Feasibility study on sediment thickness estimation in Tung Chung Bay using HVSR and GPR

Abstract

A feasibility study of sediment thickness estimation in Tung Chung using HVSR and GPR has been carried out in this project. Both techniques are aimed to determine different material properties including mechanical properties and electromagnetic properties. Both methods can be used to reveal different soil structure conditions in a speedy and effective way. The objective of the study is to utilize two geophysical techniques, Horizontal-to-vertical Spectral Ratio (HVSR) and Ground Penetrating Radar (GPR), to estimate the sediment thickness at a site in Tung Chung Bay. If the methods prove to be effective, they could be a method to reduce cost and ground disturbance during ground investigation stage. Data were obtained from field works with the aid of the support teams from the Hong Kong Polytechnic University and Sixense Ltd (HK). The data are presented in the form of shear velocity block and radargram which show the depth and thickness of the simulated soil layers and the suspected horizontal soil layers. The data are interpreted in relation to the transfer function on HVSR and relative permittivity on GPR. Both methods use frequency, wavelength and velocity to calculate sediment thickness information. It is concluded that the two techniques are suitable for distinct conditions. For HVSR, it is recommended to be used where soil-rock interface can be clearly defined; also, this passive seismic equipment is suitable for studying deep soil-rock interfaces. For GPR, the penetrating depth depends on its frequencies. With a lower frequency, we can penetrate further; however, the resolution at shallow layer will be reduced. To optimize its capacity, it is recommended to use this to study the properties of the top layer. Another reason is that the noise from water level or heterogenous soil will affect the reflections from the bottom, therefore, deeper reflections are always less credible than the shallower reflections.