Experiment study on shear behavior and properties of granite fractures under real-time high-temperature conditions

Direct shear tests were conducted on granite fractures with similar joint roughness coefficients under real-time high temperatures (up to 400 °C) and constant normal stiffness conditions. In this study, the shearing process was monitored via acoustic emission, and fracture surface morphology was measured with three-dimensional laser scanning. With increasing temperature, peak and residual shear strengths, peak friction coefficient, and maximum normal dilation became higher. In contrast, peak normal displacement and peak shear displacement decreased. The apparent cohesion and internal friction angle exhibited opposite trends as temperature increased, primarily due to competition between thermal hardening and thermal cracking. The elastic strain energy of stick-slip events increased with temperature. From 100 °C to 400 °C, the degradation of fracture roughness and the volume of sheared-off asperities grew. Real-time temperature influences shear properties and is mainly attributed to physical and geometrical changes. Acoustic emission parameters, including count, energy, and hit, show segmented variation during fracture shearing. Based on parameter analyses of the average frequency and rise angle values, during the shearing process, the proportion of shear cracks at each stage varied with temperature. Shear failure was the predominant failure mode. Results from this study provide insight into the shear behavior of granite fractures under real-time high temperatures.