Effects of delay time on fragmentation.
Nutting-MJ; Stagg-MS; Barlet-DR
Paper in 27th Symposium on Rock Mechanics Univ Alabama, 1989 Jun; :1-6
Single-row bench blasts at a reduced scale in the field were used to study the effects of delay-time on fragmentation. Nine shots with a spacing of 21 in and a burden of 15 in(s/b = 1.4) and nine shots with a spacing of 30 in and a burden of 15 in (s/b = 2.0) Were completely screened to determine particle size distributions. Delay intervals between holes ranged from 0 to 45 ms, corresponding to effective delay intervals of 0 to 36 ms per foot of burden. Each shot was instrumented with strain and pressure gages to measure in situ blast dynamics and to evaluate interactions between blastholes. Finer overall fragmentation was produced for shots with delay intervals between 1 and 17 ms per foot of burden. Only for shots within this optimum delay range was it observed that the strains induced by stress waves constructively interacted with strains induced by gas pressure from an earlier detonated hole. Coarsest fragmentation resulted at delay intervals less than 1 ms/ft, where stress waves from each hole were observed to interact destructively, and at delay intervals greater than 24 ms/ft, where no interaction between holes was observed, indicating a condition that can be considered as the firing of single-hole shots independently.
Mining-industry; Rock-mechanics; Blasting-agents
Paper in 27th Symposium on Rock Mechanics, Univ., Alabama, June 23-25, 1989, Univ. Alabama, 1989 449-454