Evaluating the impact of calcite and heterogeneity on the mechanical behavior of coal: A numerical study with grain-based finite-discrete element method

Understanding the mechanical properties and fracture behaviors of coal is essential for the safety of underground mining engineering. This research aims to evaluate the impact of calcite and heterogeneity on the mechanical properties of coal. Neper, a software package for polycrystal generation and meshing, is used to create numerical models with a non-uniform grain size distribution. A random parameter assignment method is proposed to simulate the mechanical properties and failure behavior of coal using the combined finite-discrete element method (FDEM). A comprehensive parametric investigation of the properties of triangular and joint elements is conducted, and calibration procedures are suggested for numerical modeling. The model was calibrated to experimental results and then used to understand the impact of calcite grains on the mechanical behavior of coal. After calibration, a triaxial compression was performed on coal samples with and without calcite grains at different confining pressures. It is found that the presence of calcite in a coal sample increases Young's modulus and decreases the peak strength of coal. This research uses Voronoi tessellation technology to present a Weibull statistical grain-based model (GBM) to investigate the microstructural heterogeneity induced by grain morphologies. The deformation response, strength characteristics and cracking behavior are investigated by varying the heterogeneity of numerical models under compressive tests with different confining pressures. The simulation results of triaxial compression indicate that the compressive strength increases linearly as the heterogeneity m value increases. The consistency of the numerical results with the experimental observations suggests that the GBM approach can be used to better understand the mechanics of brittle rock failure at the micro-structure scale.