Crack development and damage patterns under combined dynamic-static loading of parallel double fractured rocks based on DIC technique

In this paper, the combined static-dynamic loading tests on refabricated parallel fissured granite were conducted with SHPB system at six confining pressures (0, 10, 20, 30, 50, and 60% of the UCS) and three dip angle (0, 45, and 90 °). Moreover, a non-contact monitoring device, the DIC, was used to fully detect the full-field strain of the specimen. Comprehensively the initiation, expansion, penetration process and failure mode of double-fractured specimens were investigated, and the deformation and failure characteristics and strength change law during the failure process were discussed. The fractures had a significant degradation effect on the dynamic compressive strength of the rock. Parallel double fractures showed the large principal and shear strains at and near the fissure tips firstly during damage and extended through each other, causing damage to the specimens. There were two main types of cracks: tensile cracks and shear cracks in the failure process. The displacements of key cracks in 45 and 90 ° specimens were analyzed, which showed that the slip displacement gradually increased with the increase in axial pressure, while the tension displacement showed an increase first and then a decrease. The angle of inclination of parallel double fissures is critical to the initial generation of tensile strain zones and the subsequent development and expansion of tensile strain zones. The research results will provide an important theoretical basis for the development and utilization of underground engineering structures and disaster prevention and mitigation.