Stress-structure controlled time-dependent fracture mechanism of deep jointed granite: Acoustic emission moment tensor method

It is crucial to investigate the time-dependent fracture mechanism of jointed rock for understanding the time-delayed disaster development process induced by joints in deep underground engineering construction. The creep tests of natural jointed granite under true triaxial stress were conducted. The complete process of stress-structure controlled failure was analyzed from the perspectives of spatio-temporal evolution of microcracks, nature of microcracks and spatial relationship between microcracks and joint plane. Furthermore, the fracture mechanism and the effect of joints were revealed. The results show that the fracture of jointed rock is essentially a process in which tensile and shear cracks gradually approach the joint plane and cluster around it. When the microcracks gather to a certain extent, the local area of the joint cracking, which triggers the global shear fracture of the joint. In detail, during the creep test of jointed granite, the proportion of shear cracks decreases first and then increases. The evolution of AE event number with time shows the characteristics of attenuation, then steady-state behavior. When the rock is in critical failure, the three types of microcracks begin to increase rapidly, and the response speed and increase rate of shear microcracks is the fastest.