Dynamic tensile failure mechanism of hollow rocks: a numerical study based on AE moment tensors

In underground excavations at great depths, rocks are likely to experience complex in-situ stresses such as coupled static and dynamic loads. The current work numerically investigates the dual effects of pre-tension and structural defect (i.e., prefabricated hole) on the dynamic tensile behavior of hollow rock using the flattened Brazilian disc (FBD) method. The split Hopkinson pressure bar (SHPB) system for dynamic loading is established based on the discrete element method (DEM). The results show that the total tensile strength of the specimen decreases with the increase of the hole radius and is independent of the pre-tension ratio. The dynamic tensile strength decreases with increasing pre-tension ratio in rocks with different hole radii. The fragmentation analysis shows that the rock is more discretized with a smaller hole size and fails more evenly with a greater mean fragment size as hole radius increases. In addition, the acoustic emission (AE) moment magnitude is further discussed to interpret the rock cracking process microscopically, incorporating the wave transmission trajectory within the specimen. The primary cracks initiated in the vicinity of the hole along the loading direction have a higher moment magnitude than those of the secondary cracks that start at the upper and lower boundaries of the rock.