While Tom Miller recovered from his punctured lung myself and his two other employees kept mining on the 10 x 10 foot tunnel out of Oakley, Idaho. We stayed in pretty competent ground, but it required wood timber sets all the way. Tom returned to work and the progress on the tunnel wasn’t bad. By the time we got several hundred feet into the mountain the ground took a change. We got into a zone of crushed altered rock from a shear zone or fault. The zone started on the lower left side of the tunnel and as we progressed it moved up into the quarter arches and crown. As the bad rock got closer to the crown we shortened the distance between our wood timber sets. Tom bought a load of hay bales to use as softener on the sides outside of the solid three inch lagging. Like any owner Tom was doing his best to minimize timber quantities used for cribbing above our timber sets. He wanted to stay safe, but he wanted to save timber cribbing too. As the tunnel advanced the bad ground was in the right side crown and going up at about a 45 degree angle. It was blocky, fractured, and dry. Our progress was slow. We had about 300 feet of cover between us and the surface of the mountain.
Each time we advanced a round in the tunnel there was deterioration of the ground behind us as the fractured ground dribbled around the cribbing. This isn’t uncommon and normally the caving ground will fill the voids and choke itself off over time. I would use my mine lamp to inspect above the timber behind us every round. The ground was working, but didn’t appear to be a problem. The caps and posts didn’t show any significant weight from the ground above us. We shot a round and I was about half way mucked out with the little 910 Cat loader. I had about half a bucket of muck when I felt a minor air blast in the tunnel. A rounded two foot rock blew through the three inch lagging about four feet above the floor of the tunnel fifty feet behind me. As I backed out the loader wouldn’t climb over the two foot rock. I went forward and scraped enough muck to fill the bucket. I was wide open as the loader bounced over the rock on my way to the portal. Trickles of dust and sand were falling everywhere and several log caps on the timber sets broke as I retreated. The caps were 16 to 20 inch diameter logs framed ten feet across 12 inch log posts. They sounded like a cannon when they broke. I cleared the portal, parked at the edge of our dump area, climbed on the roof of the loader, and watched as I listened. The tunnel caved full of muck and I suspected the bad ground would cave to the surface. The crew outside came running. They knew the tunnel caved in, but couldn’t understand what I was watching on the mountain. When the sagebrush started disappearing in an ever widening circle they knew the ground had daylighted.
I was running on adrenalin once I felt the small air blast………and thankful for the opportunity to be outside watching the sagebrush drop out of site.