share the same principles, much ofthe software used to perform CDP stacking, migration and deconvolution can be applied to theGPR signals. GPR and seismic surveys complement each other since one is sensitive to contrastsin electromagnetic properties and the other to contrasts in mechanical properties.Siggins (1990) and Daniels & Roberts (1994) recommend measurement of the sitespecificelectrical properties of representative soil and rock prior to carrying out the GPR survey,especially at sites with deep weathering as GPR may not yield good results in clay-rich soils.Annan & Chua (1992) used three types of modelling to help evaluate GPR success in aparticular situation. Radar range predictions were used to predict depth of penetration. Syntheticradargrams were used to assess the type of response from a given target. Simple twodimensionalray tracing was used to determine two-way travel times to evaluate the effect ofantenna separation; depth of target and radius of target on the observed

- 89 -The depth of penetration of a radar wave depends upon the electrical properties of theground, centre band frequency of the antenna and the power output of the antenna. Dryhomogenous rock can be penetrated up to 35m but 10m-15m is more common. Conversely themaximum penetration though a montmorilonite-rich clay could be as small as 50mm.Roggenthen (1993) demonstrates that by using higher power output to the antennas deeperpenetration can be obtained in highly conductive soils. Gogh et al (1994) suggest that, based onthe pulseEKKO IV system, penetration of 10m to 25m can be obtained with 25-100MHzantennas and 1m to 5m penetration can be obtained with 300-lOOOMHz antennas. They suggestusing 100MHz antennas for investigations up to 10m deep. Grasmueck (1994) reports 40m to50m penetration in dry granite using a GSSI SIR-3 unit with 100MHz antenna. Siggins (1990)reports penetration of about 10-15 wavelengths in high resistivity rocks and about 1 wavelengthin conductive materials. Generation of very low frequency waves is not feasible due to the largeantennas required for long wavelength production.Conventional GPR equipment offers antennas with fixed centre-band frequency andhence a fixed range and resolution. Frequency selection for a given survey is a function of range,resolution, field conditions and what is available to the end user. Often the user requires severalantennas with different centre frequencies to perform a survey. Economic constraints will resultin the geophysicist only owning a certain number of antennas with a range of commonly-usedfrequencies. The variable frequency antenna helps solve some of these problems. Thomas (1992)describes an antenna with a variable frequency capability. Both Noon et al (1994) and Steven &Michael (1992) describe the development of the step frequencyGPR. This system synthesises astep frequency which matches the spectrum of the antenna band width. It has advantages overconventional impulse systems, e.g. the control of the signal waveform leads to better targetresolution, ringing is reduced through the use of windowing, and penetration is improved as thesignal bandwidth matches the antenna frequency and energy contained in the lower frequenciesis not lost.The following features have a high dielectric contrast and are therefore potentiallydetectable with GPR: cavities; changes in rock porosity; water table; plastic containers; concretefoundations; oil and petroleum spills and geological contrasts. Other features which are highlyconductive and therefore also detectable by GPR are barrels, tanks, pipes, clay and saltsdissolved in the ground water.B.2.5.2 Case HistoriesA summary of case histories obtained from published literature on GPR in identifyingboth man-made and natural sub-surface anomalies is contained in Table B2.B.2.5.3 Applications in Hong KongGPR has potential applications to determine the thickness of retaining walls, and detectclay-filled discontinuities, hydrothermally altered zones, voids and zones of enhanced moisturecontent. The combined use of GPR and thermography may also be useful in mapping voids andelevated zones of moisture behind hard surface protection to slopes (see Table B2, Gourry et al.,1995)

- 90 -B3 CONCLUSIONSThe main conclusions from the review of relevant literature are as follows:(i) Shallow seismic reflection may be useful in mapping the baseof extensive fill bodies. Seismic refraction is unlikely to besuccessful in identifying instability indicators other than thebedrock level. Surface wave methods could be useful in themapping of weathering profiles if a relationship existsbetween stiffness and weathering grade.(ii) Resistivity imaging may be useful in the location of shearzones or faults and the mapping of zones of elevated moisturecontent and high clay content. Void mapping may also bepossible. The self potential method could be utilised in thedetection of leaking services.(iii)Both frequency-domain and time-domain electromagneticmethods could be utilised in the mapping of zones of highmoisture content, location of voids and the location of shearzones and altered dykes.(iv)It is unlikely that gravity or magnetic methods would beparticularly useful in Hong Kong.(vi) It is possible that GPR will be able to determine the thicknessof retaining walls, detect clay filled discontinuities,hydrothermally altered zones, voids and zones of enhancedmoisture content. The combined use of GPR andthermography may also be useful in mapping voids andelevated zones of moisture behind hard surface protection toslopes.B.4 RECOMMENDATIONS(a) The applicability of the following non-invasive engineering geophysical methodsshould be tested in Hong Kong:(i) Shallow Seismic Reflection;(ii) Spectral Analysis of Surface Waves;(iii) Resistivity Imaging;(vi) Self Potential;(v) Electromagnetic Methods;

- 91 -(vi) Ground Penetrating Radar; and(vii) Thermal Imaging.B.5 REFERENCESB.5.1 References Cited in theM-Shayea, N., Gilmore, P. & Woods, R. (1994). Detection of buried objects by the GPRmethod. Proceedings of the Fifth International Conference on Ground Penetrating RaAy.Waterloo Centre for Ground water Research, Ontario, pp 1-18.Annan, A.P. & Chua, LX (1992). Ground Penetrating Radar Performance Predictions. GroundPenetrating Radar, Edited by Pilon, J.A., Canada Communications Group, Ottawa, pp5-13.Anon (1988). Engineering geophysics. Quarterly Journal of Engineering Geology. Report by theGeological Society Engineering Group Working Party, vol.21, pp 207-271.Arzi, A.A. (1975). Microgavity for engineering applications. Geophysical Prospecting. 23 (3),pp 408-425.Beck, A. & Ronen, A. (1994). The application of ground penetrating radar in Israel: SelectedCase Histories. Proceedings of the Fifth International Conference on Ground PenetratingRadar. Waterloo Centre for Groundwater Research, Waterloo, Ontario, pp 1101-1105.Bjelm, L., Follin, S. & Svensson, C (1983). A radar in geological subsurface investigation.International Syrnpogimn on Soil and Rock Investigations by In situ Testjpg.International Association of Engineering Geologists, Paris, pp 175-179.Butler, D.K. (1991). Microgravimetric Techniques for detection and delineation of subsurfacecavities. Proceedings of the Symposiuni op t)he Applications of Geophysics toEngineering and Environmental Problems (SAGEEP 91). Knoxville, pp 179-215.Chignell, RJ. (1993). Sixteen channel ground probing radar detection and imaging of tunnelsand other sub-surface features. Proceedings of the Fourth Tunnel Detection Symposiumon Subsurface Exploration Technology. Golden. Colerado. pp 65-69.Cisar, D., Dickerson, J. & Novotny, T. (1993). Electromagnetic data evaluation using a neuralnetwork: initial investigation-underground storage tanks. Proceeding of the Symposiumon the Application of Geophysics to Engineering and Environmental Problems,fSAGEEP 93V San Diego, pp 599-612.Collar, F,A., Ridley-Thomas, W.N. & Lai, W.C. (1990). A detailed gravity survey in the YuenLong area to map the shallow limestone subcrop. Proceedings of a Conference on "KarstGeology in Hong Kong"., Edited by Langford, RJL, Hansen, A & Shaw, R GeologicalSociety of Hong Kong Bulletin # 4, pp. 227-243.

- 92 -Colley, G.C. (1962). The detection of caves by gravity measurements. Geophysical Prospecting.'ll,ppl-9.Corwin, R.F. (1990). The Self-Potential Method for Environmental and EngineeringApplications. Geotechnical and Environmental Geophysics, edited by Ward, S.H.,Society of Exploration Geophysicists, Tulsapp 127-145.Daniels, J.J. & Roberts, R.L. (1994). Ground Penetrating Radar for Geotechnical Applications.Geophysical Characterisation of Sites, pp 1-13. Volume Prepared by ISSME TechnicalCommitee # 10 for XTTT International Conference on Soil Mechanics and FoundationEngineering. New Deli, India.Davis, J.L. & Annan, A.P. (1992). Applications of Ground Penetrating Radar to Mining,Groundwater, and Geotechnical Projects: Selected Case Histories. Ground Penetratingedited by Pilon, J.A., Canada Communications Group, Ottawa, pp.49-55.Deng, S., Zuo, Z. & Wang, H. (1994). The application of ground penetrating radar to detectionof shallow faults and caves. Proceedings of the Fifth International Conference on GroundPenetrating Radar fGPR '941. Ontario, pp. 1115-1120.Dobrin, M.B. and Savit, C.H. (1988). Introduction to Geophysical Prospecting. (Fourth Edition).McGraw-Hill Book Company, New York, p 867.Evans, R.B. (1990). Hong Kong Gravity Observations in July 1990 with BGS Lacoste andRomberg Meter No.G97 and International Connections to IGSN 71. British GeologicalSurvey Technical Report WK/90/24R.Frischnecht, F.C. & Raab, P.V. (1984). TDES at the Nevada Test Site, Nevada. Geophysics. 49,pp. 981-892.Gogh, E., Pattantyus-A, M. & Pronay, Z. (1994). Application of Ground Penetrating Radar forSite Characterisation. Geotechnical and Environmental Geophysics, edited by Ward,S .H., Society of Exploration Geophysicists, Tulsa, pp. 69-70Gourry, J.C., Sirieix, C, Bertrand, L. & Mathieu, F. (1995). 3D diagnosis of a tunnel throughinfrared thermograpy combined with ground penetrating radar. Proceedings of theSvmDOSium on the Application of Geophysics to Engineering and EnvironmentalProblems. (SAOKKP 951 Orlando, Florida edited by Bell, R.S., pp. 139-148.Grasmueck, M. (1994). Application of seismic processing techniques to discontinuity mappingwith ground penetrating radar in crystalline rock of the Gothard Massif, Switzerland.Proceedings of the Fifth International Conference on Ground Penetrating Radar. GPR'94.Ontario, pp. 1135-1149.Griffiths, D.H. and King, R.F. (1983). Applied Geophysics fnr Geologists and Engineers.(Second Edition). Pergmon Press, Oxford, p 230.

- 93 -Hall, D.H. and Hajnal, Z. (1962). The gravimeter in studies of buried valleys. Geophysics.Volume XXVII, No. 6, Part II, pp 939-951.Hiltunen, D.R. and Gucunski, N. (1994) Annotated Bibliography on SASW. GeophysicalCharacterisation of Sites, Volume Prepared by ISSME Technical Commitee # 10 for XIHInternational Conference on Soil Mechanics and Foundation Engineering. New Deli,India.pp. 27-34.Hinze, WJ. (1990). The Role of Gravity and Magnetic Methods in Engineering andEnvironmental Studies. Geotechnical and Environmental Geophysics, edited by Ward,S.H., Oklahoma, pp. 75-126.Hiromasa, S. & Hideki, K. (1990). A case study of rock investigation using resistivity imageprofiling. Proceedings of the Symposium on the Applications of Geophysics toEngineering and Environmental Problems. SAGEEP 1990 r Golden, Colorado, pp295-307.Hoekstra, P. and Blohm, M.W. (1990). Case Histories of Time Domain ElectromagneticSoundings in Environmental Geophysics. Geotechncal and Environmental Geophysics.1st Edition, Vol 2, edited by Ward, S.H., Series Editor Neitzel, E.B., Investigations inGeophysics. No. 5. Society of Exploration Geophysicists, Tulsa, pp 1-14.King, R.F. (1992). High resolution shallow seismology: history, principles and problems.Quarterly Journal of Engineering Geology. Volume 25, No.3, pp 177-182.Larkston, R.W. (1990). High Resolution Refraction Seismic Data Acquisition andInterpretation. Geotephnqal ayid Environmental Geophysics. 1st Edition, Vol 2, edited byWard, S.H., Series Editor Neitzel, E.B., Investigations in Geophysics, No. 5. Society ofExploration Geophysicists, Tulsa, pp 45-73.Langford, R.L. (1990). Trial magnetometer survey in Yuen Long Industrial Estate, Hong Kong.Proceedings of a Conference on "Karst Geology in Hong Kong". Edited by Langford,R.L., Hansen, A & Shaw, R. Geological Society of Hong Kong Bulletin # 4, pp. 215-245.McCann, D.M., Jackson, P.D., Culshaw, M.G. (1987). The use of geophysical surveyingmethods in the detection of natural cavities and mine shafts. Quarterly Journal ofEngineering Geology, Volume 20, pp 59-73.McCann, D.M., Baria, R., Jackson, P.D., Culshaw, M.G., Green, A.S.P., Suddaby, D.L andHallam, J.R. (1982). The use of geophysical methods in the detection of natural cavities,mineshafts and anomalous ground conditions. British Geological Survey, EngineeringGeology Research Group, Report 82/5. p 272.Matthews, M.C., Hope, V.S., Clayton, CR.L (in press*). The geotechnical value of groundstiffness determined using seismic methods. To be published in the Proceedings of the30th Annual Conference of the Engineering Geology Group of the Geological Society.Modern Geophysics in Eqprawmg Geology. Liege, Belgium, p 15.

- 94 -Matthews, M.C., Hope, V.S., Clayton, C.R.I (in press 5 ). The use of surface waves in thedetermination of ground stiffness profiles. To be published in the Proceedings of theInstitution of Civil Engineers, Geotechnical Journal, p 20.McDowell, P.W. (1975). Detection of clay filled pipes. Quarterly Journal of EngineeringGeology. 8. pp 303-310.McDowell, P. (1981). Recent developments in geophysical techniques for the rapid location ofnear surface anomalous ground conditions. Groimd Engineering, vol. 14, no., pp. 20-23.McNeill, DJ. (1995). Application of electromagnetic techniques to environmental geophysicalsurveys. Geonics Limited booklet of selected papers and examples in groundwaterenvironmental geotechnical and buried hazardous waste detection Unpublished, Ontario,Canada, p 8.Miller, R.D., Steeples, D.W., Hill, R.W., Jr. & Gaddis, B.L. (1990). Identifying Intra-AUuvialand Bedrock Structures Shallower than 30 Meters using Seismic Reflection Techniques.Geotechncal and Environmental Geophysics. 1st Edition, edited by Ward, S.H., SeriesEditor Neitzel, E.B., Investigations in Geophysics. No. 5. Society of ExplorationGeophysicists, Tulsa, pp. 89-97.Nelson, R.G. & Haigh, J.H. (1990). Geophysical Investigations of Sinkholes in LateriticTerrain's. Geotechncal and Environmental Geophysics. 1st Edition, edited by Ward,S.H., Series Editor Neitzel, E.B., Investigations in Geophysics, No. 5. Society ofExploration Geophysicists, Tulsa, pp 133-153.Nobes, D.C (1994) Troubled waters: environmental applications of electric and electromagneticmethods. 12th Workshop. Brest, pp 125-158.Noon, D.A., Longstaff, D. & Yelf, RJ. (1994). Advances in the development of step frequencyground penetrating radar. Proceedings of the Fifth International Conference on GroundPenetrating Radar. (GPR'94) r Ontario, pp. 117-131.Northmore, K. and Jackson, P.(1995) Tropical roads-preventing embankment collapse.Earthworks PDA. Issue 7, British Geological Survey, Keyworth, pp 5.Papamarinopoulos, StP., Papaioannou, M.G., Kappopoulos, X. & Balalsas, Y. (1995). Multiplegeophysical studies at urban central environment of Athens in connection with theconstruction of metro's main station. Symposium on the Application of Geophysics toEngineering aM Environmental Problems. S AGERP 95, Florida, pp. 159-169 .Piccolo, M. & Zanelli, A. (1994). GPR surveys inside an hydroelectric water supply tunnel toinvestigate the rock-concrete interface and the fractures affecting the host rocks.Proceedings of the Fifth International Conference on Ground Penetrating Riftfer, GPR'94Ontario, pp 914-923.

- 95 -Pullan, S.E. & Hunter, J.A. (1990). Delineation of Buried Bedrock Valleys Using the OptimumOffset Shallow Seismic Reflection Technique. Geotechnical and Environmental•Geophysics, 1st Edition, edited by Ward, S.H., Series Editor Neitzel, E.B., Investigationsin Geophysics, No, 5, Society of Exploration Geophysicists, Tulsa, pp 75-87.Ridley Thomas, N.W. (1982). The application of engineering geophysical techniques to siteinvestigations in Hong Kong. Proceedings of the Seventh South East Asian GeotechnicalConference, vol. 1, Hong Kong, pp. 205-226.Robillard, C, Niccolas, P., Armirat, P., Gariepy, M. & Goupil, F. (1994). Shallow bedrockprofiling using GPR. Proceedings of The Fifth International Conference on GroundPerpetrating Radar. GPR'94 r Ontario, pp. 1167-1179.Roggenthen, W.M. (1993). Pulsed GPR detection of voids in layered geologic materials.Proceedings of the Fourth Tunnel Detection Symposium on Subsurface ExplorationTechnology. Golden, Colorado, pp 85-92Sasahara, K., Tsuchida, T. & Fenner, TJ. (1995). An investigation of cracks in rock slope usingground penetrating radar. Proceedings of the Symposium on the Application ofGeophysics to Engineering and Environmental Problems. SAGEEP 95. Florida, pp149458.Scullion, T. & Saarenketo, T. (1995). Ground penetrating radar technique in monitoring defectsin roads and highways. Proceedings of the Symposium on the Application of Geophysicsto Engineering and Environmental Problems. SAGEEP 95. Florida, pp 63-72.Siggins, A.F. (1990). Ground penetrating radar in geotechnical applications. ExplorationGeophysics, vol. 2L no., pp. 175-186.Steven, K. & Michael, B. (1992). The development of energy's ground penetrating radar (gpr),an fm-cw system. Unknown Source, pp 44-64.Stokoe, K.H., Wright, S.G., Bay, J.A. & Roesset, J.M. (1994). Characterisation of GeotechnicalSites by SASW Method. Geophysical Characterisation of Sites. Volume Prepared byISSME Technical Commitee # 10 for XTO International Conference on Soil Mechanicsand Foundation Engineering. New Deli, India.pp. 15-25Thomas, J.F. (1992). Recent advances in subsurface interface radar technology. Proceedings ofthe Fourth International Conference on Ground Penetrating Radar, Geological Survey ofFinland, Espoo, Finland, pp 1349.Vaish, J.N. & Gupta, S.C. (1994). Detection of an abandoned mining channel under aresidential complex by ground penetrating radar. Proceedings of the Fifth InternationalConference on Ground Penetrating Radar. GPR'94. Florida, pp 1193-1199.Ward, S,H. (1990). Resistivity and T^H^H Polarisation ; Tteotechnical- and EnvironmentalGeophysics. 1st Edition, edited by Ward, S.H., Series Editor Neitzel, E.B., Investigationsin Geophysics, No. 5. Society of Exploration Geophysicists, Tulsa, pp 147-189.

- 96 -Ward, S.H. (1990). nontechnical and Environmental Geophysics. (First Edition) Investigationsin Geophysics No.5. (Serise Editor Neitzel, E.B.) Society of Exploration Geophysicists,Tulsa,.Whiteley, RJ. (1983). Recent developments in the application of geophysics to geotechnicalinvestigation. Proceedings of an Extensjop Course on Tn Situ Testing for GeotechnicalInvestigations. Sydney, edited by M.C.Ervin, A.A.Balkema, Rotterdam, pp 87-110.B.5.2 Other References ReviewedAdams, J.M. & Hinze, W.J. (1990). The Gravity Geologic Technique of Mapping BuriedBedrock Topography. Geotechnicg] anr 1 finvironrnentaiGeophysics. (1st edition), editedby S.H. Ward, series editor E.B. Neitzel, Investigations in Geophysics, vol. 3, Society ofExploration Geophysicists, Tulsa, pp. 99-105.Aigotti, D., Armando, E., Barla, G. & Forlati, F. (1983). Geophysical and geomechanicalmeasurements along a natural slope. International Symposium on Field Measurements inGeomechanics. vol. 1, Zurich, pp. 98-109.Allen, D.M., Moorman, BJ. & Michel, F.A. (1994). Gravity and ground penetrating radar asinvestigative methods for delineating fault structures for a ground water energy system.Geological Association of Canada: Mineralogical Association of Canada: AnnualMeeting, Waterloo. Geological Association of Canada, Waterloo, p. 2.Annan, A.P. & Cosway, S.W. (1992). Ground penetrating radar survey design, proceedings ofthe Symposium on the Application of Geophysics to Engineering and EnvironmentalProblems. SAGEEP 92. vol. 2, Oakbrook, pp. 329-351.Becker, S.R., Richard, B.H. & Wolfe, P.I (1990). Delineation of buried valleys using integratedgeophysical techniques. Proceedings of the Symposium on the Application ofGeophysics to Engineering and Environmental Problems, SAGEEP 90. Golden, pp.309-322.Benson, R.C. & Yuhr, L. (1992). Summary of methods for locating and mapping fractures andcavities with emphasis on geophysical methods. Proceedings of the Symposium on theApplication of Geophysics to Engineering and Environmental Problems, SAGEEP 92,vol. 2, Oakbrook, pp. 471-486.Boms, D.J., Newman, G., Stolarczyk, L. & Mondt, W. (1993). Cross borehole electromagneticimaging of chemical and mixed waste landfills. Proceeding of the Symposium on theApplication of Geophysics to Engineering and Environmental Problems, SAGEEP 93,vol. 1 5 San Diego, pp. 91405.Bullard, R.F., Cuenod, Y. & Jenni, J.P. (1983). Detection of karst cavities by geophysicalmethods. International Symposium on Soil and Rock Investigation.^ by In situ Testing,voL 1, International Association of Engineering Geology, Paris, pp. 153-157.

