The Wehrhahn Line, a 300 mill. euro project is intended to relieve traffic in the centre of Düsseldorf considerably once it is opened in 2015. The 3.4 km long Underground line will replace a number of tram lines on the surface. Towards this end roughly 2.3 km of tunnel tubes with 8.30 m internal diameter are to be bored by mechanised means for 2 directional tracks –one after the other in 2 single drives (1,290/955 m) using the same 65 m long and roughly 1,300 t heavy TBM with bentonite-supported face, a mix-shield with 9.49 m diameter (S-491 from the Herrenknecht AG).
The first section of tunnel embraces the bore from the Bilk access shaft to the target shaft at the Benrather Straße Underground Station and largely runs beneath the urban area. The TBM was able to break through in late-September 2010 in less than 7 months – a month ahead of schedule. The shield was then dismantled and returned to the access shaft at the Corneliusplatz and reassembled there to drive the second tunnel section. The TBM backup was pulled back through the bored tunnel to the Bilk access shaft, dismantled and also transported to the access shaft at Corneliusplatz. Starting from that point the second tunnel section will be produced with the TBM heading to the target shaft Am Wehrhahn, which partially runs beneath existing buildings and partially under the road grid.
The tunnel is to be lined with reinforced concrete segments (45 cm) in 1.5 m wide rings (7+1/ring) with conic keystone, cam and groove couplings and external sealing strip. The method selected to construct the tunnel sections as well as the underground stations contributes towards ensuring that traffic is hampered as little as possible during the construction phase. ⇥G. B.