The mechanical properties and microscopic failure mechanism of fractured granite under fissure water pressure

The deep fractured rock mass undergoes damage and failure under the combined effects of high geostress and high permeability water pressure, leading to engineering geological disasters such as collapses and strong water inrush in underground projects. This study investigates the mechanical behavior of granite under fissure water pressure by conducting uniaxial compression tests on rock samples with varying crack inclinations using the RMT testing system. The FiniteDiscrete Element Method (FDEM) was subsequently employed to examine the mechanism through which fissure water pressure affects the initiation and propagation of cracks in the rock mass. The results indicate that: (1) Under the influence of fissure water pressure, the peak strengths of specimens with varying fracture inclinations decreased by approximately 20% to 30%, while the acoustic emission signals decreased by 68% to 98%. (2) Based on the modified maximum tangential stress (MTS) criterion taking into account the T-stress, the calculation methods for crack initiation angle and crack initiation stress considering the rock fissure water pressure are derived. (3) The tensile effect on the wing cracks induces a rapid expansion of the fissure water pressure, while the secondary cracks are subsequently closed, thereby preventing further expansion of the water pressure. (4) The degree of fragmentation of the specimens was significantly lower than that of the standard cracked specimens. These specimens exhibited tensile failure parallel to the crack surface, shear slip along the crack surface, and tensile splitting failure perpendicular to the crack surface.