Failure mechanism of brittle rock with 3D parallel preset flaws based on the particle displacement trend method

Abstract Original fracture structure in brittle rock mass usually has a bad influence on the safety and stability of artificial underground structures. The former laboratory test results proved that the secondary failures on the surface or inside the samples showed different development procedures and distributions when a 3D internal open-type preset flaw was inside the sample. However, researchers cannot obtain the secondary cracks' accurate failure mode and initiation mechanism in experimental tests. Accordingly, the discrete element numerical simulation (PFC3D software) is applied in this study to reproduce the laboratory tests. The main results are as follows: 1) The 2D through preset flaw strongly influences the state of the surface displacement field, the crack distribution near the surface, and the initiation strengths of secondary tensile and shear cracks. 2) When a 3D internal preset flaw in the sample, the local failures initiated from the internal 3D flaw would keep hiding during the majority period of the test. 3) By applying the particle displacement trend method, it is evident that rock adjacent to the inclination boundary of the internal flaw suffers “Mode II” shear failure; rock near the strike boundary of the 3D flaw presents “Mode II & III” shear failure.