The bonded-particle model as a tool for rock mechanics research and application: current trends and future directions

We generalize our view of a bonded-particle model (BPM) to consist of a base material (that is a packed assembly of rigid grains joined by deformable and breakable cement at grain-grain contacts) to which larger-scale joints can be added and whose mechanical behavior is simulated by the distinct-element method using the two-and three-dimensional discontinuum programs PFC2D and PFC3D. The micromechanical processes that control brittle fracture, and thus, should inform any micromechanical theory or model, are summarized. The rich variety of microstructural models that can be produced by the bonded-particle modeling methodology are described and classified with respect to their microstructural and larger-scale features. These models provide a wide range of rock behaviors that encompass both compact and porous rock at both an intact and rock-mass scale, and examples are provided of how BPMs are being used to model rock at these scales. The examples include an intact anisotropic material that may swell and contract in response to changes in saturation, the behavior of two alternative BPMs that can match both the uniaxial and tensile strengths of compact rock and the embedding of an intact BPM within a larger continuum model to study fracturing around a gold-mine stope in quartzite.