Predicting advance rates in faulted rock

The difficulties caused by faulted rock were discussed in earlier chapters, and are well illustrated by the examples given by Robbins (1982) and Grandori et al. (1995b) (see Figs 5 and 37 ). Faulted rock presents a difficulty not only to the TBM but also to the engineering geologist, because the operator has to ‘over-rule’ the natural tendency of the machine to penetrate faulted rock faster (at first), until either the cutterhead gets blocked, or the buckets or conveyor get overloaded, or a new set of problems arise when the grippers enter the same zone. This makes prediction of delays more difficult, because an unstable situation can develop in many different negative directions, and is decision-dependent or operator-dependent.