Coupled Thermal-Hydraulic-Electromagnetic Properties of Frozen Soils

This study focuses on the investigation of the electromagnetic properties of multiphase inorganic materials (i.e., soils) in changing subsurface environmental conditions that are induced by climate warming. Subsurface warming in cold regions exacerbates the spatial and temporal evolution of frozen soil properties; therefore, an accurate characterization of the unfrozen water and ice content of frozen soils under different thermal conditions has become a pressing need. Several studies focused on the effect of the initial hydraulic properties on the electromagnetic properties of soils. However, detailed systematic studies on the influence of the combined effects of temperature, initial degree of saturation, applied frequency fields, and experiment scales are limited. This study aims to characterize the dielectric and electrical behavior of ice-bearing inorganic soils under the coupled effects of thermal, hydraulic, and electromagnetic conditions. A series of laboratory experiments were performed on soil samples that had different initial degrees of saturation and dry density values by electromagnetic impedance spectroscopy (EIS) and time domain reflectometry (TDR) between −10°C and 5°C. The results from the experiments revealed that the dielectric constant of the inorganic soils decreased with increasing frequency, decreasing initial volumetric water content (VWC), and temperature. The electrical resistivity values decreased with increasing frequency values, initial water content, and temperatures. In addition, the unfrozen water contents at different temperatures were calculated using a modified power law that accounts for the temperature-dependent dielectric permittivity of water and was compared with the TDR measurements. The outcomes of this study could help elucidate the intricate mechanisms of the particle–water–ice interface and their influence on the behavior of frozen soils that are needed for sustainable built and natural environments in cold regions.