Abstract: The heat and mass transfer, pore fluid phase transition process and salt frost heave deformation of sulfate saline soil under water and salt supply conditions were studied theoretically and experimentally. Based on unsaturated soil mechanics and thermoelastic continuum theory, a mathematical model of water-thermal-salt-force coupling in unsaturated sulfate-saline soil was established, in which the influence of phase transformation in pores on thermodynamic and hydraulic parameters was considered. The variation process of temperature field, water field, salt field and stress field in soil under unidirectional freezing condition of open system was analyzed by numerical simulation, and the validity of the theoretical model was verified by indoor cooling test. The results show that the latent heat released by salt during crystallization directly affects the process of water freezing into ice. Under the influence of the unidirectional freezing condition of the open system, the concentration of soil pore solution first increases rapidly to the peak value and then decreases gradually over time, and finally tends to be stable. Under the influence of negative temperature, the water phase inside the soil becomes ice, and gradually forms the freezing front. With the downward movement of the freezing front, the degree of salt frost heave is increasing.

Key words: sulphate saline soil, numerical model, water-salt migration, salt frost heave