Investigations of the mechanical behavior and failure mechanism of fractured rock samples

As excavation is often very deep with large unloading forces in the construction of a high-level radioactive waste (HLW) disposal repository, microcracks in the surrounding rock are unavoidable. In this work, a series of uniaxial compression tests were conducted on intact samples and samples with fractures at different inclination angles (30°, 45°, and 60°), to investigate the mechanical behavior and failure mechanism of fractured rock samples. According to the experimental results, a more inclined angle of the fractures would dramatically reduce the compressive strength of the sample. After the compression tests, the granite samples with different fracture inclinations have different failure modes and distribution characteristics of cracks on sample outside surfaces and the premade fracture planes. Higher dip angles of the premade fractures have less surface density of cracks on the sample outside surface after compression. The instability failure of granite samples with 60° fracture inclination is entirely due to shear deformation between the premade fractures. Based on this single failure mode, the compressive strength of a granite sample with 60° fracture inclination has a positive correlation with the difference in fractal dimensions induced by compression. The greater the difference in fractal dimensions, the higher the compressive strength.