Study on phase changes of ice and salt in saline soils

摘要

The occurrence of different ice and salt phases in saline soils may result in severe failure in engineering practice. Therefore, studying the phase changes of these two components may improve the understanding of saline soils. Through a series of cooling experiments on sulfate saline soils, the internal temperature variation of soils is obtained to study the rule of salt crystallization and the effect of salt on liquid water content. Based on the thermodynamic principle, the heat transfer equation is expressed considering the phase changes of ice and salt, and the control volume approach is applied to discretize the differential equation of heat transfer. Combined with the internal temperature curve of the soils, the discrete equations allow the calculation of ice porosity variation, salt crystal porosity, and unfrozen water content in saline soils. Additionally, the equations provide a useful general criterion for salt crystallization at different temperatures. Experimental and theoretical results confirm that unfrozen water content in saline soils decreases as the salt content increases, and that liquid water content is lower in salt-free soils. In addition, the concentration of salt solution in soils with low salt content increases owing to the phase change between water and ice; salt crystallization can only occur if the concentration reaches 20% at a negative temperature.