For Information and Communication in the Fields of
Slides, cave-ins, flowing ground which sometimes occur in tunnels are some of the unexpected problems during tunnel excavations. Some comments on this are shown in the paper Collection of geo-data – limitations and uncertainties.
See also abstract of the paper on Slides in Norwegian water tunnels
Some comments on uncertainties can be seen here
You find some classifications on geological features here and here
Important quotations will be presented here from time to time
Karl Terzaghi:
Even a very comprehensive and appropriately conducted geological survey of the site of a proposed tunnel cannot accomplish more than a very crude estimate of the length of the tunnel sections in which each of the principal types of rock conditions will be encountered. Further differentiation cannot be expected. Hence, even if methods for accurately computing the rock load under given rock conditions were available, they would have very little practical value on account of the inevitable uncertainties associated with predicting the rock conditions.