ABSTRACT
The worst type of problem with which an underground excava tion designer can be faced is the unexpected problem. With in the confined space of a tunnel or mine, it is both diffi cult and dangerous to deal with stability or water problems which are encountered unexpectedly. On the other hand, given sufficient warning of a potential problem, the engineer can usually provide a solution by changing the location or the geometry of the excavation, by supporting or reinforcing the rock mass around the opening or by draining or diverting accumulations of groundwater.
