NATM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 621

Thus, the conventional tunneling method is characterized by a high degree of flexibility
with regard to alternating rock mass conditions and groundwater conditions and chang-
ing shapes of cross-sections. It normally enables a change of excavation class, that is, a
modified method of excavation and support, and a change of cross-section as well as an
adjustment of the type and amount of support at short notice and without problems.
Figure 20.3 Sidewall adit heading
20.2.2 Construction of the Shotcrete Membrane
Figure 20.4 shows the components of a reinforced shotcrete membrane. It normally
comprises one or more layers of shotcrete, an outer and an inner reinforcement consist-
ing of steel fabric mats, and steel sets with specified spacing.
Figure 20.4 Components of the reinforced shotcrete membrane
Before the shotcrete is applied, loose rock must be removed from the excavation surface.
The surface of application must be carefully cleaned with compressed air in order to
achieve the best possible adhesion of the shotcrete (Wittke et al. 2002).