Study on water and salt migration and deformation properties of unsaturated saline soil under a temperature gradient considering salt adsorption: Numerical simulation and experimental verification

Based on porous media theory and the principle of continuum mechanics, a mathematical model is established to describe a fully coupled process in a thermo-hydro-solute-gas-mechanical multi-field under a temperature gradient. The model considers the influence of factors, such as porosity evolution, water seepage and its evaporation–condensation, gas transport, salt adsorption/precipitation-dissolution dynamic conversion process, solid particles and pore fluid compressibility. Comsol Multiphysics is used to numerically simulate the previously mentioned multi-field coupling process. In the simulation process, some important physical parameters (such as porosity and medium density) depend on state variables (such as temperature, pore water pressure and salt content). The mathematical model and simulation results are verified through the actual measurement results of the indoor test. Thus, salt adsorption influences the heat and mass transfer process and deformation characteristics of unsaturated saline soil. The results show that the model can better reveal the water and salt transfer mechanism and deformation mechanism of unsaturated saline soil under the action of a temperature gradient, adsorption effects on the heat and mass transfer process and its deformation characteristics by affecting the porosity of the soil. Although in the process of establishing the theoretical model, the elastic constitutive model (including the effective stress principle) is used to describe the momentum conservation of the soil. Additionally, the study of salt adsorption provides theoretical preparation for further research on salt expansion in saline soil.