DILATATION ANALYSIS OF ROCK SPECIMEN UNDER UNIAXIAL COMPRESSION BASED ON GRADIENT-DEPENDENT PLASTICITY
基于梯度塑性理论的岩样单轴压缩扩容分析

Non-uniform shear dilatancy of rock specimen due to plastic shear strain localization is analyzed considering strain gradient effect. The constitutive relation of rock material is linear elastic and linear strain softening. Localization is initiated in the form of a single shear band when peak strength is rearched. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,analytical solutions for local plastic volumetric strain,increment of local plastic volume and increment of total plastic volume due to shear localization are presented,which can not be deduced from classical elasto-plastic theory. So the advantages of the gradient-dependent plasticity over the classical theory are apparent in analysis of localized shear dilatancy. In addition,a bi-linear relation between axial compressive stress and volumetric strain is proposed under uniaxial compression of rock specimen subjected to shear failure. It is noted that the exclusive reason for plastic volumetric strain is assumed to be shear dilatancy in the present paper,therefore,the relation between axial stress and volumetric strain is size-independent and is not concerned with the thinkness of shear band. However,it is influenced by dilation angle,shear softening modulus and Poisson ratio. For the same stress level,larger dilation angle leads to increment of the volumetric strain,and higher shear softening modulus results in lower volumetric strain. However,Poisson ratio does not influence the plastic volumetric strain in the stage of strain softening.