NATM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 650

permeable alternating sequence (Fig. 20.26), advanced grouting for sealing of the rock
mass was foreseen and carried out (Section 20.3.6).
Figure 20.33 Construction lots 72 and 92, plan with drawdown cone (Wittke et al. 2006)
In the early stages of the project, three-dimensional, transient seepage flow analyses were
conducted by WBI to investigate the influence of the tunnel heading on the groundwater
conditions for tunnel sections located mainly in claystone underneath the runway. These
analyses and their results were presented in Section 10.6.3. Accordingly, the permeability
of the shotcrete membrane is one of the decisive factors for the lowering of the groundwa-
ter table. The shotcrete support thus had to be constructed with a low water permeability
and also designed to withstand the water pressure (Wittke-Gattermann & Wittke 1997,
Wittke 2000, Tegelkamp et al. 2000, Wittke et al. 2002). As a consequence, a statically
favorable circular profile was selected for the tunnel's cross-section (Fig. 20.27).
An advancing vault excavation was not a reasonable option under the given conditions be-
cause on the one hand an open invert over great lengths could not be permitted since this
would lead to groundwater lowering, and on the other hand, a watertight support of the