A 3D Subspring Network Breakable Voronoi Model for Rock: Laboratory-Scale Behavior

Abstract

ABSTRACT: A micromechanical model based on the distinct element method that employs the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model) is described. The SNBV model is an excellent model for rock microstructure that reproduces the damage mechanisms (heterogeneity-induced local tension, closure of an initial microcrack fabric, and grain breakage) that occur at the grain scale. The laboratory-scale behavior of the synthetic material is summarized as follows. The material exhibits behavior during direct-tension and triaxial compression tests that matches the behavior of intact compact rock. The material can be calibrated to match all of the standard material properties and characteristic stresses as well as the microstructural behavior (including grain breakage) of intact pink Lac du Bonnet granite. The material properties consist of Young's modulus and Poisson's ratio corresponding with uniaxial compression and Young's modulus corresponding with direct tension, as well as tensile strength, crack-closure stress, crack-initiation stress, secondary crack-initiation stress to mark the onset of grain breakage, crack-damage stress, and compressive strengths up to 4 MPa confinement. 1. INTRODUCTION Bonded-particle models (BPMs) provide a synthetic material consisting of a packed assembly of rigid grains joined by deformable and breakable cement at grain-grain contacts, and whose mechanical behavior is simulated by the distinct-element method. BPMs are being used for rock mechanics research and application (Potyondy, 2015). A new type of BPM called the Hybrid Lattice/Discrete Element Model (hybrid LDEM — a version of the DEM that employs Rigid Body Spring Network interactions) with grain breakage was proposed by Rasmussen (2022), who obtained excellent laboratory-scale behavior for pseudo-3D models consisting of a 3D Voronoi tessellation in which each Voronoi cell is one element thick. The subspring network contact model in PFC3D (Itasca, 2024) is like the hybrid LDEM model. This contact model is combined with a new grain-breakage scheme to provide the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model). The SNBV model provides excellent laboratory-scale behavior in fully 3D models of cylindrical specimens. The work described in this paper is part of a larger effort to evaluate the ability of the PFC3D code to model spalling by constructing a calibrated SNBV material and studying its laboratory-scale behavior during direct-tension and triaxial compression tests, and its tunnel-scale behavior during excavation of the Mine-by Experiment test tunnel (Read and Martin, 1991). This paper focuses on the laboratory-scale behavior of the SNBV material — refer to Potyondy et al. (2024) for a comprehensive discussion that includes the tunnel-scale behavior as well as a mechanistic explanation of the spalling process.