循环动载下饱和粉土变形弱化与非共轴失稳机理

Significant losses will be induced by instable failure of silt ground. So far, the study on saturated silt instability under large number non-proportional cyclic load induced by wave and traffic is still absent. Revealing the mechanism is a prerequisite for preventing instability of silt ground. In this research, the dynamic hollow cylinder torsional shear test will be firstly carried out to simulate macroscopic deformation behavior under cyclic load stress path induced by wave and traffic. The corresponding macroscopic mechanism of deformation degradation and non-coaxial instability will be then revealed by analyzing the macroscopic rule of instability. Meanwhile, the microscopic test of scanning section under electron microscope will be also carried out on the samples before and after the instability. Through analysis and comparison of the fabric and its evolution law before and after the instability, the microscopic mechanism of deformation degradation and non-coaxial instability will be revealed. Then the criteria for judging the silt instability will be proposed by analyzing the evolution law of parameters reflecting deformation degradation and non-coaxial instability. Based on above study, the method for predicting deformation degradation instability will be developed and the constitutive model which can predict non-coaxial instability will be established. Finally, the prediction theory of saturated silt instability is formed. The results of this research can help us understand the silt instability more insightfully, and have profound theoretical significance and practical value for instability prevention of silt ground as well as the construction and operation of geotechnical engineering at the silt region.

粉土地基失稳破坏会造成重大损失，目前对于饱和粉土在波浪、交通大数目非比例循环动载下失稳尚未有深入研究，揭示其机理是防治粉土地基失稳的前提。本项目首先采用动态空心圆柱扭剪试验模拟波浪、交通循环动载应力路径下的宏观变形行为，通过分析发生失稳的宏观规律，揭示变形弱化及非共轴失稳的宏观机理；与此同时，进行失稳前后试样电镜扫描切片微观试验，分析对比失稳前后组构及其演化规律，揭示变形弱化和非共轴失稳的微观机理；分析表征变形弱化与非共轴失稳的参量演化规律，提出粉土失稳标准；在此基础上，提出预测变形弱化失稳的方法，构建预测非共轴失稳的本构模型，最终形成饱和粉土失稳预测理论。本项目研究成果可以深化当前对于粉土失稳的认识，对粉土地基失稳的防治、粉土地区岩土工程建设及运营有重要的理论意义和应用价值。

针对循环动载下粉土循环弱化与累积变形等问题，综合采用理论分析、单元试验、微观试验、本构理论等多种研究手段，揭示循环交通动载下变形弱化宏微观机理，建立循环荷载下土体循环弱化变形预测方法。开展了循环三轴应力路径下黄河流域冲积粉土试验，模拟交通循环动载下粉土宏观行为，探讨了含水率、循环应力比、围压对变形规律影响，获得了粉土循环变形弱化宏观规律；进而开展了变形弱化前后电镜扫描切片微观试验，获得变形弱化前后孔隙尺寸分布、孔隙率、平均形状系数、平均分形维数、概率熵等微观特征演化规律，揭示了试样变形弱化微观机理；基于粉土变形弱化宏观变形规律，提出粉土变形累积变形计算显式公式，建立了考虑非共轴变形的土体静力本构模型，在此基础上，考虑土体循环弱化、小应变刚度特性、累积变形规律等循环变形特性，构建了循环弱化的非共轴边界面本构模型，形成了循环动载下土体弱化及变形预测方法。本项目成果建立了循环动载下诱发地基循环弱化及变形的预测方法，为循环动载下粉土地基岩土工程变形控制提供了理论支撑。