Investigation of damage evolution and heterogeneity in intact Wombeyan marble using a continuum grain-based model

A realistic simulation of the emergent macroscopic behavior of brittle rocks requires an explicit representation of rock microstructure. Grain-based models (GBMs), which divide material space into individual granular blocks (grains) separated by joints, are widely employed to represent rock microstructures. While discontinuum-based GBMs effectively capture failure processes, their high computational demand limits practical applicability. Consequently, a continuum GBM (CGBM) is used in this study to simulate the failure processes of laboratory-scale intact Wombeyan marble, as the CGBM can maintain computational efficiency of models while preserving key aspects of stress and strain heterogeneity and failure patterns under unconfined and confined conditions. For this purpose, the CGBM of Wombeyan marble was calibrated to match its macro-mechanical properties obtained from the laboratory tests, and the progressive failure mechanisms were observed at different stages of applied load under unconfined and confined conditions. Using the calibrated model, the study novelly investigated the evolution of stress heterogeneity in Wombeyan marbles under confined conditions using CGBMs, providing advanced insights. In addition to stress heterogeneity, this study also investigated the evolution of strain heterogeneity in Wombeyan marbles. As CGBMs are incapable of accounting for the strains that evolve at the grain contact areas during grain separation, a two-dimensional digital image correlation (2D-DIC) approach and finite element (FE) equations were explicitly employed to quantify the strains. The results demonstrated that CGBM effectively captures the localized stress concentrations and heterogeneous stress distribution at the grain-scale, specifically during the early stages of loading under confinement, due to the interlocking effect of grains. The strain estimation from FE and DIC techniques closely matched the CGBM stress-strain behavior. However, limited crack interconnectivity restricted grain movement and led to inconsistent strain heterogeneity trends at higher levels of loading. An alternative model with enhanced interconnectivity was developed that exhibited strain heterogeneity trends consistent with experimental observations.