Experimental Investigation on Temperature-dependent Shear Behaviors of Granite Discontinuity

Abstract

Understanding the temperature-dependent shear behaviors of rock discontinuity would be critical for evaluating the stability of deep underground engineering structure. However, there are few documents available in the literature. In this study, a number of direct shear tests were performed on granite discontinuities with equal/similar joint roughness coefficient (JRC) after high temperatures from room temperature to 800 °C under five levels of normal stress, respectively. A linear increase in peak shear strength can be observed as the temperature increased from room temperature to 400 °C, then followed by a non-linear decline trend as the temperature continuously increased until to 800 °C. Cohesion and internal friction angle exhibited similar trends (reverse S-shape) with the increase in temperature, while the extent of thermal treatments on the two parameters was different. Peak shear displacement and secant peak shear stiffness were also greatly influenced by the thermal treatments, and two temperature-dependent empirical equations with the inclusion of temperature were developed. From room temperature to 400 °C, thermal treatments caused little influence on the surface degradation, while such an effect gradually became prominent with the increase in temperature from 400 to 800 °C. The temperature-dependent shear mechanisms for the failure of the granite discontinuities can be divided into three types (i.e., physical, chemical and geometrical), while the thermally induced over-closure, stated by Barton, would not be suitable for the increase in discontinuities’ peak shear strength due to the different heating procedures.