Experimental investigation of thawing behavior of saline soils using resistivity method

Electrical resistivity method has been widely used to study permafrost and to monitor the process of freezing-thawing. However, a thorough understanding of the mechanism of electrical response during thawing is missing. In this study, we investigated the thawing behavior of saline soils in the temperature range ∼-10 to 15 °C considering the effects of soil type and salinity. A total of nine experiments were performed with three soil types (silica sand, sandy soil and silt) and three salinities (0.01 S/m, 0.1 S/m and 1 S/m). The results show that resistivity variations with temperature can be divided into three stages. In Stage I, tortuosity and unfrozen water content play major roles in the decrease of resistivity. In Stage Ⅱ, which is an isothermal or near isothermal process, resistivity still decreases slightly due to the thawing of residual ice and pore water movement. In Stage III, ionic mobility plays an important impact on decreasing resistivity. In addition, the isothermal process is found to only occur in silica sand which can be explained by latent heat effect. Exponential and linear models linking temperature with resistivity are used to fit the experimental data in Stage I and Stage III. The fitting parameter in different models shows great correlation with soil type and salinity. Furthermore, unfrozen water content below 0 °C is also estimated and uncertainty of estimation is analyzed.