A multifunctional shear apparatus for rocks subjected to true triaxial stress and high temperature in real-time

Abstract

Deep engineering disasters, such as rockbursts and collapses, are more related to the shear slip of rock joints. A novel multifunctional device was developed to study the shear failure mechanism in rocks. Using this device, the complete shear–deformation process and long-term shear creep tests could be performed on rocks under constant normal stiffness (CNS) or constant normal loading (CNL) conditions in real-time at high temperature and true-triaxial stress. During the research and development process, five key technologies were successfully broken through: (1) the ability to perform true-triaxial compression–shear loading tests on rock samples with high stiffness; (2) a shear box with ultra-low friction throughout the entire stress space of the rock sample during loading; (3) a control system capable of maintaining high stress for a long time and responding rapidly to the brittle fracture of a rock sample as well; (4) a refined ability to measure the volumetric deformation of rock samples subjected to true triaxial shearing; and (5) a heating system capable of maintaining uniform heating of the rock sample over a long time. By developing these technologies, loading under high true triaxial stress conditions was realized. The apparatus has a maximum normal stiffness of 1000 GPa/m and a maximum operating temperature of 300 °C. The differences in the surface temperature of the sample are constant to within ±5 °C. Five types of true triaxial shear tests were conducted on homogeneous sandstone to verify that the apparatus has good performance and reliability. The results show that temperature, lateral stress, normal stress and time influence the shear deformation, failure mode and strength of the sandstone. The novel apparatus can be reliably used to conduct true-triaxial shear tests on rocks subjected to high temperatures and stress.

Keywords

• True-triaxial shear apparatus
• Rocks
• Complete shear stress–deformation process
• Creep
• Real-time high-temperature