Dynamic properties and failure mechanism of granite with non-persistent joints subjected to impact load

A Split-Hopkinson pressure bar was used to carry out a series of impact tests on prefabricated granite specimens containing joints with different inclination angles and at different joint persistency values. The results were used to determine the degradation effect of the non-persistent joints on the specimens and investigate the failure mechanism of the granite subjected to impact load. The effect of varying the length and inclination angle of the joint on the dynamic characteristics of the granite was systematically analyzed based on a consideration of the specimens’ dynamic mechanical properties. A continuum-discrete coupled model was subsequently established based on the results of the laboratory tests and used to investigate the failure mechanism and crack propagation behavior occurring on a microscopic scale. The results show that the geometric parameters of the joints and the loading rate have a significant effect on the dynamic response of the granite. Moreover, there is a good power function relationship between the dynamic increase factor and loading rate of the prefabricated jointed rock specimen when the loading rate is low to medium. As the inclination angle of the joint increases, the failure mode of the specimen transitions from tensile splitting failure → mixed tensile–shear failure → main shear failure → micro-damage failure. As the penetration of the joint increases, the failure mode of the specimen evolves from micro-damage failure → tensile splitting failure → mixed tensile–shear failure. When subjected to uniaxial impact loading, the main cracks in the jointed rock specimen are usually wing cracks and coplanar cracks. Anti-wing cracks are not generated by themselves but appear alongside other cracks as a supplementary means of achieving stress release. The present results offer a sound basis for evaluating the stability of jointed rock mass under the dynamical loading.