Experimental Investigation of the Effect of Delay Time on Rock Fragmentation in Multi-Hole Bench Blasting

Rock fragmentation by blasting influences ore recovery and the cost of downstream operations. The development electronic detonators makes it possible to improve controlling initiation timing in projects, effect mechanism delay on rock should be studied. Fragmentation granite bench specimens with different was investigated blast experiments. Conclusions are obtained studying surface strain field post-blast specimens. A total six tests were carried out four boreholes each having a diameter 10 mm length 450 mm. Each borehole used pentaerythritol tetranitrate (PETN) as explosive charge, which approximately 4.84 g charge 5.5 Delay times between adjacent same row set 0, 50, 100, 150, 200, 250 µs. specimen under loading analyzed using three-dimensional digital image correlation (3D-DIC) techniques based two cameras that captured high-speed images. Additionally, also observed recorded. Fragments carefully collected, weighed, sieved sieves, including very fine particles. According 3D-DIC analysis for specimens, propagation pattern main concentration zone transformed from horizontal vertical increase inter-hole delay. maximum excavation weight an 100 µs, while longest (250 µs) minimum weight. By combining results fragment size distribution all optimal 200 Compared simultaneous detonation, median decreased about 14.5% experiments show time significantly fragmentation, but stress wave superposition short delays cannot fragmentation. For long delays, blast-induced crack regarded influential factor when choosing proper time. experimental findings this study could provide better understanding