Development work was carried out on the 6,500-foot level of First Nickel Inc.’s Lockerby Mine in early 2013, wrapping up in March of that year.
That work included blasting out a drift – the 65-2-1-West area – that did not proceed as planned. The entranceway was off-line, so corrective blasting was done to try and straighten it out, and wire mesh, split sets (long metal tubes that help to reinforce a ceiling) and shotcrete (sprayed-on cement) were used to strengthen the ceiling and walls in preparation for production drilling and blasting.
The wider-than-expected entrance created a structural integrity issue, as the arch that was in place to help distribute the stress from the backfilled-area one level above was not large and strong enough.
Water also began leaking from the level above and due to it being slightly acidic from exposure to nickel ore, weakened the wire mesh and split sets underneath the shotcrete. The area then sat idle for one year.
When production drilling and blasting got underway in the area in the spring of 2014, seismic activity in the mine, as well as vibrations from drilling and blasting, all contributed to the further weakening of the drift’s ground control measures.
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