Laboratory investigation of mechanical behavior of granite samples containing discontinuous joints through direct shear tests

The effect of the normal stress and joint persistency on the mechanical behavior of granite samples containing discontinuous joints was investigated in the laboratory through direct shear tests. The test results revealed three different failure modes occurring at the rock bridge: (a) shear failure, (b) compressive-shear failure, and (c) tensile failure. The failure mode depends on the joint persistency and normal stress level and influences the peak shear strength. Moreover, the joint persistency and normal stress level were also found to have a considerable influence on the post-failure behavior such as the fracture roughness and residual shear strength based on rock bridge area. The conducted investigation provided better understanding of the effect of a rock bridge on mechanical behavior of granitic discontinuous joints towards estimating the resistance capacity of rock bridges and hence to allow evaluation of stability of rock masses in both surface and underground excavations in rock engineering.