Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 280

Figure 10.56 Hydraulic parameters (Wittke 2000b)

The alternating sequence and the claystone belong to the Lias α formation of the Low-

er Jurassic. Below the layers of the Lias α the so-called “Knollenmergel”, also being a

claystone was encountered (Fig. 10.56).
For lowering the groundwater table due to tunnel driving it could not be ruled
out that the loss of uplift in the near-surface soils would lead to subsidence of the
ground surface in the area of the runway. In addition, shrinking of the organic
valley deposits due to loss of water might lead to settlements. The airport author-
ity therefore did not allow any groundwater lowering in the area of the runway as
a consequence of the tunnel driving.

In order to investigate to what extent the groundwater table is affected by the tunnel
excavation three-dimensional transient seepage flow analyses were carried out using the
FE-mesh represented in Fig. 10.54 (Wittke 2000b).
According to the exploration results, the permeability of the claystone is consider-
ably smaller than that of the alternating sequence. Although inhomogeneous with
regard to its permeability, the alternating sequence can be considered as homo-
geneous compared with the scale of the computation section. Thus, the different
permeability coefficients of the individual layers were converted in an anisotropic
equivalent permeability with the aid of formulas (6.46) and (6.47) presented in
Section 6.4.2 (Figs. 6.17 and 6.18). This resulted in permeability coefficients of