Numerical Investigation of Coupled Effects of Temperature and Confining Pressure on Rock Mechanical Properties in Fractured Rock Mass Using the Thermal-stress-aperture Coupled Model
Mengyi LI#+, Zhijun WU
Wuhan University, China

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 thermo-mechanical analyses in fractured rock mass. With thorough considerations of the aperture-dependent thermal and meso-mechanical parameters for the fractured rock, the model performed more realistic thermo-elastic responses of 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 modelling the thermo-mechanical behaviors of fractured rock. Then, a series of numerical compression simulations with heating temperatures of 20-600oC 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 thermo-mechanical properties were further revealed. The results indicated that the compressive strength and elastic modulus increase with the increase in confining pressure for each temperature scenario. The thermal strengthening behavior of rock extrapolated to about 400oC takes place in confined compression tests, and is more pronounced at higher confining pressures. The evolutions of thermal properties, micro-cracks and meso-structure 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 average fracture aperture variation, the dual effects of increased porosity and thermal-induced micro-cracks, and the negative effect of stress-induced micro-cracks should be comprehensively considered.