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- 99 -Guenther, M. & Kathage, A.F. (1994). The geophysical investigation of drilling obstacles formicrotunnelling projects by means of GPR. Proceedings of the Fifth InternationalConference on Ground Penetrating Radar, vol. 3, Waterloo Centre of GroundwaterResearch, Kitchener, Waterloo, pp. 1151-1165.Harry, M J. & Derald, G.S. (1991). Ground penetrating radar of northern lacustrine deltas. Can,J T Earth Sci, vol. 28, Department of Geography, The University of Calgary, Calgary, Alta,Canada, pp. 1939-1947.Heimmer, D. HL, Davenport, C, Lindeman, J. & Gilmore, J. (1989). Geophysics forarchaeological assessment: Fort William discovered? Foil Laiamie national historicalsite, Wyoming. Proceedings of the Symposium on the Applications of Geophysics toEngineering and Environmental Problems. SAGEEP R9 : Golden, pp. 448-455.Hoekstra, P. (1991). Ground water geophysics. Proceedings of the Symposium on theApplication of Geophysics to Engineering and Environmental Problems. SAGEEP 91,Knoxville,p. 111.Hollyway, A.L. (1992). Fracture Mapping in Granitic Rock Using Ground Probing Radar.Ground Penetrating Radar, edited by J. Pilon, Geological Survey of Canada, pp. 85-100.Home, W.A., Stevens, D. & Baston, G. (1991). Ground penetrating radar study of "bridge scour"in New York State. Proceedings of the 42nd Annual Highway Geology Symposium, NewYork, Geologic Complexities in the Highway Environment, Highway GeologySymposium, Atlanta, pp. 179-186.Huggenburger, P., Meier, E. & Pugin, A. (1994). Ground probing radar as a tool forheterogeneity estimation in gravel deposits: advances in data processing and faciesanalysis. International Symposium on Geophysics and Environment. Lausanne. Elsevier,Amsterdam, pp. 14-16.Irons, L. (1989). Investigation of ordnance disposal sites using ground and aerial geophysics.Proceedings of the Symposium on the Application of Geophysics to Engineering andEnvironmental Problems. SAGEEP 89. Golden, pp. 412-423.Isiorho, S.A., Taylor-Wehn, K.S. & Nikereuwerm, T.O. (1992). The relationship betweenlineaments and fractures in Chad Basin. Proceedings of the Symposium on theApplication of Geophysics to Engineering and Environmental Problems, SAGEEP 92,vol. 2, Oakbrook, pp. 509-518.James, B.A, & Borns, D.J. (1993). Two-dimensional subsurface imaging with transient em formapping of a buried dissolution structure near the waste isolation pilot plant. Proceedingsof the Symposium on the Application of Geophysics to Engineering and EnvironmentalProblems, SAGEEP 93. vol. 2. San Diego, pp. 633-656.Jansen, J., Pencak, M., Gnat, R. & Haddad, B. (1993). Some applications of frequency domainelectromagnetic induction surveys for landfill characterisation studies, proceedings of theSymposium on the Apportion of Geophysics to Engineering and EnvironmentalProblems, SAGEEP 93. vol. 2, San Diego, pp. 633-656.

- 100 -Johnston, M.A. & Carpenter, PJ. (1993). Fracturing of glacial drift and bedrock over longwallmine panels: integrated geophysical and hydrological measurements. Proceedings of jfaeSymposium on foe Application of Geophysics to Engineering and EnvironmentalProblems. SAGEEP 93. vol. 2, San Diego, pp. 395414.Jones, R. (1962). Surface wave techniques for measuring the elastic properties and thickness ofroads. British Journal of Applied Phvsics. vol. 13, pp. 13,21-29.Kilty, K.T. & Lange, A.L. (1990). Acoustic tomography in shallow geophysical explorationusing a transform reconstruction. Geotechnica.1 and Environmental Geophysics. (1stedition), edited by S.H. Ward, series editor E.B. Neitzel, Investigations in Geophysics,vol. 3, Society of Exploration Geophysicists, Tulsa, pp. 23-35.Kofman, L., Canaan, D., Gadot, I. & Klar, I. (1994). Detection of underground caves and voidsusing georadar. Tsraei Geological Society. Annual Meeting, Israel Geological Society,Jerusalem.Lahti, R.M. & Hoekstra, P. (1991). Geophysical surveys for mapping migration of brines fromevaporation pits and ponds. Proceedings of the Symposium on the Application ofGeophysics to Engineering and Environmental Problems. SAGEEP 91. Knoxville,TN,pp. 65-79.Langman, A. & Inggs, M.R. (1994). A SFCW polarimetric ground penetrating radar.Proceedings of the Fifth International Conference on Ground Penetrating Radar, vol. 1,Waterloo Centre for Groundwater Research, Waterloo, Ontario, pp. 63-77.Leggo, PJ., Glover, J.M. & Wajzer, M.R. (1992). The detection and mapping of kaolinitic clayby ground probing radar in the cornish granites of southwest England. Proceedings of theFourth International Conference 013 Ground Penetrating Rad^r. edited by H. Pauli & A.Sini, Geological Survey of Finland, Espoo, Finland, pp. 205-215.Lepper, CM. & Dennen, R.S. (1990). Selection of antennas for GPR system. Proceedings pf theSymposium on the Applications of Geophysics to Engineering and EnvironmentalProblems. SAGEEP 90 : Golden, p. 229.Madsen, J.A., McGeary, S., Pizzuto, J.E., Macintire, S.S. & Petaccia, MLJ. (1994). Using groundpenetrating radar to characterise the geologic setting of shallow unconfined aquifersystems. Geological Society of America. 1994 Annual Metffog, Geological Society ofAmerica, Boulder, pp. 24-27.Mark, S. (1993). Architectural element analysis within the kayenta formation (Lower Jurassic)using ground-probing radar and sedimentological profiling, South-western Colorado.Sedimentary Geology 90 (1994), Department of Geology, University of Toronto,Toronto, pp. 179-211.

- 101 -Maynard, K.C. & Field, O.K. (1992). Geophysical evaluation of rock mass conditions forsub-sea tunnelling: Strategic Sewage Disposal Scheme, Hong Kong. Proceedings of theSixth Australia-New Zealand Conference on Geomechanics. (in press edition).Christchurch.Mellett, J.S, & Maccarillo, BJ. (1991). Highway construction in karst terranes; avoiding andremediating collapse features. Proceedings of the 42nd Annual Highway GeologySymposium, Albany, Geologic Complexities in the Highway Environment, HighwayGeology Symposium, Atlanta, pp. 37-43.Minior, D.V. & Smith, S. (1993). Neutral networks for highway maintenance investigationsusing ground penetrating radar. Proceedings of the Symposium on the Applications. ofGeophysics to Engineering and Environmental Problems. SAGEEP 93, vol. 2, SanDiego, pp. 449-462.Nazarian, S. (1990). Detection of the deterioration within and beneath concrete pavements withsonic and ultrasonic waves. Proceedings. Non-destructive Evaluation of Civil Structuresand Materials. University of Colorado, Boulder, Colorado, pp. 391-406.Nazarian, S. & Stokoe, K.H.LL (1984). In situ shear wave velocities from spectral analysis ofsurface waves. Proceedings of the Eighth World Conference on Earthquake Engineering,vol. 3, San Francisco, pp. 31-38.Ohya, S. (1983). Current state of field measurement in japan - on the new developments ingeophysical and geotechnical instruments. International Syniposjpffi on FiejdMeasurements in Geomechanics, vol. 1, Zurich, pp. 128-137.Pieter, H. & Mark, B. (1988). Surface geophysics for mapping faults, shear zones andkarstification. Proceedings of the Symposium on the Applications of Geophysics toEngineering and Environmental Problems. SAGEEP 1988. vol. I, The Environmentaland Engineering Geophysics Society, U.S.A., pp. 598-620.Ridley Thomas, W.N. (1986). Contribution to the session "site investigation and geophysics".Proceedings of the Conference on Rock Engineering and Excavation in the UrbanEnvironment. Hong Kong, p. 441.Ridley Thomas, W.N., Lai, M.W.C. & Nieuwenhuijs, G.K. (1987). Marine geophysicalmethods. Proceedings of the Seminar on Marine Sources of Sand, edited by P.G.D.Whiteside & N. Wragge-Morley, Marine and Sand Resources of Hong Kong, HongKong, pp. 109-120.Robert, R., Daniels, JJ. & Peters, L. (1992). Improved GPR interpretation from analysis ofburied target polarisation properties. Proceedings of the Symposium on the Applicationof Geophysics to Engineering and Environmental Problems; SAGEEP 92, vol. 2,Oakbrook, pp. 353-373.

- 102 -Roberts, R., Daniels, JJ. & Peters, L. (1993). Accounting for near field conditions wheninterpreting 3-D GPR data. Emcesdiofls of the Symposiam on the Applicatifln&^fGeophysics t n F PgifKfriir»f?; and Envirnpniental Problems, SAGEEP 93, vol. 2, SanDiego, pp. 575-594.Rossiter, J.R. & Davis, J.L. (1991). Environmental geophysics-breaking the cost barrier,of fog Symposium on the Applications of-Geophysics to EngipssringjapdProblems. SAGEER1L Knoxville, pp. 347-356.Saito, BL, Shima, H. & Toshioka, T. (1990). Applications of geotomography to rockinvestigations. Proceedings of the Symposium on the Applications.. of Geophysics toProblems. SAGEEP 90. Golden, pp. 279-293.Sakayama, T., Hara, T. & Imai, T. (1983). Study of the combined use of ground probing radarand electric profiling in soil exploration. International Symposium on Soil and RpqkInvestigations by Tn situ Testing, vol. 1, International Association of EngineeringGeology, Paris, pp. 309-313.Sauman, P., Sallomy, J., Wong, T. & Hardisty, P. (1993). Geophysical data processingtechniques as related to groundwater contamination studies. Proceedings of theSymposium on the Application of Geophysics to Engineering and EnvironmentalProblems. SAGEEP 93. vol. 1, San Diego, pp. 167-180.Simmons, G., Fields, G,, Hanger, J. & Conboy, D. (1990). Application of GPR and seismictechniques to investigate bridge abutments. Proceedings of the. SympPsiu.m. on theApplications of Geophysics to Engineering and Environmental...KroblgJED^ SAS£BP,-9Q>Golden, p. 241.Sides, P.C. & Viksne, A. (1990). Site-Specific Shear Wave Velocity Determinations forGeotechnical Engineering Applications. Geotechpicftl and Environmental,,QgophysiCS.(1st edition), edited by S.H. Ward, series editor E.B. Neitzel Investigations inGeophysics, vol. 3, Society of Exploration Geophysicists, Oklahoma, pp. 121-131.Snodgrass, JJ. & Lepper, CM.. (1993). Geophysical characterisation of mineral waste sites.Proceedings of the Symposium on the Application of GeophysicsfeE.Q.&in.ggrif.lg an dEnvironmental Problems. SAGEEP 93, vol. 2, San Diego, p, 433.Steeples, D.W. & Miller, R.D. (1990). Seismic Reflection Methods Applied to Engineering,Environmental, and Groundwater Problems. Geotechnical and EnvironmentalGeophysics, (1st edition), edited by S.H. Ward, series editor E.B. Neitzel, investigationsin Geophysics, vol. 1, Society of Exploration Geophysicists, Oklahoma, pp. 1-30,Stokoe, E.H. & Nazarian, S. (1985). Use of Rayleigh Waves in liquefaction studies.of a Geotechnical Engineering Division Session atU f Sh WUse of Shear Wave Velocity for Evaluating Dynamic Soil Properties, Denver, pp. 1-17.

- 103 -Stokoe, K.H., Nazarian, S., Ricks, G.J., Sanchez-SaJinero, I, Sheu, J.C. & Mok, YJ. (1988). Insitu seismic testing of hard to sample soils by surface wave method. Proceedings of anASCE—GeotechBical Engineering Division Specialty Conference, EarthquakeEngineering and Soil Dynamics II - Recent Advances in Ground Motion Evaluation,Geotechnical Special Publication No. 20, Park City, Utah, pp. 264-278.Ticken, EJ. (1993). A geophysical program to aid in the environmental investigation of the u.s.army base at Fort Ord ? California. Proceedings of the Symposium on the Applications ofGeophysics to Engineering and Environmental Problems. SAGEEP 93. vol. 1, SanDiego, p. 107.Tillard, S. (1994). Radar experiments in isotropic and anisotropic formations (granites andschist's) Geophysical Prospecting, vol. 42, pp. 615-636.Tl, D. (1989). A seismic investigation of fracturing within an earth embankment. Proceedings ofthe Symposium on the Applications of Geophysics to Engineering and EnvironmentalProblems, SAGEEP 1989. The Environmental and Engineering Geophysics Society,U.S.A., pp. 221-234.Wang, H., Li, D. 9 Qi, M. & Deng, S. (1992). Application of ground penetrating radar toengineering geology in China. Proceedings of the Fourth International Conference onGround Penetrating Radar, edited by H. Pauli & A. Sini, Geological Survey of Finland,Espoo, Finland, pp. 79-83.Wightman, W.E, (1988). Water table depth estimation using electrical sounding and refractionseismic measurements. Proceedings of the Symposium on the Applications ofGeophysics to Engineering and Environmental Problems. SAGJ5EP 1988, vol. 1, TheEnvironmental and Engineering Geophysics Society, U.S.A., p. 597.Whiteley, RJ. (1990). Engineering geophysics - a geophysicist's view. ExplorationGeophysics, vol. 21, pp. 7-16.Wilfred, P.H. (1990). Results of shear-wave measurements. Proceedings of the Symposium onthe Applications of Geophysics to Engineering and Environmental Problems, SAGEEP1990. The Environmental and Engineering Geophysics Society, U.S.A., p. 201.Wolfe, PJ. & Richard, B.H. (1992). Integrated geophysical studies over buried valleysProceedings of the Symposium on the Application of Geophysics to Engineering ffldEnvironmental Problems, vol. 2, Oakbrook, pp. 531-550.

- 104 -LIST OF TABLESTableNo.p a g eNo.B1 Summary of Land Geophysics Carried Out for GEO to 1995 105B2 A Summary of GPR Case Histories 109

- 109 -Table B2 - A Summary of GPR Case HistoriesAuthorsYearEquipmentFeatures DetectedCommentsDaniels &RobertsGogh et al19941994Not given in paper.pulseEKKO IVStopes, drifts and rises in asulphide mine in Montana.(i) Loosely backfilled mine shafts.(ii) Cellars and a cave system inBudapest.(iii) Junction between limestone,clay and sandy sedimentsalong a 200m length ofhighway.Voids detected to a depth exceeding10m.(i) Combined approach usingelectrical, electromagnetic andGPR.(ii) Cellars detected 1.5 to 2m b.g.l.and the caves to about 15m b.g.l.(iii) 100MHz antennas to map thelayer to about 10m.(iv) Seismics combined with GPR -fault system below a proposedpower station.(iv) Fault system mapped to 100musing the combined approach.(v) Buried bunkers at a disusedmilitary site.RoggenthenVaish & Gupta19931994GSSI, Inc. with100MHz antenna.pulseEKKO III with200MHz antennas.Old mine stopes and caves.Depth and lateral extent ofabandoned mica and kaolin mine insouth Delhi.High power output to the antennasproduced 10m penetration at siteswith highly conductive soils.Mining works located to 3m b.g.l.Deng et al1994pulseEKKO IVKarstic features in dolomite.Voids within Quaternary superficialstogether with karstic features withindolomite were identified to 14m b.g.l.Beck & Ronen1994SIR-10 with 500MHzand 100MHzantennas.(i) Dolomite cave system in Israel.(ii) Location of a smugglerstunnel.(iii) Concrete road pavementthickness.(i) GRP towed across survey areausing an ATV at 15km/hr.(ii) Tunnels located 3.5m b.g.l. in asandy clay.Davis & Annan1992pulseEKKO III with100MHz antennas.(i) Bedrock surface,(ii) Fractures and dykes in granite.Bedrock surface mapped throughsaturated sands to 20m.Bjelm et al1983Not given in paper.Bedrock and water table belowglacial till in Sweden.Good correlation with excavations to5m. Ground water at 11m b.g.l.Robillard et al1994SIR 10Bedrock along a cable route to 2m.Mapped alternating limestone andmarl beds and identified a fault.Penetration greatly reduced when soilswere clay rich.Grasraueck1994SIR 3 with 100MHzantennas.Sub-horizontal stress reliefdiscontinuities in dry granite.Penetration depths of 50m achieved.CDP and migration techniques wereused to obtain better depth resolutionand signal to noise ratio.Siggins1990SIR 8 WITH 500MHzantennasClay filled sheeting joints in agranite quarry.Sheeting joints identified to 6m.Sasahara1995SIRlOwithlOOMHzto 900MHz antennasLandslip prevention study to locatepotential critical rock massdiscontinuities in a tuff quarry.Only clay filled discontinuities ordiscontinuities with water percolationwere identified.Scullion &Saarenketo1995Various GPR systemsVarious types of road damage.Investigate frost damage, subgradecompressibility, cracks, stripping andvoids.Piccolo & Zanelli1994SIRlOwithlOOMHzand 500MHz antennasCavities and fractures behindconcrete tunnel lining.Delamination of the rock concreteinterface, geo-structural features, openfractures, voids and honeycombalteration identified.Gourry et al1995pulseEKKO 1000with 275MHz to900MHz antenna.Location of anomalies behind amasonry tunnel lining.Thermography was used to detectsmall voids in the masonry only, GPRlocated voids at the masonry host rockinterface.

