基于水气运移的非饱和黄土强度演化机理研究

A large number of unsaturated loess distribute in arid and semiarid northwest area of china, and the research on water-air transmission and strength deformation of unsaturated soil under the climate environment of weak rainfall and strong evaporation has become a new growing point and hotspot in unsaturated soil research field. Positive water vapor adsorption experiment of unsaturated loess plans to be carried out from the perspective of moisture migration and soil strength evolution under evaporation environment in this project, which aims to study adsorption, diffusion and seepage characteristics of water vapor in unsaturated loess and propose the theory of water vapor adsorption of unsaturated loess. Reverse evaporation test of unsaturated loess is conducted to analyze main influencing factors of soil evaporation, which aims to establish evaporation theory model of unsaturated loess. Based on the Fredlund and the Van Genuchten model, prediction model of the soil water characteristic curve is established considering evaporation effect, and change regulation of unsaturated loess matrix suction under evaporation effect is researched. In order to research the influence of evaporation on soil strength, unsaturated soil triaxial test of moisture loess with controlled suction is conducted, which helps to analyze strength variation of unsaturated loess in the different stages of the evaporation. The interaction model of evaporation-moisture migration-strength of unsaturated loess is established to research on the strength evolution regulation in the process of evaporation. The research results can provide useful theoretical basis for the engineering construction in the loess region.

干旱与半干旱西北地区分布着大量的非饱和黄土，弱降雨、强蒸发气候环境下非饱和土的水气运移与强度变形研究，已成为非饱和土研究领域新的生长点。本项目拟针对非饱和黄土，从蒸发环境下水气运移与土体强度演化的角度出发，进行正向非饱和黄土水蒸气吸附试验，研究水蒸气在非饱和黄土中吸附、扩散与渗透特性，提出非饱和黄土水蒸气吸附理论。进行逆向非饱和黄土蒸发试验，分析影响土体蒸发的主要影响因素，建立非饱和黄土蒸发理论模型。并基于Fredlund和Van Genuchten模型，建立考虑蒸发效应的土水特征曲线预测模型，研究蒸发作用下非饱和黄土基质吸力的变化规律。针对蒸发作用对土体强度的影响，进行含湿黄土控制吸力非饱和土三轴试验，分析在不同蒸发阶段，非饱和黄土强度的变化规律，建立蒸发-水气运移-非饱和黄土强度相互作用模型，对蒸发过程中强度演化规律进行研究。研究成果能够为黄土地区的工程建设提供理论依据。

浅层非饱和黄土暴露于大气环境中，受到诸如太阳辐射、蒸发、降水等气候因素影响，使得非饱和土含水状态不断处于动态平衡变化中，研究非饱和黄土水分的运动规律、规避含水状态变化对工程造成的危害具有重要的现实意义。本项目从蒸发和增湿条件下水-热-汽耦合运移出发，开展天然黄土、强酸作用下黄土、盐化作用下黄土等温吸附试验，得出不同地区黄土的比表面积随着深度、酸溶液腐蚀情况、盐溶液侵蚀情况等变化规律。通过比表面积，直接反映黄土颗粒与气相或者液相物质相互作用的强烈程度。考虑不同环境温度、风速、初始含水率、压实度等影响因素，通过室内一维土柱蒸发模型试验，分析蒸发过程中各因素对土体蒸发速率及累积蒸发量的影响规律。建立二相水-气-热耦合作用基本理论方程及相关参数的确定方法，考虑水蒸气弥散运移方式，研究水蒸气弥散运移机制对土体蒸发过程的影响机理。考虑土体孔隙水非平衡相变情况，探讨土体蒸发过程中液态水相变率变化机理。建立大气自由流-多孔介质两相流耦合模型，实现两个子域内9个主变量耦合数值求解，研究主要气候因素、界面条件及土体参数等对蒸发过程的影响规律。选用非饱和重塑黄土填筑室内模型，通入一定压力的高温水蒸气，研究蒸汽压梯度、温度梯度和含水率梯度耦合作用下的水热迁移规律。推导出含湿多孔介质水热迁移方程的一组代数显式解析解，并将解析解和试验结果对比分析。将水蒸气增湿黄土与高能强夯法相结合，开发蒸汽增湿夯实法处理湿陷性黄土地基的新技术与新方法。从增湿作用下土中水-热运移与土体强度变化的角度出发，开展不同蒸汽压力下重塑黄土高温高压水蒸汽增湿模型试验，对增湿处理后的土体强度进行测试，分析增湿作用下重塑黄土强度演化规律。研究成果可供西北干旱区、半干旱区水土保持措施制定、土工结构物防排水措施设计等提供相关理论依据；水蒸气增湿联合强夯地基处理新技术，可为大厚度湿陷性黄土地基处理提供了新的思路与技术参考。