初始各向异性砂土非共轴特性的产生机理及本构关系研究

The generation mechanism of non-coaxial behavior and non-coaxial influence on soil strength and deformation characteristics has been an important research subject in the field of soil mechanics. This study aims to research the interaction between soil inherent anisotropy and loading direction, in hopes that the generation mechanism and constitutive relation of non-coaxial behavior would be revealed. This study will carry out shearing tests on inherent anisotropic sand with non-proportional loading, analyze the transfer mechanism of load and change rule of stress and strain, found the interaction between inherent anisotropy and loading direction, reveal the generation mechanism of non-coaxial behavior. Basing on the soil mechanism characteristic at critical state, the expression formation of the non-coaxial plastic modulus will be suggested in view of the optimum fitting of the non-coaxial characteristic and the physical and mechanical states of sand during the rotation process of the principal stress direction. Basing on the non-coaxial yield theory, the non-coaxial plastic strain increment will be calculated by the non-coaxial plastic modulus, and then, a non-coaxial elasto-plastic constitutive model of sand will be developed. The non-coaxial influence on the strength and deformation characteristics of sand will be researched by numerical simulation and modeling tests with multi-dimension loading, and then, the applied range of the non-coaxial model will be discussed. The research results will promote the development and application of the non-coaxial theory, and provide a basis for the design of important engineering structures and foundations.

研究非共轴特性的产生机理，揭示该特性对土体强度与变形特性的影响，已成为土力学学科的重要研究课题。本课题以土体初始各向异性与加载方向之间的作用机制为出发点，期望揭示非共轴特性的产生机理和本构关系。本课题在非比例加载条件下对初始各向异性砂土试样进行剪切试验，分析荷载传递机理以及应力和应变的变化规律，建立初始各向异性与加载方向之间的作用机制，揭示非共轴特性的产生机理。基于土体临界状态力学特性，对非共轴特性与物理-力学状态在主应力方向旋转过程中的对应关系进行优化拟合，建立非共轴塑性模量表述形式。以屈服角点非共轴理论为基础，通过非共轴塑性模量计算非共轴塑性应变增量，建立砂土非共轴弹塑性本构模型。结合模型试验和数值分析方法，研究非共轴特性对复合加载条件下砂土地基强度和变形特性的影响，探讨非共轴本构模型的适用范围。研究成果将有助于推动非共轴本构理论的发展和应用，为重大工程结构和地基设计提供依据。

以砂土初始各向异性与加载方向之间的作用机制为出发点，研究主应力方向旋转状态下的非共轴现象，揭示非共轴特性的产生机理和本构关系。结合砂雨法和砂土毛细特性，确立了一种能够控制沉积方向的制样方法，在不同应力路径条件下分析了该方法的适用性。以屈服角点非共轴理论为基础，引入初始各向异性砂土剪切试验结论，建立了一种能够考虑砂土初始各向异性特性的非共轴本构模型，将该模型应用到有限元数值计算中。通过对砂土三轴剪切试验进行数值模拟，分析了沉积方向对应力应变关系、体积变化和主应力方向的影响。针对吸力式桶形基础在复合受力状态下的力学特性，采用所建立的本构模型进行数值分析，研究主应力方向旋转和非共轴特性的影响。研究结论表明：基于砂土毛细特性的制样方法适用于初始各向异性砂土的剪切试验和特殊应力路径试验。当沉积方向与试样破坏面接近时，试样更容易达到破坏状态，所对应的峰值强度更低，达到峰值和残余状态更早。随着砂土密实程度的变化，沉积方向对砂土不排水剪切强度的影响也发生变化。荷载倾斜角度对桶形基础竖向荷载-位移关系的影响比较微弱，对水平荷载-位移关系的影响则比较显著。随着长径比的增加，非共轴特性对桶形基础水平、竖向荷载-位移关系的滞后作用逐渐显著。随着偏心距的增加，非共轴特性也将减弱，非共轴特性对竖向荷载-沉降关系的影响逐渐减小。所建立的初始各向异性本构模型能够准确反映沉积方向对强度、体变和主应力方向的影响。项目研究成果有助于推动非共轴本构理论的发展，为重大工程结构和地基设计提供依据。