盐分对土的冻结温度及未冻水含量的影响研究

利用测温法和核磁共振法测量了不同浓度典型盐溶液(Na Cl、Na2CO3)饱和重塑粉土的冻结温度及冻结特征曲线,并与不同浓度的Na Cl、Na2CO3纯溶液作对比分析,研究初始含盐量对冻结温度及未冻水含量的影响。结果表明:土样冻结温度随初始含盐量的增加而逐渐降低;相同浓度Na Cl溶液饱和土样的冻结温度低于相应纯溶液的冻结温度,但相同浓度(<0.6mol/L)Na2CO3溶液饱和土样的冻结温度却比纯溶液的冻结温度高;同一负温下,土样中未冻水含量随Na Cl初始含盐量的增加而增多,但随Na2CO3初始含盐量的变化不明显。通过机制分析,表明盐类型和含盐量对土水势具有不同的影响。基于改进的广义Clapeyron方程,将含盐分土冻结温度表达式引入未冻水含量预测模型,得到了能够考虑不同含盐量影响的土体未冻水含量的定量表达,并与实测数据进行对比,验证了该模型能够较为合理的预测不同温度下含盐土体的未冻水含量。

Effects of salinity on soil freezing temperature and unfrozen water content

The freezing point and freezing characteristic curves of saturated remolded silt with solution (NaCl, Na2CO3) were measured by thermocouple and nuclear magnetic resonance method. Upon comparing the NaCl and Na2CO3 solutions, the effects of initial salt content on freezing temperature and unfrozen water content were studied. The results show that the freezing temperature of soils decreases with the increase of initial salt content; the freezing temperature of saturated soils with NaCl solution is lower than that of the corresponding pure solution with the same concentration. But the freezing temperature of saturated soils with Na2CO3 solution (<0.6 mol/L) is higher than that of the pure solution. At the same temperature, the content of unfrozen water in soils increases with the initial salt content of NaCl, but does not change obviously with the initial salt content of Na2CO3. The mechanism analysis shows that the salt type and salt content have different effects on soil water potential. Based on the improved generalized Clapeyron equation, the freezing temperature of salt-bearing soil was introduced into the prediction model of unfrozen water content. The quantitative expression of unfrozen water content of soil was obtained, and compared with the measured data with considering the effect of salt content. It is verified that the model can reasonably predict the unfrozen water content of saline soils at different temperatures.