Numerical Investigation of Coupled Effects of Temperature and Confining Pressure on Rock Mechanical Properties in Fractured Rock Mass Using Thermal-Stress-Aperture Coupled Model

The mechanical performance of rock mass subjected to the coupled influences of the elevated temperature and in situ stresses has always been a hot topic in underground rock engineering projects. In this study, a thermal-stress-aperture coupled model was first developed and then incorporated into the particle flow code for the coupled thermomechanical analyses in the fractured rock mass. With thorough considerations of the aperture-dependent thermal and mesomechanical parameters for the fractured rock, the model performed more realistic thermoelastic responses of the fractured rock to the temperatures and confining pressures. Comparative studies between the numerical simulations and previous experimental results indicated that the proposed model was suitable for modeling the thermomechanical behaviors of the fractured rock. Then, a series of numerical compression simulations with heating temperatures of 20°C–600°C and confining pressures of 0–20 MPa were conducted to comprehensively explore the interplay of the temperature and confining pressure on mechanical properties of fractured rock specimens. Finally, the mechanisms that affect the rock thermomechanical properties were further revealed. The results indicated that the compressive strength and elastic modulus increase with an increase in confining pressure for each temperature scenario. The thermal strengthening behavior of rock extrapolated to about 400°C takes place in confined compression tests and is more pronounced at higher confining pressures. The evolutions of thermal properties, microcracks, and mesostructures are the most decisive factors that could induce the variations of rock properties under the coupled temperature and confining pressure treatment. For analyzing the mechanisms behind strengthening and weakening contribution to rock properties, the positive effect of the decrease in average fracture aperture, the dual effects of increased porosity and thermal-induced microcracks, and the negative effect of stress-induced microcracks should be comprehensively considered.