Study on Deformation and Strength Characteristics of Hollow Cylindrical Rock Under Complex Loading Conditions

Drilling a borehole and inserting high-pressure fluid to induce rock fracture is a rock-mass pre-conditioning method in block caving mining of hard rock metal mines, and the borehole surrounding rock is under the complex loading conditions with in-situ stress and borehole inner pressure. In order to further understand the failure mechanism of borehole rock during hydraulic fracturing, a numerical model of hollow cylindrical rock sample was built with FLAC3D and the deformation and strength characteristics of this sample was studied by conducting simulation tests. The results show that oblique shear failure was found during uniaxial compression test and the uniaxial compression strength and elastic modulus of hollow cylindrical rock sample were weakened with the increasing of inner hole diameter. The rock triaxial compression strength increased linearly with the confining pressure during triaxial compression tests. The confining and internal pressure were the major factors to induce rock failure during hydraulic fracturing tests and the breakdown pressure increased linearly with confining pressure. For the rock type in this paper, the breakdown pressure was 2.28 times confining pressure plus rock tension strength.