Review of unstable falling of roof rock blocks under dynamic disturbance

Roof caving has been the main threat to the safety of underground mining, in which the caving of roof rock blocks is particularly concerning. The secondary structural planes of surrounding rocks around underground excavations, such as roadways and stopes, are developed. The rock mass is prone to break into several independent blocks, and these rock blocks may slide and fall under the action of static in-situ stress or external dynamic disturbances. Under quasistatic stress conditions, the instability and collapse of roof rock blocks are mainly caused by structural plane extensions and changes in the stress balance condition of the rock block system. However, under external dynamic disturbances, the sliding process and instability of roof rock blocks are associated with the development of fractures triggered by stress waves. Further, they are affected by the variation of stress balance conditions of the rock block system and the transmission of stress waves in the block system. This paper summarized the existing studies on roof rock block stability under quasistatic and dynamic disturbance conditions. Previous studies have proposed relatively mature theoretical systems for the stability analysis of roof rock blocks under static or quasistatic situations. However, a majority of the studies on rock block stability under an external dynamic disturbance condition examine stress wave propagation in a rock block system while overlooking the analysis of the crack development mechanism and dynamic variation in stress balance conditions. Therefore, further research is necessary to reveal the caving mechanism of roof rock blocks triggered by a dynamic disturbance. By summarizing relevant work, the difficulties encountered in the study of roof rock block caving under a dynamic disturbance are discussed. The key scientific problem is to uncover the fundamental mechanism behind roof rock block instability induced by a dynamic disturbance. Finally, a series of experimental and numerical simulations conducted on the sliding and instability of roof rock blocks under a dynamic disturbance revealed clear differences in the mechanism of the sliding instability of roof blocks due to dynamic disturbances in different directions. The reduction in friction between the blocks is the fundamental cause of the key block sliding under a lateral disturbance, while the sliding of the rock blocks under a vertical disturbance is mainly driven by the dynamic load. This finding can provide a theoretical reference for preventing and controlling roof caving in underground mines.