Characteristic temperatures of saline soil during freezing

The characteristic temperatures appearing in freezing process of saline soil include the freezing temperature and the supercooling temperature. The former is the point at which chemical potentials of ice and liquid achieve equilibrium, and the latter is the point of ice nucleation. The characteristic temperatures are important for the analysis of the freezing state of soil. In the beginning, the characteristic temperatures are obtained through the freezing tests on the saline soil with different salt contents. And then, a model for calculating the characteristic temperatures is provided based on the thermodynamics and the classical nucleation theory. The model is proved to be reliable by comparing the calculated data with the test data. Finally, the influence factors for the model are analyzed, and especially the influences of salt precipitation on the characteristic temperatures are considered. The results show that the proposed model can effectively predict the characteristic temperatures of the saline soil. The salt content corresponding to the salt precipitation can be acquired by the relationship curve between the characteristic temperatures and the salt contents of the saline soil. The freezing temperature has a negative correlation with the concentration of pore solution, and the salt precipitation will induce the depression of the concentration of pore solution so as to increase the freezing temperature. The reason for the increase of the supercooling temperature of the saline soil is the double-effect of the depression of solution concentration and the decrease of contact angle between ice and soil particles.