Quantitative Evaluation of the Meso-thermal Cracking Law and Force Field Evolution of Granite Based on GB^3D-DEM Numerical Simulations

The influence of temperature on the evolution of the meso-structure of granite in deep rock engineering has received considerable attention. In this study, a novel thermo-mechanical-coupled grain-based discrete element model (GB^3D-DEM) is proposed to investigate the meso-thermal cracking behavior and deterioration mechanism of granite. The model reproduces the differences in the mineral mechanical properties, thermal conduction properties and temperature-dependent expansion characteristics of granite. Intra-grain cracks are found to gradually initiate above 450 °C, where the occurrence of thermally induced microcracks promotes crack propagation. With increasing temperature, the average contact force first increases and then decreases after 600 °C, being approximately 1.5 times larger at the grain boundaries than within the grains. The meso-thermal damage coefficient varies from 0 to 0.7 as the temperature increases from 20 to 750 °C, where the maximum rate of increase in this coefficient occurs at 450–600 °C. Our results can serve as guidelines for geothermal energy extraction and the prevention of deep engineering disasters.