Thermal-Stress-Aperture Coupled Model for Analyzing the Thermal Failure of Fractured Rock Mass

When rock is subjected to thermal load, primary fractures in the rock will block the heat conduction and greatly affect the temperature distribution, which in turn modifies the distribution of thermal stress and, hence, causes additional cracks to the rock. Therefore, it is essential to reasonably describe the heat conduction and thermal fracturing processes of the rock mass upon heating treatment. This study proposed a thermal–stress–aperture coupled model for investigating the thermally induced failure process of fractured rock mass. First, the mesomechanical parameters of the bonds in the cluster model based on the particle flow code were calibrated and verified under different temperatures. To more realistically simulate the thermal and mechanical behaviors across the fractures, the relationships of the aperture with the thermal and mesomechanical parameters of the bonds, including the thermal conductivity, effective modulus, tensile strength, and shear strength, were established and calibrated. The thermal–aperture- and stress–aperture-dependent models were introduced to the thermal–stress–aperture coupled model. Finally, the proposed coupled model was adopted to numerically investigate the influences of the discrete fracture network on the heat conduction, thermally induced failure, and mechanical behaviors of the fractured rock. The results indicate that the temperature distribution, thermal-induced failure, and stress–strain curves are significantly sensitive to the average fracture aperture, average fracture length, and fracture density. In addition, with an increase in the average fracture aperture, average fracture length, and fracture density, both the uniaxial compressive stress and elastic modulus exhibit decrease trends. The fracture density has the most significant influence on the mechanical behaviors of the fractured rock.