基于微观力学的胶结岩土材料破损规律离散元模拟

采用离散元法（DEM）研究胶结岩土材料在不同加载条件下的结构破损规律。首先，基于微观力学理论，考虑胶结岩土材料颗粒间胶结特性，给出表征结构性损伤的破损参数式。该式具有微观物理意义，但不能直接用于建立宏观本构模型。其次，采用二维离散元源程序NS2D模拟等向压缩、等应力比压缩以及双轴压缩试验，分析破损参数在不同加载条件下随宏观力学变量（体积应变和剪应变）的演变规律。最后，根据模拟结果提出破损参数数学表达式，其为大主应变的函数。研究结果表明：胶结强度、应力比以及围压均在一定程度上影响了数值试样的结构破损规律。在等向压缩和等应力比压缩试验中，容易用函数式描述数值试样破损参数随体积应变或偏应变的演变规律；而在双轴压缩条件下，由于数值试样有剪胀特性，破损参数随体积应变的演变规律则不易描述。建议的破损参数数学表达式能够较好地描述数值试样在不同加载条件下结构破损规律。

Distinct element simulation of degradation evolution for bonded geomaterials based on micromechanics

The degradation evolution of the bonded geomaterials under different loading conditions is investigated by using distinct element method (DEM). First, considering the bonding behavior at contacts between bonded geomaterials, an equation of degradation parameter, which is used to describe the degradation process in bonded geomaterials, is established based on the micromechanics theory. The equation has microscopic physical significance, which cannot be directly used to establish macroscopic constitutive model. Second, a series of isotropic, constant stress ratio and biaxial compression tests are performed on the numerical specimens by using a two-dimensional DEM code, NS2D; and the evolution of the degradation variable varying with macro variables, i.e. volumetric and shear strains, is investigated under the three loading conditions. Finally, a simple evolution equation for the degradation parameter is proposed; and it is a function of the major principal strain. It is shown that three variables, i.e. bond strength, constant stress ratio, and confining pressure, can influence the degradation evolution of the numerical specimens to a certain extent. The evolution of the parameter varying with the volumetric or deviatoric strains can be easily described by functions in the isotropic and constant stress ratio compression tests. The evolution of the parameter varying with the volumetric strain cannot be easily described due to the dilatancy in the specimens under biaxial compression tests. The equation proposed for the degradation parameter can well describe the degradation evolution observed in the three loading conditions.