Performance analysis of TBM excavation parameters related to small-diameter horizontal and inclined tunnels

Horizontal, inclined, and vertical ways through the rock are needed for several mining and civil purposes (hydropower, transportation, sewer collector, underground transports), and quite often, in the same project, horizontal, inclined, and vertical ways are necessary. These cases offer an excellent opportunity to compare the performance of excavation systems in similar geological-geomechanical environments. The basic mechanism of rock breakage, either cyclical (Drill and Blast) or continuous (TBM or Raise Borer), is the same for horizontal or inclined ways. In the latter case, the fixed motor option (Raise Borer) tends to be preferred for short, small-diameter, easily accessible top-point cases. The drill and blast system tends to be employed only in horizontal or very short inclined ways. In the first part of the paper, a general discussion of the techniques for horizontal, inclined/vertical ways excavation is provided, comparing some real cases of tunnel driving by TBM under the aspect of the machine’s average performance. The comparison of the cases makes it possible to draw some prediction criteria applicable to the TBM performance in horizontal and inclined tunnel driving.