Study on the effect of micro-geometric heterogeneity on mechanical properties of brittle rock using a grain-based discrete element method coupling with the cohesive zone model

The micro-geometric heterogeneity has a significant effect on the mechanical behavior and failure mode of brittle rocks. To study the influence of the size distribution and preferred orientation of mineral grains, a statistical grain-based discrete element method coupling with the cohesive zone model is proposed on the basis of the universal distinct element code (UDEC) in this study. First, a mixed-mode cohesive model was developed and implemented in UDEC to simulate the nonlinear behavior of grain interfaces. Then, a micro-parameter calibration procedure based on the Plackett-Burman design, central composite design, and particle swarm optimization was established to reproduce the macro-properties of the Lac du Bonnet granite. Finally, the strength characteristics, deformation response, and failure mode of rocks were numerically examined using the proposed model by varying the size distribution and preferred orientation of mineral grains. The relationship between the micro-geometric heterogeneity and the uniaxial compressive strength, the crack initiation stress, the crack damage stress, the elastic modulus, the Poisson's ratio, and the failure mode of rocks are obtained respectively.