Abstract: In order to investigate the law of water and salt migration, understand the deformation characteristics of saline frozen soil, and explore the mechanism of soil salinization in cold and arid regions, a model test of silty clay with different salinities is carried out. Results indicate that the temperature, water, salt and deformation of the saline frozen soil are coupling with each other. The temperature reduction is advantageous to precipitate the salt crystals and freeze the unfrozen water, while the temperature rise is liable to dissolve the salt crystals and thaw the ice. Heat release or absorption during the phase change of salt and water influences the soil temperature. Salt influences the water content significantly by changing the dynamic viscosity of the fluid and freezing temperature the soil, and generating a great suction when salt crystals precipitate from the supersaturated solution. Salt migrating with unfrozen water in ionic form means that water is the medium for salt migration. Salt and water are moving upward to the surface during cooling period, while the opposite direction is observed during warming period. The migration rate is related to the soil suction, and the greatest soil suction in the freezing fringe results in the fastest migration velocity. The deformation of saline frozen soil is the result of the combined effect of salt and water. Frost heave and thaw settlement caused by water freezing and thawing are the mainly deformation of saline frozen soil with low salinity, while salt heave and dissolve settlement caused by salt crystallization and dissolution play the dominant role with high salinity.

Key words: seasonally frozen soil, salt migration, deformation characteristics, model test