Effects of water/salt phase transition on matric suction of sulfate saline soil

The sulfate saline soil is the main type of saline soil in cold and arid regions of Northwest China. As the environmental temperature changes, the ice formation and salt crystallization may change the matric suction of saline soil. The effects of water/salt phase transition on the matric suction of soil are investigated. The results show that the matric suction of soil linearly increases with the decreasing temperature before the phase transition occurs, and when ice forms or salt hydrate crystallizes in the soil, the matric suction of saline soil changes abruptly at the phase transition point. The matric suction of saline soil is closely related to the liquid water fraction of soil. Because the second phase transition occurs in the sulfate saline soil during cooling, the matric suction of saline soil also has a sudden change at the eutectic point, and the amount of the second phase transition directly affects the value of matric suction. Based on the experimental results, the prediction method for the matric suction of desalinized soil is further analyzed, and the water migration driving force of sodium sulfate saline soil is discussed during the freezing process. This study is helpful for the deep understanding of water migration driving force of saline soil and provides a reference for the development of multi-physical field coupling theory of saline soil.