Numerical study of unstable failure behavior in heterogeneous rock pillar

Strain bursting in deep-buried tunnels is a common engineering disaster closely related to the failure mechanism and loading system stiffness (LSS). The rock failure mechanism cannot be explicitly captured using the homogeneous model. In this study, the failure characteristics of heterogeneous rock pillars under different LSS were simulated using the combined finite-discrete element method (FDEM), and the grain-based model in FDEM was constructed using a C++ subroutine. The simulation results show that with the decrease of the LSS, the post-peak stressstrain curve of the specimen slows down, the specimen undergoes unstable failure, and the fragmentation degree of the specimen, released kinetic energy, and post-peak crack increase rate grow. Under soft loading conditions, rock heterogeneity is an important factor affecting the degree of rock failure. The ratio of shear cracks to tensile cracks, strain energy of the loading system (LSSE), and post-peak crack increase rate can be regarded as indicators for distinguishing between stable and unstable failure of rocks. Furthermore, by comprehensively considering the LSS, rock heterogeneity and failure phenomena, an empirical index for evaluating the degree of rock failure was proposed.