Subsurface characterization of a construction site in Nanjing, China using ERT and CPTU methods

Abstract

In geotechnical engineering, the need for efficient and economical site characterization is the main motivation for the development of new techniques. This study combines electrical resistivity tomography (ERT) with piezocone penetration test (CPTU) to develop a rapid site characterization tool. The feasibility and efficiency of delineating subsurface structures, mapping the lithology, and estimating the hydraulic conductivity of subsoils are verified at a construction site. The lithologic information obtained via this rapid tool is validated using borehole data. According to CPTU results, the subsurface discontinuity exhibited in the ERT section is related to variation in the water content of silty sands. Accordingly, rapid and economical subsurface characterization can be achieved by using ERT survey to optimize the number and locations of point-based geotechnical tests, especially CPTU. We outline the applicability of using CPTU and ERT-derived resistivity data to predict the hydraulic conductivity of cohesive and sandy soils, respectively. A non-simplified Archie's law is used to relate the resistivity of sandy soils to their hydraulic conductivity, and appropriate values of this law's model parameters are proposed.