Evaluation of resistivity attenuation models in geotechnical media with penetration depth

Abstract

The electrical resistivity of geotechnical materials effectively characterizes their physicochemical properties and structural features. The commonly used four-electrode method minimizes the effects of electrode polarization and contact resistance. However, it requires electrode insertion into the soil, which may disturb the sample structure and affect measurements. Variations in probe depth also lead to different current field attenuations, impacting resistivity results. Additionally, this method is unsuitable for hard geomaterials. To address these issues, this study analyzes the four-electrode testing principle and conducts penetration depth-resistivity experiments on sandy and cohesive soils. It investigates how resistivity varies with probe depth and establishes a depth-based attenuation model. Results show that increasing penetration depth reduces current attenuation, causing resistivity to increase, with a generally linear relationship observed. Water content and dry density also affect resistivity trends. The study further explores the influence of moisture, dry density, and soil type on electrical conductivity with penetration depth. A multivariate nonlinear regression model is developed to describe resistivity attenuation based on water content and dry density. An exponential relationship between resistivity growth rate and penetration depth is used to define a minimum effective depth. Based on this, a surface-to-internal (S-I) resistivity conversion model is proposed and validated. These findings demonstrate that the results are applicable to soft geomaterials such as sandy soil and kaolin, achieving the purpose of predicting the internal resistivity of geomaterials based on their fundamental state parameters and surface resistivity.