基于工后地下水分场再平衡过程的超深黄土填方体沉降变形机理研究

In the process of urbanization of the Loess Plateau in China where gullies are crisscrossed, deep filled foundation has been a typical and commonplace engineering measure to expand urban area. Furthermore, the moistening deformation induced by rebalance of moisture field after construction has been found to be the fundamental internal factor which would affect the development of post-construction settlement in such constructions. This project aims to reveal the mechanism of moistening deformation induced by rebalance of moisture field of deep filled loess foundation. Based on results of previous groundwater monitor, the continuously monitor of moisture and deformation of deep filled foundation is planed to be conducted to reveal the law of moisture migration. Secondly, the unsaturated permeability characteristics of compacted loess under different stress states are planed to be explored through triaxial permeability test and analysis of SWCC, based on results of these tests, mathematical model of moisture migration in compacted loess will be carried out. Moreover, the mechanical mechanism and evolution of microstructure of moistening deformation of compacted loess will be found out by moistening compression test and the test of scanning electronic microscope, based on these, the constitutive model of compacted loess’s moistening deformation will be constructed. Based on above, numerical model with coupled moisture field and stress field will be constructed to reveal the characteristics of settlement of deep filled foundation induced by rebalance of moisture field. Overall, the mechanism of the effect of moisture field’s rebalancing process on settlement of deep filled loess foundation will be revealed through this project, and the systematic results could provide theoretical basis to control the post-construction settlement of deep filled loess foundation and prevent engineering diseases.

在我国黄土沟壑地区城市化的进程中，超深黄土填方是一种典型而普遍的工程措施，而工后地下水分场再平衡引发填方体的增湿变形是影响工后沉降发展的关键因素。本项目重点围绕超深黄土填方工后地下水分场再平衡引发填方体增湿变形的宏细观机理开展研究。通过全深度范围的水分、变形连续同步监测，揭示超深黄土填方工后地下水分场的迁移规律；通过大型三轴渗透试验、水土特性试验，探索应力状态对填方黄土非饱和渗透特性的影响机理，构建超深黄土填方体内部水分运移的数理模型；通过增湿压缩试验结合电镜扫描分析，研究不同含水率、压实度的填方黄土在不同应力状态下的增湿变形机理，构建填方黄土增湿变形本构模型。通过应力场-水分场耦合数值模拟揭示水分场再平衡过程对超深黄土填方体沉降变形的影响机理。通过项目研究，深刻揭示工后地下水分场再平衡过程中超深黄土填方体的沉降变形机理，其成果将为超深黄土填方工后沉降控制和病害防治提供重要的理论依据。

本项目以黄土填方土体地下水分场变化切入点，通过现场监测、现场试验结合数值模拟研究手段，揭示了黄土沟壑高填方工后地下深层与浅层水分场的运移规律与内在机制，结果表明工后24个月内填方区原始沟壑下游水位上升最为显著，黄土沟壑高填方深层水分场受地下水位控制，挖填结合部位在高自重应力与深层水分场上移作用下产生隐蔽的深部湿化变形，成为填方体滑移、大面积开裂的主要原因。浅层水分场的变化主要受降雨影响，入渗深度普遍小于10m，长期工程振动与浅层水分场变化的耦合作用是导致地表局部开裂、塌陷的主要原因。在此基础上通过柔性壁渗透试验结合土样微细观结构数字表征图像，分析了不同应力状态对填方黄土饱和渗透系数的影响规律，通过考虑应力状态的压力板试验分析了高填方内部应力场差异对土样结构、渗透系数的影响机理。结合理论模型从微观及细观层面深入阐明了地下水分场环境变化条件下水土作用的实质，得到了不同条件水分场的变化规律，以及不同条件下填方土体的工后变形规律。探索了采用小比例有机硅疏水材料对填方黄土渗透特性改良的新方法。并结合现场调研情况，进一步通过模型试验与数值模拟，探索了工程振动作用对黄土填方地基浅层土体及典型线性结构的动态影响规律。项目研究结果可为黄土地区填方工程的合理利用、地质环境保护和防灾减灾提供理论依据。