Influences of water phase change/migration factors in hydro-thermal coupling model for unsaturated soils

The numerical simulation is an important technique for investigating the coupled hydro-thermal behavior of unsaturated soils. In order to simplify calculation, the researchers often assume that water-vapor phase change is ignored during numerical study on the hydro-thermal behavior. To study the rationality of the hydro-thermal coupling problem of simplified calculation, based on the existing theory of hydro-thermal coupling model, which fully considers the coupling effects of heat conduction, water-vapor phase change, temperature gradient, moisture gradient and gravity, the FreeFem++-compiled hydro-thermal coupling model is used to study the application and evolution characteristics of the moisture and temperature fields. Based on the boundary conditions of groundwater level, surface evaporation, infiltration and wetting-drying in practical slope conditions, the rationality and coupling mechanism of factors such as latent heat, gravity, water vapor motion and permeability coefficient in the simplified calculation of coupled hydro-thermal problems are analyzed. The results show that, under the above boundary conditions, whether the latent heat is considered or not and the value of phase change coefficient significantly affect the distribution characteristics of the temperature field of soils, but the influences on the water migration are insignificant. In addition, the water migration of surface soil is faster, and water content is lower with the gravity considered and a larger permeability coefficient.