Influences of confining pressure and fracture inclination on mechanical behavior of granite

The mechanical behavior of host rock with fractures is crucial for the long-term stability and safety of a high-level radioactive waste geological disposal facility. To investigate the influences of confining pressure and fracture inclination on the mechanical behavior of granite host rock, the uniaxial compression and triaxial compression tests are conducted on the intact granite and granite with single fractures of different inclinations. The results show that within the confining pressure range of 0~10 MPa, the granite with fractures inclined at 30° and 60° experiences the failure of newly formed cracks that penetrate through the pre-existing fracture surfaces and the slip failure along the fracture surface, respectively. As the confining pressure increases, the granite with fractures inclined at 45° undergoes a transition from composite failure to failure through the fracture surfaces. It then transits back to a tilted "Z"-shaped composite failure under a confining pressure of 10 MPa. The presence of confining pressure constrains the deterioration of pre-existing fracture surfaces. The compressive strength and deformation development curves of low-angle fractured granite under triaxial compression conditions are similar to those of the intact granite, and the axial strains at the peak failure of these specimens are approximately 0.38%, 0.49%, 0.59% and 0.75% under confining pressures of 0, 2, 5, and 10 MPa, respectively. The compressive strength and axial strain at peak failure of specimens that experience slip failure are significantly lower than those of specimens that experience failure through the fracture surface, and the compressive strength shows a power-law relationship with the difference in fractal dimensions between the fracture surfaces before and after the tests.