Letters TIGHT SQUEEZE

“A Rockburst Primer” by Dr. David Hedley, which appeared in your July issue, brought back memories. In 1937 or 1938, I was working in a large, flat-back stope in the Lake Shore mine in Kirkland Lake, Ont. The stope had been mined, timbered and backfilled from the 3,000-ft level to within about 30 ft of the 2,800-ft level. Because of the proximity, we ate in the lunchroom which was situated in the No. 1 shaft pillar on the 2800.

Each entry or exit from drift to stope and vice-versa was made through a manway, which seemed to get smaller by the week. I was sort of skinny, but I had to hold my lamp battery tight to my side while squeezing my way up or down the ladders. We often joked that we’d better eat a light lunch or we’d never get back into the stope. As was usual on entering the lunchroom, we took off our hard hats and batteries, placing them on the floor and our lunchpails on our knees.

Wham] There was a moment of disorientation as the benches on which we sat bounced as if hit by a sledgehammer. Our lunchpails landed on the floor and the overhead electric lights went out. In the next second, aided by the lights of a few headlamps which had been left on, about 30 men scrambled over each other to reach the door leading into the drift. I had been sitting on the side of the lunchroom remote from the door and, by the time my turn came to push my way out, I realized that the drift was in total darkness and that I was safe in the dimly lit lunchroom.

Some of the men, who had barely exited, returned quickly to the lunchroom, while others further away shouted for a light to direct their way back. In the nervous excitement of the moment, we kidded them for leaving without their lights] No one was hurt in that rockburst, although the drift that we had walked along a few minutes previously was filled with debris. The railroad tracks, the air- lines, the ventilator pipe and square- set cribbing were all jumbled up in a rock-filled mess.

Fortunately, the crosscut from No 1 to No 5 shaft suffered no damage, so after a head count at the No 5 station, the men from the 2800 level got a priority lift to the surface. Naturally, work was curtailed in that part of the mine and I never did hear what became of the contracting manway leading into the big, flat-back stope.

As a fledgling miner, I wasn’t all that interested in what caused “air blasts.” However, in later years, I concluded that Lake Shore had two problems. First, the problem of supporting the hanging wall, which is normal for any mine. Second, there were two veins, approximately parallel, which gradually converged with depth. As the veins were mined, a huge wedge of waste rock that lay between them had to be supported by rock, pillars, timber and backfill. When the supports became overstressed in one area, the huge mass of waste rock or part of it weighing millions of tons might shift in small fractions of an inch. The sudden shift in loading caused rock to literally explode and shock waves could be felt on surface for as far away as 30 miles around. George Wallace, Cobden, Ont.