Influence of delay time on the blasting effect of multiple charging forms in single free-face rock masses

In this study, we considered coal mine rock roadway blasting excavation as a background to examine the influence of delay time on the blasting effect of different charging structures under single free-surface conditions. Single-pore dispersed-charge models, dual-pore continuous-charge models, and dual-pore composite charge models were established. Their respective explosive rock-breaking mechanisms were explained using different models. These three numerical models were used to analyze the influence of delay time changes on the pressure and velocity of the measurement points near boreholes. The models were used to evaluate the blasting effects by determining the number of free-surface rocks. Engineering experiments were conducted to validate the numerical findings. The results showed that a single-hole dispersed charge creates a cavity and a new free surface, which increases the impact of deep-hole blasting compared to stress wave superposition. Dual-hole continuous-charge detonation is difficult, and short-delay detonation can effectively use stress wave superposition and prolong the action time of the explosive gas. The cavities created by the dispersed charges can be used to increase the efficiency of dual-hole composite charge blasting.