- 110 -TJST OF FIGURESFigureNo.PageNo.B1 Shallow Seismic Reflection Ray Paths 111B2 Seismic Refraction Ray Paths and Time-Distance Graph 112after Larkston (1990)B3 Common Arrays Used in Resistivity and Induced-Polarisation 113after Ward (1990)B4 Pole-pole Electrode Array used in Resistivity Imaging 114after Shimaetal( 1990)B5 Sounding Configuration and Transient Current Flow in 115TDEM after McNeil (1994)B6 The GPR Reflection Process after Daniels and Roberts 116(1994)

- Ill -Figure Bl - Shallow Seismic Reflection Ray Paths

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- 117 -APPENDIX CPROFILES OF CONTRACTOR AND FIELD WORK PROGRESS

- 118 -CONTENTSPageNo.CONTENTS 118C. 1 PHASE 1 FIELD TRIALS 119C.2 PHASE 2 FIELD TRIALS 120C.3 REFERENCES 121LIST OF TABLES 123

- 119 -C.I PHASE 1 FIELD TRTATSBachy Soletanche (BS) tested seven geophysical methods between 5 and 13 December1995. The contractor completed the trials eight days ahead of programme. The field teamconsisted of four geophysicists and two labourers. The exact location of the additional traversesmade by BS can be found in the contractors report (Bachy Soletanche, 1996 a ). During the GPRsurvey at Sites A and B the contractor combined different frequency antennas in bistatic mode.The lower frequency (500MHz) antenna was used as the transmitter in order to obtain betterpenetration and the higher frequency (900MHz and IGHz) antenna was used as the receiver toobtain higher resolution. The contractor profile and field records for Phase 1 can be found onTables Cl and C2 respectively.Fugro Geotechnical Services (HK) Ltd (FGS) tested three geophysical methods between6 and 13 December 1995 (Fugro Geotechnical Services (HK) Ltd, 1996 a ). FGS completed thetrials on programme. The field team consisted of three geophysicists and two labourers. FGSwere the only contractor to use two different types of GPR equipment. They used the SIR 2system manufactured by Geophysical Survey Systems Inc. and also the pulseEKKO 1000 systemmanufactured by Sensors and Software Inc. They also used a 35MHz antenna manufactured bySwedish firm Radarteam with the SIR 2 system. The contractor profile and field records forPhase 1 can be found on Tables C3 and C4 respectively.Guandong South China EGTD Co.(GSC) tested four geophysical methods between 10and 17 January 1996. They completed all the works one day ahead of programme. They hadtwelve geophysicists on site working in teams of three to four with one senior geophysicist incharge of each method. The exact location of the additional traverses made by GSC can be foundin the contractor's report (Guandong South China EGTD Co., 1996 a ). The contractor profile andfield records for Phase 1 can be found on Tables C5 and C6 respectively.The Institute of Geophysical and Geochemical Exploration (IGGE) tested fivegeophysical methods between 15 to 29 January 1996. They completed all the works onprogramme. They had fifteen personnel on site split into five teams. Each team had a seniorgeophysicist dedicated to one of the geophysical methods. The exact location of the additionaltraverses made by IGGE can be found in the contractor's report (Institute of Geophysical andGeochemical Exploration, 1996 a ). For the GPR survey, the contractor used the SIR 10 systemwhich is designed for mounting into a vehicle for highway investigations and can utilise up to 4channels, allowing simultaneous operation of antennas with different frequencies. The system isnot as compact as the SIR 2 system which is designed for field use. The contractor profile andfield records for Phase 1 can be found on Tables C7 and C8 respectively.Meinhardt Works (MW) tested five geophysical methods between 15 and 27 January1996. They completed the trials on programme. The field work team consisted of twogeophysicists and three labourers. The exact location of the additional traverses made by MWcan be found in the contractor's report (Meinhardt Works, 1996 a ). The contractor profile andfield records for Phase 1 can be found on Tables C9 and C10 respectively.Golder Associates (GA) tested eight geophysical methods between 16 January and 12February 1996. They completed the trials on programme. The field trial team consisted of twogeophysicists and one labourer. The exact location of the additional traverses made by GA can

- 120 -be found in the contractor's report (Golder Associates, 1996 a ). The field work team madedetailed site plans for each traverse, identifying every source of potential noise that couldinfluence the geophysical results. They also used magnetic and electromagnetic utility detectorsto locate metallic services which ran close to or across the traverse lines. The contractor profileand field records for Phase 1 can be found on Tables Cll and C12 respectively.C.2 PHASE 2 FIELD TRIALSGolder Associates carried out the full suite of tests between 1 and 10 October 1996. Theworks were carried by one senior geophysicist and a graduate geotechnical engineer. Thepreliminary results and interpretation based on the geophysics only can be found in thecontractor's preliminary report (Golders, 1996 b ). The equipment and site methodology used wasessentially the same as described in Appendix D apart from the following; the AGI model StingRl Earth Resistivity Meter was combined with the Swift system of 28 smart electrodes for theRI which improved the speed of the survey, and the seismic data for the SASW were collectedusing an lotech Wavebook 512 instead of a spectral analyser. The team completed the works toprogramme. The contractor profile and field records for Phase 2 can be found on Tables C13 andC14 respectively.Bachy Soletanche Group carried out the full suite of tests between 5 and 16 October1996. The works were carried out by three geophysicists and two labourers. The preliminaryresults and interpretation based on the geophysics only can be found in the contractor'spreliminary report (Bachy Soletanche, 1996 b ). The equipment and site methodology used wasessentially the same as described in Appendix D, The contractor profile and field records forPhase 2 can be found on Tables C15 and C16 respectively.Fugro Geotechnical Services (HK) Ltd. carried out GPR, RI and FDEM between 10 and22 October 1996. The works were carried out by one senior geophysicist, graduate geophysicistand one labourer. The preliminary results and interpretation based on the geophysics only can befound in the contractor's preliminary report (Fugro, 1996 b ). The equipment and sitemethodology used was essentially the same as described in Appendix D apart from thefollowing; the pulsEKKO 1000 GPR equipment was not used, and the Geopulse resistivitymetre combined with an Imager 50 control module was used for the RI which improved thespeed of the survey. Due to problems with the resistivity equipment the team completed thetrials three days later than programmed. The contractor profile and field records for Phase 2 canbe found on Tables C17 and C18 respectively.Guandong South China EGTDC carried out GPR, RI and SASW between 22 and 29October 1996. The RI survey was carried out at their own cost since they did not use this methodin the Phase 1 trials. The works were carried out by a team of eight geophysicists. Thepreliminary results and interpretation based on the geophysics only can be found in thecontractors preliminary report (Guandong South China EGTDC, 1996 b ). The equipment and sitemethodology used was essentially the same as described in Appendix D, apart from the RIequipment which is described in Table C19. The contractor also carried out SASW at all foursites at his own cost. The field trials were completed on programme, the contractor profile andfield records for Phase 2 can be found on Tables C19 and C20 respectively.

- 121 -The Institute of Geophysical and Geochemical Exploration (IGGE) carried out GPR, RIand SASW between 24 October 1996 to 1 November 1996. The works were carried out by ateam of nine geophysicists. The preliminary results and interpretation based on the geophysicsonly can be found in the contractor's preliminary report (Institute of Geophysical andGeochemical Exploration, 1996 b ). The equipment and site methodology used was essentially thesame as described in Appendix D. SASW was carried out at all four sites at the contractors owncost. The field trials were completed to programme. The contractor profile and field records forPhase 2 can be found on Tables C21 and C22 respectively.C.3 REFERENCESBachy Soletanche (1996 a ) Site Characterisation Study Phase 1 Field Trials EngineeringGeophysical Methods. Dated June 1996.Bachy Soletanche Group (1996 b ) Preliminary Report, Site Characterisation Study Phase H FieldTrials Engineering Geophysical Methods, 34p, 65 Figures, 2 Appendices.Fugro Geotechnical Services (HK) Ltd. (1996 a ) Final Interpretative Report Site CharacterisationStudy Non-Invasive Engineering Geophysical Field Trials Phase I. Report No.572048,Revision No.02, dated 19 April 1996.Fugro Geotechnical Services (HK) Ltd. (1996 b ). Preliminary Interpretative Report. SiteCharacterisation Study Non-invasive Engineering Geophysical Trials Phase n, in fourVolumes, Vol.1 13p, 22 Figures, Vol.2 6p, 34 Figures, Vol.3, 6p, 25 Figures, Vol.4 7p,33 Figures.Golder Associates (1996 a ) Final Report to Government Engineering Office of Hong Kong -Field Trial of Eight Geophysical Techniques to Investigate Retaining Walls and Man-Made Slopes in Hong Kong. Dated May 17 1996, Reference 959-1029/IC3-1216.Golder Associates Inc. (1996 b ). Preliminary Interpretative Report to Government EngineeringOffice of Hong Kong. Site Characterisation Study Non-Invasive Trials Phase II FieldTrials Hong Kong, 969-1010/IC3-1278, 39p, 48 Figures, 1 Appendix.Guangdong South China EGTDC. (1996 a ) Site Characterisation Study Phase 1 Field TrialsEngineering Geophysical Methods Final Interpretative Report of GPR, SASW, HRSRand TDEM on Site "A", "B". "C" and "D". Dated March 1996.Guandong South China EGTDC (1996 b ). Preliminary Interpretative Report of GPR. SASW andRI on Site E. R G and H. Site Characterisation Study Phase 2 Field Trials EngineeringGeophysical Methods, 19p, Appendix 1-48 Figures, Appendix 2-71 Figures.Institute of Geophysical and Geochemical Exploration (1996 a ) Final Interpretative Report onEngineering Geophysical Methods. Dated June 3,1996.

- 122 -Institute of Geophysical and Geochemical Exploration (1996 b ). Preliminary Interpretative.Report, on Site Characterisation Study - Phase 2 Field Trials Engineering GeophysicalMethods. 23p, 120 Figures.Meinhardt Works (Hong Kong) Ltd. (1996) Final Report Site Characterisation StudyGeophysical Field Trials -Phase 1. Dated January 1996.

- 123 -LIST OF TABLESTableNo.PageNo.C1 Contractor Profile - Phase 1 Field Trials - Bachy Soletanche 125GroupC2 Field Records - Phase 1 Field Trials - Bachy Soletanche Group 126C3 Contractor Profile - Phase 1 Field Trials - Fugro Geotechnical 127Services (HK) Ltd.C4 Field Records - Phase 1 Field Trials - Fugro Geotechnical 128Services (HK) Ltd.C5 Contractor Profile - Phase 1 Field Trials - Guandong South 129China EGTD Co.C6 Field Records - Phase 1 Field Trials - Guandong South China 130EGTD Co.C7 Contractor Profile - Phase 1 Field Trials - Institute of 131Geophysical and Geochemical ExplorationC8 Field Records - Phase 1 Field Trials - Institute of Geophysical 132and Geochemical ExplorationC9 Contractor Profile - Phase 1 Field Trials - Meinhardt Works 133C10 Field Records - Phase 1 Field Trials - Meinhardt Works 134C11 Contractor Profile - Phase 1 Field Trials - Golder Associates 135(HK) Ltd.C12 Field Records - Phase 1 Field Trials - Golder Associates (HK) 136Ltd.C13 Contractor Profile - Phase 2 Field Trials - Golder Associates 137(HK) Ltd.C14 Field Records - Phase 2 Field Trials - Golder Associates (HK) 138Ltd.C15 Contractor Profile - Phase 2 Field Trials - Bachy Soletanche 139GroupC16 Field Records - Phase 2 Field Trials - Bachy Soletanche Group 140

- 124 -TableNo.PageNo.C17 Contractor Profile - Phase 2 Field Trials - Fugro Geotechnical 141Services (HK) Ltd.C18 Field Records - Phase 2 Field Trials - Fugro Geotechnical 142Services (HK) Ltd.C19 Contractor Profile - Phase 2 Field Trials - Guandong South 143China EGTD Co.C20 Field Records - Phase 2 Field Trials - Guandong South China 144EGTD Co.C21 Contractor Profile - Phase 2 Field Trials - Institute of 145Geophysical and Geochemical ExplorationC22 Field Records - Phase 2 Field Trials - Institute of Geophysical 146and Geochemical Exploration

- 125 -1. Main Contractor :Bachy Soletanche Group (BSG)2. Joint Venture Companies :Europeanne De Geophysique (EDG)Table Cl - Contractor Profile - Phase 1 Field Trials3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Electromagnetic Methodd) High Resolution Thermal Imaginge) Resistivity Imagingf) Self Potentialg) Acoustic/Sonic Tool *(To be carried out at the contractor's own cost)4. Names of Staff to be Employed on the Site Trials :- F. Lantier (EDG) - S. Geophy. & Geologist, ENSG NANCY, 28 years exp.• R. Foillard (EDG) - Geophysical Engineer, ENSG NANCY, 18 years exp.-M. Lassoved (EDG) - Physics degree, 4 years exp.- H X Burbidge (BSG) - Geotechnical Engineer, MSc, 12 years exp.5. Equipment Details :Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ElectromagneticMethodd) High ResolutionThermal Imaginge) ResistivityImagingf) Self Potentialg) Acoustic/SonicToolManufacturerGeophysicalSurvey Systems Inc.MetravibScientific AtlantaMetravibGeonicsAPPAAREDGGeoinstrumentGeotrodeMetravibScientific AtlantaPUNDITType- SIR 2 System- 500,900 and 1000MHz antenna's- RAIO Seismograph- Spectral Dynamics SD380 Signal Ana.- CSH 05 Piezoelectric Accelerometer- EM38 terrain conductivity meter-IRS 3- Multiplex voltmeter- Non-polarizing Electrodes- Millivdtmeter- Non-polarizing Electrodes- RAIO Seismograph- Spectral Dynamics SD380 Signal Ana.- 24 & 54 kHz Transducers

- 126 -Table C2 - Field Records - Phase I Field Trials - Bachy Soletanche GroupGeophysicalMethodsGPRTrialSiteABCStartDate06.12.9508.12.9505.12.95EndDate06.12.9508.12.9505.12.95PersonIn ChargeR. FoillardRemarksProblems encountered at sites B and Cwith scaffolding obstructing the lowerinof antenna's down the wall profiles.SASWDA07.12.9506.12.9507.12.9507.12.95M.Metravib CSH 05 (3KHz) piezoelectricB08.12.9508.12.95_,assovedaccelerometers used.C05.12.9505.12.95EMDABC07.12.9506.12.9509.12.9505.12.9507.12.9506.12.9509.12.9505.12.95: . Lantiernitial site reading influenced by surfacemetallic objects such as manholecovers, drain pipes and metal windowD07.12.9507.12.95rames.HRTIA10.12.9510.12.95?. LantierSurveys made between 00:00hrs andB10.12.9510.12.9502:00hrs.C10.12.9510.12.95D09.12.9509.12.95RIA06.12.9507.12.95F. LantierHilti Bolts used as electrodes.B09.12.9509.12.95Dipole-dipole electrode array adopted.CD05.12.9507.12.9505.12.9508.12.95SPA06.12.9507.12.95F. LantierGeotrode non-polarising copper sulphateB08.12.9508.12.95electrodes with sponge soaked in copperCD05.12.9508.12.9505.12.9508.12.95sulphate attached to base to ensure goodcontact. Fixed base electrode(AST)ABCD06.12.9508.12.9505.12.9507.12.9507.12.9508.12.9505.12.9507.12.95M.Lassovedconfiguration adopted.PUNDIT equipment used to measureseismic velocity in masonry wall facingand concrete tie beams.Key:Trial Site "A" - Kennedy Town Police QuartersTrial Site "B" - Eliot Halt, University of Hong KongTrial Site "C M - Sir Ellis Kadoori School, So Kan PoTrial Site "D tt - Cape CoHisinson Crematorium, thai WanGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRl - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool(SR) - Seismic Refraction(MEMUS) - Magnetic/EM Utility Scan( ) - To be carried out at the contractors own cost

- 127 -Table C3 - Contractor Profile - Phase 1 Field Trials1, Main Contractor :Fugro Geotechnical Services (HK) Ltd. (FGS)2. Joint Venture Companies :British Geological Survey (BGS)3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Electromagnetic Methodc) Resistivity Imaging4. Names of Staff to be Employed on the Site Trials :- A. K. Whittle (FGS) - Geophysicist, 20 years exp.- D. A. Pearks (FGS) - BSc, MSc(Geophy)- Dr J. P. Busby (BGS) - BSc, PhD, 12 years exp.5. Equipment Details:Techniquea) GroundPenetratingRadarb) ElectromagneticMethodc) ResistivityImagingManufacturerGeophysicalSurvey Systems Inc.RadarteamSensors & SoftwareInc.GeonicsABEM InstrumentsABType-SIR2 System- 500 MHz antenna-35 MHz antenna (2no.)- pulsEKKO 1000 console- 225,450 and 900 MHz antenna's- EM31 conductivity meter- Terrameter SAS 300B- Steel electrodes

- 128 -Table C4 - Field Records - Phase 1 Field Trials - Fugro Geotechnical Services (HK) Ltd.GeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRA08.12.9509.12.95Dr. J.P.A.K. Whittle in charge of the SIR 2B06.12.9507.12.95Busby andsystem and Dr. J.P. Busby in chargeC11.12.9512.12.95A.K.of the pulsEKKO 1000. 35 MHzD13.12.9513.12.95Whittleanten. used in bistatic mode at site C.EMA08.12.9508.12.95Dr. J.P.Scaffolding at site B and C interferedB06.12.9506.12.95Busbywith the lowering of the EM31 downC11.12.9511.12.95the wall profile (3.6m boom). HighD13.12.9514.12.95levels of interference caused by surfacemetallic objects noted.RIA09.12.9509.12.95Dr. J.P.10mm diameter stainless steel pinsB07.12.9507.12.95Busbyinserted into pre-drilled holes used asC12.12.9512.12.95electrodes. Dipole-dipole electrodeD13.12.9514.12.95array utilised.Key:Trial Site "A" - Kennedy Town Police QuartersTrial Site W B" - Eliot Hall, University of Hong KongTrial Site "C 11 - Sir Ellis Kadoori School, So Kan PoTrial Site M D M - Cape Collisinson Crematorium, Chai WanGPR - Ground Penetrating RadarSASW -Spectral Analysis of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRI - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool(SR) - Seismic Refraction(MEMUS) - Magnetic/EM Utility Scan( ) - To be carried out at the contractors own cost

- 129 -1. Main Contractor :Guangdong South China EGTD Co.2. Joint Venture Companies :NoneTable C5 - Contractor Profile - Phase 1 Field Trials3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Electromagnetic Methodd) High Resolution Seismic Reflection4. Names of Staff to be Employed on the Site Trials :- Lin Youcong - Sen. Geophysic Engineer, MCSST, MCSG, 30 years exp.- Huang Weiyi - Sen. Geophysic Engineer- Zhang Xihong - Sen, Geophysic Engineer- Zhao Ming - Geophysic Engineer- Huang Jianxin - Geophysic Engineer5. Equipment Details:Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ElectromagneticMethodd) High ResolutionSeismic ReflectionManufacturerGeophysicalSurvey Systems Inc.GeometricHe CaomingSpecialist GroupGeometricType- SIR 2 and SIR 10H System- 100(2no>), 500 and 900MHz antenna's- Strata View R24 signal seismograph- 10 and 60 Hz geophones- WDC-2 Time Domain ElectromagneticObserving System- Strata View R24 signal seismograph- 60 - 100 Hz geophones

- 130 -Table C6 - Field Records - Phase 1 Field Trials - Guangdong South China EGTD Co.GeophysicalTriaiStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRA13.01.9613.01.96HuangSIR 2 system only used at site D whereB17.01.9617.01.96Jianxinaccess was difficult down the fill slope.C11.01.9611.01.96100MHz antenna's used in bothD10.01.9610.01.96monostatic and bistatic mode.SASWA13.01.9613.01.96ZhangMultiple geophone array utilised inB17.01.9617.01.96Xihongconjunction with Strata View 24.C11.01.9611.01.96D10.01.9610.01.96EMA13.01.9613.01.96HuangTime domain electromagnetic methodB17.01.9617.01.96Weiyitested. Electrical interference fromC11.01.9611.01.96metallic objects noted during field workD10.01.9610.01.96especially at sites A, B and C.HRSRA13.01.9613.01.96ZhangB17.01.9617.01.96XihongC11.01.9611.01.96D10.01.9610.01.96Key:Trial Site "A" - Kennedy Town Police QuartersTrial Site "B w - Eliot Hall, University of Hong KongTrial Site "C" - Sir Ellis Kadoort School, So Kan PoTrial Site "D" - Cape CoUtsinson Crematorium, Chat WanGPR - Ground Penetrating RadarSASW -Spectral Analysis of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRI - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool(SR) - Seismic Refraction(MEMUS) - Magnetic/EM Utility Scan( ) - To be carried out at the contractors own cost

- 131 -Table C7- Contractor Profile - Phase 1 Field TrialsL Main Contractor:Institute of Geophysical and Geochemical Exploration, China (IGGE)2. Joint Venture Companies :Forest Engineering Geophysics Exploration Co. (FEGE)3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Electromagnetic Methodd) High Resolution Seismic Reflectione) Resistivity Imaging4. Names of Staff to be Employed on the Site Trials :- Yi Yongsen (IGGE) - Senior Geophysicist, Director of IGGE- Yie Shumin (IGGE) - Senior Geophysicist, deputy Director of IGGE- Yang Piyuan (IGGE) - Senior Geophysicist- Zhou Anchang (IGGE) - Senior Geophysicist- Wu Zhiping (IGGE) - Senior Geophysicist- Hu Ping (IGGE) - Senior Geophysicist- Xu mingcai (IGGE) - Senior Geophysicist5. Equipment Details:Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ElectromagneticMethodd) High ResolutionSeismic Reflectioe) ResistivityImagingManufacturerGeophysicalSurvey Systems Inc.Hewlett-PackardHewlett-PackardHewlett-PackardHewlett-PackardCrone Geophysics &Exploration Ltd.GeometriesZonge Engineering &Research OrganizationType- SIR 10A System- 100(2no.), 500 and 900, MHz antenna's- Dual-channel Dynamic Singal Analyzer- Computer- Thermo printer- Ploter with six pen- Digital pulse EM system- ES-240'1 Seismograph- lOOHzgeophones- GRP-32 wide-band electric survey system

