FDEM simulation of rock damage evolution induced by contour blasting in the bench of tunnel at deep depth

One highly effective approach for tunnelling in rock at deep depth is blasting. The damage and in-situ stress redistribution in the surrounding rock mass induced by the blast loading during this process is, however, unavoidable. In this study, a powerful GPGPU-parallelized combined finite-discrete element method is implemented to study the damage evolution during controlled contour blasting in the bench of a deep-buried tunnel. The proposed method is characterized by the simulation of the blasting-induced pressure variation via the pressure-gas volume history curve and the modelling of the transition from continuum to discontinuum behaviour in the surrounding rock mass. The in-situ stress distribution, the blasting-induced stress wave propagation, and the corresponding rock fracture and fragmentation process are modelled and analysed. The numerical simulation results indicate that the in-situ stresses play a key role in the damage evolution around the tunnel, strongly influencing the stress redistribution pattern and thus the fracture initiation and propagation around the tunnel during blasting. Several different in-situ stress regimes are considered and discussed, revealing the dominating effects of the major principal stress and lateral pressure coefficient on the rock damage behaviour. Moreover, the blasting results obtained from employing the pressure–time history curve with varying decay time ratios and decoupling ratios are also studied. Longer decay time ratios and higher decoupling ratios induce additional rock fracture and fragmentation, indicating that the model can enable the selection of stemming and explosive type for effective breakage with limited damage around a tunnel.