开放系统下硫酸钠盐对土体冻胀的影响

易溶盐在土中的存在及其在冻结过程中的重新分布对土体的冻结过程有重要影响.在开放系统单向冻结条件下,对青藏铁路沿线粉质红粘土进行了冻结试验.结果表明:随着冷能的持续传递,硫酸钠盐和水分向温度较低处迁移,土体0℃曲线持续降低;但基于测定的含盐土大量冻结温度的基础上,对土体冻深的研究发现,在开放单向冻结条件下土体冻深随着水盐迁移进程的发展而减小,造成与补蒸馏水的土体相比,土体的冻胀较小.同时,利用冻深发展曲线和硫酸钠水溶液相图及溶解度曲线,对土柱中的冻胀和盐胀分别进行了计算,结果认为:土体变形主要是由冻胀引起,硫酸钠结晶膨胀只发生在未冻土段,这与试验结束后对土体冻土段和未冻土段的干密度分层测定的试验结果相一致.

Influence of Sodium Sulfate on Soil Frost Heaving in an Open System

The existence of solutes and their redistribution during freezing have a deep influence on the process of soil freezing.Unidirectional freezing experiments were performed in an open system with red clay collected at the Beiluhe test site along the Qinghai-Tibet Railway.Groundwater supply of the soil was simulated in the experiments by attaching a liquid replenishment system to the bottom of the specimen container.In order to see the influence of the salt on the evolution of the specimen during the unidirectional freezing,two types of experiments were done.(i) The soil specimen was supplied with a sodium sulfate solute of 5% concentration,and(ii) only distilled water without any salty component was added.Based on the freezing temperature measurements of salty soil,with the migration of sodium sulfate solution towards the lower temperature zone,it is found that during freezing 0℃ isothermal in the soil falls gently,but frost depth of the soil ascends slowly when cool is given constantly.Compared to the experiments with distilled water replenishment,amount of frost-heaving is lesser in the specimen with sodium sulfate solution replenishment.Moreover,based on the frost depth curve,Na₂SO₄-H₂O system and solubility curve of sulfate sodium,amounts of frost heaving and salt expansion in the specimens have been calculated,respectively.From the calculations,one can see that deformation of the specimen is mainly caused by frost heaving in early stage,and by crystallization of sulfate sodium in later stage,which is demonstrated by the dry density after the experiments.