冻融循环作用下含盐量对Na_2SO_4土体变形特性影响的试验研究

冻融循环作用下,土体孔隙溶液中的盐分不断结晶与溶解,水分不断冻结与融化,使得含盐土体的变形不断变化。以青藏高原粉质黏土为研究对象,对洗盐后的素土分别加入质量分数为0%,1%,2%,3%的Na_2SO_4盐,研究了封闭系统下Na_2SO_4盐渍土在冻融循环作用下的变形规律。结果表明,在冻融循环过程中,不含盐土体和较低含盐量的土体表现出明显的冻胀融沉现象,且土体的融沉大于其的冻胀。而较高含盐量的土体在冻结过程中,土体的冻—盐胀作用显著,融沉现象却不再明显,甚至消失。利用多孔介质力学的方法,探讨了Na_2SO_4盐渍土在冻融循环作用下土体的变形规律,得出土体的变形由冰水/盐分相变、热胀冷缩、相变过程中的密度变化等引起的变形综合而成。结合Na_2SO_4溶液的性质,还分析了Na_2SO_4的结晶机理,从而为进一步研究盐渍化冻土中的变形机理提供一些参考。

Experimental study on impact of salt content on deformation characteristics of sodium sulfate soil under freeze-thaw conditions

Due to the sharp fluctuations of temperature in cold regions, salt may crystallize and water may freeze, resulting in the deformation of soil. In order to investigate the impact of salt content on soil deformation under freeze-thaw cycles, the freeze-thaw tests on soil with different salt contents are conducted. The desalinized Qinghai-Tibet silty clay is used, then different salt contents 0%, 1%, 2%, 3% are added, respectively. By testing the deformation of soil in a close system, the impact of salt content on deformation characteristics of sodium sulfate soil is studied. The results demonstrate that the frost heave and thaw settlement occur when the soil is desalinated or the salt content is 1%, and the thaw settlement is larger than the frost heave. However, when the salt content of soil is higher, though the frost heave still exists, the thaw settlement decreases and even disappears. Based on the porous media mechanics, the mechanism of soil deformation is discussed under freeze-thaw cycles. It is obtained that the deformation of soil is the results of combined effect of many factors, such as the phase change effect, thermal expansion and contraction and so on. In addition, considering the sodium sulfate properties, the crystallization mechanism of sodium sulfate is investigated. The research will help to provide some theoretical basis for the studies on saline frozen soil.