Predicting the unfrozen water content in unsaturated frozen soils using the electrical conductivity method

Determination of the unfrozen water and ice contents in frozen soils is a critical issue in cold region geotechnics. The electrical conductivity method has been adopted in both laboratory and in-situ applications, but the exact correlation of unfrozen water content as a function of the electrical conductivity remains an unanswered question. This research conducts a series of lab experiments on the unfrozen water content and electrical conductivity of frozen soils using a temperature-controlled apparatus. The test results indicate that the electrical conductivity-temperature relationship determined at positive temperatures cannot be directly applicable at negative temperatures. The electrical conductivity variation with the temperature of frozen soils is clarified based on the measured data. By quantifying the soil surface and bulk conductivities, a new physically-based model for soils is then developed that can be applicable at positive and negative temperatures. A simplified electrical conductivity model involving the unfrozen water content is developed by analyzing the impact of bulk and surface conductivities on overall electrical conductivity. The accuracy of this simplified model is verified against the experimental data and those obtained with the previous method in the literature. It is found that the results obtained with the new model agree with the measured data, and the new model exhibits a simple form and is easy to apply.