Numerical investigation of impact fracture behaviors of rocks under confining pressure

Underground rocks in coal mining and oil exploration are usually subjected to in-situ stress and dynamic loading. In this paper, the tensile fracture behaviors of brittle rocks under coupled in-situ stress and dynamic loading are investigated numerically via the simulation of Brazilian disc (BD) tests of the modified split Hopkinson pressure bar (SHPB). To achieve this purpose, a cohesive zone model in the framework of the finite element method is used to model the cracking of the rock Brazilian disc under confining pressure. The pressure-dependent property of the rock is considered using the recently proposed bi-linear constitutive law. Dynamic Brazilian disc tests of the SHPB with two impact velocities of a striker are simulated for the rock. Comparisons between the simulated results and the reported experimental ones show a good agreement, demonstrating the accuracy and validity of the simulation models and the numerical approach. Due to the existence of holes in the rock in underground rock engineering practices, a pre-hole is inserted in the BD rock specimen in the modified SHPB tests to more realistically consider the rock fracture. The effects of the in-situ stress, the pre-hole size, and the pre-hole position on the dynamic fracture characteristics of the rock are numerically investigated using the modified SHPB test for BD rock specimen.