Mechanical properties of rocks under high temperature and high pressure are important for the design and stability analysis of rock mass in deep-buried underground engineering. This study is devoted to investigating the strength and deformation behaviors of granite as well as the thermal degradation mechanism under coupled high-temperature and high-pressure conditions in triaxial compression tests. Two groups of triaxial compression test under six different temperatures (20, 50, 70, 90, 110, 180 °C) and five different pressures (0, 2, 15, 30, 40 MPa) designed by the orthogonal method were performed by a self-developed thermo-mechanical true triaxial testing device on the granite samples drilled from the borehole at the depth of 600 m. The multi-scale features of the sliding surface of the post-failure samples were characterized by field optical microscopy and 3D laser scanning. Temperature effects on the granite mechanical properties, especially the friction properties were identified and discussed. It is found that increasing temperature induces obvious thermal degradation of strength and elastic modulus of the tested granite under triaxial compression. The deformation and failure pattern of the tested granite are dominantly governed by the confining pressure rather than temperature when the temperature varies between 20 °C and 180 °C. Temperature plays a crucial role in the friction behavior in triaxial compression, and the increase in temperature leads to the increase of gouge particles and the linear decrease of the roughness of the sliding surface. Both thermal cracking and friction weakening contribute to the thermal degradation of strength at high pressure. The findings are helpful in comprehensively understanding the mechanical behavior of granite under coupled high temperature and high pressure, and in revealing the thermal degradation mechanism of hard rocks.

高温高压下岩石的力学特性对于深埋地下工程岩体的设计和稳定性分析具有重要意义。本研究致力于在三轴压缩试验中研究花岗岩在高温高压耦合条件下的强度和变形行为以及热降解机制。由正交法设计的六种不同温度（20、50、70、90、110、180℃）和五种不同压力（0、2、15、30、40MPa）下的两组三轴压缩试验由自主研制的600m深钻孔花岗岩试样热力真三轴试验装置。通过场光学显微镜和 3D 激光扫描表征失效后样品滑动表面的多尺度特征。确定并讨论了温度对花岗岩力学性能的影响，尤其是摩擦性能。结果表明，随着温度的升高，受试花岗岩在三轴压缩下的强度和弹性模量发生了明显的热退化。当温度在 20 °C 和 180 °C 之间变化时，测试花岗岩的变形和破坏模式主要受围压而不是温度控制。温度对三轴压缩的摩擦行为起着至关重要的作用，温度的升高导致凿痕颗粒的增加和滑动表面粗糙度的线性减小。热裂纹和摩擦减弱都会导致高压强度的热退化。该研究结果有助于全面了解高温高压耦合作用下花岗岩的力学行为，揭示硬岩的热降解机理。