Multi-field coupling process of heat-moisture-salt in unsaturated soil

On the basis of porous media theory, the multi-field coupling problem of temperature-moisture-salt in unsaturated soils under non-steady state conditions is studied. Considering that the pores are filled with liquid water, dissolved salts, water vapor and dry gas, the mass conservation equations for water, gas and salt in unsaturated soils and the relevant energy conservation equations are obtained on the basis of mass and energy conservation. For the one-dimensional unsteady state problem, the state equations for the problem are obtained by selecting temperature, pore pressure, pore water pressure, salt solution concentration and their derivatives as the state variables. The Laplace transform is used to transform the state equations in the time domain to those in the frequency one. Under the given boundary conditions, the shooting method is used to solve the strongly coupled nonlinear variable coefficient differential equations. The stability algorithm based on the Hausdorff moment problem transforms the numerical solutions in the frequency domain to those in the time one, and the validity of the model is verified by comparing with the existing experimental results. On the basis of numerical examples and parameters, the influences of pressure gradient, temperature gradient and porosity on the distribution of temperature field, water field and salt field in unsaturated soils are discussed.