Damage and failure characteristics of coal and surrounding rock under shaped blasting

The high crustal stress in deep coal mining undermines the efficiency and safety of blasting operations conducted to increase gas permeability in the coal seam. Therefore, in this study, theoretical research, computer-based numerical simulations, and experiments were conducted to investigate the damage and fracture characteristics of a coal body and surrounding rock subjected to shaped blasting. ANSYS LS-DYNA was employed for numerical simulations to understand how a shaped jet is formed and how damage occurs in shaped blasting. A model of crack evolution under the influence of detonation gases that is based on fracture mechanics theory was constructed to analyze the mechanism underlying the directional propagation of detonation cracks in shaped blasting. In the conducted experiments, shaped blasting resulted in the creation of an oval-shaped fragmentation area, which was evidence that the shaped cartridge limited the loss of energy in fragmentation, allowed detonation cracks to evolve further in the specimen, and caused the formation of a main crack that propagated in the direction along which energy was concentrated (i.e., directional damage). Compared with ordinary blasting, shaped blasting facilitated more efficient blast energy use and reduced undesirable blast disturbance to the surrounding rock by 58% according to the computed tomography image of resistivity. The results of this study provide valuable insights on safe and efficient coal production.