盐渍土冻结过程中的特征温度研究

盐渍土在降温冻结过程中出现过冷温度和冻结温度两种特征温度,分别表示在降温过程中孔隙溶液中晶核形成和孔隙溶液与冰晶共存时的临界温度,对判断土体的冻结状态有着重要的意义。首先,通过不同含盐量的土体冻结试验,得到了相应的过冷温度和冻结温度;然后,基于热力学与经典成核理论给出了盐渍土冻结过程中的两种特征温度的理论计算模型,并与试验结果进行对比,验证了该模型的有效性;最后,分析了盐渍土特征温度的影响因素,重点考察了孔隙溶液中结晶盐析出对冻结温度和过冷温度的影响。结果表明,提出的模型可以实现对盐渍土冻结特征温度的有效预测。通过冻结特征温度随含盐量的关系曲线,可以得到结晶盐析出时的含盐量。冻结时孔隙溶液的浓度与冻结温度存在负相关关系,结晶盐的析出引起冻结时孔隙溶液浓度下降,从而使冻结温度升高。而结晶盐析出导致孔隙溶液浓度降低和土颗粒与冰晶接触角减小的双重影响,是盐渍土过冷温度的升高的原因。

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.