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In China, the seasonally frozen ground is mainly distributed in the area north of latitude 30 °, accounting for 53.5% of the land area. Seasonal frozen soil is a special soil-water system containing ice crystals, ice, soil particles, pore water, gas consisting of a four-phase geological body. Soil freeze, causing water to migrate to the freeze zone, which caused problems in agriculture, water resources, environment and human engineering research occupies a very important position. The seasonal frost damage has been plagued road construction in northern China is an important issue, of common salt expansion, frost heaving, boiling and phenomena are caused by the migration of moisture, heat, salt. With the cold regions and polar resource development, project construction and environmental protection to carry out the subgrade soil hydrothermal salt transport increasingly cause for concern. Seasonally frozen ground frost heaving a correct understanding of the mechanism of salt expansion of road development and construction needs of Sulphate Salty Soil seasonally frozen ground saline soil engineering and construction hazards most typical saline soil. In order to grasp the subgrade soil water thermohaline dynamic, effective control of the the subgrade soil hydrothermal salt migration process, hydrothermal salt migration mechanism on the basis of research subgrade, we do the following: (1) In this paper, the simplified model without compromising the principles of migration law, according to the law of conservation of energy, respectively, established a season Permafrost Embankment moisture migration, heat transfer, the salt migration of two-dimensional partial differential equations. Moisture migration equation: heat transfer equation: salt transport equation: (2) Frozen system freeze time moisture, temperature, salinity dynamic variation obtained total volumetric water content in the soil increases are focused on the the upper soil layer less than 1m, the the Frozen Soil temperature gradient is greater than not Frozen Soil salinity showed the law first and then decrease and then increase as the temperature and moisture changes, and the calculated results with the measured results were compared, verify the coupling model is reasonable. (3) in the finite-difference time period using the finite element method to solve the stress and deformation field of the roadbed, come to the the roadbed surface displacement Center large settlement, the settlement of the roadbed position was symmetrical pattern. Comparison of the fourth and fifth sections of roadbed displacement values, we can see that the setting of the subgrade barrier layer can effectively improve the seasonally frozen ground sulphate saline soil subgrade stability.
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