Microscopic mechanism analysis of soil resistivity variation with pore water content

Abstract Soil resistivity is the main factor affecting the performance of grounding system. Existing studies show that soil moisture determines soil resistivity. However, the microscopic mechanism of soil resistivity change driven by pore water content remains unclear. To solve this problem, a three-dimensional fractal model of soil was developed to study the electrical conductivity of soil in this paper. The effect of water content on soil resistivity is as follows: At high water content, pore water forms a complex, interconnected network, resulting in low resistivity. With the decrease of water content, the complexity of the network decreases and the complex network becomes a cluster of isolated paths. Below a critical water content value, the connected path suddenly breaks, resulting in a sharp increase in resistivity of several orders of magnitude. Through Monte Carlo method, the probability of forming a connected path under different pore water content is studied. It is found that for the same soil type, even if the soil porosity changes, the water content required to form a connected path is basically the same. Finally, this paper takes red soil as an example to verify the correctness of the proposed model. This study highlights that changes in pore water connectivity fundamentally govern soil resistivity variations and offers a reference for further analysis of soil electrical conductivity.