Application of electrical method (resistivity logs) in ground investigation for natural terrain hazard assessment

Abstract

With the raise the significance of Natural Terrain Hazard Assessment (NTHA) for future Hong Kong development, this thesis would like to explore the feasibility of application of the electrical method in ground investigation for NTHA purpose to improve the cost-effectiveness of the development works. On site field measurement at three natural terrain underlain by three difference rock types have been performed with reference to 4 nos. of existing drillholes during the period of 27 July 2024 to 25 January 2025. Interpretation of both qualitative (i.e. the Plot of Focus) and quantities analysis (with the computer software RES1D) have been carried out for investigation on consistency of interpretation result and thus the reliability of the ERM. Surprisingly, consistent conclusion are made with reference to the two difference interpretation method. Both method shows that the ERM are technical capable to identify the change in strength of stratum underneath existing ground (i.e. with correlation to SPT-N value) and suggest similar stratigraphy profile to the existing drillhole record. From field experience in this study, list of fundamental guidance of the application of the ERM at natural terrain have been listed in this thesis. The field works also recorded that the ERM is a practically cost-effect ground investigation method which can be carried out by single person and with no extra provision of engineered access to targeted field. In accordance to limitation of resources and time of this study, focus was made on the ability of reflecting the subsurface stratigraphy for the result of field works, which the author believes is a fundamental information for most kind of further geotechnical design, especially for GI works design. For accurate correlation of exact type of material, material properties (e.g. c’, ' Es, k) and hydrogeology setting (i.e. presents of groundwater), further massive field data and related laboratory test are required.