Temperature-dependent peak shear-strength criterion for granite fractures

Rock-engineering applications at different depths experience different high-temperature environments, the temperatures of which can reach 400 degrees C or higher. To investigate the temperature-dependent peak shear strength of rock fractures, a number of direct shear tests were conducted, using granite fractures that were first subjected to thermal treatments at different temperatures (20, 100, 200, 300, 400, 500, 600, and 800 degrees C). The basic friction angle, joint roughness coefficient (JRC), and uniaxial compressive strength (UCS) demonstrated nonlinear reductions with increasing temperature. However, no simple function could be deduced to capture the evolutions. The peak shear strength exhibited a linear decrease with the increase in temperature under each normal loading condition. However, the thermal effect gradually became less pronounced as the normal stress increased. Using multivariate regression analysis, an empirical equation was developed to describe the ratio between the peak shear strengths of the fractures before and after thermal treatments; this equation was a simple function of the normal stress and treatment temperature. Comparisons illustrated that the new criterion could provide the best evaluation of the peak shear strength of a rock fracture after thermal treatments. Possible reasons for the thermally induced reduction in the fracture peak shear strength were preliminarily analyzed, and the limitations of the developed criterion were also stated. The failure criterion can provide new insights for evaluating the stability of surrounding rock masses for temperature-dependent underground engineering.