Modelling polarization effect in electrical conductivity of frozen soil

Abstract

Unfrozen water content is a critical index for understanding the hydromechanical behavior of frozen soil in cold regions. The electrical conductivity of frozen soil has been commonly used to determine the unfrozen water content in soil in both laboratory and field tests. However, the polarization effect caused by the frequency of the alternating current significantly influences measurements of the electrical conductivity of frozen soil. The mechanism of the polarization effect has yet to be thoroughly investigated and understood, and a precise theoretical model is lacking. This study first develops a polarization model for soil at positive and negative temperatures based on the multi-peak Cole-Cole model, which can theoretically give a better frequency range for electrical conductivity. Furthermore, the relationship between the test frequency range and temperature is established based on Arrhenius' law. A series of electrical conductivity tests are performed on multiple soil samples at positive and negative temperatures to validate the proposed model. It found that the polarization area of silt and sand increased rapidly with increasing frequency and gradually expanded to low frequencies with decreasing temperature. This study finally recommends an accurate reference range of test frequency for measuring the electrical conductivity of frozen soils.