Experimental investigation of the influence of salt on the phase transition temperature in saline soil

摘要

Phase transition temperatures are important indexes to distinguish salt expansion and frost heave in frozen saline soil. By a series of cooling experiments, the phase transition temperatures of sodium chloride and sodium sulfate saline soils were measured for different salt concentrations. The results showed that the freezing temperature of saline soil is lower than that of a bulk solution of equivalent concentration. Affected by the surface energy of the ice/liquid solution, the freezing temperature deviations between the soil pore solution and bulk solution gradually increase with increasing salt concentration, whereas the degree of supersaturation of saline soil decreases. The eutectic temperature of saline soil is not constant but varies with the salt concentration. The accumulation of both ice and salt crystals affects the eutectic temperature. Though the freezing temperatures and salt crystallization temperatures between loess and silty clay are similar, prominent deviations appear in the eutectic temperatures. In addition, the phase diagram of the pore solution in saline soil is discussed. This work promotes an understanding of the phase transition process and the deformation of saline soil during cooling.