STRENGTH EVOLUTION OF CARBONACEOUS PHYLLITE UNDER THERMAL MECHANICAL COUPLING

Temperature field and stress field are important factors that affect the surrounding rock strength of diversion tunnel in carbonaceous phyllite stratum. 16 groups of experiments with 2 factors and 4 levels were set. Based on the results of uniaxial and triaxial tests, the behavior of stress-strain curve and the failure mode of carbonaceous phyllite under thermal mechanical coupling are discussed, and the variation law of peak strength is obtained. Based on Mohr-Coulomb (M-C) criterion and Heok-Brown (H-B) criterion, two calculation methods of failure strength, Mohr-Coulomb-Thermal (M-C-T) method and Heok-Brown-Thermal (H-B-T) method, are established respectively. The experimental results and theoretical analysis show that with the increase of confining pressure and temperature, the failure of carbonaceous phyllite changes from brittle to ductile. The cohesion, uniaxial compressive strength and parameter n increase linearly with the increase of temperature, but the internal friction angle is not affected remarkably by temperature. The results show that both M-C-T method and H-B-T method can quantify the strength evolution of carbonaceous phyllite under thermal mechanical coupling. Error analysis shows that the calculation error of the former is -28.5%~7.7%, and that of the latter is -8.9%~5.6%. The results of H-B-T method show less scattering, hence the method is more stable and more safety oriented.