Effects of Delay Blasting on Crack Propagation in Defective Empty Hole

ABSTRACT To investigate the effects of delay blasting on crack propagation in a defective empty hole, this study employed dynamic caustics experiments and numerical simulation to analyze crack propagation behavior and stress distribution. The results show that the stress waves' superposition enhances dynamic mechanical parameters (including crack propagation velocity, dynamic stress intensity factors [DSIFs], and energy release rates) at the crack tip, especially during the initial phase. When boreholes are detonated simultaneously or when the borehole near the empty hole is detonated first with a short delay, the interaction between the stress waves from the remote borehole and the running crack significantly enhances dynamic mechanical parameters and promotes crack propagation. When the delay time is long, the stress waves from the remote borehole can induce the crack to initiate again, and the dynamic mechanical parameters are higher than in the first phase. Additionally, because of the diffraction of stress waves in the empty hole, the hoop tensile stress on the back blasting side initially increases and subsequently decreases with increasing distance. These research results provide a reference for optimizing delay times and improving rock breaking efficiency.