深部地热开采、核废料地下封存等工程中,高温作用会诱发花岗岩内部微裂纹萌生、扩展与贯通,进而导致围岩失稳和流体泄漏等安全问题.为揭示高温后花岗岩力学劣化及微裂纹演化规律,采用矿物晶体模型方法(GBM)和热-力耦合离散元模拟,对直切槽式巴西圆盘开展劈裂数值试验,分析其微裂纹分布、力学响应和断裂演化机制.结果表明:100 ℃以下花岗岩热致微裂纹不明显,500 ℃以上微裂纹数量显著增加并趋于贯通,热损伤明显加剧;随温度升高,微裂纹倾角由集中分布转为离散分布,600 ℃及以上裂纹扩展趋于各向同性,破裂路径更加复杂;力-位移曲线由脆性破坏逐渐向延性破坏转变,700 ℃时峰后跌落不明显,耗能能力增强.断裂韧度随温度升高呈三阶段下降,400 ℃可视为结构劣化加速发展的临界温度.
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.
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