Freeze–Thaw Infiltration Governed by Soil Freezing Characteristic Curves and Hydraulic Impedance in Unsaturated Sands

Abstract

Seasonally frozen soils strongly influence infiltration, runoff generation, and infrastructure performance in cold regions. However, infiltration modeling in partially saturated sandy soils remains poorly constrained due to limited experimental characterization of hydraulic parameters under freezing conditions. This study investigates coupled thermo–hydraulic behavior in sandy soils using laboratory column experiments and finite element modeling implemented in COMSOL Multiphysics. Instrumented soil columns were subjected to controlled freeze–thaw cycles to measure transient temperature and liquid water content profiles. A coupled TH model incorporating the van Genuchten–Generalized Clausius–Clapeyron formulation was used to represent phase change and cryosuction. The soil freezing characteristic curve and impedance factor were experimentally determined. Model simulation reproduced measured thermal and hydraulic responses with good agreement. Results show that frozen hydraulic conductivity is highly sensitive to the impedance factor and initial moisture conditions, with an approximately exponential relationship. Freeze–thaw cycling caused hysteresis in the soil–water retention behavior, which is attributed to pore structure modification caused by ice formation and thawing. These results improve parameter estimation for frozen sandy soils and establish a validated framework for simulating coupled heat and moisture transport in cold-region environments.