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 investigation<br>in a characterisation study of a hillslope in Hong Kong. Rayleigh waves with frequencies that<br>modulated incrementally from 2 to 100 Hz were used to reconstruct in-situ stiffness profiles<br>along designated traverses. The phase velocity and the stiffness modulus were computed based<br>on phase angles recorded for the different frequencies by geophones. The stiffness profiles were<br>then used to delineate the interface between the overlying colluvium and the weathered bedrock<br>at the site. The colluvium generally has a relatively low but highly varying shear modulus while<br>the shear modulus of the underlying weathered bedrock increases linearly with depth, The<br>colluvium isopachs reconstructed based on the CSW results were consistent with results from<br>drillhole and trial pit records. Variations in the penetration range and the shape of the stiffness<br>profiles at different locations are probably caused by the varying boulder-matrix ratio in the<br>colluvium. The study shows that the CSW method can be an important supplementary method<br>for engineering geology ground investigation.