宏-细观结合的砂土单剪试验非共轴特性分析

Analysis of non-coaxial characters of sand for simple shear test with the method of macro-meso-incorporation

针对传统本构理论无法描述土体单剪试验非共轴变形的不足,采用非共轴修正模型进行改进。模型基于材料状态相关临界状态理论,采用宏-细观结合的方法,将1个新的各向异性状态变量引入本构模型来描述砂土的各向异性。考虑细观组构张量和应力张量的几何关系的变化,模型可以描述砂土在主应力轴旋转条件下材料状态的变化,材料状态变化直接导致模型的硬化规律和剪胀性发生变化,因此,模型可以描述该条件下原生向异性对砂土变形的影响。引入非共轴理论对本构模型进行修正,建立了三维非共轴各向异性模型。单剪试验的加载条件会造成主应力轴相对土体沉积面发生旋转,修正模型不但能够描述砂土在主应力轴旋转条件下其原生各向异性对变形的影响,而且可以描述主应力轴旋转造成的应力诱发各向异性对土体变形的影响,因此,该模型能够对整个单剪试验的变形规律进行描述,而且物理意义清晰。通过铝棒堆积体和Toyoura砂单剪试验验证表明,非共轴修正各向异性模型能对单剪试验的整个变形过程进行较好的模拟。

Aiming at the shortcomings of traditional constitutive theory failure to describe the non-coaxial deformation of soil for simple shear test, a constitutive model amended with non-coaxial plasticity theory is employed to improve it. Based on the critical state and state-dependent theories, with the method of macro-meso-incorporation, a novel anisotropy state variable is introduced in the model to describe the anisotropy of sand. In view of the geometric relationship of meso-fabric and stress state, the state of sand changes in the principal stress axes rotation condition, and the dilatancy and hardening law of model is the fimction of sand state, so the model can describe the effect of inherently anisotropy on deformation of sand in this condition. The non-coaxial plasticity theory employed to amend the constitutive model, a three-dimensional non-coaxial model for anisotropic sand is presented. The loading conditions of simple shear test causes the rotation of principal stress axis relative to the soil deposition direction; the amended constitutive model can describe the effect of inherently anisotropy and stress-induced anisotropy on deformation characters under the principal stress rotation conditions; so the amended model can describe the whole characters of simple shear test with clear physical meaning. The verification with simple shear test results of rod mass and Toyoura sand shows that the amended model can well simulate deformation properties.