ABSTRACT
The left hand margin sketch gives a simplified picture of the underground excavation stability problems which are encountered with increasing depth below surface.
At shallow depth in overburden soil or heavily weathered poor quality rock, excavation problems are generally asso ciated with squeezing or flowing ground and very short standup times. This means that cut and cover or soft ground tunnelling techniques have to be used and adequate support has to be provided immediately behind the advancing face. The stability of underground excavations in very poor quality rock or soil will not be discussed in detail in this book and the interested reader is referred to books such as those by Pequignot190, Hewett and Johannesson191 and Szechy192 and to journals such as Tunnels and Tunnelling for further deta i1 s.