- 132 -Table C8 - Field Records - Phase i Field Trials - Institute of Geophysical and GeochemicalExplorationGeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRA24.01.9624.01.96WulOOMhz antenna's used in bothB19.01.9619.01.96Zhipingmonosatic and bistatic mode.C16.01.9616.01.96D18.01.9618.01.96SASWA25.01.9625.01.96YangSASW tried along concrete tie beamB19.01.9629.01.96Piyuanat site B.C15.01.9616.01.96D27.01.9627.01.96EMA24.01.9624.01.96Hu PingTime domain electromagnetic methodB19.01.9619.01.96tested.C16.01.9616.01.96D17.01.9617.01.96HRSRA24.01.9624.01.96XuAt site B, geophones set up along TB03B20.01.9629.01.96Mingcaiwith energy source initiated atC16.01.9616.01.96increasing distances from wall along theD18.01.9618.01.96May Hall platform.RIA25.01.9625.01.96ZhouDipole-dipole electrodes array utilisedB20.01.9620.01.96Anchangwith both stainless steel and copperC15.01.9616.01.96electrodes.D27.01.9627.01.96Key:Trial Site "A" - Kennedy Town Police QuartersTrial Site "B" - EHot Hall, University of Hong KongTrial Site H C M - Sir Ellis Kadoori School, So Kan PoTrial Site "D" - Cape CoIUsinson Crematorium, Chai WanGPR - Ground Penetrating RadarSASW -Spectral Analysis of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRI - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool(SR) - Seismic Refraction(MEMUS) - Magnetic/EM Utility Scan( ) - To be carried out at the contractors own cost

- 133 -1. Main Contractor:Meinhardt WorksTable C9 - Contractor Profile - Phase 1 Field Trials2. Joint Venture Companies :Fong On Construction (FOC), Bay Geophysical Associates Inc., (BG) andWorks Consultancy Service. (W)3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Electromagnetic Methodd) Resistivity Imaginge) Self Potential4. Names of Staff to be Employed on the Site Trials :- A. J. Sutherland (W) - NZCScience(Geo), 12 years exp.- S, Mcquown (BG)- S. Lai (FOC) - HD(Eng), 5 years exp.5. Equipment Details:Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ElectromagneticMethodd) ResistivityImaginge) Self PotentialManufacturerGeophysicalSurvey Systems Inc.ToshibaMetrabyteBruel & KjaerBruel & KjaerGeonicsABEMABEMType- SIR 2 System- 200,400, 500MHz antenna's- T4700CS laptop computer-DAS 1602 A/D board- Model 4384 Accelerometer(Piezoelectric transducer)- Model 2635 Charge Amplifier- EM 31-D terrain conductivity meter- Tetrameter (SAS 300) resistivity meter- 24 no. 6mm diameter stainless steel tubeelectrodes- Terrameter (SAS 300) resistivity/SP meter- Copper-copper sulphate non-polarizingelectrodes

- 134 -Table CIO - Field Records - Phase 1 Field Trials - Meinhardt WorksGeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRA22.01.9623.01.96S.Problems encountered on sites B and CB15.01.9618.01.96Vlcquownwith scaffolding obstructing to loweringC17.01.9618.01.96of the antenna's down the wall profiles.D19.01.9620.01.96SASWA20.01.9620.01.96A.Voids below surface slabs at sites AB24.01.9625.01.96Sutherlandand B caused coupling problems.C26.01.9627.01.96No spectral analysis made on site, onlyD23.01.9623.01.96data collection.EMA22.01.9623.01.96S.High level of interference caused byB16.01.9616.01.96Mcquownsurface metallic objects, especially atCN.A,N.A.sites A, B and C.D20.01.9620.01.96RIA19.01.9620.01.96A.Dipole-dipole electrode array used.B24.01.9625.01.96SutherlandC26.01.9626.01.96D22.01.9622.01.96SPA19.01.9619.01.96A.Fixed base and gradient array electrodeB24.01.9625.01.96Sutherlandconfiguration used.C26.01.9626.01.96D23.01.9623.01.96Key:Trial Site n A" - Kennedy Town Potice QuartersTrial Site "B" - Eliot Halt, University of Hong KongTrial Site "C* - Sir Ellis Kadoort School, So Kan PoTrial Site "D" - Cape ColHsinson Crematorium, Chai WanGPR - Ground Penetrating RadarSASW - Spectral Analysts of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRI - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool(SR) - Seismic Refraction(MEMUS) - Magnetic/EM Utility Scan( ) - To be carried out at the contractors own cost

- 135 -Table Cl 1 - Contractor Profile - Phase 1 Field Trials1. Main Contractor :Golder Associates (HK) Limited (GAL)2. Joint Venture Companies :Dr. Soheil Nazarian Independent Consultant (SNIC) and Testconsult (HK) Ltd. (TCL)3. The Non-invasive techniques used:a) Ground Penetrating Radar f) Resistivity Imagingb) Spectral Analysis of Surface Waves g) Self Potentialc) Seismic Reflection h) Seismic Refraction *d) Electromagnetic Methode) Infrared Thermography * (carried out at the contractor's own cost)4. Names of Staff to be Employed on the Site Trials:- G. Schneider (GAL) * MSc, (Geophysics)- Dr. I. Bishop (GAL) - MSc, PhD(Geophysics), 10 years exp.- Dr. S. Nazarian (SNIC) - PhD, 13 years exp.- C. Stanley (TCL) - 30 years exp. in infra-red thermograph5. Equipment Details :Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) High ResolutionSeismic Reflectiond) ElectromagneticMethode) High ResolutionThermal Imagingf) ResistivityImagingg) Self Potentialh) SeismicRefractionManufacturerGeophysicalSurvey Systems Inc.EPCSeikoTektronixBison InstrumentsMark ProductsGeonicsAGEMAAdvanced GeoscienceInc.Advanced GeoscienceInc.Bison InstrumentsMark ProductsType- SIR 2 & SIR 8 Systems- 100, 300, 500, 900 and 1000MHz antenna's- 8700 Thermal Printer- SII printer- 2630 Fourier Analyser- 1 Hz, 4.5Hz and 30Hz geophones- lOOOHz seismic accelerometers- Geological pick or sledge hammer- 24-channel Bison 7024 digital instantaneousFloating point stacking seismograph- 30Hz geophones- EM 31-D and EM38 terrain conductivitymeter- Thermovision 880 longwave infraredscanner- Sting Rl Earth Resistivity Meter- 30 cm long steel electrodes- Sting Rl Earth Resistivity Meter- Non-polarizing Electrodes- 24-channel Bison 7024 digital instantaneousFloating point stacking seismograph- 3 OHz geophones

- 136 -Table C12 - Field Records - Phase 1 Field Trials - Golder Associates (HK) Ltd.GeophysicalMethodsGPRSASWHRSREMHRTIRISP(SR)TrialSiteABCDABCDABCDABCDABCDABCDABCDABCDStartDate16.01.9622.01.9619.01.9624.01.9631.01.9631.01.9601.02.9630.01.9618.01.9627.01.9620.01.9625.01.9616.01.9622,01.9619.01.9624.01.9631.01.9612.02.9612.02.96N/A17.01.9629.01.9623.01.9626.01.96N/AN/AN/A25.01.9618.01.9627.01.9620.01.9625.01,96EndDate18.01.9627.01.9623.01.9624.01,9631.01.9631-01.9601.02.9630.01.9618.01,9627.01.9620.01.9625.01.9616.01.9629.01.9623.01.9624.01.9607.02.9612.02.9612.02.96N/A17.01.9629.01.9623.01.9626.01.96N/AN/AN/A26.01.9618.01.9627.01.96•20.01.9625.01.96-PersonIn ChargeDr. I.3ishopDr.S.^azarianG.SchneiderG.SchneiderC. StanleyG.SchneiderDr. I.BishopaSchneiderRemarksSIR 8 system with thermal printer usedinitially to obtain a feeling for groundCondition. Majority of work done withSIR 2 system.Acceierometers used for small spacingle. high resolution high freq. waves.Geophones used for large spacing lowfrequency waves. Voids below surfaceslab caused some problems.On site inspection of the seismic recordsindicated that no reflected waves wereDeing recorded only direct and air wavesand possibly refracted waves.Only success was at site D where theEM31 was used to survey the horizontalplatform at a 1 m grid spacing.Surveys made during late part ofafternoon to ensure surfaces had beenexposed to max. amount of sunlightapart from site C which was surveyedin the morning.Both the Wenner and Dipole-dipoleelectrode arrays were used during thetrials.Self potential method only made at siteD where direct contact with the soilcould be made with the electrodes.Fixed base electrode configuration used.Refraction data collected during HRSRsurvey. Good refraction data collectedat site D.Key:Trial Site "A" - Kennedy Town Police QuartersTrial Site "B* -Eliot Hall, University of Hong KongTrial Site "C H - Sir Ellis Kadoori School, So Kan PoTrial Site W D" - Cape Collisinson Crematorium. Chai WanGPR - Ground Penetrating RadarSASW •••- Spectral Analysis of Surface WavesHRSR - High Resolution Seismic ReflectionEM - Electromagnetic MethodHRTI - High Resolution Thermal ImagingRl - Resistivity ImagingSP -SelfPotential(AST) - Acoustic/Sonic Tool

- 13'1. Main Contractor:Golder Associates (HK) Limited2. Joint Venture Companies :NoneTable C13 - Contractor Profile - Phase 2 Field Trials3, The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Resistivity Imagingd) Spectral Analysis of Surface Waves4. Names of Staff to be Employed on the Site Trials :- Dr. I. Bishop - MSc, PhD(Geophysics), 10 years exp.5. Equipment Details:Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ResistivityImagingd) ElectromagneticMethodManufacturerGeophysicalSurvey Systems Inc.SeikoTektronixAdvanced GeoscienceInc.GeonicsType-SIR 2 Systems-100, 500 and 900 MHz antenna's- SII printer- 2630 Fourier Analyser- 4.5Hz geophones- sledge hammer- Sting Rl Earth Resistivity Meter- 30 cm long steel electrodes- EM 31-Dterrain conductivity meter

- 138 -Table C14 - Field Records - Phase 2 Field Trials - Golder Associates (HK) Ltd.GeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRE01.10.9601.10.96I. BishopBamboo scaffolding at site GF03.10.9603.10.96obstructed the antenna's steadyG07.10.9607.10.96movement along the horizontalH09.10.9609.10.96traverses.SASWH09.10.9609.10.96I. BishopEMG05.10.9608.10.96I. BishopSurveys made at lm centers in a gridH09.10.9609.10.96pattern at both sites.RIEF02.10.9604.10.9602.10.9604.10.96I. BishopSteel nails used as electrodes.•G08.10.9608.10.96H09.10.9609.10.96Key:Trial Site "E" -North of Stubbs Villa, Stubbs RoadTrial Site "F" - Police Quarters, Block B, Hollywood RoadTrial Site M G M - Blue Pool RoadTrial Site "H" - Sze Yu House, Choi Wan EstateGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesEM - Electromagnetic MethodRI - Resistivity Imaging

- 139 -1. Main Contractor:Bachy Soletanche Group (BSG)Table C15 - Contractor Profile - Phase 2 Field Trials2. Joint Venture Companies :Europeanne De Geophysique (EDG)3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Electromagnetic Methodc) Resistivity Imagingd) Spectral Analysis of Surface Waves4. Names of Staff to be Employed on the Site Trials :- F. Lantier (EDG) - S. Geophy. & Geologist, ENSG NANCY, 28 years exp.- R. Foillard (EDG) - Geophysical Engineer, ENSG NANCY, 18 years exp.- M. Lassoved (EDG) - Physics degree, 4 years exp.- J.M. Ragot (EDG) - Geophysical Engineer, BSc, 14 years exp.5. Equipment Details:Techniquea) GroundPenetrating Radarb) ElectromagneticMethodc) ResistivityImagingd) Spectral Analysisof Surface WavesManufacturerGeophysicalSurvey Systems Inc.GeonicsEDGMetravibScientific AtlantaMetravibType-SIR2 System- 500, 900 and 1000MHz antenna's- EM38 terrain conductivity meter- Multiplex voltmeter- Non-polarizing Electrodes- RAIO Seismograph- Spectral Dynamics SD380 Signal Ana.- CSH 05 Piezoelectric Accelerometer

- 140 -Table C16 - Field Records - Phase 2 Field Trials - Bachy Soletanche GroupGeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRE05.10.9605.10.96R. FoillardBamboo scaffolding at site G obstructedF08.10.9608.10.96the antenna's steady movement alongG09.10.9610.10.96the horizontal traverses.H07.10.9607.10.96SASWH10.10.9612.10.96M.Generator used to produce constantLassovedfrequency vibrations.EMG10.10.9610.10.96J.M. RagotAnomalies caused by fence, vehiclesH07.10.9607.10.96and a Towngas pipe.RIE05.10.9605.10.96J.M. RagotHilti-bolts used as electrodes.F08.10.9608.10.96G09.10.9610.10.96H07.10.9607.10.96Key:Trial Site "E"Trial Site H F MTrial Site "G"Trial Site "H M•North of Stubbs Villa, Stubbs Road• Police Quarters, Block B, Hollywood Road• Blue Fool Road• Sze Yu House, Choi Wan EstateGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesEM - Electromagnetic MethodRI - Resistivity Imaging

- 141 -Table C17 - Contractor Profile - Phase 2 Field TrialsL Main Contractor:Fugro Geotechnical Services (HK) Ltd.2. Joint Venture Companies :None3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Electromagnetic Methodc) Resistivity Imaging4. Names of Staff to be Employed on the Site Trials :- A. K. Whittle - Geophysicist, 20 years exp.- D. A. Pearks - BSc, MSc(Geophy)5. Equipment Details :Techniquea) GroundPenetratingRadarb) ElectromagneticMethodc) ResistivityImagingManufacturerGeophysicalSurvey Systems Inc.RadarteamGeonicsABEM InstrumentsABType- SIR 2 System- 500 MHz antenna- 35 MHz antenna (2no.)- EM31 conductivity meter- Terrameter SAS 300B- Steel electrodes

- 142 -Table C18 - Field Records - Phase 2 Field Trials - Fugro Geotechnical Services (HK) Ltd.GeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRE10.10.9610.10.96A.K.G.P.R. over heating problem at site G.F12.10.9612.10.96WhittleOnly relatively low frequency antenna'sG15.10.9615.10.96used 200MHz + 35MHzH16.10.9616.10.96EMG15.10.9616.10.96A.K.EM surveys carried out at lm grid atH17.10.9617.10.96Whittleboth sitesRIE11.10.9618.10.96A.K.Delays in RI survey caused byF19.10.9619.10.96Whittleequipment failureG22.10.9622.10.96H17.10.9617.10.96Key:Trial Site "E"Trial Site M F"Trial Site n G nTrial Site M H"• North of Stubbs Villa, Stubbs Road• Police Quarters, Block B, Hollywood Road• Blue Pool Road• Sze Yu House, Choi Wan EstateGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesEM - Electromagnetic MethodRI - Resistivity Imaging

- 143 -1. Main Contractor:Guangdong South China EGTD Co.2. Joint Venture Companies :NoneTable C19 - Contractor Profile - Phase 2 Field Trials3. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Resistivity Imaging4. Names of Staff to be Employed on the Site Trials :- Lin Youcong - Sen. Geophysic Engineer, MCSST, MCSG 5 30 years exp.- Huang Weiyi - Sen. Geophysic Engineer- Zhang Shihong - Sen. Geophysic Engineer- Zhao Ming - Geophysic Engineer- Ge Rubing - Geophysic Engineer- Meng Fangiang - Assist Geophysic Engineer- Zhang Yuming - Assist Geophysic Engineer5. Equipment Details:Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ResistivityImagingManufacturerGeophysicalSurvey Systems Inc.GeometricMachinery & Electron.Institute, Ministry ofGeology & MineralResources, PRC.Type- SIR 2 and SIR 10H System- 100(2no.), and 500 MHz antenna f s- Strata View R24 signal seismograph- 4.5, 10 and 60 Hz geophones- MIS-2 Multi-electrode Switch- MIR-1C Voltmeter

. 144 -Table C20 - Field Records - Phase 2 Field Trials - Guandong South China EGTD Co.GeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRE22.10.9623.10.96ZhaoBoth continuous profiling and pointF24.10.9624.10.96Mingby point profiling was used.G26.10.9628.10.96H29.10.9629.10.96SASWE22.10.9622.10.96ZhangContractor experienced problemsF24.10.9624.10.96Shihongwith noise from traffic at sites E, FG26.10.9628.10.96& G and from construction plant atH29.10.9629.10.96Site H.RIE22.10.9623.10.96HuangThree different electrodes configurationsF24.10.9624.10.96Weiyiwere used at each site - Wenner,G26.10.9628.10.96Dipole - Dipole and Differential.H29.10.9629.10.96Key:Trial Site M E"Trial Site "FTrial Site "G"Trial Site "H w> North of Stubbs Villa, Stubbs Road• Police Quarters, Block B, Hollywood Road• Blue Pool Road• Sze Yu House, Choi Wan EstateGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesEM - Electromagnetic MethodRI - Resistivity Imaging

- 145 -Table C21 - Contractor Profile - Phase 2 Field TrialsI. Main Contractor:Institute of Geophysical and Geochemical Exploration, China (IGGE)2. The Non-invasive techniques used :a) Ground Penetrating Radarb) Spectral Analysis of Surface Wavesc) Resistivity Imaging3. Names of Staff to be Employed on the Site Trials :- Luo Zhuangwei (IGGE) - Senior Geophysicist, deputy Director of IGGE- Zhou Anchang (IGGE) - Professor in Geophysics- Yang Piyuan (IGGE) - Professor in Geophysics- Hu Ping(IGGE) - Senior Geophysicist- Yuan Shoucheng (IGGE) - Senior Geophysicist- Yuan Guanding (IGGE) - Senior Geophysicist- Feng Nian (IGGE) - Senior Geophysicist- Zhong Qing (IGGE) - Senior Geophysicist- Liu Feng (IGGE) - Senior Engineer4. Equipment Details :Techniquea) GroundPenetrating Radarb) Spectral Analysisof Surface Wavesc) ResistivityImagingManufacturerGeophysicalSurvey Systems Inc.Hewlett-PackardHewlett-PackardZonge Engineering &Research OrganizationChina Geology UniverChina Geological Inst.Type- SIR 10A System- 100(2no.), and 500 MHz antenna's- Dual-channel Dynamic Singal Analyzer- Computer- GRP-32 wide-band electric survey system-DUM-1 Swith

- 146 -Table C22 - Field Records - Phase 2 Field Trials - Institute of Geophysical and GeochemicalExplorationGeophysicalTrialStartEndPersonRemarksMethodsSiteDateDateIn ChargeGPRE26.10.9628.10.96YuanF29.10.9629.10.96ShouchengG31.10.9631.10.96H25.10.9625.10.96SASWE .28.10.9628.10.96YangG31.10.9631.10.96GuandingH25.10.9625.10.96RIE15.10.9628.10.96YangF29.10.9630.10.96GuandingG31.10.9631.10.96H24.10.9624.10.96Key:Trial Site "E M - North of Stubbs Villa, Stubbs RoadTrial Site "F" - Police Quarters, Block B, Hollywood RoadTrial Site "G" - Blue Pool RoadTrial Site "H" - Sze Yu House, Choi Wan EstateGPR - Ground Penetrating RadarSASW - Spectral Analysis of Surface WavesEM - Electromagnetic MethodRI - Resistivity Imaging

- 147 -APPENDIX DASSESSMENT OF THE PHASE 1 FIELD TRIAL RESULTS

- 148 -CONTENTSPageNo.CONTENTS 148D. 1 HIGH RESOLUTION SEISMIC REFLECTION 150D.I.I Operation Procedure 150D.I.2 Summary of Results 150D.1.3 Assessment of the Method 151D.2 SPECTRAL ANALYSIS OF SURFACE WAVES 152D.2.1 Operation Procedure 152D.2,2 Summary of Results 152D.2.3 Assessment of the Method 153D.3 RESISTIVITY IMAGING 154D.3.1 Operation Procedure 154D.3.2 Summary of Results 154D.3.3 Assessment of the Method 155D.4 SELF POTENTIAL 156DAI Operation Procedure 156D.4.2 Summary of Results 157D.4.3 Assessment of the Method 157D.5 ELECTROMAGNETIC METHODS 157D.5.1 Frequency-Domain Electomagnetics 157D.5.1.1 Operation Procedures 157D.5.1.2 Assessment of the Method 158D.5.2 Time-Domain Eletromagnetics 158D.5.2.1 Operation Procedure 158D.5.2.2 Assessment of the Method 158D.6 GROUND PENETRATING RADAR 159D.6.1 Operation Procedure 159D.6.2 Assessment of the Method 160

- 149 -D.7 THERMAL IMAGING 161D.7.1 Operation Procedure 161D.7.2 Assessment of the Method 162LIST OF TABLES 163LIST OF PLATES 165PageNo.

