Numerical Study of the Influence of Joint Angle on the Failure Behavior of Randomly and Nonpersistently Jointed Rock Mass

The generation of nonpersistent joints in numerical specimens is not easy to achieve in some geotechnical numerical software. In this paper, the synthetic rock mass modeling method was used to construct a group of numerical specimens based on triangular grain-based model and random joint set (RJS) model in universal discrete element code. The randomly distributed nonpersistent joints have seven dominant inclination angles. Then the unconfined compressive strength (UCS) tests of the seven groups of specimens were carried out numerically to obtain some insight into the influence of dominant inclination angle on strength behaviors, failure modes and fracture development. The inclination angles of the nonpersistent RJS have fluctuant effect on the UCS of the specimens. The maximum UCS appeared when the RJS angle is 90°, and small UCS values appeared when the RJS angles are 45°, 60° and 75°. With decreasing RJS angle, the brittleness gradually changes into ductility, and strain hardening occurs. During the whole uniaxial compression process, shear fractures take the dominant role during the preliminary stage and then reduce gradually, while the tensile fractures have an inverse variation trend during the initial stage and significantly increase when the axial strain exceeds 0.6% and then keeps growing until the compression ending. The nonpersistent RJSs with small and large angles have little contribution to the shear fracture development, and only the RJSs with median inclination angles (45°, 60°) significantly promote the shear fracture propagation and development, while the RJS makes an increasing contribution to the tensile fracture propagation and development with the increase in the RJS inclination angle.