Crack propagation mechanism of rock-like specimens containing non-parallel flaws subjected to internal hydraulic pressure and shear loading

The rock masses with existing discontinuous joints are more prone to failure under the combination of fissure water and shear loading. Therefore, combining laboratory experiments with discrete element simulation, the mechanism of crack initiation, propagation, and coalescence in rock-like specimens (a type of high brittle cement mortar material) with non-parallel flaws under shear loading and internal water pressure is investigated. The results reveal that for specimens with various flaw dip angles the propagation direction of all newly generated cracks is basically parallel to the shearing loading. When the flaw inclination angle reaches -30 degrees, the cracks initiated near pre-existing flaw tips are the result of the combined effects of fluid pressure and compressive stress fields. Compared with the hydraulic fracturing curve, both plateau period and water pressure fluctuations appear in the selected domain near the crack propagation paths, which can demonstrate that the evolution of water pressure is extremely complex due to the constant crack healing and opening. With the increase of water pressure, the global stress field becomes more uniform, and the stress concentration near pre-existing flaw tips is weakened, indicating that water pressure can lead to local stress redistribution. Ultimately, the work is expected to provide guidance to the safe construction of tunnel excavation under complex geological conditions.