Theoretical and Numerical Analyses on Hydro–Thermal–Salt–Mechanical Interaction of Unsaturated Salinized Soil Subjected to Typical Unidirectional Freezing Process

The freezing process of salinized soil is a complex, dynamic, and interactive hydro–thermal–salt–mechanical (HTSM) coupled physical phenomenon. In many recent studies, soil was assumed to be saturated, and the theoretical models established were based on the framework of saturated soil, in which the influence of the vapor phase in freezing soil was neglected. In this paper, by considering the effect of vapor flow on heat movement and the relation between saturation and void ratio, an improved mathematical model will be established based on previous research. This improved hydro–thermal–salt–mechanical (IHTSM) model simulates the dynamic process of water migration, heat transfer, vapor flow, solute transport, and deformation. The numerical simulation implemented by the IHTSM model under the typical conditions of unidirectional freezing will be compared with previous research to verify the model's validity, and the various characteristics of the curves and their physical meaning will be analyzed by comparing them with the previous research. The dynamics of temperature, mass moisture content, displacement, salt content, volumetric vapor content and saturation degree in soil column will be discussed for the salinized soil during the freezing process. The results indicated that this improved model could provide a reference for the destruction process analysis of the harsh geological environment in cold, arid, and saline areas.