Fracture evolution and failure behavior around an opening in brittle jointed rocks subjected to uniaxial compression

Abstract

To investigate the fracture evolution and failure behavior around an opening in brittle jointed rocks, an experimental study was carried out in which cross-jointed samples with granite cavities were uniaxially loaded while the mechanics, acoustics and optics were simultaneously observed. These results were compared and analyzed to better understand the deformation and cracking process. The results show that the presence of cross joints and the change in included angles play a crucial role in influencing the strength and deformation properties of the samples. The peak strength and elastic modulus depend on the included angle and first decrease and then increase with increasing included angle, reaching the minimum values when β equals 45°. A stress fluctuation point generally corresponds to a large acoustic emission (AE) event and a turning point in the accumulated AE count curve. The good correlation of the three observations provided a reasonable holistic picture of the process zone nucleation and the subsequent cracking processes. The cracking behavior around openings and cross joints is significantly affected by the included angle because of drastic changes in the stress distribution surrounding the defects. The highlighted strain localization zones formed near the joint tip and around the chamber interact with each other and jointly dominate the initiation and propagation mode of new cracks, eventually leading to more complex failure patterns and severe fracture degrees. Moreover, there will also be an interaction between the same set of cross joints, and the tips can be connected, showing the characteristics of intensified deformation in local areas. The unstable failure of a sample is primarily dominated by tensile cracks and locally by shear cracks around the cavern and the joint tips. Microcrack zones are regarded as white patches macroscopically, and microcrack nucleation is considered to be the microformation mechanism of a white patch.