- 150 -D.I HIGH RESOLUTION SEISMIC REFLECTION.D.I.I Operation ProcedureThe method was practised by three of the six contractors (see Appendix C). Theequipment and set up used in the field by the three companies were very similar. A 2-6 kgsledge hammer was used as the power source (Plate Dl). At Sites A, B and C spike geophoneswere inserted into pre-drilled holes (Plate D2). Along the vertical slope and wall traverses,geophones with flat surfaces were used by GSC to allow attachment using rapid hardeningglue (Plate D3). This appeared to work reasonably well unless the surface was rough as in thecase of the shotcrete along TAOl or some of the masonry blocks. In such cases a smooth areawas prepared first. IGGE used plaster of paris to couple the geophones to hard surface cover(Plate D4). The geophone spacing used was lm by GA, 0.5m to lm by GSC and 0.25m to0.7m by IGGE. Typically hammer blows were repeated 3-6 times at the source for stacking ofseismic traces to enhance signals. The source location was moved along the traverse lines atpredetermined intervals and the seismic data were recorded in separate data files. Notch andcorner filters were sometimes applied during the field collection of data. Filters were normallyapplied in the data analysis.A number of operations were carried out to process the field data. It appears that all ofthe three companies have canned software programs to process the data, but only GSC andGA detailed the data processing operations and the sequence of the data processing in theirreports. Certain pre-processing operations were done as standard procedures. The data werefirst combined into a single file and converted into common depth point format. Subsequentdata analyses differed between the companies but normally involved the following operations:adjustments and equalising of gains of seismic traces, filtering of noise, velocity analysis,dynamic correction, applying f-k domain filters, and stacking. The processing software usedby IGGE was not standard and therefore the reliability of the results are difficult to assess.D.I.2 Summary of Results(a) IGGE presented seismic sections of all traverses withreflectors marked on the sections. Interpretative crosssections are given along with the seismic cross sections.They claimed to have reliably determined the geometry ofthe retaining walls and identified subsurface strata at everysite. They also claimed to have detected accurately thelocations of anomalous structures.(b) GSC presented seismic results of all traverses except TC03and TD04. Interpreted cross sections are presented. Thisreport suggests that the method did not determine thethickness and geometry of retaining walls but was able toidentify voids, bedrock interfaces, and structural fractures.(c) GA claimed that the method failed to identify unambiguousreflectors from any of the traverses, perhaps with the

- 151 -exception of TB04. Generally, no coherent reflectors wereconvincingly mapped.D.I.3 Assessment of the MethodAn experienced team can finish the fieldwork of shooting a traverse in 3-4 hours.Normally at least two persons are needed to conduct the survey. The layout of the seismicspread requires substantially more time than the data collection, especially if the geophonesneed to be glued onto the surface. Seismic methods are sensitive to environmental noise,especially vibrations caused by traffic and machinery operating nearby.The seismic reflection surveys conducted by the three companies did not produceconsistent and reliable results. The cross sections produced, even for the same traverse, differsubstantially. The final section produced depends greatly on the parameters used in the dataprocessing. A high level of subjectivity appears to have been involved in the selection of theseparameters.The claim made by IGGE in its draft interim report that the method produced accuratedetermination of the wall thickness and subsurface stratigraphy has not been repeated by othercontractors. The reflectors in IGGE's report are ambiguous and unconvincing. Theinterpretation and placement of layer interfaces and subsurface anomalies were consideredarbitrary and not well justified. Both IGGE and GSC made some speculative correlation'sbetween the borehole information and the seismic results. Without any borehole information,it is considered that many features and interfaces would not have been identified on theseismic sections alone. GA's assessment of the method in that it failed to image majorinterfaces between different materials is considered to be a realistic evaluation.The efficiency of the method also depends on the condition of the structure beingsurveyed. Air space present beneath the surface coverings can greatly affect the coupling ofthe geophones to the material beneath. Such problems may be remedied by burying thegeophones deeper into the underlying material, but the process would then be invasive innature.Engineering and man-made structures, such as storm water drains and concrete tiebeams, appear to have acted as wave guides along which seismic energy is diverted andchannelled, resulting in strong attenuation of seismic energy with depth. The mortared jointsbetween masonry blocks in a retaining wall greatly attenuated the wave velocity.Since the surveyed structures are all relatively shallow, ground roll was a majorproblem because of the short separation between the arrival of the direct wave and thereflected wave.Sucessful use of the method depends on a strong contrast in acoustic impedancebetween the target and the surrounding geology. The longitudinal compression wave velocityof the material itself is an undetermined factor that could affect the interpretation. In thecontracted surveys, the velocity was generally estimated using either seismic refraction orfrom multiple reflectors. No consistent velocities were given. The depth profiles were

- 152 -normally constructed based on a single constant velocity which is an invalid assumption.Theoretically, the method has unlimited penetration dictated by the power source. Voids aredifficult to locate and identify with the method, since it produces a negative acousticimpedance at the material-void interface.D.2 SPECTRAL ANALYSIS OF SURFACE WAVESD.2.1 Operation ProcedureSASW was carried out by five of the six contractors, each using different equipment(see Appendix A). Piezoelectric accelerometers coupled to hard surface protection usingplaster of paris and spiked magnetic pads were used by BS and MW (Plates D5 and D6). BothIGGE and GSC used geophones coupled by inserting the spiked end into pre-drilled holes orwith plaster of paris (Plates D7 and D8). GA used low-frequency geophones and seismicaccelerometers (Plate D9), They coupled the geophones and accelerometers to the surface byvarious methods depending on site conditions. Hammers of various sizes were used as thepower source. Small light hammers were used to generate high frequency waves and heaviersledge hammers were used to generate lower frequency waves (Plates D10 & Dl 1). Typicallythe hammer blow was repeated 4 to 5 times at the source for stacking to enhance the signals.The site procedures were fairly consistent apart from GSC who used a multiple geophonearray to collect the field data (Plate D12). The other contractors used either two or fourgeophones in a common receiver mid-point array (Plate D13). In this array the geophonesspacing is doubled after each test about a common mid-point. Hammer blows were made ateither end of the geophone spread.All the contractors except MW used a spectral analyser on site to allow real timespectral calculations so that the quality of the data collected could be monitored and fieldadjustments made (Plate D14). MW recorded acceleration time histories on a laptop computeron site, with signal analysis carried out later using MATLAB software. Typically after signalanalysis, dispersion curves (velocity versus wavelength) are constructed. From the dispersioncurves, shear wave velocity depth profiles can be constructed by inversion or forwardmodelling techniques. Only GA, IGGE and MW have presented details of the full analysisprocedure and produced depth versus shear wave velocity profiles.D.2.2- Summary of Resnifc(a) BS did not carry out the full SASW analysis, only presentingthe characteristic Rayleigh wave velocity and frequency forsurface materials.(b) IGGE present interpretation of the SASW data for alltraverses in the form of contoured shear wave velocityversus depth sections. They claim to have measured thethickness of retaining walls and have characterised thegeology at each of the sites.

- 153 -(c) GSC present pseudo-dispersion curves and interpretedgeological models for all the traverses. The interpretation isbased on the pseudo-dispersion curves as no inversion orforward modelling has been made. They claim to havesuccessfully measured the thickness of the retainingstructures and located voids below the shotcrete surfaceprotection along TA02 and behind the masonry wall alongTB03.(d) MW present contoured shear wave velocity versus depthsections for the longer traverses. They were not able tomeasure the thickness of the retaining walls but were able todetermine shear wave velocity depth information for fill andnatural materials.(e) GA present selected dispersion curves and shear wave depthprofiles for all of the sites. They were unable to measure theretaining wall thickness but obtained consistent data formost of the horizontal traverses at the top of walls or at theslope sites.D.2.3 Assessment of the MethodAn experienced team of one geophysicist and a labourer can complete the field work ofshooting one traverse in 1 to 2 hours. None of the contractors reported problems withvibration noise at any of the sites. The depth of penetration of the method is dependent ongeophone spacing and is therefore constrained by site conditions. Where voids exist below arigid surface cover, such as a concrete slab, de-coupling of the geophone from the soil belowis reported by most of the contractors.Depth of penetration and resolution is dependent on the wave length of the Rayleighwave produced and detected. As noted above, the physical limitation of space on site will alsoaffect the maximum penetration depth. MW and GA achieved resolution of between OJm to0.2m while GSC and IGGE achieved resolution to between 0.5m and 1.0m. At sites withlimited space, penetration depths of 3m to 4m were generally achieved. At Site D, themaximum depth of penetration was 12m. Depths to discrete objects were not reported by anyof the contractors.Both MW and GA were not able to interpret the SASW data obtained from themasonry walls at Sites B and C. They both report that reproducible dispersion curves couldnot be obtained for shallow depths into the walls. They suggest that this is probably due to thewall facing being made up of discrete blocks separated by cement mortar and therefore notbeing a continuum and producing very complex wave propagation patterns which cannot beinterpreted with existing algorithms. The horizontal tie beams also cause similar effects, asdemonstrated in the GA report (Golder Associates, 1996a).

- 154 -The technique has the ability to produce high resolution cross sections to depths of12m to 15m (see Meinhardt Works, 1996, Site D) if soundings are made at close spacing.The dispersion curves obtained by each contractor were generally consistent in form.However, interpretation of the dispersion curves is inconsistent apart from at Site D. Theinconsistency is likely to be due to the complex ground conditions, especially at the masonrywall sites. The consistency of the results obtained at Site D support this conclusion since theground conditions are simple compared with the other three sites.D.3 RESISTIVITY IMAGINGD.3.1 Operation ProcedureThe method was practised by five of the contractors (see Appendix C). The dipoledipolearray configuration was used by most of the companies, except IGGE who used atripolar configuration and GA, who employed dipole-dipole at one site and the Wennerconfiguration at others. Electrode spacing between lm and 2m were generally used. BS drilledand inserted "Hilti" bolts into hard surface protection at calculated distances, which were usedas electrodes (Plate D15). Most other contractors used steel pins inserted into pre-drilled holesthrough surface protection so that they could make direct contact with the soil beneath (PlateD16). Multi-conductor cables with takeouts for electrode connections which enabled currentto be cycled to particular pairs of electrodes helped to minimise the time required for theelectrode deployment (Plate D17).In the tripolar or dipole-dipole configuration, the resistivity measured was plotted atthe intersection of two lines extending at 45° from the centres of the current and potentialelectrode pairs. As the current and potential electrodes were moved, a pseudosection ofresistivity readings of the subsurface is obtained. The depth depicted in the pseudosectiondoes not represent true depth but is relative in nature. GA modelled the Wennerpseudosections using the programme RESIST to produce two-dimensional resistivity versusdepth sections.D.3.2 Summary of Results(a) BS conducted resistivity surveys at the relatively longprofiles, including TA03, TA04, TB04, TB05, TC03, TD01,TD02. The depth of the section produced was generallyabout 5m. High resistivity areas were attributed to relativelyunweathered rock where as low resistivity areas wereattributed to high moisture zones.(b) IGGE conducted resistivity surveys on all of the traverses.For the longer traverses (TA01, TA02, TB04, TB05, TB03,TD01, TD02) the depths of the pseudosections extended toabout 8m. For the shorter sections, penetration depths areonly about 2m. Their report contains cross sections showing

- 155 -interpretations of subsurface materials, and thickness ofmasonry walls.(c) FGS conducted resistivity surveys on TA03, TA04, TB04,TB05, TCG3, TD01, TD02. The report claimed to havesuccessfully mapped out variations in resistivity valuesbeneath slopes, which can be correlated to geologicalfeatures.(d) MW made resistivity surveys on all traverses and state thatthey have successfully obtained data of enhanced moisturezones and the geometry of structures.(e) GA conducted the survey on the relative long sections,including TA03, TA04, TB04, TB05, TC03, TD01, TD02.Two dimensional cross-sections are produced from IDmodels at point locations along each traverse.D.3.3 Assessment of the MethodThe method is efficient and quick in the field. The teams completed the measurementof a traverse in about 3-4 hours with a minimum of 1-2 persons to operate in the field. Goodcoupling between the electrodes and the ground is required. Short circuiting due to thepresence of metallic objects in the ground severely affected the results at Site A, traverseTA04. Such problems can be partially overcome by using a conductive gel or cotton woolsaturated with salt water around the electrodes (Plate 18). Resistivity surveying theoryassumes point current source at a known position. However, by inserting the electrode into theslab only, this condition may not be satisfied, especially if a void exists between the slab andsoil directly below the electrode position. This potential problem did not appear to affect theresults obtained by BS. The method is not truly non-invasive, since it requires electrodeinsertion into pre-drilled holes, although no structural or irreparable damage occurred duringthe trials.The usefulness of the method is limited by the extent of the traverse/On the relativelyshort traverses of about 6m to 10m, only a depth of approximately 2m is attained. For thelonger traverses over 20m, a depth of 7m can normally be achieved. Resistivity sections atboth end portions of the lines are normally not obtainable, because the resistivity valueobtained is for the intersection point located along a line extending at 45° from the electrodes.Generally, the different resistivity sections obtained by different contractors and involvingdifferent methods are consistent. A comparison of the results on selected traverses is givenbelow.(i) TA03. A zone of low resistivity (less than lOOOm), centredat traverse distance 28m, have been located by all of thecontractors. This zone corresponds to the area affected bydrainage water overflow (Figure 3).

- 156 -(ii) TA04. All five profiles show a zone of low resistivity attraverse distance Orn to 14m and depth less than 2m. This islikely to be electrical noise from the electricity sub-stationlocated at the beginning of this traverse (Figure 3).(iii)TB04 and TB05. All of the reported resistivity sectionsshow a value of about 25012m for the surface covering.Except for MW and IGGE's reports, the ranges of variationsare quite similar, although individual reports may showdifferent anomalies at various locations and depths.(iv) TC03. All of the reported sections show a resistivity of over800Qm associated with the masonry wall and generaldecrease in resistivity with depth. Three to four isolatedanomalies have been detected by some contractors but notall.(v) TD01. A large zone of very high resistivity (greater thanlOOOOm) located at distance 40m to 60m and depth 0m to6m has been located by all of the contractors. All of thecross sections show substantial variations in the resistivityvalues of the profile.In general the results obtained by the different contractors, despite the differentequipment, electrode configuration, and software used, are in good agreement with each other.D.4 SELF POTENTIALD.4.1 Operation ProcedureThe self potential method was tested by three of the contractors (see Appendix C). Theequipment used is simple, consisting of two non-polarising electrodes and a resistivity meter(Plate D19). All three contractors used the fixed base electrode array in which one electroderemains stationary whilst the roving electrode is moved along the traverse, generally at lmintervals. At Sites A, B and G, MW also used a gradient-type electrode array where the pair ofelectrodes are moved along the traverse at a fixed spacing of lm. At vertical surfaces, MWand BS fixed a high porosity foam pad to the base of each electrode, saturated with eithercopper sulphate or conductive gel to lower the electrode-ground contact resistance andincrease the excitation current (Plate D20). GA only carried out a survey at Site D as the fieldteam stated that the measurements are only meaningful if direct contact with the soil can bemade. This was not possible at the other three sites without excavating through hard surfaceprotection. At Site D, GA excavated small holes for insertion of the non-polarising electrodes(Plate D21). During the survey the fixed base electrode was protected from the sun. Thesurvey was repeated twice, once without soaking the soil at electrode locations and secondlyafter the electrode positions had been soaked with water overnight.

- 157 -None of the contractors carried out any post-survey data processing and simplypresented the data in the form of millivolt profiles along each of the traverses surveyed.D.4.2 Summary of Results(a) BS present profiles for all the traverses but nointerpretations.(b) MW present profiles and self potential vectors for traversesTA04, TB04, TBG5, TC01, TC02, TC03, TD01 and TD02.Zones of higher moisture content at the base of the wall atSite C is inferred. Self potential lows along TD01 coincidedwith surface drain locations.(c) GS present a profile for TD01 only. A self potential lowcoincided with a surface drain location.D.4.3 Assessment of the MethodThe self potential method was severely affected by surface or sub-surface metallicobjects rendering it impossible to verify the interpretation of the survey results at Sites A, Band C. Only at Site D, which was relatively free from surface metal and had no hard surfacecover which allowed positive contact of electrodes with the soil, could repeatable results beobtained by GA.The results obtained by all three contractors for traverse TD01 are to a certain degreeconsistent. All show a slight general increase in self potential from north-west to south-east.Small negative anomalies were recorded at the location of surface water drains.D.5 ELECTROMAGNETIC METHODSD.5.1 Frequency-Domain ElectromagneticsD.5.1.1 Operation ProceduresFour of the contractors tested the frequency-domain electromagnetic method (seeAppendix C). Each used equipment manufactured by Geonics, either the EM 31-D or thesmaller EM38 (Plates D22 & D23). They both measure quadrature and in-phase componentsof the electromagnetic field produced by induced eddy currents. The sampling depth of theEM 31-D and the EM38 is about 5.5m and 1.5m respectively and is related to the inductioncoil spacing. In the field, readings were taken at 1m intervals along each traverse. At Site D,the survey made by GA was on a lm grid over the platform area (Plate 24). Data loggers wereused on site to collect the raw data.

- 158 -Very little data processing is required and results are plotted as conductivity profilesalong each traverse. GA did however produce contour plans of terrain conductivity for Sites Cand D using the griding programme RANGRID and the contouring programme GEOSOFT.D.5.1.2 Assessment of the MethodUsing either the EM31-D or the EM38, surveys are efficient and quick and can becarried out by a single geophysicist. Depth of penetration is limited by coil separation and theresistivity of the sub-surface soil and rock. The technique is best suited to producingconductivity contour maps of near surface-geology.Anomalies due to surface or buried metallic objects are orders of magnitude greaterthan anomalies produced by geological or geotechnical features. All four contractors reportedthat near-surface metal or nearby machinery affected the results such that interpretation wasimpossible at Sites A and B. At Site C, generally consistent results were obtained by FGS, BSand GA. Along traverse TC01 and TC02, the measured conductivity increases towards thebase of the wall. This may be due to an increase in wall thickness or an increase in moisturecontent in the lower part of the wall. At Site D consistent results were obtained by allcontractors along TD01. Significant anomalies were measured at chainages 30m and 80m,attributed to a manhole cover and an electricity cable respectively. The backgroundconductivity measured is low and constant along the traverse. No useful interpretationregarding the thickness or nature of the fill at this site could be made from the results.D.5.2 Time-Domain ElectromagneticsD.5.2.1 Operation ProcedureThe TDEM method was used by two out of the six contractors (see Appendix C). Bothused similar equipment consisting of coincident loop transmitter and receiver coils. IGGEused a square (2m by 2m) transmitter coil with a horizontal circular 500mm diameter receiverlocated at the centre of the transmitter coil (Plate D25). GSC used a rectangular (2m by lm)transmitter coil with a vertical rectangular (lm by 0.5m) receiver coil which wasmanufactured in-house (Plate D26). Receiver coil orientation determines which component ofmagnetic flux is being measured. A horizontal coil measures the vertical magnetic fluxcomponent while a vertical coil measures the horizontal magnetic flux component. Soundingswere made by both contractors at lm intervals along each traverse.A number of operations were carried out to process the data. Initially voltage versustime sections are produced from the raw data after initial filtering. Apparent resistivitypseudosections are then constructed from the voltage versus time sections. Thepseudosections can then be inverted into resistivity versus depth sections. GSC present bothvoltage versus time sections and apparent resistivity pseudosections. IGGE present inverteddata in the form of resistivity versus depth profiles. The inversion process was carried outusing an in house inversion software package TEMPRO.

