Effect of Thermal Treatment on the Basic Friction Angle of Rock Joint

There is a growing demand of knowledge on the behavior of rock masses after thermal treatment in both academic and practical aspects due to the high demand of construction of underground structures under the high-temperature environment. The peak shear strength of rock joints has a significant role in evaluating the stability problems of surrounding rocks. However, there is a lack of information about the temperature-dependent nature of the basic friction angle of rock joints, which serves as an essential parameter to evaluate the peak shear strength. The present study experimentally investigates the influences of temperature magnitude (20, 200, 400, 600, and 800 °C) on the basic friction angle of granite, marble, and red sandstone joints. The basic friction angles of the three kinds of rock joints exhibit linear trends with the increase in the treatment temperature. The basic friction angles of granite and red sandstone joints increase with the increase in the treatment temperature, while the values for marble joints continually decrease. The mechanisms for the thermally altered variations in the basic friction angle of rock joint are mainly related to dehydration process, uneven expansion of mineral grains, thermally weakened asperities distributed on the surfaces, and change in physical and mechanical properties of minerals. In addition, other test conditions, including tilting rate, specimen size, repetition number, and cooling rate, are also analyzed. The present study provides useful data in establishing a peak shear strength criterion for rock joints by considering the temperature effect.