Abstract: The multi-field coupled heat-moisture-salt behavior of unsaturated soils under steady state is investigated using porous media theory. It considers that the pores are filled with liquid water, dissolved salts, water vapor, and dry gas. The mass conservation equations of moisture, gas, and salinity in unsaturated soils and the energy conservation equations are presented. Considering one-dimensional steady-state problems, the state equations are obtained by using the temperature, pore pressure, pore water pressure and salt solution concentration and their first-order derivatives as the state variables. Under given boundary conditions, the coupled nonlinear differential equations for the varying coefficients are solved by shooting method. The validity of the model is verified by comparing with the existing experimental results. Based on numerical examples, the influence of moisture content, temperature boundary and porosity on the distribution of temperature field, water field and salt field in unsaturated soils was discussed in detail.

Key words: unsaturated soil, heat-moisture-salt coupling, steady state condition, shooting method