More information on the Open Book is available. Copyright 1993, the National Academy Press. Keywords, machine extracted. Top 50 words repeated twice, next 100 once, plus phrases. Instabilities occur during all phases of the life of the circular opening, from excavation to utilization.
Several processes can occur simultaneously and contribute to the damage of the hole.
Depending on the local conditions, one of the mechanisms will dominate. The purpose of this chapter is to establish a list of the different mechanisms which could lead to a circular hole failure. This will be done by describing the different states of an opening during its life. If the distressing caused by the approaching opening is important, fracturing of the rock mass might occur even before the hole face has reached it. Innis has been observed, at a fairly large scale, in deep hard-rock mining.