Civil Engineering Reference
In-Depth Information
8
Case studies
This chapter focuses on three different case studies. Each case study
describes distinctive aspects of the tunnelling works and how some of the
information described in previous chapters is applied in practice.
8.1 Eggetunnel, Germany
Unexpected invert failures of sprayed concrete linings are not unusual,
despite a rigorous monitoring regime within the observational method. This
case study gives an example of an invert failure, explains the failure
mechanism and how to detect an invert failure by means of monitoring.
8.1.1 Project overview
The railroad line connecting Kassel and Paderborn, Germany, of which the
Eggetunnel is a part, has been upgraded to allow higher speeds and to
increase the route capacity. The Eggetunnel crosses the so called Egge
Mountains between the towns of Willebadessen and Neuenheerse, both
located in the federal state of North-Rhine-Westphalia. The tunnel became
necessary because the existing railroad was affected by landslides which
caused damage and delays. It was found to be safer, more efficient and less
costly to build a tunnel right through the mountains rather than to stabilize
the unstable slopes. The two-track railroad tunnel, length 2880 m and width
14.5 m, was constructed between 1998 and 2000, and was opened in 2003.
Construction commenced from both ends of the tunnel. From the
northern portal, where hard rock formations were dominant (sand and
limestone), the excavation was achieved using drill and blast, and from the
south portal, where soft rock (clay) was present, excavator and side wall
drifts were used. Temporary support was provided by a sprayed concrete
lining, lattice girders and wire mesh reinforcement throughout the tunnel.
Some parts of the sprayed concrete-supported invert of the soft rock
section experienced heavy cracking and failure, and despite a rigorous
displacement monitoring regime this remained undiscovered for a long time
and created some critical situations when finally detected.
