Numerical Modelling of Coupled Thermal–Hydraulic–Mechanical Processes in Unsaturated Soils During Freezing and Thawing

Most existing studies investigate the effect of the overburden pressure and external temperature on the freezing process in unsaturated soils. However, the hydraulic and thermal properties of soil have a significant outcome as well. For this purpose, a coupled Thermal–Hydraulic–Mechanical theory, to investigate unsaturated fine sands, is developed and deployed in a finite element method simulation with COMSOL Multiphysics. Validation of the model’s accuracy is achieved by comparing the numerical to the experimental soil freezing and thawing results published in the literature. After validating the model’s reliability, five cases are simulated to examine the impact of soil particle thermal conductivity and saturated hydraulic conductivity on the freezing and thawing processes. Results indicate that the saturated hydraulic conductivity has a slightly greater effect on the position of the freezing front and on the amount of heave than particle thermal conductivity. Finally, this study shows the effect inflicted by the temperature gradient, water flux, and vertical stress build-up on both thermal and hydraulic properties during the freeze–thaw cycles.