考虑中主应力和基质吸力影响的湿陷性黄土增湿变形机理研究

The wetting deformation of collapsible loess is closely related to the safety of the engineering. The existing researches on wetting deforming characteristics of loess have been less considered the influence of matrix suction and intermediate principal stress, while the research results of true triaxial collapsibility tests under the condition of measuring suction are few reported. This project intends to use the collapsible true triaxial for unsaturated soil, taking the intact loess as the research object, and adopting the double-line methods and the single-line methods. The change characteristics of suction of prewetting and post wetting under the coupling of stress and water are studied, the water holding characteristics of intact loess under three-dimensional stress are obtained, the soil-water characteristic curve equation is established considering the influence of intermediate principal stress, which is used to quantitatively analyze the deformation strength characteristics of collapsible loess under three-dimensional stress state. The influence of suction, intermediate principal stress and stress ratio on humidification deformation is studied, and the influence of stress path and stress state on the wetting deformation is analyzed, the wetting deformation mechanism of collapsible loess considering the influence of suction under three-dimensional stress state is revealed, the deformation development of loess under three-dimensional stress state is represented by the stress humidification path and the stress humidification deformation surface. The research of this project is of great theoretical significance for the construction of collapsible loess.

湿陷性黄土的增湿变形与工程安全密切相关，已有黄土增湿变形特性的研究，较少考虑基质吸力和中主应力的影响，而测量吸力条件下真三轴湿陷试验的研究成果报道较少。本项目拟利用非饱和土湿陷真三轴仪，以原状黄土为研究对象，采用双线法和单线法试验，研究真三轴预湿法和后湿法中力、水耦合作用下吸力的变化特性，得到预湿法和后湿法中原状黄土在三维应力作用下的持水特性，建立考虑中主应力影响的土-水特征曲线方程，用于定量地分析三维应力状态下湿陷性黄土的变形强度特性；研究吸力、中主应力和应力比对增湿变形的影响，分析应力路径和应力状态对增湿变形的影响，揭示三维应力状态下考虑吸力影响的湿陷性黄土的增湿变形机理，采用应力增湿路径和应力增湿变形曲面表示三维应力状态下黄土的变形发展过程。本项目的研究对于湿陷性黄土的工程建设具有重要的理论意义。

湿陷性黄土的增湿变形与工程安全密切相关，已有黄土增湿变形特性的研究，较少考虑基质吸力和中主应力的影响，而测量吸力条件下真三轴湿陷试验的研究成果报道较少。本项目利用改进的非饱和土湿陷真三轴仪，以西安北郊原状Q3黄土为研究对象，采用双线法和单线法试验，研究了真三轴预湿法和后湿法中力、水耦合作用下基质吸力的变化特性，得到了预湿法和后湿法中原状黄土在三维应力作用下的持水特性，建立了考虑中主应力影响的土-水特征曲线方程，可用于定量地分析三维应力状态下湿陷性黄土的变形强度特性；研究了吸力、中主应力和应力比对增湿变形的影响，分析了应力路径和应力状态对增湿变形的影响，揭示了三维应力状态下考虑基质吸力影响的湿陷性黄土的增湿变形机理；通过考虑真三轴条件下中主应力和吸力对大主应变的影响，提出了一个真三轴条件下非饱和原状黄土的非线性本构模型；研究了真三轴压缩条件下非饱和黄土的有效应力屈服变化规律，通过分析有效应力与塑性应变关系得出有效应力空间中不同子午平面内的塑性势面呈椭圆形，且随着中主应力的增大，椭圆屈服面增大；应用修正剑桥模型作为推广，将饱和度这一参数引入到非饱和土的弹塑性模型中，并基于SMP准则变换应力方法建立了三维应力条件下非饱和黄土的弹塑性模型，该模型可以统一描述三维应力状态下非饱和黄土的力学特性和持水特性。本项目模拟了天然土层中的初始应力状态、地基浸水前的应力状态、以及降雨入渗对湿陷性黄土地基的影响，研究成果能够反映湿陷性黄土的变形性质，可以用来解释湿陷性黄土地基上建筑结构的水平位移和垂直位移产生的原因，对于湿陷性黄土的工程建设具有重要的理论意义。