Evolution of microcracks and energy of granite during shear test with PFC3D

Abstract

In order to investigate the influence of normal stress on the internal meso-scale damage process during rock shearing, direct shearing experiments and PFC3D numerical simulation experiments of granite under different normal stresses were carried out, combined with acoustic emission signal monitoring and analysis of acoustic emission information characteristic values of RA (ratio of rise time to amplitude) and AF (ratio of acoustic emission ring count to duration). The results show that the PFC3D model based on the parallel adhesive contact model is not only similar to rock physics experiments in macroscopic mechanical parameters and failure modes, but also basically consistent with rock physics experiments in the evolution of meso-cracks and energy in rock. Tensile micro-cracks are mainly produced in the process of shear failure of granite, and the microcracks produced before the peak stress point only account for 10%−30% of the total number of cracks, and the larger the normal stress, the smaller the number of microcracks produced inside the rock before the peak stress point. In the process of granite shear deformation, the acoustic emission signal can be divided into calm period, stable period and accelerated period, the greater the normal stress, the more obvious the calm period, i.e. the normal stress inhibits the generation of microcracks inside the rock.With the increase of the normal stress, the cumulative acoustic emission ring count and the total number of microcracks inside the rock gradually increase in the process of granite shear damage. With the increase of normal stress, the number of shear cracks produced during the shear damage of granite and its proportion to the total number of microcracks gradually increased. The work done by the external force during the shear deformation of granite is converted into elastic energy and dissipation energy, with the increase of normal stress, the total energy required for rock shear failure gradually increases, and the elastic energy and dissipation energy increase approximately linearly, in which the proportion of dissipation energy gradually increases.

Keywords

• rock mechanics
• meso-cracks
• granite
• direct shear test
• pfc3d simulation