Theoretical and experimental bases for the equivalent circuit model for interpretation of silty soil at different temperatures

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The exploitation of underground space is accompanied by complex geotechnical problems. The development of electromagnetic exploration technology provides a new perspective for preventing and avoiding these problems. In this work, electrochemical impedance spectroscopy (EIS) was used to test the single-phase and mixed-phase medium. Based on the unsaturated soil theory and the dual-water conductivity theory, an equivalent circuit model to describe the electrochemical characteristics and microstructure of silty soil with temperature changes through comparative research. The results indicate that the resistance of near-water layer is not affected by temperature, the resistance of silty soil increases mainly results from the influence of the far-water layer until which increases significantly after freezing. The capacitance change of silty soil is mainly affected by the slowing down of the orientation movement of polar molecules in the far-water layer. Based on the fitting data, a mathematical model for calculating the unfrozen water content of frozen soil was proposed, which reasonably verified the relationship between the unfrozen water content and electrical resistance. By improving the testing conditions of electrochemical impedance spectroscopy, this method may provide new insights for future research of soil electromagnetic testing technology.