Simulation of Fracture Coalescence in Granite via the Combined Finite–Discrete Element Method

Fracture coalescence is a critical phenomenon for creating large, inter-connected fractures from smaller cracks, affecting fracture network flow and seismic energy release potential. In this paper, simulations are performed to model fracture coalescence processes in granite specimens with pre-existing flaws. These simulations utilize an in-house implementation of the combined finite–discrete element method (FDEM) known as the hybrid optimization software suite (HOSS). The pre-existing flaws within the specimens follow two geometric patterns: (1) a single-flaw oriented at different angles with respect to the loading direction, and (2) two flaws, where the primary flaw is oriented perpendicular to the loading direction and the secondary flaw is oriented at different angles. The simulations provide insight into the evolution of tensile and shear fracture behavior as a function of time. The single-flaw simulations accurately reproduce experimentally measured peak stresses as a function of flaw inclination angle. Both the single- and double-flaw simulations exhibit a linear increase in strength with increasing flaw angle while the double-flaw specimens are systematically weaker than the single-flaw specimens.