Abstract: In engineering projects such as deep geothermal exploitation and underground nuclear waste disposal, high temperature can induce the initiation, propagation, and coalescence of microcracks in granite, further causing safety problems such as surrounding rock instability and fluid leakage. Therefore, clarifying the mechanical degradation behavior and microcrack evolution of granite after high-temperature treatment is of great engineering significance. A grain-based model (GBM) and thermo-mechanical coupled discrete element simulation were used to conduct splitting numerical tests on cracked straight-through Brazilian disc samples. The microcrack distribution, mechanical response, and fracture evolution mechanism were analyzed. The results show that thermally induced microcracks are not obvious below 100 ℃, whereas the number of microcracks increases significantly and tends to coalesce above 500 ℃, indicating intensified thermal damage. With increasing temperature, the microcrack inclination distribution changes from concentrated to dispersed. At 600 ℃ and above, crack propagation tends to be isotropic, and the fracture path becomes more complex. The load-displacement curve gradually changes from brittle failure to ductile failure. At 700 ℃, no obvious post-peak drop is observed, indicating enhanced energy dissipation capacity during fracture. The fracture toughness decreases in three stages with increasing temperature, and 400 ℃ can be regarded as the critical temperature at which structural degradation shifts from slow deterioration to accelerated damage.

Key words: granite, high temperature, grain-based model(GBM), fracture characteristics, discrete element