Numerical Study on the Multifield Mathematical Coupled Model of Hydraulic-Thermal-Salt-Mechanical in Saturated Freezing Saline Soil

Freezing in saturated saline soil is a dynamic, coupled hydraulic-thermal-salt-mechanical (HSTM) process. The aim of this paper is to establish a model to describe the coupling process. In the model, mass conservation law, Darcy’s law, and the energy conservation law are applied. The Clapeyron equation is used to illustrate the phase equilibrium in the multiphase system of soil, ice, and water, which contributes to the simplification of the soil-water potential. A freezing experiment using a 20-cm soil column with top-side freezing was performed, and the model was solved using transient finite elements. The numerical simulation fit well with the experiment data. The results show the temperature distribution, the water content distribution, the frost heave amount, and the salt distribution at different times along the one-dimensional column. In addition, it was found that the temperature in the frozen zone changes faster than that in the unfrozen zone, and the temperature distribution tends to be stable after freezing for 96 h, resulting in upward water migration toward the freezing front from the unfrozen zone and the formation of ice lenses. Because of the water migration, an expansion process is produced, and salt is transported upward constantly. Excess salt is precipitated if the solute concentration exceeds the solubility. These results provide a reference for soil salinization and frost heave behavior in saline soils in cold regions.