Shear mechanical characteristics and fine-scale fracture evolution of borehole sample

For the problem that is difficult to coordinate the borehole pressure relief and support in rock burst roadway, through the variable angle shear experiments and numerical simulation of different borehole diameters, and study the shear mechanical properties of the rock surrounding the borehole pressure relief and the evolution characteristics of the microscopic rupture, in order to provide a theoretical basis for the damage mechanism of the rock surrounding the borehole pressure roadway and roadway support research. Comparative analysis of the test and numerical simulation results show that with the increase of borehole diameter, the peak shear strength and peak strain of the rock show a linear trend of decreasing. The reduction of shear surface area and the stress concentration around the borehole are the main reasons for the reduction of shear strength. The trends of cohesion and internal friction angle with borehole diameter are different. The cohesion tends to decrease linearly with the increase of borehole diameter, and the internal friction angle roughly show a small and then increasing pattern. With the increase of borehole diameter, the number of cracks decreases and changes from multiple vertical penetrating cracks to a single crack occurring on the shear surface, and the stress concentration around the boreholes and spearheading of the damage are the essential reasons for this transition. Compared with the intact spamples, the energy required to reach damage in the borehole samples is greatly reduced, and the dissipated energy generated during damage is reduced, which is a phenomenon conducive to the reduction of energy accumulation in the rock surrounding the rock burst roadway. This study can provide a reference for the study of borehole pressure relief mechanism and the support and stability assessment of borehole pressure relief roadways.