Effect of initial damage on remotely triggered rockburst in granite: an experimental study

A remotely triggered rockburst is a typical engineering geology disaster that occurs during the excavation of hard rock at depth. Damage in the rock mass naturally exists and will also be induced by the construction of underground excavation. These damages, in turn, influence the occurrence and intensity of a rockburst. However, this problem, which draws significant public attention, remains unsolved. In the present study, the effect of the initial damage on a triggered rockburst of granite is investigated. Rectangular prismatic rock specimens with different initial damage D (0, 0.2, 0.3, 0.4, 0.6, and 0.7) are prepared by using heat-treatment (25, 200, 300, 400, 500, and 600, respectively). The initial damage is determined by the ratio of the P wave velocity of the specimen heat-treated at a specific temperature to that without heat-treatment. Then, remotely triggered rockburst simulations are conducted on the specimens with coupled static-dynamic loads exerted using an improved true-triaxial testing machine. The failure mode, deformation characteristics, fracture features, and kinetic energy of the ejected fragment of the tested specimen are systematically investigated. The experimental results indicate that for a given initial damage, a threshold of static stress exists, and beyond this threshold, a dynamic disturbance can trigger a rockburst. Additionally, it is found that a dynamic disturbance can much more easily induce a triggered rockburst as the level of initial damage increases. However, the kinetic energy of ejected fragments increases to a peak and then decreases as the initial damage increases. The maximum kinetic energy appears at an initial damage D = 0.3. Therefore, another interesting finding is a specific initial damage can induce the most violent triggered rockburst.