Experimental study on impact of salt content on deformation characteristics of sodium sulfate soil under freeze-thaw conditions

Due to the sharp fluctuations of temperature in cold regions, salt may crystallize and water may freeze, resulting in the deformation of soil. In order to investigate the impact of salt content on soil deformation under freeze-thaw cycles, the freeze-thaw tests on soil with different salt contents are conducted. The desalinized Qinghai-Tibet silty clay is used, then different salt contents 0%, 1%, 2%, 3% are added, respectively. By testing the deformation of soil in a close system, the impact of salt content on deformation characteristics of sodium sulfate soil is studied. The results demonstrate that the frost heave and thaw settlement occur when the soil is desalinated or the salt content is 1%, and the thaw settlement is larger than the frost heave. However, when the salt content of soil is higher, though the frost heave still exists, the thaw settlement decreases and even disappears. Based on the porous media mechanics, the mechanism of soil deformation is discussed under freeze-thaw cycles. It is obtained that the deformation of soil is the results of combined effect of many factors, such as the phase change effect, thermal expansion and contraction and so on. In addition, considering the sodium sulfate properties, the crystallization mechanism of sodium sulfate is investigated. The research will help to provide some theoretical basis for the studies on saline frozen soil.