NATM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 632

Glass fiber anchors are therefore often installed at locations where they have to be re-
moved in the course of further excavation, such as for the support of the inner walls of
sidewall adits or for the support of the temporary face (Fig. 20.14). However, glass fiber
anchors can only carry very small shear forces and the transfer of point loads into the
anchor at the anchor head is difficult to accomplish.
Figure 20.14 Drilling and cutting of temporary face anchors
Rock bolts can be drilled using a drilling vehicle such as a so-called “drilling jumbo”
(Fig. 20.15) or manually (Fig. 20.16). In NATM tunneling, rock bolts are usually in-
stalled as systematic anchoring with a grid spacing being determined on the basis of
stability analyses. Rock bolt lengths of 3 - 6 m are common. Using sleeve connections
anchor lengths up to about 18 m are feasible (Wittke et al. 2002).