Inter-row delay time optimization and vibration control in blasting caving of insulating pillar based on the HJC constitutive model

When using the blasting caving method to treat goaf, the collapsing ore and rock can cause shock disturbances to the roof of the lower stope, which may lead to stability risks. This study takes the goaf treatment project of Baiyinnuoer No.1 ore body for analysis to protect the stability of the lower stope roof. Specifically, HJC constitutive parameters were calibrated using the physical and mechanical parameters of the ore and rock; SHPB tests were conducted to investigate the dynamic constitutive behavior of the ore and rock, and the reliability of the HJC constitutive model was verified through simulation results. Using LS-DYNA and HJC constitutive parameters, the inter-row delay time was simulated and optimized for insulating pillar blasting caving. Results show that under low impact air pressure, the dynamic stress-strain curves of both types of ore exhibit hysteresis effects. At identical impact pressure, the insulating pillar specimen shows limited damage, while the ore in the lower stope roof experiences more severe fragmentation. In the simulation under different inter-row delay times, the 100 ms working condition yields significant stress superposition effect, extensive disintegration of the insulating pillar, through-going cracks at the top, and failed unit of 998 m3. The collapsed insulating pillar after blasting forms an effective buffer layer in the goaf, isolating the open-pit mine from the underground space, and preventing the instability of the lower stope roof caused by shock disturbances. The peak particle velocity at the tunnel blasting vibration measurement point was 0.64 cm/s, much lower than the allowable lower limit of 15.0 cm/s.