- 159 -D.5.2.2 Assessment of the MThe method is quick to use. A single traverse can be carried out by one to two personsin about one hour using the small coincident loop configuration equipment. It has distinctadvantages over the more conventional resistivity traverses since installation of electrodes isnot required and information is gathered to the full depth of investigation along the completetraverse with the small transmitter coils adopted. Depth of penetration is determined by thetransmitter coil size and both contractors report investigation up to 20m deep with the coilsused in the trials, however this depth will be significantly reduced if high-conductivitymaterials are encountered. Resolution is dependent on how quickly the transmitter current canbe turned off and the receiver gates opened and shut. GSC used current turn-off time of Sjixsand a first receiver gate cycle time of 20JIS. IGGE used current turn-off time of 11.25jis andthe first receiver gate cycle time of 15.75|is. Sampling times at short time intervals arerequired to investigate shallow surface materials with any accuracy. Both contractors reportthat high levels of noise was experienced at Sites A, B and C due to near-surface metallicobjects which made the results difficult to interpret.The results presented by each contractor are not directly comparable since differentmagnetic flux components have been measured and the results are presented in slightlydifferent forms. However, there does not appear to be any consistency in the results. Theclaims made by both contractors that they are able to determine wall thickness andstratigraphy by this method are not substantiated by the GI results. The interpretation andplacement of structural and stratigraphic boundaries appear arbitrary and poorly justified.The apparent resistivity pseduosections produced by GSC and to some extent theresistivity depth sections produced by IGGE should be directly comparable to the apparentresistivity pseudosections obtained using the resistivity imaging method. However, there doesnot appear to be any consistency in the results between these two methods.D.6 GROUND PENETRATING RADARD.6.1 Operation ProcedureGround penetrating radar was tested by all six contractors (see Appendix C). Each usedradar equipment manufactured by Geophysical Survey Systems Inc. (GSSI), either the SIR 2or SIR 10 systems antennas ranging from high-frequency 900MHz and IGHz (Plate D27) tolow-frequency 100MHz (Plate D28) and 200MHz (Plate D29). GA also used a SIR 8 systemwith a thermal printer for initial surveys. FGS also used equipment manufactured by Sensorsand Software Inc. (SSI) (Plate D30) and a 35MHz antenna manufactured by Radarteam (PlateD31). All the equipment used provide real time radargram sections.The antennas were pulled along horizontal surfaces and either lowered or pulled up thesub-vertical and vertical structures using ropes attached to the antennas (Plate D32). MW andIGGE both used survey wheels which provide encoded distance information automatically onthe radargram (Plate D33). The other contractors recorded manually electronic fiducialdistance markers onto the radargram, generally at lm intervals, It was noted that the teamsfrom BS, MW and GA repeated traverses more than once, making adjustments to the gain

- 160 -levels, ranges, sampling interval and filter settings. FGS, MW and BS carried out commondepth point surveys (Plate D34) and GA used known depths to reflectors such as utilities to tryto measure radar wave velocity at each of the sites.Sophisticated data processing techniques borrowed from seismic reflection dataprocessing can be applied to ground penetrating radar data. All the contractors used the GSSIRadan 3 software which is an advanced signal processing package designed to process SIRsystems data. The processing package includes high and low pass filters, gain control andcolour tables, together with more sophisticated processing techniques such as migration,deconvolution and spatial filtering. General processing made by all the contractors consistedof applying low or high cut filters to remove noise, gain adjustments and colour enhancement.More complex Kirchhoff migration processing was made by GA.D.6.2 Assessment of the MethodAn experienced team consisting of one geophysicist and one technician can complete asingle traverse in one to two hours. The equipment is robust and relatively light and can easilybe moved by one person, especially the SIR 2 and pulseEKKO 1000 systems. The larger low -frequency antennas are not as easy to manoeuvre and require two to three persons for thevertical traverses (Plate D35).The method is not affected by vibration noise, however reinforcement in concrete slabsgreatly reduces penetration depth as the radar waves are attenuated dramatically. Somepenetration can be obtained by using high-frequency antennas such as 900MHz or lGHzwhich effectively see between the reinforcing bars if the bar spacing is not too small. This wasdone at Site A along TA01 and TA04 by several of the contractors. Other metallic objectssuch as manhole covers, steel gratings and metal pipes cause localised high amplitudereverberations on the radargram which can obscure other information. This phenomenon wasevident at most of the sites surveyed. All radar antennas used in the trails were shielded fromextraneous radar waves, however, GA report that air wave interference with the 100MHzantenna was recorded at Site C.The depth of penetration of radar waves are dependent on frequency and the dielectricconstant of the ground. The high-frequency antennas achieve high resolution but poorpenetration depths. At the trials the 900MHz and lGHz antenna generally achievedpenetration depths between 0.25m and 0.75m with resolution of 50mm at some sites. The500MHz and400MHz antennas generally achieved penetration depths of between 1m and 4mwith a resolution of 100mm. The low-frequency antennas such as the 200MHz and 100MHzachieved penetration depths of up to 8m to 10m but resolution was relatively poor at aboutlm.The determination of depth is dependent on the electromagnetic wave velocity used inthe analysis. Most of the contractors used values from published data or used a bulk velocitycalculated from depth to known reflectors or from common depth point surveys made on site.The wave velocity used by each contractor varied by as much as 50% for the same site andtraverse. In general, velocities ranged between 0.12m/ns to 0.08m/ns but values as low as0.05m/ns were used by some of the contractors. It should also be noted that a single velocity

- 161 -was generally used by all contractors to calculate depths. This assumption is incorrect sinceeach material through which the radar wave penetrates has a different velocity. The depths ofpenetration reported are therefore not accurate. For accurate determination of depth toreflectors the dielectric constant of each material in the section should be measured.Maintaining antenna contact onto the vertical walls was problematic especially for thelarger, low-frequency antennas (Plate D36). Antenna contact was also a problem along thelower section of the fill slope traverse TD02 due to the surface being composed of angularcobbles and boulders of rock fill (Figure 11). This was not a problem for FGS who used anon-contact 35MHz antenna (Plate D37).Due to the complex data processing, a high level of expertise is required in both datacollection, manipulation and interpretation. It is evident from the results contained in thecontractors' reports that certain contractors were able to capture clearer radar images thanothers using the same equipment. It is considered that the best results were obtained by GA,MW and BS who all used the SIR 2 system with a wide range of antennas. It is noticeable thatthese three contractors repeated traverses more than once, making adjustments to the gainlevels, ranges, sampling interval and filter settings at the data acquisition stage. Contractorswho used the SIR 10 system did not produce as good as results as those using the SIR 2. It isnot clear, however if this is contractor- or equipment-dependent. Results obtained using thepulseEKKO 1000 were not useable at any of the sites except for traverse TC03.Consistent results were obtained by the different contractors along many of thetraverses and are summarised in Table Dl. An interesting point to note is the interpretationmade by MW along traverses TB04 and TB05. Parabolic anomalies with long diffraction tailshave been interpreted as thin vertical structures running perpendicular to the traverse line.Other contractors also recorded parabolic and other anomalies at the same locations butinterpreted them as either utilities or surface artefacts such as manhole covers. Thisdemonstrates the potential problems with differing interpretations of similar anomalies.D.7 THERMAL IMAGINGD.7.1 Operation ProcedureOnly BS and GA tested this method (see Appendix C). BS employed a thermal probe(Plate D38)which has a resolution of about 0.0 l m C and measures air and surface temperatureswhich are recorded on a data logger. GA used a Thermovision scanner (Plate D39) accurate to0.05 m C and recorded the infrared image on video. BS carried out the surveys between24:00hrs and 02:00hrs and reported that 50 readings could be obtained in 30 minutes.Readings were made at lm intervals along each traverse. GA carried out the survey duringdaylight after the surveyed object had been exposed to direct sunlight. Because of the lowsolar angle and the proximity of adjacent structures, direct sunlight only lasted for a few hoursat each site. GA did not carry out any thermography at Site D.BS did not carry out any post-survey processing and simply presented profilescomprising the air temperature, ground temperature and temperature difference along eachtraverse. GA analysed the data using the AGEMA C.A.T.S. image enhancing software whichcan present the data in either a grey scale or a colour enhanced image.

- 162 -D.7.2 Assessment of the MethodThe method is quick and easy to carry out by one person. The equipment is portableand robust. There are some conflicting views as to the optimum time to undertake the survey.BS recommended that surveys are best done at night to minimise background noise fromartificial heat sources. GA suggest that surveys should be made in the early evening so that thefeature has adsorbed as much direct radiation as possible. The method appears to be subject toconstraints of time, weather and climatic conditions. The radiance from the surveyed surfaceswas dependent on the orientation of the surface with respect to the sun, time and duration ofexposure to solar heat, weather conditions at the time of the survey, and seasonal conditionssuch as the strength of the solar radiation and the attitude of the sun. GA recommend thatsurveys should be made during the summer months when solar radiation is at its highest. Thiswould also be beneficial in that zones of high moisture content would be at a maximumduring the wet season. The temperature of "hot" and "cold" spots relative to the surroundingmaterial can reverse from day to night if the anomaly is produced by an air-filled void. Duringthe day an air-filled void heats up quicker than its surroundings and therefore appears as a"hot 11 anomaly. During the night it cools down quicker than its surroundings and appears as a"cold" anomaly. Therefore it is important to carry out the survey when the anomaly is either"hot" or "cold" rather than during its transition phase.Only traverses TA01, TA02 and TB04 have thermal results from both teams forcomparison. There appears not to be any consistency between the results obtained. It alsoappears that the temperature anomalies identified by GA are related to surface reflectivity,organic growth and shadows, rather than to sub-surface features.

- 163 -LIST OF TABLESTableNo.PageNo.Dl Summary of Results Obtained using Ground Penetrating 164Radar

- 164 -Table Dl - Summary of Results Obtained using Ground Penetrating RadarTraverseFGSBSKX3EGSCMWGATA01Shotcretethickness notresolved.Reinforcedshotcrete 500mmthick.Shotcrete 50mmthick.Reinforcedshotcrete200mm -290mm thick.No radargram.Reinforcedshotcrete 50 -100mm thick.TA02Not consistent.Parabolic anomalyat 10m from top ofslope lmdeep.Not consistent.Not consistent.No radargram.Parabolic anomaly10m from top ofslope lmdeep.TA03Not consistent.Point anomaly at27m. Voids belowslab at 0m-14m,26m and 38m-48m.Poor penetrationwith 500MHzantenna at 10m-12mand28m-30m.Point anomaliesat 2m, 8m, 14mand 27m.Voids belowslab at llm-13m and 27m-29m. Poorpenetration with500MHzantenna at 10m-12m and 28m-30m.No radargram.Point anomalies at2m, 8m and 14m.Voids below slabat 0m-14m, 26mand 38m-48m.Poor penetrationwith 500MHzantenna at 10m-12m and 28m-30m.TA04Not consistent.Reinforced slab at15rn-34m.Poor data.Poor dataReflector 3mdeep.Reinforced slab at24m~34m.TB01Poor data.Concrete tie beamsextend 2m-2.5mfrom face of wall.Bright reflectorsdirectly behindfacing. Verticalreflectors frombody of wall. Wall2m thick.Poor data.Poor data.Section not madeatTAOl but goodwall resolutionobtained fromhorizontaltraverseperpendicular towall.Concrete tie beamsextend 2m-2.5mfrom face of wall.Bright reflectorsbehind facing.Vertical reflectorsfrom body of wall.Two wall models.TB04Manhole cover at7m. Parabolicanomaly at 18m.Point anomaly at10m. Joint in slabat 18m.Poor data.Poor data.Four parabolicanomaliesinterpreted asvertical structuresat 7m, 9m, 13.5mand 18m.Manhole cover at7m. Parabolicanomaly (utility)at 9m. Parabolicanomaly (utility)at 13.5m. Steeldrain at 18m.TB05Parabolicanomalies at1.8m, 6m and20m. Anomalouszone at 7m-10m.Parabolic anomalyat 6m. Pointanomaly at 20m.Zone of highpermittivitycontrast at 7m-10m.Poor data.Poor data.Two parabolicanomaliesinterpreted asvertical structuresat 1.8m and 6m.Parabolicanomaly (utility)at 20m.Not radargram.TC01Poor data.Wall 0.9m at top,1.5m at bottom.Poor data.Poor data.Wall 1.3m at top,1.6m at bottom.Wall 1 mat top,1.5m at bottom.TC02Poor data.Wall 1.6m at top,1,5m at bottom.Poor data.Poor data.Wall 1.2m at top,1.8m at bottom.Wall 1.5m at top,1,8m at bottom.TC03TD01Wall 1.5m thick.Poor reflection at17n>31m.Internal structuresin fill evident onradargram but notinterpreted.Cavity at 45m.Wall 1.3m thick.Point anomaly at3.5m and 32m. Fillnot as thick at DH2as log indicates.Poor penetration at45m.Poor data.Poor data.Walll.75m-2mthick.Internalstructures in fillevident onradargram butnot interpreted.Fill not as thickat DH2 as logindicates.Walll .9m thick.Poor reflection at19m-31m.Internal structuresinfill.No radargram.Internal structuresin fill Pointanomalies at 3.5m-5m and 32m. Fillnot as thick atDH2 as logindicates.

- 165 -LISTOFPT.ATF.SPlateNo.PageNo.D1 6 kg sledge hammer being used at Site A (TA04) as energy 169source for high resolution seismic reflection. ContractorGolder Associates.D2 Spiked geophone adjacent to pre-drilled hole prior to high 169resolution seismic reflection survey at Site A. ContractorGuandong South China EGTD Co,D3 65Hz geophone being fixed to shotcrete slope surface during 170high-resolution seismic reflection survey at Site A (TA01).Contractor Guandong South China EGTD Co.D4 Geophones attached to the masonry wall with plaster of Paris 170at Site C (TC01) during seismic reflection survey.Contractor Institute of Geophysical and GeochemicalExploration.D5 Metravib CSH05 piezoelectric accelerometer attached to 171masonry wall with plaster of Paris at Site C (TC03) duringSASW survey. Contractor Bachy Soletanche.D6 Bruel & Kjaer piezoelectric transducer coupled to the concrete 171slab through a spiked magnetic mandrel during a SASWsurvey at Site A (TA04). Contractor Meinhardt Works.D7 SASW geophone inserted into pre-drilled hole along the 172masonry wall tie beam at Site C (TC01). Contractor Instituteof Geophysical and Geochemical Exploration.D8 Plaster of Paris being used to fix lOHz geophones to masonry 172wall at Site B (TB02) during SASW survey. ContractorInstitute of Geophysical and Geochemical Exploration.D9 Low-frequency IHz geophone used to record long wavelength 173surface waves during SASW survey at Site D (TD01).Contractor Golder Associates.D10 20 gram hammer being used at Site A (TA02) to produce 173high frequency surface waves for SASW survey. Highfrequency accelerometers being used as.sensors. ContractorGolder Associates,

- 166 -PlateNo.Pa § eNaDl 1 6kg sledge hammer being used at Site D (TD01) to produce 174low frequency surface waves during SASW survey.Contractor Golder Associates.D12 SASW survey in progress with a multiple geophone array at 174Site B (TB04). Contractor Guandong South China EGTDCo.D13 Common mid-point receiver array being used for SASW 175survey at Site B (TB05). Sounding point is mid-waybetween the two geophones. Contractor Institute ofGeophysical and Geochemical Exploration.D14 Metravib RAJO seismograph and Scientific - Atlanta Spectral 176Dynamics SD380 Signal Analyser used for SASW survey.Contractor Bachy Soletanche.D15 Hilti-bolts being inserted into pre-drilled holes and used as 177electrodes at Site A (TA03) during resistivity imagingsurvey. Contractor Bachy Soletanche.D16 Steel pin electrodes inserted through concrete slab to ensure 177contact with soil beneath at Site A (TA03) during resistivityimaging survey. Contractor Fugro Geotechnical Services(HK) Ltd.D17 Multi-takeout cable being attached to electrodes during 178resistivity imaging survey at Site C (TC03). This systemallows each electrode to be identified so that surveys withdifferent electrode spacing can be made automatically.Contractor Bachy Soletanche.D18 Cotton wool soaked in salt water and wrapped around 178electrode inserted into wall to improve contact resistance atSite C (TC03) during resistivity survey. Contractor Instituteof Geophysical and Geochemical Exploration.D19 • Geotrode non-polarising copper sulphate electrodes with 179voltmeter for self potential survey at Site A. ContractorBachy Soletanche.D20 Non-polarising copper sulphate electrode being held against 179the masonry wall at Site C (TCO3). Copper sulphate soakedsponge has been attached to base of electrode to ensure goodelectrode - wall contact. Contractor Bachy Soletanche.

- 167 -plateNo.PageN aD2 1 Sting non-polarising copper sulphate electrode inserted into 180a shallow excavation at Site D (TDOl) during self potentialsurvey. Contractor Golder Associates.D22 Geonics EMS 1 conductivity meter being used at Site A (TAO1). 180Two-man job to carry out the survey up the slope at the site.Contractor Fugro Geotechnical Services (HK) Ltd.D23 Geonics EM38 conductivity meter being used at Site D (TDOl). 181Contractor Bachy Soletanche.D24 Geonics EM-31 being used for FDEM survey of fill slope 181platform at Site D. Red flags define the 1m grid used tocarry out the survey. Contractor Golder Associates.D25 Crone Geophysics & Exploration Ltd. digital pulse TDEM 182system being lowered down fill slope at Site D (TDG2).Contractor Institute of Geophysical and GeochemicalExploration.D26 Time Domain EM coils (lm by 2m), power pack and 182voltmeter at Site B (TB04). Contractor Guandong SouthChina EGTD Co.D27 lGHz GSSI antenna being used to penetrate mesh reinforced 183shotcrete at Site A (TAOl) - Contractor Golder Associates.D28 GSSI 100MHz bistatic antenna being used in GPR survey at 183Site D (TDOl). Contractor Guandong South China EGTDCo.D29 GSSI 200MHz monostatic antenna being pulled along 184platform above the masonry wall at Site B (TB05) duringGPR survey. Contractor Meinhardt Works.D30 Sensors & Software Inc. PulsEKKO 1000 bistatic 225MHz 184antenna being used during GPR survey at Site A (TA04).Contractor Fugro Geotechnical Services (HK) Ltd.D31 Radarteam - Sweden A - Model subecho 40 - monostatic 18535MHz non-contact antenna being used during GPR surveyat Site C (TCO3). Contractor Fugro Geotechnical Services(HK)Ltd.

- 168 -PlateNo.PageNo.D32 GSSI 500MHz monostatic antenna being lowered down 186vertical masonry wall on a rope at Site B (TB02). ContractorGuandong South China EGTD Co.D33 GSSI 200MHz monostatic antenna being pulled up fill slope 187at Site D (TD02) during GPR survey. Note survey wheelattached which automatically ecodes the radargram with adistance measurement. Contractor Meinhardt Works.D34 Sensors & Software Inc. PulsEKKO 1000 System 225MHz 187antenna's being used in a Common Depth Point (CDP) GPRsurvey for masonry wall velocity determination at Site C(TC03). Contractor Fugro Geotechnical Services (HK) Ltd.D35 GSSI 100MHz antenna being lowered dowm masonry wall 188at Site C (TC02). Note three men required to manhandle thelarge antenna to ensure proper contact with the wall.Contractor Institute of Geophysical and GeochemicalExploration.D36 SIR 2 System 500MHz monostatic antenna being held aginst 189masonry wall at Site B (TB01) during ground penetratingradar survey. Contractor Bachy Soletanche.D37 Radarteam - Sweden A - Model subecho 40 - monostatic 19035MHz non-contact antenna being used during GPR surveyat Site D (TD02). This non-contact antenna has obviousadvantages over the contact type of antenna in rough groundconditions. Contractor Fugro Geotechnical Services (HK)Ltd.D38 AP PAARIRS3 thermal imaging equipment. Contractor 190Bachy Soletanche.

