ABSTRACT
An underground excavation is an extremely complex structure and the only theoretical tools which the designer has avail able to assist him in his task are a number of grossly sim plified models of some of the processes which interact to control the stability of the excavation. These models can generally only be used to analyse the influence of one part icular process at a time, for example, the influence of structural discontinuities or of high rock stress upon the excavation. It is seldom possible theoretically to deter mine the interaction of these processes and the designer is faced with the need to arrive at a number of design decisions in which his engineering judgement and practical experience must play an important part.
