Abstract: The regularities of water and salt migration in sulfate saline soil as well as their impacts on the frost heave of soil were investigated via indoor soil column test. The changes in moisture content, electrical conductivity, temperature, and displacement during the freeze-thaw cycles were measured by teros-12 and displacement meter. The experimental results demonstrated that in the freezing process from top to bottom, the bottom water moved toward the freezing front, driving the salt accumulating upwards. Meanwhile, the cycles of temperature rising and falling generated a notable hysteresis effect on volumetric moisture content and electrical conductivity of soil. The soil swelled during freezing, and the vertical deformation can be divided into three stages: the adjustment stage caused by the formation of mirabilite; the rapid deformation stage induced by the combined action of mirabilite and ice crystal; the gradual deformation stage resulted from a small amount of ice crystals. During melting, the vertical deformation of soil mass underwent swift melting at a certain melting rate. For saline soil containing sodium sulfate, the curve of vertical deformation during freeze-thaw cycles against time presented a peach-shaped trend, and the vertical deformation rate of each cycle was basically consistent. The salt frost heaving rate increased with the proceeding of freezing and thawing. Higher salt content had more evident impact on vertical deformation. The research findings offer data support for revealing the hysteresis effect and also for the establishment of water-salt-thermo-mechanics coupling model.

Key words: saline soil, freeze-thaw cycle, water-salt transport, salt frost heaving, hysteresis effect