硫酸盐渍土晶体析出规律与结晶压力试验研究

The complicated and varied crystallization environments and crystal forms of sulfate saline soil result in seriously damage of structures such as road, channel, airport and so on. Salt heaving of saline soil, currently, is not only one of the hot and difficult issues in theory research, but also one of the engineering problems should be resolved urgently. However, the precipitation of salt crystals and corresponding crystallization pressure in saline soil have received little attention so far. Consequently, typical sulfate saline soils on Hexi Corridor are taken as research object: (1) The patterns for precipitation of crystals in sulfate saline soil under unsteady conditions are studied by environmental scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance. (2) The crystallization pressure induced by phase change is studied theoretically and experimentally. Furthermore, the pore size distribution characteristics are analyzed to establish the micro-macroscopic crystallization pressure model, and the criterion of crystallization damage of saline soil is given. (3) The freeze-thaw cycle tests are carried out by using benzene with volume shrinkage during cooling instead of sodium sulfate solution, and the deformation and soil pressure were analyzed to clarify the mechanism of salt heaving. The research results are expected to provide a theoretical guidance for solving the problem of salt heaving in western sulfate saline soil, and ensure the safe operation of foundation engineering and related buildings.

硫酸盐渍土结晶环境和晶体形态复杂多变，使道路、渠道、机场等构筑物遭到严重破坏，盐胀是盐渍土理论研究中的热点和难点问题，也是亟待破解的工程难题。迄今为止，盐渍土中晶体析出规律，及相应的结晶压力尚未引起足够重视。为此，本项目拟以河西走廊典型硫酸盐渍土为研究对象：（1）通过环境扫描电镜、X射线衍射分析和核磁共振测试等方法，研究非稳态条件下硫酸盐渍土中晶体析出规律；（2）通过理论分析和试验测试研究相变产生的结晶压力，根据孔隙分布特征，建立微观-宏观结晶压力转化模型，给出盐渍土结晶破坏判据；（3）采用降温时体积收缩的苯代替硫酸钠溶液进行冻融循环试验，分析土体变形和土压力变化规律，阐明盐胀力学机理。研究成果有望为解决我国西部硫酸盐渍土盐胀问题提供理论依据，确保基础工程及相关建筑安全运营。

硫酸盐渍土随温度和水分变化会出现严重盐胀，使道路、渠道和机场等发生不均匀隆起、松胀和开裂，给工程建设带来巨大困难。研究硫酸盐渍土晶体析出规律，揭示盐胀和冻胀力学机理，具有重要的理论价值和实践意义。采用光学显微镜试验、爬升试验和环境扫描电子显微镜试验观察硫酸盐渍土晶体析出规律，发现土体中硫酸钠晶体具有多层多级生长特征，观察到盐晶体和土颗粒之间具有一层液态膜，液膜上的溶液浓度增大时将土颗粒推开，证明了结晶压力是通过液膜施加在土颗粒上并导致土体变形。通过压汞试验和核磁共振试验表征晶体析出对盐渍土微观结构的影响，探究了含盐量、含水率及干密度等因素对晶体析出形态，揭示了冻融条件下盐渍土内部孔隙的变化规律。开展不同含水率、干密度、含盐量条件下硫酸盐渍土结晶压力测试，基于相变动力学理论建立了微观结晶压力计算方法，在此基础上建立了盐渍土微观-宏观结晶压力转化模型，模型计算结果与实测土结晶压力十分吻合。此外，开展不同含盐量、含水率、干密度的多次冻融循环实验，研究温度、未冻水含量、孔隙水压力、基质吸力和土体位移的变化规律；类比于非饱和土有效应力原理，给出了冻结盐渍土的有效应力方程，将土体变形分为温度应变、盐胀、冻胀、溶陷和融沉应变及残余应变，很好的解释了冻结盐渍土变形机理。研究成果有望为解决我国西部硫酸盐渍土盐胀问题提供理论依据，确保基础工程及相关建筑安全运营。