Simulation of fracture coalescence in granite via the combined finite-discrete element method

TL;DR

This study uses the combined finite-discrete element method to simulate fracture coalescence in granite, revealing how crack orientation influences fracture behavior and strength, with implications for understanding rock failure and seismic activity.

Contribution

It demonstrates the effectiveness of FDEM in modeling fracture coalescence, including crack initiation, propagation, and patterns, in granite with various crack orientations.

Findings

Simulations match experimental peak stresses for different crack angles.

Strength increases linearly with crack inclination angle.

Double-crack specimens are weaker than single-crack specimens.

Abstract

Fracture coalescence is a critical phenomenon for creating large fractures from smaller flaws, affecting fracture network flow and seismic energy release potential. In this paper, simulations of fracture coalescence processes in granite specimens with pre-existing cracks are performed. 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 cracks within the specimens follow two geometric patterns: 1) a single crack oriented at different angles with respect to the loading direction, and 2) two cracks, where one crack is oriented perpendicular to the loading direction and the other crack is oriented at different angles. The intent of this study is to demonstrate the suitability of FDEM for modeling fracture coalescence processes including: crack initiation and propagation, tensile and shear fracture behavior, and patterns of fracture coalescence. The simulations provide insight into the evolution of fracture tensile and shear fracture behavior as a function of time. The single-crack simulations accurately reproduce experimentally measured peak stresses as a function of crack inclination angle. Both the single- and double-crack simulations exhibit a linear increase in strength with increasing crack angle; the double-crack specimens are systematically weaker than the single-crack specimens.