The Use of Continuous Surface Wave Method to Determine In‐Situ Stiffness Profiles within a Natural Terrain Setting in Hong Kong

A continuous surface wave survey was conducted in conjunction with geotechnical investigationin a characterisation study of a hillslope in Hong Kong. Rayleigh waves with frequencies thatmodulated incrementally from 2 to 100 Hz were used to reconstruct in-situ stiffness profilesalong designated traverses. The phase velocity and the stiffness modulus were computed basedon phase angles recorded for the different frequencies by geophones. The stiffness profiles werethen used to delineate the interface between the overlying colluvium and the weathered bedrockat the site. The colluvium generally has a relatively low but highly varying shear modulus whilethe shear modulus of the underlying weathered bedrock increases linearly with depth, Thecolluvium isopachs reconstructed based on the CSW results were consistent with results fromdrillhole and trial pit records. Variations in the penetration range and the shape of the stiffnessprofiles at different locations are probably caused by the varying boulder-matrix ratio in thecolluvium. The study shows that the CSW method can be an important supplementary methodfor engineering geology ground investigation.