Abstract: Aiming at the issues of a high large-block rate and low construction operation efficiency in deep-hole blasting within underground mining sectors,this study investigates the influence mechanism of inter-group delay time on rock fragmentation effects. A blasting optimization method to reduce the large-block rate is proposed. An evaluation standard for rock fragmentation based on the damage effect is established, and the fan-shaped hole group blasting technology is further optimized. Through numerical simulation,the evolution law of rock damage,the propagation characteristics of stress waves,and the variation trend of effective stress under different inter-group delay times are analyzed. A residual volume evaluation index based on the rock fragmentation threshold is introduced. The parameters of volume residual rate and large-block rate are quantitatively correlated,and 3 ms is determined as the optimal inter-group delay time. Field tests demonstrate that,under conditions of a hole diameter of 90 mm and a single explosive consumption of 0. 46 kg / m 3 ,the application of 3 ms inter-group delayed blasting reduces the large-block rate from 9. 3% to 6. 2%,achieving significantly better fragmentation performance compared to designs without delayed blasting. The group-delayed blasting technology enhances rock damage by regulating the superimposed effect of stress waves,verifies the scientific validity of the residual volume evaluation index,and provides an effective method for controlling the large-block rate in fan-shaped hole blasting within underground mines. 

Key words: underground mine,fan-shaped hole,explosive load,numerical simulation