Mechanical behavior and failure analysis of granite specimens containing two orthogonal fissures under uniaxial compression

The mechanical behavior, crack initiation stress, cracking modes, and crack coalescence process due to uniaxial compressive loading for brittle granite specimens (70x 140x29 mm in size) containing two orthogonal fissures with different virtual ligament length were first modeled experimentally. Intact granite specimens present typical axial splitting failure, and the ultimate failure of specimens containing a single fissure results mainly from tensile cracks initiated from the fissure tips. Basically, mechanical parameters of granite specimens containing two orthogonal fissures are lower than the values for intact specimens, and the reduction extent is distinctly related to the virtual ligament length. The uniaxial compressive strength, peak axial strain, Young's modulus, secant Young's modulus, and crack initiation stress of granite specimens containing two orthogonal fissures present the same trend with the increasing virtual ligament length, i.e., first decrease and then increase, finally once again decrease. The effect of virtual ligament length on the crack initiation type and ultimate failure modes of granite specimens containing two orthogonal fissures is analyzed. Crack types based on the fissure geometry and crack propagation mechanism are identified, and three different crack initiation types are summarized. The crack coalescence is observed and characterized from tips of pre-existing fissures. Relation between the real-time cracking process and axial stress-strain curves of granite specimens containing two orthogonal fissures for the entire deformation process is captured, and the corresponding axial stress for crack coalescence is also obtained. Each sharp stress drop in axial stress-strain curves indicates an obvious crack coalescence.