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191 -APPENDIX EDETAILED ASSESSMENT OF THE PHASE 2PRELIMINARY FIELD TRIAL RESULTS

- 192 -CONTENTSPageNo.CONTENTS 192E.1 INTRODUCTION 193E.2 RESULTS FROM SITE E 193E.3 RESULTS FROM SUE F 195E.4 RESULTS FROM SITE G 196E.5 RESULTS FROM SITE H 197LIST OF FIGURES 198

- 193 -E.I INTRODUCTIONGround penetrating radar results are presented as radargram time sections which haveone axis being distance along the traverse the other being two-way-travel-time measured innanoseconds (ns). These time sections can be converted into depth sections if theelectromagnetic wave velocity of the medium being investigated is known. Thus depths toreflectors interpreted from the time sections can be calculated. The accuracy of the depthcalculation is dependent on how realistic a velocity is used together with the resolution of theantenna. Different material layers will have a different velocity and thus a composite velocitycalculation should theoretically be made. The contractors in Phase 2 used a "bulk" or "average 59velocity which they applied to the whole time section.Resistivity imaging results are presented as true iso-resistivity versus depth sections inohm - meters (Dm). The resistivity values calculated from the raw data is an apparent resistivityrelated approximately to depth.. This data is then modelled using inversion software to producetrue iso-resitivity depth sections. Different contouring packages have been used to present thedata which account to some extent for the variability in the styles of presentation betweendifferent contractors.Iso-conductivity maps have been produced to present the FDEM data in milli-Seimensper meter (mS/m). Measurements were generally taken on a lm grid over the slope and theresults simply contoured with little data processing. Both in-phase and conductivity arepresented results (see Appendix B).SASW results are presented as pseudo-dispersion curves and shear wave velocity depthprofiles by IGGE and GSC.E.2 RESULTS FROM SITE EFigure El presents two radargrams made along the vertical traverse TE01 at site E(Figure 12). Figure El a was produced by GA and Elb was produced by IGGE. Both radargramshave been produced using 500MHz antennas and essentially the same equipment (GA used theSIR 2 system and IGGE used the SIR 10 system). The GA radargram is presented in grey scalewith wiggle trace superimposed, the lighter grey tone and higher amplitude wiggles indicating ahigh energy/amplitude reflection. The IGGE radargram is presented as a wiggle trace only. InFigure El a three zones of different reflection characteristics and energy have been identified onthe radargram: zone 1 is characterised by parallel sets of low energy reflectors, zone 2 ischaracterised by poorly defined reflectors and zone 3 by well defined high energy reflectorswhich appear to be located directly above each tie beam. The limit of penetration is about 55ns.The three well-defined zones are not evident on Figure Elb. However, zones of higher energyreflectors do occur above each tie beam between 9ns to 40ns which compared to the GAradargram would put them in zone 2 rather than zone 3.Figure E2 presents two radargrams also made along traverse TE01 produced using100MHz antennas. Figure E2a was produced by GSC and E2b was produced by IGGE.Although identical equipment has been used, GSC carried out the radar survey by moving theradar antenna point by point along the traverse at 0.25m intervals in order to stack the radar

- 194 -signal to improve the signal to noise ratio. IGGE carried out the radar survey in continuous modewhere the antenna is moved at a constant rate along the traverse. Both radargrams are presentedas wiggle traces. It should be note that on both radargrams the time scale is over 100ns whereasthe radargrams on Figure El the time scale was between 40ns and 50ns. In Figure E2a thecontractor has interpreted a stepped wall profile with increases in wall thickness coinciding witheach tie beam. The series of parallel reflectors within the first 25ns are direct wave events andnot real reflectors. A high-energy reflector parallel to the wall face is evident at 25ns but only thetop 2m has been interpreted as being significant. Other intermittent high energy reflectors areevident in the radargram. At two-way travel times greater than about 90ns the reflected eventsare obscured by noise and gain-controlled artefacts which manifest themselves as parallel,equally-spaced high-energy events on the radargram. The first of these artefacts has beeninterpreted by GSC as the interface between fill and highly decomposed rock (Figure E2a). Thesame reflectors are not evident on Figure E2b; however the three zones of high energy reflectorslocated above each tie beam at about 50ns agree well with the similar reflectors in zone 3 of theGA 500MHz radargram (Figure El a). Reflection events are obscured by noise at two-way traveltimes greater than about 75ns on Figure E2b.Figures El and E2 demonstrate the following points;(i) the penetration depth of 500MHz antenna is approximately50ns,(ii) the noise to signal ratio can be improved and hence depth ofpenetration by stacking,(iii) different contractors produce different radargrams using thesame equipment, and(iv) gain controlled artefacts were interpreted as real reflectors byseveral contractors.Figure E3 presents three iso-resistivity sections made along TE03 at site E (Figure 12).These are horizontal sections through the wall orientated with east to the left which is the highpart of the wall. All three sections have a zone of high resistivity of greater than about 400Omwhich extends to a depth of 3m in the east and thins westwards to approximately 2m. This highresistivityzone has been interpreted as the masonry wall by each contractor. A sharp decrease inresistivity is seen behind the wall There are also some similarities in the details of the sections,especially Figures E3a and E3b produced by GA and FGS respectively. Two resistivity lows canbe identified within the zone of high resistivity, one centred at about 10m on both sections andanother which extends from 14m to 21m on Figure E3a and from about 15m to 18m and at 20mon Figure 18b. These zones are not observed on Figure 18c produced by BS. Low-resistivityvalues (less than lOO&rn) are shown on Figure E3c running the full length of the wall, extendingfrom the face to about 0.5m into the wall It is considered unlikely that this low-resistivity zoneis real since the wall facing is composed of slightly decomposed granite blocks which shouldhave a resistivity greater than 400Qm. The low-resistivity zones identified on Figures E3a andE3b were interpreted by GA as associated with zones of high moisture content within the wallwhich corresponded with seepage from weepholes (Figure 12). A parallel traverse 3.5m above

- 195 -TE03 carried out by GA also show the same pattern of low resistivity. FGS did not comment onthe zones of low resistivity.These examples demonstrate that:(a) the general characteristics of the iso-resistivity depth sectionsproduced by different contractors are similar even thoughdifferent equipment, electrode spacing, electrode type andinversion software has been used;(b) the detail contained in each section can differ and is probablyrelated to some extent to the contouring package used, and(c) the interpretation of anomalies is dependent on the experienceof the geophysicist.E.3 RESULTS FROM STTKFThe geophysical results and interpretation presented in this section were all made by GAand are used to demonstrate the information which may be gained from a combined GPR and RIsurvey. Only the key information which supports the interpretation contained in the GA report ispresented. For more details the contractors final interpretative report should be consulted(Golders, 1997). Two horizontal radargrams made along TF02 (Figure 13) using a 500MHz anda lOOMHz antenna are presented in Figure E4. The 0m chainage is located at the south easternend (Figure 13). The 500MHz radargram is presented in grey scale and the lOOMHz radargramin grey scale with a wiggle trace overlay. The first obvious feature, which shows up best in the500MHz data, is the zone of subdued reflectors starting at chainage 21m. This has beenattributed to conductive soils such as clay fill directly behind the masonry wall which attenuatethe radar waves and reduce penetration. This change in the radargram coincides with the changein masonry wall height. The wall is interpreted to be about lm thick along this section assumingan electromagnetic wave velocity of 0.122m/ns. From 0m to 21m the 500MHz radargram ischaracterised by many parabolic reflectors. Close inspection of the data reveal several features: achange in signal character at about 36ns suggesting a change in the material type, intermittentcoherent reflectors occur at this two-way travel time in the lOOMHz radar data, and a zone ofless pronounced parabolic reflectors between chainage 12m and 17m. Preliminary interpretationof these features are that the bright parabolic reflectors represent individual masonry blockswithin the wall, possibly with associated voids, the change in nature of the reflectors at 36nscould be the back of the wall ( at 2m assuming a velocity of 0.122m/n$X and the zone of lesspronouncedreflectors represents an area within the wall with less voids between each masonryblock.Two inverse modelled resistivity sections are shown on Figure E5. The lower was madealong TF02, the upper along a parallel traverse about 2m above TF02. Both sections have azone of high resistivity of greater than about 400Om which extends to a depth of between 2.5mand 3.2m. From chainage 22m this zone reduces in depth to about lm along TE02 (note that theupper section does not extend into the lower part of the wall). This high resistivity zone has beeninterpreted as being the masonry wall. The reduction in wall thickness at chainage 21m agrees

- 196 -well with the GPR results and the change in wall height. However, GA suggest that this couldalso be due to geometrical effects and possible short circuiting as the top of the wall beyondchainage 21m is closer to the traverse. The geometrical effect could also explain the apparentgradual thinning of the wall to the south east from about chainage 4m due the presence of thestair case. However, the wall may thin in this area since the stair case would add to the stabilityof the wall above it.Two zones of relatively higher resistivity can be observed in the section TF02 fromchainage 4m to 15m and from 17m to 22m. These are interpreted by GA as zones of higher voidcontent and generally correspond to the areas of bright parabolic reflectors in the GPR data. Thearea of lower resistivity from 15m to 17m roughly corresponds to the zone of less pronouncedreflectors in the GPR data and supports the interpretation of a low-void zone within the wall (airhas a very high resistivity compared to rock). The upper section also contains a zone of highresistivity but of limited extent, which suggests that the lower part of the wall has more voidsthan the upper part.The preliminary interpretation made by GA showing the various anomalous areas withinthe wall is presented on Figure E6. The geophysical interpretation suggests that the wall hasessentially three different characteristics: areas with many voids characterised by zones of highresistivity and bright parabolic GPR reflectors, areas with less voids characterised by lowerresistivity and less pronounced GPR reflectors (which appear to be located around the part of thewall containing the weepholes), and an area where the wall is thinner with conductive materialbehind characterised by zone of poor GPR penetration. Based on this interpretation, horizontaldrillholes were located within the three zones (Figure 13). The GI generally confirmed thisinterpretation. The findings of the GI are described in Section 4.43 and a section through thewall is shown on Figure 18. The area of many voids appear to correspond with areas of the wallcomposed of cobbles and boulders of partially weathered rock without any mortar infill, whilstthe zone of less voids appear to coincide with an area of wall composed of mass concrete. TheGI confirmed that wall thickness reduces to 1.5m (Figure 19) at chainage 21m and has clay fillbehind its rear face.E.4 RESULTS FROM SITE GIso-conductivity maps produced by GA and FGS are presented on Figures E7 and E8respectively. GA used a Geonics EM-38 conductivity meter which has a depth range of about2m whilst FGS used a Geonics EM-31 conductivity meter which has a depth range of about 5m.The GA map is therefore showing responses to near surface changes in conductivity whilst theFGS map is showing responses to deeper changes in conductivity. However, the larger EM-31should also be influenced to a greater extent than the EM-38 by cultural interference since boomlength and therefore zone of influence is much greater (see McDowell (1981) referenced inAppendix B). Both iso-conductivity maps have large high conductivity anomalies running alongthe toe of the slope. These are probably associated with services located within the pavementand the metal safety barrier erected along the slope toe. It is worth noting that higherconductivities were recorded by the EM-31. Other conductivity highs are associated with theTowngas pipe running up the slope along the western boundary. This anomaly was onlyobserved by the EM-38. Conductivity lows associated with a concrete drainage gully and aconcrete-filled pipe are also shown by the EM-38 (Figure E7). The pipe anomaly is also picked

- 197 -up by the EM-31 (Figure E8). The conductivity of the rest of the slope generally falls between 8and 20 mS/m. A change in conductivity is evident across the middle portion of the slope asshown on Figure E7, but this change is not seen in the EM-31 data. The variation across theslope could be due to subtle changes in moisture content of the near-surface materials, changesin the chunam, or subtle changes in the geology across the slope. This change in conductivityappears to have been masked by cultural anomalies along the toe and north west edge of theslope and was not observed by the EM-31. Both conductivity meters were affected by culturalobjects. The EM-38 appears to be effected more by surface objects as compared to the EM-31,which had larger anomalies associated with buried services and metallic safety fences remotefrom the survey location. The GI did not identify any geological or man-made feature whichcould explain the change in conductivity across the slope recorded by the EM-38E.5 RESULTS FROM STTRHFour contractors carried out SASW at the fill slope (see Appendix C). However, onlyBS, GSC and IGGE present the results in their preliminary report. Both GSC and IGGEpresent wave velocity versus depth curves together with shear wave velocity-depth sectionsderived from these curves. An example of the wave velocity versus depth curves is shown onFigure E9. The depth element is only approximate and has been estimated as being half theappropriate wavelength for a specific velocity. This is a crude method of depth calculation anddoes not conform to the methods recommended by Stokoe et al (1994) (see Appendix B). Thevelocity versus depth curves presented by GSC and IGGE are therefore effectively dispersioncurves (velocity versus wavelength) and are termed pseudo-dispersion curves in this report. Thepseudo-dispersion curves shown on Figure E9 are complex and it is likely that the coherencevalue, which is an indicator of the quality of the data at various frequencies, is less than one(Stokoe et al, 1994) for most of the data. For instance, the pseudo-dispersion curve at 4.5mshown on Figure E9 indicates that the wavelength equivalent to a depth of 4m has at least fourcorresponding velocities, which is uninterpretable. The velocity-depth sections produced fromthese pseudo-dispersion curves are therefore not reliable and cannot be used with anyconfidence. There is also no consistency between the IGGE and GSC velocity-depth sections.BS present SASW data in a different form which also does not conform to the methodsrecommended by Stokoe et al (1994). BS plot wavelength, frequency and acceleration againstchainage along a particular traverse. Some qualitative interpretation is then made regarding thenature of the near surface materials along the traverse line based on the measured surface wavevalues.GA present dispersion curves for the site in their final interpretative report (GolderAssociates, 1997) and state that the coherence value is very low for the results at the site,probably due to the heterogeneous nature of the fill.There does not seem to be a universally-accepted method of carrying out the SASW,which makes it difficult to directly compare between the different contractors results. However,the dispersion curves presented by GA and the pseduo-dispersion curves presented by IGGE andGSC do exhibit the same low coherence values, which is probably due to the heterogeneousnature of the fill at the site as confirmed by the GI.

- 198 -TXST OF FIGURESFigureNo.PageNo.El Examples of Radargrams Made Along Traverse TEOl at Site E 199Using 500MHz AntennasE2 Examples of Radargrams Made Along Traverse TEO1 at Site E 200Using 100MHz AntennasE3 Examples of Inverse Model Resistivity Sections Made Along 201TE03 at Site EE4 Examples of 500MHz & 1000MHz Radargrams Made Along 202TF02 at Site F, after Golder Associates (1996b)E5 Inverse Model Resistivity Sections Made Along TF02 and 2m 203' above TF02 at Site F, after Golder Associates (1996b)E6 Preliminary Interpretation of Anomalous Area within the Wall 204at Site F, after Golder Associates (1996b)E7 Examples of Iso-conductivity Map Made Using the Geonics 205EM38 at Site G, after Golder Associates (1996b)E8 Examples of Iso-conductivity Map Made Using the Geonics 206EM31 at Site G, after Fugro Geotechnical Services (HK) Ltd(1996b)E9 Example of SASW Pseudo-dispersion Curves Made at Site H, 207after Guandong South China EGDT Co. Ltd (1996b)

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GEOTECHNICAL ENGINEERING OFFICE PUBLICATIONSGeotechnicaJ Manual for Slopes, 2nd Edition (1984), 295 p.(English Version), (Reprinted, 1997).HK$90(US$20)HK$90(US$20)Guide to Retaining Wall Design, 2nd Edition (1993), 258 p. Geoguide 1(Reprinted, 1998).Guide to Site Investigation (1987), 359 p. (Reprinted, 1996). Geoguide 2Guide to Rock and Soil Descriptions (1988), 186 p. (Reprinted, Geoguide 31997).Guide to Cavern Engineering (1992), 148 p. (Reprinted, 1998). Geoguide 4Guide to Slope Maintenance, 2nd Edition (1998), 91 p. Geoguide 5(English Version).HK$60(US$13)HK$83(US$17.5)HK$58(US$12.6)HK$60(US$13)HK$40(US$8.5)HK$40(US$8.5)Layman's Guide to Slope Maintenance, 2nd Edition (1998),54 p. (Bilingual).FreeModel Specification for Prestressed Ground Anchors, 2ndEdition (1989), 164 p. (Reprinted, 1997).Model Specification for Reinforced Fill Structures (1989),135 p. (Reprinted, 1997).Mid-levels Study : Report on Geology, Hydrology and SoilProperties (1982), 265 p. plus 54 drgs. (Reprinted, 1997).Prediction of Soil Suction for Slopes in Hong Kong, by M.G.Anderson (1984), 242 p. (Reprinted, 1996).(Superseded by GCO Publication No. 1/85)Geospec 1Geospec 2GCO PublicationNo. 1/84GCO PublicationNo. 2/84HK$62(US$11)HK$58(US$10.5)HK$534(US$86)HK$132(US$24)

(Superseded by Geospec 1)GCO PublicationNo. 3/84Review of Superficial Deposits and Weathering in Hong Kong, GCO Publication HK$40by J.D. Bennett (1984), 58 p. (Reprinted, 1993). No. 4/84 (US$8)Review of Hong Kong Stratigraphy, by J.D. Bennett (1984), GCO Publication HK$2586 p. No. 5/84 (US$5.5)Review of Tectonic History, Structure and Metamorphism of GCO Publication HK$20Hong Kong, by J.D. Bennett (1984), 63 p. No. 6/84 (US$5)(Superseded by GCO Publication No. 1/88)GCO PublicationNo. 1/85Groundwater Lowering by Horizontal Drains, by D.J. Craig & GCO Publication HK$74I. Gray (1985), 123 p. (Reprinted, 1990). No. 2/85 (US$ 12)(Superseded by GEO Report No. 9)GCO PublicationNo. 1/88Review of Design Methods for Excavations (1990), 187 p. GCO Publication HK$40(Reprinted, 1996). No. 1/90 (US$10)Foundation Properties of Marble and Other Rocks in the Yuen GCO Publication HK$58Long - Tuen Mun Area (1990), 117 p. No. 2/90 (US$10)Review of Earthquake Data for the Hong Kong Region (1991), GCO Publication HK$42115 p. No. 1/91 (US$11.5)Review of Granular and Geotextile Filters (1993), 141 p. GEO Publication HK$32No. 1/93 (US$19)Pile Design and Construction (1996), 348 p. (Reprinted, 1997). GEO Publication HK$62No. 1/96 (US$13.5)Report on the Kwun Lung Lau Landslide of 23 July 1994, 2 - FreeVolumes, 400 p. (English Version), (Reprinted, 1996).Report on the Fei Tsui Road Landslide of 13 August 1995, - Free2 Volumes, 156 p. (Bilingual). ^5||

Report on the Shum Wan Road Landslide of 13 August 1995,2 Volumes, 123 p. (Bilingual).FreeWhat to Do When You Receive a Dangerous Hillside Order(1996), 32 p. (Bilingual).Free(Hong Kong) Rainfall and Landslides in 1984, by J. Premchitt(1991), 91 p. plus 1 drg. (Reprinted, 1995).(Hong Kong) Rainfall and Landslides in 1985, by J. Premchitt(1991), 108 p. plus 1 drg. (Reprinted, 1995).(Hong Kong) Rainfall and Landslides in 1986, by J. Premchitt(1991), 113 p. plus 1 drg. (Reprinted, 1995).Hong Kong Rainfall and Landslides in 1987, by J. Premchitt(1991), 101 p. plus 1 drg. (Reprinted, 1995).Hong Kong Rainfall and Landslides in 1988, by J. Premchitt(1991), 64 p. plus 1 drg. (Reprinted, 1995).Hong Kong Rainfall and Landslides in 1989, by K.L. Siu(1991), 114 p. plus 1 drg. (Reprinted, 1995).Aggregate Properties of Some Hong Kong Rocks, by T.Y.Wan, A. Cipullo, A.D. Burnett & J.M. Nash (1992), 212 p.(Reprinted, 1995).Foundation Design of Caissons on Granitic and VolcanicRocks, by T.Y. Wan & G.E. Powell (1991), 85 p. (Reprinted,1995).Bibliography on the Geology and Geotechnical Engineering ofHong Kong to December 1991, by E.W. Brand (1992), 186 p.(Superseded by GEO Report No.39)Bibliography on Settlements Caused by Tunnelling, by E.W.Brand (1992), 50 p. (Reprinted, 1995). (Superseded by GEOReport No.51)Direct Shear Testing of a Hong Kong Soil under VariousApplied Matric Suctions, by J.K. Gan & D.G. Fredlund (1992),241 p. (Reprinted, 1995).GEO ReportNo. 1GEO ReportNo. 2GEO ReportNo. 3GEO ReportNo. 4GEO ReportNo. 5GEO ReportNo. 6GEO ReportNo. 7GEO ReportNo. 8GEO ReportNo. 9GEO ReportNo. 10GEO ReportNo. 11HKS118(US$17.5)HK$126(US$20)HK$126(US$20)HK$122(US$19.5)HK$106(US$16)HK$126(US$20)HK$120(US$19.5)HK$62(US$10.5)HK$48(US$8.5)HK$136(US$21.5)

