冻融循环条件下盐渍土工程特性研究

There distributed a large of seasonal frozen soil and saline soil in Xinjiang; With the developmeent of the western, the construction of roads and water conservancy projects becomes more and more, the damage which caused by the crystallization and frost heaving of the salt in the saline filling becomes outstanding. Saline soil, as a special soil, due to temperature changes and evaporation, soil water solution of salt will be part of the precipitation and crystallization of the salt from warm areas to cold areas, wet areas to dry areas migration, aggregation and crystallization of the salt accumulation and the desalination process frequently alternating, so that it demonstrated the unique engineering features. Under the effection of the seasonal frost heave and thaw, salt expansion and melting, there occurrence a large number of engineering disease. It becomes very critical and urgent to furter carry depth study about the saline soil frost heaving and salt expansion laws as well as to produce the dynamic changes of the microscopic structure of soil salt expansion and salt expansion process to ensure the safe operation of engineering and construction. We would select several typical saline soil, carry the test of indoor freeze-thaw cycle to study the cycle fluctuations in temperature conditions, frost, salt expansion and melting, explore the mechanisms of the saline soil area engineering diseases. Combination of soil, water, salt, temperature, power and micro-structure aspects of salt on saline soil, frost heave features in-depth study based on field surveys and freeze-thaw cycle test. Through disease prevention and treatment about saline soil. We could provide some important reference for future construction projects.

新疆广泛存在季节性冻土和盐渍土；随着西部开发的逐步深入，修建道路、水利等工程项目进一步增多，盐渍填土中由结晶引起的盐、冻胀破坏问题越来越突出。盐渍土作为一种特殊土，由于温差变化与蒸发作用，土体水溶液中盐分将部分析出并结晶，盐分由暖区向冷区，湿区向干区迁移、聚集和结晶，积盐与脱盐过程频繁交替，使其表现出特有的工程特性。在季节性冻胀和融沉、盐胀和溶沉的共同作用下，发生大量的工程病害。深入研究盐渍土冻胀和盐胀规律以及产生盐胀时土体微观结构和盐胀的动态变化过程，确保工程建筑安全运行及病害治理已十分关键和迫切。本课题选取几种典型的盐渍土进行室内冻融循环试验来研究其在周期波动温度条件下冻胀、盐胀和融、溶沉特性，探讨盐渍土地区工程病害产生的机制。采用实地调查和冻融循环试验相结合，从土、水、盐、温、力及微观结构等多方面对盐渍土的盐、冻胀特性进行深入的研究。为工程建设中的盐、冻胀病害防治提供重要的参考依据。

采用罗布泊和艾丁湖地区的典型天然盐渍土，模拟自然条件下，天然盐渍土在经历多次冻融循环时的盐冻胀特性试验研究，得出典型天然盐渍土在该条件下的盐冻胀和融陷规律，以及盐胀率、融陷率与冻融循环周期的关系。采用电镜扫描仪、常规土工试验仪和自制冻融循环仪，进行天然盐渍土在冻融循环条件下水分和盐分迁移研究，得出相应规律。且对多次冻融循环后盐渍土内部结构的微观变化进行研究，揭示盐冻胀的实质。.结果表明：.（1）不同含水率的强氯盐渍土进行三轴固结排水剪切试验时，最优含水率条件下，强氯盐渍土的应力应变曲线以应变硬化型为主；含水率小于最优含水率时，强氯盐渍土的应力应变曲线以应变软化型为主；含水率大于最优含水率时，强氯盐渍土的应力应变曲线在低围压状态下呈现应变软化型，在高围压状态下呈现应变硬化型。强氯盐渍土的结构强度随着含水率及冻融循环次数的增加而减小。. （2）罗布泊地区（亚）硫酸盐渍土的溶陷系数随初始干密度、初始含水率增加而减小；溶陷系数随含盐量增大而增大。硫酸和亚硫酸盐渍土存在峰值溶陷压力，分别为300kPa和200kPa。.（3）在经历7个冻融循环周期时，（亚）硫酸盐渍土随着冻融循环次数和初始含水率的增加，盐-冻胀率不断增大；在相同含水率下，随着初始干密度的增加，盐-冻胀率、融沉量相差不大，含水率比干密度对盐渍土的盐-冻胀率影响更大。硫酸盐渍土和亚硫酸盐渍土最大盐-冻胀增量和最大融沉量周期分别出现在第4周期和第3周期。.（4）罗布泊地区亚氯盐渍土在冷端阶梯式持续降温过程中，土体膨胀变形可分为3个阶段，第一阶段主要为盐胀起胀，第二阶段为盐胀增长，第三阶段为盐-冻胀共同增长阶段。冻融循环降温过程中土体温度变化成抛物线型。.（5）冻融循环后的盐渍土内部微观结构变化是：当盐渍土中硫酸盐含量较多时盐结晶的形状变化各异，且体积较大，形成的盐结晶易将土颗粒包裹，土体颗粒之间被结晶盐填充。土体以氯盐为主时，土体盐结晶形状相对硫酸盐较为规则，多数附在土体颗粒表面。.（6）压力的作用会抑制盐渍土的盐-冻胀性，且缩短了盐-冻胀变形达到最大的周期，但加剧了融陷变形。融陷系数在第1、2周期冻融循环后急剧增大，而后逐渐减小，当压力为0 kPa、8.33 kPa时土样的盐-冻胀具有叠加效应；而在压力为33 kPa-66 kPa时，盐-冻胀叠加性仅仅表现在前几周期；含盐量较大时压力也不能完全消除盐冻胀现象。

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