Temperature effects on the failure of deep circular tunnel under true-triaxial compression

The failure characteristics of thermal treated surrounding rocks should be studied to evaluate the stability and safety of deep ground engineering under high-ground-temperature and high-ground-stress conditions. The failure process of the inner walls of fine-grained granite specimens at different temperatures (25–600 °C) was analyzed using a true-triaxial test system. The failure process, peak intensity, overall morphology (characteristics after failure), rock fragment characteristics, and acoustic emission (AE) characteristics were analyzed. The results showed that for the aforementioned type of granite specimens, the trend of the failure stress conditions changed with respect to the critical temperature (200 °C). When the temperature was less than 200 °C, the initial failure stress increased, final failure stress increased, and failure severity decreased. When the temperature exceeded 200 °C, the initial failure stress decreased, final failure stress decreased, and failure severity increased. When the temperature was 600 °C, the initial and final failure stresses of the specimens decreased by 60.93% and 19.77% compared with those at 200 °C, respectively. The numerical results obtained with the software RFPA3D-Thermal were used to analyze the effect of temperature on the specimen and reveal the mechanism of the failure process in the deep tunnel surrounding rock.