A BLASTING AGENT HAVING UNUSUALLY LOW VELOCITY AND PRODUCING UNUSUALLY LOW GROUND VIBRATION AND LARGE BURDEN DISPLACEMENT

摘要

Detonation propagates in the subject blasting agent at about 2.7 km/sec when it is heavily primed but explosion propagates in it at only about 0.43 km/sec when it is lightly primed. When propagating at 0.43 km/sec, it produces a borehole pressure that is slightly less than 1 kb, but no yellow fumes or other sign of incomplete reaction. It is a pumped AN/emulsion blend to which additional water is added by circumferential injection at the inlet of the hose through which it is pumped.In side-by-side 12-hole quarry blasts in gabbro, instrumented with Corrtex lines down every hole, such a composition gave propagation rates of 0.429 ± 0.022 km/sec and the ANF0 in the control blast gave propagation rates of 4.29 ± .06 km/sec for those charges which gave satisfactory measurements and performance. The blast with the low-velocity composition (density 1.32 g/cm3) contained 1.42 times the masses of explosive and rock as the control blast with ANF0 (density 0.85 g/cm3) and therefore had the same powder factor. But it threw the burden farther and produced peak ground vibration of only 30% of that produced by the smaller ANF0 control blast. Fragmentation produced by the low-velocity explosive was poor in the gabbro, which contained many large, competent blocks of rock, but was about equal to that produced by a control blast with ANFO in more closely-jointed andesite at another quarry.This composition, when lightly primed, belongs to a new class of blasting agents which have promise for use in the following situations: where maximum throw of the burden at fixed powder factor is desired, as in coal stripping; where fixed throw at minimum powder factor is desired, as in quarry-blasting of well-jointed rock; where a clean and stable remaining face is required; where armor stone is to be produced from rock having large, competent blocks in place; or where heavy blasting is to be done at locations where ground vibration is a problem.