Study on the combined influence mechanism of temperature, density and moisture content on the resistivity of loess

In view of the limitations of single-point temperature measurement and single-factor analysis in soil resistivity research, this study takes the Malan loess in the southeast of the Loess Plateau in Shaanxi Province as the research object, and uses the four-electrode method to conduct dynamic monitoring of the resistivity variation process of soil samples with different dry densities and moisture contents throughout the full temperature range. By means of the grey relational degree algorithm and entropy weight method, the influence weights of each factor on the resistivity of loess are quantitatively analyzed. From both macro and micro dimensions, the coupling mechanism of temperature, moisture content and dry density on the resistivity of loess is comprehensively revealed. The experimental results show that there is a significant inflection point for the resistivity of loess near 0℃. Soil samples with high moisture content will experience a temperature plateau period lasting approximately 2 h, during which the resistivity shows a continuous downward trend. Further research has found that the influence of moisture content on resistivity near 0℃ shows an opposite effect: when the temperature is below 0℃, temperature is the primary factor affecting resistivity. As the moisture content increases, the freezing of pore water hinders ion migration, and the resistivity of the soil increases. When the temperature is above 0℃, the increase in moisture content enhances the electrical conductivity of the soil, and the resistivity shows a slow downward trend. There is a very strong correlation between temperature and the resistivity of loess, showing a significant exponential decay relationship. Furthermore, when the temperature exceeds 0℃, the unique collapsibility of loess will significantly alter the correlation between its resistivity and moisture content. An increase in moisture content leads to soil collapsibility, which in turn causes the resistivity to decrease exponentially at a slow rate. When the temperature is 0℃ and the soil is in a frozen state, the freezing of pore water hinders ion migration, causing the resistivity to increase exponentially with the increase of moisture content. Soil moisture content reshapes the electrical conductivity of soil through water phase change and affects the ion migration process. Soil dry density acts on resistivity by altering pore structure and reconstructing the current conduction path. The influence of temperature on the resistivity of soil with different dry densities shows bidirectional differences, which reveals the complex interaction relationship among various soil factors. This research achievement not only deepens the understanding of the electrical evolution law of loess, but also provides a key theoretical support for the application of resistivity tomography (ERT) technology in complex environments.