Numerical modelling of blast-induced crack propagation in pre-fractured rock

Abstract

This paper presents a series of numerical simulations to investigate blast-induced crack propagation in rock specimens embedded with a pre-existing fracture. The simulation is conducted using the particle-based discrete element method, which can effectively capture many important geomechanical processes such as solid vibration, crack growth and fracture sliding. Particles are assembled based on the grain size distribution of Beishan granite using a Voronoi tessellation algorithm, with the parameters of particle contacts calibrated against to the laboratory testing results. The pre-existing fracture is represented using the model of smooth-joint contacts. In this study, three sets of models are established to explore the effects of stress state, fracture length and fracture orientation on the damage evolution in the rock specimen subject to a blast load. In the first set of models, we observe that when the horizontal stress σx is not equal to the vertical stress σy, the maximum slip of the pre-existing fracture is positively correlated with the differential stress, i.e. Δσ= σx − σy, which further leads to the generation of different numbers of secondary cracks. The second set of models shows that the number of secondary fractures grows as a quadratic power function with the increased length of the pre-existing fracture. Furthermore, extensive tensile stress regions emerge around the tips of secondary fractures. The third set of models focuses on the sensitivity analysis of fracture orientation, showing that with the clockwise rotation of the pre-existing fracture from the vertical direction, the number of secondary fractures decreases significantly but they are still concentrated locally at the tips of the pre-existing fracture. The research findings of our paper have important implications for the assessment of excavation damaged zone properties around nuclear waste repositories built using the drilling and blasting method.