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Mineralogy and Fabric Characterization and Classification ofWeathered Granitic Rocks in Hong Kong, by T.Y. Man (1996),158 p.Performance of Horizontal Drains in Hong Kong, by R.P.Martin, K.L. Siu & J. Premchitt (1995), 109 p.Hong Kong Rainfall and Landslides in 1993, by W.L. Chan(1995), 214 p. plus ldrg.General Report on Landslips on 5 November 1993 atMan-made Features in Lantau, by H.N. Wong & K.K.S. Ho(1995), 78 p. plus ldrg.Gravity Retaining Walls Subject to Seismic Loading, by Y.S.Au-Yeung & K.K.S. Ho (1995), 63 p.Direct Shear and Triaxial Testing of a Hong Kong Soil underSaturated and Unsaturated Conditions, by J.K.M. Gan & D.G.Fredlund(1996),217p.Stability of Submarine Slopes, by N.C. Evans (1995), 51 p.Strength Development of High PFA Content Concrete, byW.C. Leung & W.L. Tse (1995), 84 p.AAR Potential of Volcanic Rocks from Anderson RoadQuarries, by W.C. Leung, W.L. Tse, C.S. Mok & S.T. Gilbert(1995), 78 p.Bibliography on the Geology and Geotechnical Engineering ofHong Kong to March 1996, by E.W. Brand (1996), 111 p.Bibliography on Settlements Caused by Tunnelling to March1996, by E.W. Brand (1996), 70 p.Investigation of Some Major Slope Failures between 1992 and1995, by Y.C. Chan, W.K. Pun, H.N. Wong, A.C.O. Li & K.C.Yeo(1996),97p.Environmental Aspects of Using Fresh PFA as Fill inReclamation, by K.S. Ho & P.Y.M. Chen (1996), 46 p.Hong Kong Rainfall and Landslides in 1994, by W.L. Chan(1996), 161 p. plus 1 drg.GEO ReportNo. 41GEO ReportNo. 42GEO ReportNo. 43GEO ReportNo. 44GEO ReportNo. 45GEO ReportNo. 46GEO ReportNo. 47GEO ReportNo. 48GEO ReportNo. 49GEO ReportNo. 50GEO ReportNo. 51GEO ReportNo. 52GEO ReportNo. 53GEO ReportNo. 54HK$70(US$13.5)HK$65(US$17.2)HK$110(US$18.5)HK$64(US$17)HK$40(US$8)HK$65(US$12.5)HK$46(US$8.5)HK$60(US$10.5)HK$58(US$10)HK$45(US$9)HK$31(US$6.5)HK$44(US$8.5)HK$30(US$5.5)HK$70(US$13.5)

Conventional and CRS Rowe Cell Consolidation Test on SomeHong Kong Clays, by J. Premchitt, K.S. Ho & N.C. Evans(1996), 93 p.Application of Prescriptive Measures to Soil Cut Slopes, byH.N. Wong & L.S. Pang (1996), 52 p.Study of Rainfall Induced Landslides on Natural Slopes in theVicinity of Tung Chung New Town, Lantau Island, byC.A.M. Franks (1998), 102 p. plus 3 drgs. (Reprinted, 1999).(Not Used)Hong Kong Rainfall and Landslides in 1995, by C.K.L. Wong(1997), 125 p. plus ldrg.Assessment of Geological Features Related to RecentLandslides in Volcanic Rocks of Hong Kong Phase 2A - ChaiWan Study Area, by SJD.G. Campbell & N.P. Koor (1998),78 p. plus 6 drgs.Factual Report on the November 1993 Natural TerrainLandslides in Three Study Areas on Lantau Island, by H.N.Wong, Y.M. Chen & K.C. Lam (1997), 42 p.Areal Extent of Intense Rainfall in Hong Kong 1979 to 1995,by A.W. Malone (1997), 85 p.A Review of Some Drained Reclamation Works in HongKong, by J.S.M. Kwong (1997), 53 p.A Study of Hydraulic Fill Performance in Hong Kong -Phase 2, by C.K. Shen, K.M. Lee & X.S. Li (1997), 265 p.Seismic Hazard Analysis of the Hong Kong Region, by C.RLee, Y.Z. Ding, R.H. Huang, Y.B. Yu, G.A. Guo, PL. Chen& X.H. Huang (1998), 145 p. (Bilingual).GEO ReportNo. 55GEO ReportNo. 56GEO ReportNo. 57GEO ReportNo. 58GEO ReportNo. 59GEO ReportNo. 60GEO ReportNo. 61GEO ReportNo. 62GEO ReportNo. 63GEO ReportNo. 64GEO ReportNo. 65HK$35(US$7)HK$12(US$3.5)HK$264(US$39.5)HK$70(US$14.5)HK$296(US$43.5)HK$92(US$13.5)HK$43(US$8.5)HK$36(US$6.5)HK$150(US$25)HK$80(US$15.5)Mineralogical and Fabric Characterization and Classification of GEO Report HK$ 106Weathered Volcanic Rocks in Hong Kong, by T.Y. Man (1998), No. 66(US$17)113 p.

Assessment of Geological Features Related to RecentLandslides in Volcanic Rocks of Hong Kong Phase 2B-Aberdeen Study Area, by C.A.M. Franks, S.D.G. Campbell &W.W.L. Shum (1999), 106 p. plus 8 drgs. under preparation.The New Priority Classification Systems for Slopes andRetaining Walls, by C.K.L. Wong (1998), 117 p. (Reprinted,1999).Diagnostic Report on the November 1993 Natural TerrainLandslides on Lantau Island, by H.N. Wong, K.C. Lam &K.K.S. Ho (1998), 98 p. plus 1 drg.Hong Kong Rainfall and Landslides in 1996, by C.K.L. Wong(1998), 84 p. plus 1 drg.Site Characterisation Study - Phases 1 and 2, by N.P. Koor(1999), 207 p.Long-term Consolidation Tests on Clays from the Chek LapKok Formation, by D.O.K. Lo & J. Premchitt (1998), 89 p.The Natural Terrain Landslide Study Phases I and H, by N.C.Evans, S.W. Huang & J.P. King (1999), 128 p. plus 2 drgs.under preparation.Natural Terrain Landslide Study the Natural Terrain LandslideInventory, by J.P. King (1999), 127 p.Landslides and Boulder Falls from Natural Terrain : InterimRisk Guidelines, by ERM-Hong Kong, Ltd (1998), 183 p.(Reprinted, 1999).Report on the Landslides at Hut No. 26 Kau Wa Keng UpperVillage of 4 June 1997, by Halcrow Asia Partnership Ltd.(1998), 100 p. (Bilingual).GEO ReportNo. 67GEO ReportNo. 68GEO ReportNo. 69GEO ReportNo. 70GEO ReportNo. 71GEO ReportNo. 72GEO ReportNo. 73GEO ReportNo. 74GEO ReportNo. 75GEO ReportNo. 76HK$68(US$12)HK$90(US$17)HK$112(US$20)HK$292(US$43)HK$34(US$7.5)HK$308(US$45)HK$208(US$32)HK$94(US$17.5)HK$140(US$21.5)aReport on the Landslide at Ten Thousand Buddhas'" Monastery GEO Reportof 2 July 1997, by Halcrow Asia Partnership Ltd. (1998), 96 p. No. 77(Bilingual).HK$140(US$21.5)

Report on the Ching Cheung Road Landslide of 3 August GEO Report HK$2561997, by Halcrow Asia Partnership Ltd. (1998), 142 p. No. 78 (US$38.5)(Bilingual).iH(1998) > 142]:,gtInvestigation of Some Selected Landslide Incidents in 1997(Volume 1), by Halcrow Asia Partnership Ltd. (1998), 142 p.Feasibility Study for QRA of Boulder Fall Hazard in HongKong, by ERM-Hong Kong, Ltd (1998), 61 p.Slope Failures along BRIL Roads: Quantitative RiskAssessment and Ranking, by ERM-Hong Kong, Ltd (1999),200 p.Contaminated Mud Disposal at East Sha Chau : ComparativeIntegrated Risk Assessment, by EVS EnvironmentConsultants (1999), 138 p.Testing of Dredged Material for Marine Disposal, by EVSEnvironment Consultants (1999), 74 p.December 1995 Investigation of Benthic Recolonization atthe Mirs Bay Disposal Site, by Binnie Consultants Limited(1999), 89 p.The Use of Acoustic Doppler Current Profilers to MeasureSuspended Sediments, by Dredging Research Ltd (1999),34 p.Report of the Independent Review Panel on Fill Slopes, byJ.L. Knill, P. Lumb, S. Mackey, V.F.B. de Mello, N.R.Morgenstern & B.G. Richards (1999), 36 p.Strategic Re-assessment of Disposal Site Selection andManagement of Contaminated Mud, by EVS EnvironmentConsultants (1999), 50 p.Investigation of Some Selected Landslide Incidents in 1997(Volume 2), by Halcrow Asia Partnership Ltd. (1999), 202 p.Investigation of Some Selected Landslide Incidents in 1997(Volume 3), by Halcrow Asia Partnership Ltd. (1999), 145 p.Investigation of Some Selected Landslide Incidents in 1997(Volume 4), by Halcrow Asia Partnership Ltd. (1999), 147 p.GEO ReportNo. 79GEO ReportNo. 80GEO ReportNo. 81GEO ReportNo. 82GEO ReportNo. 83GEO ReportNo. 84GEO ReportNo. 85GEO ReportNo. 86GEO ReportNo. 87GEO ReportNo. 88GEO ReportNo. 89GEO ReportNo. 90HK$192(US$30)HK$58(US$10.5)HK$76(US$15)HK$52(US$12)HK$36(US$8)HK$178(US$26)HK$108(US$17)HK$30(US$5.5)HK$32(US$6)HK$278(US$41.5)HK$200(US$31)HK$232(US$35.5)

Investigation of Some Selected Landslide Incidents in 1997(Volume 5), by Halcrow Asia Partnership Ltd. (1999), 141 p.Investigation of Some Selected Landslide Incidents in 1997(Volume 6), by Halcrow Asia Partnership Ltd. (1999), 181 p.Geotechnical Area Studies Programme - Hong Kong andKowloon (1987), 170 p. plus 4 maps.Geotechnical Area Studies Programme - Central NewTerritories (1987), 165 p. plus 4 maps.Geotechnical Area Studies Programme - West New Territories(1987), 155 p. plus 4 maps.Geotechnical Area Studies Programme - North West NewTerritories (1987), 120 p. 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 3 maps.Geotechnical Area Studies Programme - Clear Water Bay(1988), 144 p. plus 4 maps.Geotechnical Area Studies Programme - North East NewTerritories (1988), 144 p. plus 4 maps.Geotechnical Area Studies Programme - East 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 4 maps.Geotechnical Area Studies Programme - Territory of HongKong (1989), 346 p. plus 14 maps.Geology of Sha Tin, by R. Addison (1986), 85 p.Geology of Hong Kong Island and Kowloon, by P J. Strange &R. Shaw (1986), 134 p.GEO ReportNo. 91GEO ReportNo. 92GASP IGASPHGASP fflGASP IVGASPVGASP VIGASP VUGASP VfflGASP IXGASPXGASP XIGASP xnGeologicalMemoir No. 1GeologicalMemoir No. 2HK$208(US$32)HK$218(US$33.5)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(US$25)HK$150(US$25)HK$150(US$25)HK$50(US$9)HK$78(US$12.5)

Geology of the Western New Territories, by R.L. Langford,K.W. Lai, R.S. Arthurton & R. Shaw (1989), 140 p.Geology of Sai Kung and Clear Water Bay by PJ. Strange, R.Shaw & R. Addison (1990), 111 p.Geology of the North Eastern New Territories, K.W. Lai,S.D.G. Campbell & R. Shaw (1996), 144 p.Geology of Lantau District by R.L. Langford, J.W.C. James, R.Shaw, S.D.G. Campbell, P.A. Kirk & RJ. Sewell (1995),173 p.Geology of Yuen Long by D.V. Frost (1992), 69 p.Geology of Chek Lap Kok by R.L. Langford (1994), 61 p.Geology of Tsing Yi by RJ. Sewell & J.A. Fyfe (1995), 43 p.GeologicalMemoir No. 3GeologicalMemoir No. 4GeologicalMemoir No. 5GeologicalMemoir No. 6Sheet ReportNo. 1Sheet ReportNo. 2Sheet ReportNo. 3HK$97(US$17)HK$87(US$13)HK$98(US$17.5)HK$136(US$28.2)FreeFreeFreeGeology of North Lantau Island and Ma Wan by R. J. Sewell Sheet Report& J.W.C. James (1995), 46 p. No. 4FreeGeology of Ma On Shan by RJ. Sewell (1996), 45 p.Geological Landscapes of Hong Kong (1998), 61 p.(Bilingual).Sheet ReportNo. 5FreeHK$130Geochemical Atlas of Hong Kong (1999), 110 p.HK$200(US$34)San Tin : Solid and Superficial Geology (1:20 000 map) Map HGM 20,(1989), 1 map. Sheet 2Sheung Shui: Solid and Superficial Geology (1:20 000 map) Map HGM 20,(1991), 1 map. Sheet3Kat O Chau : Solid and Superficial Geology (1:20 000 map) Map HGM 20,(1992), 1 map. Sheet 4Tsing Shan (Castle Peak) : Solid and Superficial Geology Map HGM 20,(1:20 000 map) (1988), 1 map. Sheet 5HK$80HK$80HK$80HK$80

Yuen Long : Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1988), 1 map. Sheet 6Sha Tin : Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1986), 1 map. Sheet 7Sai Kung Peninsula: Solid and Superficial Geology (1:20 000 Map HGM 20, HK$80map) (1989), 1 map. Sheet 8Tung Chung : Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1994), 1 map. Sheet 9Silver Mine Bay : Solid and Superficial Geology (1:20 000 Map HGM 20, HK$80map) (1991), 1 map. Sheet 10Hong Kong and Kowloon : Solid and Superficial Geology Map HGM 20, HK$80(1:20 000 map) (1986), 1 map. Sheet 11Clear Water Bay : Solid and Superficial Geology (1:20 000 Map HGM 20, HK$80map) (1989), 1 map. Sheet 12Shek Pik : Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1995), 1 map. Sheet 13Cheung Chau : Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1995), 1 map. Sheet 14Hong Kong South and Lamma Island : Solid and Superficial Map HGM 20, HK$80Geology (1:20 000 map) (1987), 1 map. Sheet 15Waglan Island: Solid and Superficial Geology (1:20 000 map) Map HGM 20, HK$80(1989), 1 map. Sheet 16*San Tin: Solid Geology (1:20 000 map) (1994), 1 map. Map HGM20S, HK$80Sheet 2Lo Wu : Superficial Geology (1:5 000 map) (1990), 1 map. Map HGP 5 A, HK$ 100Sheet 2-NE-DLo Wu : Solid Geology (1:5 000 map) (1990), 1 map. Map HGP 5B, HK$100Sheet 2-NE-DDeep Bay: Superficial Geology (1:5 000 map) (1989), 1 map. Map HGP 5A, HK$ 100Sheet 2-SW-CDeep Bay: Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B, HK$100Sheet 2-SW-C

Shan Pui: Superficial Geology (1:5 000 map) (1989), 1 map.Shan Pui: Solid Geology (1:5 000 map) (1989), 1 map.Mai Po : Superficial Geology (1:5 000 map) (1990), 1 map.Mai Po : Solid Geology (1:5 000 map) (1990), 1 map.Lok Ma Chau : Superficial Geology (1:5 000 map) (1990),1 map.Lok Ma Chau : Solid Geology (1:5 000 map) (1990), 1 map.Man Kam To : Superficial Geology (1:5 000 map) (1990),1 map.Man Kam To : Solid Geology (1:5 000 map) (1990), 1 map.Map HGP 5A,Sheet 2-SW-DMap HGP 5B,Sheet 2-SW-DMap HGP 5A,Sheet 2-SE-AMap HGP 5B,Sheet 2-SE-AMap HGP 5A,Sheet 2-SE-BMap HGP 5B,Sheet 2-SE-BMap HGP 5A,Sheet 3-NW-CMap HGP 5B,Sheet 3-NW-CHK$100HK$100HK$100HK$100HK$100HK$100HK$100HK$100Tin Shui Wai : Superficial Geology (1:5 000 map) (1989),MapHGP5A,1 map. Sheet 6-NW-ATin Shui Wai: Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B,Sheet 6-NW-AYuen Long: Superficial Geology (1:5 000 map) (1989), 1 map. Map HGP 5 A,Sheet 6-NW-BYuen Long: Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B,Sheet 6-NW-BHung Shui Kiu : Superficial Geology (1:5 000 map) (1989), Map HGP 5A,1 map. Sheet 6-NW-CHung Shui Kiu: Solid Geology (1:5 000 map) (1989), 1 map. Map HGP 5B,Sheet 6-NW-CMuk Kiu Tau : Superficial Geology (1:5 000 map) (1990), Map HGP 5A,1 map. Sheet 6-NW-DMuk Kiu Tau: Solid Geology (1:5 000 map) (1990), 1 map. Map HGP 5B,Sheet 6-NW-DHK$100HK$100HK$100HK$100HK$100HK$100HK$100HK$100

Tsuen Wan (Part): Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$ 100(1995), 1 map. Sheet 6-SE-DMa On Shan : Solid Geology (1:5 000 map) (1996), 1 map. Map HGP 5B, HK$100Sheet 7-NE-D,C(part)Chek Lap Kok : Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1993), 1 map. Sheet 9-NE-C/DTung Chung Wan: Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$ 100(1995), 1 map Sheet 9-SE-APok To Yan : Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1997), 1 map. Sheet 9-SE-BLantau Peak : Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1996), 1 map. Sheet 9-SE-CSunset Peak : Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1996), 1 map. Sheet 9-SE-DYam O Wan : Solid & Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1995), 1 map. Sheet 10-NW-BSiu Ho : Solid & Superficial Geology (1:5 000 map) (1994), Map HGP 5, HK$ 1001 map. Sheet 10-NW-CChok Ko Wan (Penny's Bay) : Solid & Superficial Geology Map HGP 5, HK$100(1:5 000 map) (1994), 1 map. Sheet 10-NW-DMa Wan: Solid and Superficial Geology (1:5 000 map) (1994), Map HGP 5, HK$1001 map. Sheet 10-NE-ATsing Yi: Solid & Superfical Geology (1:5 000 map) (1995), Map HGP 5, HK$ 1001 map. Sheet 10-NE-B/DPa Tau Kwu : Solid and Superficial Geology (1:5 000 map) Map HGP 5, HK$100(1994), 1 map. Sheet 10-NE-CTai Ho: Solid and Superficial Geology (1:5 000 map) (1995), Map HGP 5, HK$1001 map. Sheet 10-SW-AORDERING INFORMATION IS GIVEN ON THE NEXT PAGE

GE ° PUbHCati ° nS (eXCept Sheet Re P° rts l:5wrSng to'00 ° P* «1 other reports which are free of charge) may be ordered byPublications Sales Section,Information Services Department,Room 402,4th Floor, Murray Building,Garden Road, Central,Hong Kong.SSftL^Fax (852) 2598 7482 «K (852) 2598 7482The Information Services Department will issue an invoice upon receipt of a written order.In Hong Kong, publications may be directly purchased from:Government Publications Centre,Ground Floor, Low Block,Queensway Government Offices,66 Queensway, fl|^ (852) 2523 7195Hong Kong.Fax (852) 2523 7195Requests for copies of Geological Survey Sheet Reports and other reports which are free of charge should be directed to:Chief Geotechnical Engineer/Special Projects,Geotechnical Engineering Office,Civil Engineering Department,Civil Engineering Building,101 Princess Margaret Road,Homantin, Kowloon, fllK (852) 2714 0275Hong Kong.Fax (852) 2714 02751:5 000 maps may be purchased from:Map Publications Centre/HK,Survey & Mapping Office,Lands Department, i&MLBWMMM £.-.' " ^T^%&23th Floor, WK (852) 2521 8726 * *** 'North Point Government Offices,333 Java Road, North Point,Hong Kong.Fax (852) 2521 8726:All prices given in this List are for information only and may be changed without notice. The US$ prices shown are for overseasorders and are inclusive of surface postage to anywhere in the world. An additional bank charge of HK$50 or US$650 is requiredper cheque made in currencies other than Hong Kong dollars. Cheques, bank drafts or money orders must be made payable toTHE GOVERNMENT OF THE HONG KONG SPECIAL ADMINISTRATIVE REGION.Latest information on the list of GEO publications can be found at the website http://wwwinfo.gov.hk/ced/pub.htm on the Internet.Abstracts for these documents can also be found at the same website.