Influence of delay interval on blasting efficiency of parallel hole cuts with an empty hole

Time interval of short delay ignition is an important factor to affect the efficiency of blasting cuts. The motion process of rock pieces in the cut cavity is analyzed, a mechanical model to calculate the delay time of parallel hole cuts is presented for tunnel blasting, and a theoretical method to determine the volume ratio (the clearage rate) of the rock pieces within the cut cavity at different moments is proposed for the blasting cut with an empty hole. Numerical analysis results show that the optimal delay interval is proportional to the borehole depth. The suggested results are of practical value to the optimal design of the delay interval in millisecond blasting related to the parallel hole cuts with an empty hole.