The principle of blasting open pit is that you want what is called " heave", that is, you are shattering the substrate to the required depth, everything lifts a bit and then settles, fractured. Energy going straight up the blast hole is considered wasted, and gives you fly rock, which can travel considerable distance, and cause damage where it lands. I've seen a rock little larger than your fist go clean through the tin roof of a transportable, the ceiling below, then the 20mm thick plywood floor as well.
Hi Ralph, thank you for sharing your insights and experience on this. We have also seen som horrific flyrock consequences... very few things that can stop a good chunk of flyrock once it is going. Cheers for the comment
Are the line of vertical black smoke columns starting at 1:30 the right thing for that blast, or is that a big mistake? It otherwise looks like a nice, neat "heave" of material.
The blasts with holes venting at the back are presplits. But you are right - a lot of these shots were either overcharged or inadequately stemmed, wasting a lot of energy.
@@davidlittlefield4711 yeah some of the shots had presplits. Challenge with firing the open holes is the resultant overpressure/airblast. Although the presplit holes are charged significantly less your timing sequence needs to be on point to not exceed allowable airblast levels. Cheers for the comment.
