NATM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 660

Figure 20.45 Comparison of measured and calculated displacements and tangential
stresses in the shotcrete membrane (Wittke et al. 2003)

Figure 20.45 shows a comparison of measured and computed displacements at the
tunnel contour, and tangential stresses in the shotcrete membrane. Herein, the mean
values of displacements measured at different cross-sections are taken as measured
displacements (Fig. 20.45, left). Around the circumference of the shotcrete membrane
differing tangential stresses were measured. The very low stresses measured at the invert
(Fig. 20.45, right) are not considered representative. In the other areas, measured tan-
gential stresses agree reasonably with the analysis results.

20.3.8 Conclusions
During tunneling underneath the Stuttgart airport a lowering of the groundwater table
and thus larger subsidence in the area of the airfield could be avoided. It was also possi-
ble to design the shotcrete membrane against full water pressure and for high horizontal
in-situ stresses acting in the Lias α formation in which the tunnel was excavated.

This could be accomplished by the following measures:
- full-face excavation with a stepped temporary face and an early closing of the sup-

porting ring,

- construction of a low permeable shotcrete membrane with high strength,