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Drilling/blasting broken ground

Drilling/blasting broken ground

Drilling/blasting broken ground

(OP)
Has anyone had experience in open-pit production drilling/blasting of previously broken ground?

We are working down to expose old, pillar-extracted coal seam workings. The sandstone overburden for about 15metres above the seam is severely fractured due to highly variable subsidence, and has significant voids.  Our objective is to fill any major open voids to enable trucks & excavator to work on benches above.  However we are having trouble drilling blastholes (100mm holes) due to lack of air return clogging holes with cuttings, and also broken ground jamming drill and holes collapsing.  We can probably use bottom plugs/stemming & liners to contain the explosive - it is mainly a drilling rather than blasting problem.
Any advice would be appreciated.

RE: Drilling/blasting broken ground

Load the holes as soon as possible after drilling. Adjust your air pressures to the maximum on your drills. It would help if you would drill down to 3 or 4 feet off the top of coal.  This is very important, so as to not lose the energy from your blasting agent, down into the mine void.  It also protects the coal from being damaged by rubber tired equipment running over the pillar blocks and voids, during the overburden removal process. The last remaining overburden, after the shot has been removed, can be pulled with an excavator and dozers. They have a much lower bearing pressure than rubber tired equipment. This will maximize your coal recovery.

RDS CBC Engineering

RE: Drilling/blasting broken ground

(OP)
To "LowCoal"
Thanks for your interest.  We have been able to get good coal recovery from the pillars once we get there, but the big problem remains that the overburden drill loses too much air into the broken/caved ground above the old workings which in turn leads to jamming rods in holes etc.

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