site characterisation study - phases 1 and 2 - HKU Libraries - 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.