为研究水盐运移情况下硫酸盐渍土盐-冻胀规律,采用室内土柱冻融试验,利用teros-12传感器及位移计测定冻融循环过程中土体含水率、电导率、温度和位移的变化,分析了水盐运移规律及其对土体盐-冻胀变形的影响。试验结果表明:在自上而下的冻结方式中,土体底部水分向冻结锋面移动,带动盐分向上聚积,同时土体体积含水率和电导率随温度的升降循环存在明显“滞回”现象。冻结阶段土体发生膨胀,竖向变形可分为3个阶段:①调整阶段,由生成芒硝引起;②快速变形阶段,由生成芒硝与冰晶共同作用所致;③缓慢变形阶段,由生成少量冰晶所致。融化阶段土体竖向变形以一定融陷速率发生快速融沉。含硫酸钠盐渍土冻融循环过程中,竖向变形随时间的变化关系呈现“桃尖型”趋势,且每次冻融土体竖向变形速率基本一致。随冻融次数的增加,盐-冻胀率也不断增加。土体含盐量越高对土体竖向变形的影响越显著。本研究可为揭示含硫酸盐渍土盐分和水分随温度变化的“滞回”现象以及水-盐-热-力耦合模型的建立提供数据支撑。
Abstract
The regularities of water and salt migration in sulfate saline soil as well as their impacts on the frost heave of soil were investigated via indoor soil column test. The changes in moisture content, electrical conductivity, temperature, and displacement during the freeze-thaw cycles were measured by teros-12 and displacement meter. The experimental results demonstrated that in the freezing process from top to bottom, the bottom water moved toward the freezing front, driving the salt accumulating upwards. Meanwhile, the cycles of temperature rising and falling generated a notable hysteresis effect on volumetric moisture content and electrical conductivity of soil. The soil swelled during freezing, and the vertical deformation can be divided into three stages: the adjustment stage caused by the formation of mirabilite; the rapid deformation stage induced by the combined action of mirabilite and ice crystal; the gradual deformation stage resulted from a small amount of ice crystals. During melting, the vertical deformation of soil mass underwent swift melting at a certain melting rate. For saline soil containing sodium sulfate, the curve of vertical deformation during freeze-thaw cycles against time presented a peach-shaped trend, and the vertical deformation rate of each cycle was basically consistent. The salt frost heaving rate increased with the proceeding of freezing and thawing. Higher salt content had more evident impact on vertical deformation. The research findings offer data support for revealing the hysteresis effect and also for the establishment of water-salt-thermo-mechanics coupling model.
关键词
盐渍土 /
冻融循环 /
水盐运移 /
盐-冻胀量 /
滞回效应
Key words
saline soil /
freeze-thaw cycle /
water-salt transport /
salt frost heaving /
hysteresis effect
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基金
宁夏高等学校一流学科建设(国内一流建设学科)项目(NXYLXK2017A03);宁夏回族自治区重点研发计划一般项目(2018BEE03005);宁夏自然科学基金项目(2021AAC03067)
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