A synthetic study of cracking behavior and fracture mechanism of sandstone containing two non-connected fissures under uniaxial compression

Rock mass always undergone multiple geological activities, leaving behind various kinds of fissures in it. To investigate the influence of the non-connected fissures on the cracking behavior and fracture process of rock mass, experimental and numerical investigations were performed on sandstone containing two non-connected fissures, but of different fissure geometric configurations. The progressive cracking behavior and full-field strain evolution were analyzed through the mechanical-acousto-optical methods, while the stress evolution was studied by the particle flow code modeling. The results indicate that the cracks start to incubate at the tips of the prefabricated fissures in elastic deformation stage, then initiate and propagate to form megascopic fractures during stable crack propagation stage, finally rapidly intersect and expand to sample boundary at unstable crack propagation stage, forming the ultimate macro-fracture surface. The inclination angle (α) of fissure ① has significant influence on the crack type and number. The acousto-optical responses and stress field evolution both suggest that tensile cracks gradually decrease and shear cracks increase with increasing α, indicating a transformation from tensile failure to shear failure. As the tensile strength of rock is lower than shear strength, therefore, the uniaxial compressive strength and Young's modulus values both increase with increasing α. Besides, the spatio-temporal evolution of cracks and the failure modes from numerical simulation conform well to the laboratory testing results. The findings enrich the study on the fracture and failure mechanism of rock masses containing non-connected fissures, which is of great significance for rock engineering safety.