Examining the influence of the loading path on the cracking characteristics of a pre-fractured rock specimen with discrete element method simulation

Damage in a rock mass is heavily dependent on the existence and growth of joints, which are also influenced by the complex stress states induced by human activities (e.g., tunneling and excavation). A proper representation of the loading path is essential for understanding the mechanical behaviors of rock masses. Based on the discrete element method (DEM), the influence of the loading path on the cracking process of a rock specimen containing an open flaw is examined. The effectiveness of the model is confirmed by comparing the simulation results under a uniaxial compression test to existing research findings, where wing crack initiates first and secondary cracks contribute to the failure of the specimen. Simulation results confirm that the cracking process is dependent upon both the confining pressure and the loading path. Under the axial loading test, a higher confining pressure suppresses the development of tensile wing cracks and forces the formation of secondary cracks in the form of shear bands perpendicular to the flaw. Increase of confining pressure also decreases the influence of the loading path on the cracking process. Reduction of confining pressure during an unloading test amplifies the concentration of tensile stress and ultimately promotes the appearance of a tensile splitting fracture at meso-scale. Confining pressure at the failure stage is well predicted by the Hoek-Brown failure criterion under quasi-static conditions.