You need to bear in mind that as the rock is excavated that transfers the stresses into the remaining material. It also changes the direction of the stress. The undisturbed rock is basically supported from all sides. When you dig a tunnel, some of the rock is now unsupported from the side next the void. The rock next to the void is also now supporting the additional weight that used to be carried by the rock that was removed. Weird things happen. Rock expands and creeps. Stresses build up and concentrate in particular places. If you switch everything off in a mine you can hear the ground shifting and stretching.
Engineers do what they can to account for everything and make sure everything is properly supported, but it's not an exact science. It's way harder than building above ground where you only have to worry about the building itself and the ground it sits on. If you send a few shock waves through the ground, stresses may shift or structures fracture. Without an exhaustive search to eliminate as many possibilities as you can, you're inviting the possibility of somebody having "a very bad day".
For my part, I would way prefer that my mine took all reasonable precautions against harming its people.
NCM Price at posting:
$21.16 Sentiment: Hold Disclosure: Held
