Discrete element study on mesomechanical behavior of crack propagation in coal samples with two prefabricated fissures under biaxial compression

The failure behavior of coal mass caused by various shapes and distribution forms of fissures has been studied extensively. However, the effect of the Rock Bridge Dip Angle (RBDA) between fissures has not been fully reported. In this paper, the empirical equations between the macroscopic mechanical parameters and mesoscopic parameters of coal are obtained by using the Discrete Element Method (DEM), and the reasonable and accurate macroscopic parameters are determined through physical experiments. Then, a DEM numerical model of coal samples with two prefabricated fissures is established, and a numerical test of biaxial compression is carried out on the fractured coal samples. Through qualitative analysis, the stress-strain curve obtained from the numerical simulation is basically consistent with that from previous physical experiments. The arc-shaped cracks are generated at the outer tips of the fissures. The rationality of this phenomenon is verified by finite element method (FEM). Furthermore, the connection between the two prefabricated fissures is relatively complete when RBDA = 90 degrees. And the peak deviatoric stress is maximum when RBDA = 30 degrees. When RBDA>30 degrees, the number of tensile and shear cracks decreases with the increase of RBDA. In addition, high confining pressure can promote the increase of the peak deviatoric stress. (C) 2020 Published by Elsevier B.V.