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Dual-mode TBM faces Stuttgart-21 challenge 15 July 2014

Peter Kenyon, TunnelTalk

Following 13 years in the planning, and three years after contract award to a consortium led by Porr of Austria, €750 million TBM excavation of the 9.5km Filderstadt Tunnel commences.

The 10.82m diameter multi mode Herrenknecht machine will excavate the longest and most challenging of the tunnels that comprise the Stuttgart-21 high speed rail project in Germany. The Filderstadt Tunnel takes the new high speed line out of the new Stuttgart Central Station to a portal adjacent to the A8 highway to the south of the city, from where it continues in a mixture of at grade and underground alignments to the towns of Ulm and then Wendlingen.

10.82m Herrenknecht dual mode TBM
10.82m Herrenknecht dual mode TBM
Complex mixed geology
Complex mixed geology

The complex mixed geology of the Filderstadt alignment called for procurement of a dual mode machine capable of working in closed mode with a screw conveyor for the upper section of the tunnel – where the machine is launched – and open mode with a belt conveyor in the lower section of the drive into Stuttgart itself.

9.5km Filderstadt Tunnel alignment
9.5km Filderstadt Tunnel alignment

For the geological transition zone in the central section of the drive excavation will be by conventional means using drill+blast. The TBM will overcome an altitude differential of 155m at an incline of up to 2.5%, under cover of up to 223m. Following completion of the 4,035m-long upper drive by mechanized means, a 1,150m section will be excavated by drill+blast, which will then enable TBM excavation of the 3,630m drive through the lower section into Stuttgart Central Station.

The TBM will be turned around for the parallel drive after it breaks through in Stuttgart. Contract scope also comprises excavation of an access adit near the geological transition zone, as well as emergency cross passages every 500m. Geology along the alignment is sandstone with marls and clays and nodular marl in the upper section, with unleached gypsum keuper in the lower section.

In addition to the Filderstadt tunnels, Porr holds a €635 million contract (PFA2.2) to excavate 6.3km of the twin running 8.8km Bossler Tunnel using an 11.34m diameter Herrenknecht EPBM, as well as the twin running 4.5km Steinbuhl Tunnel by conventional means (both on the Wendlingen-Ulm section). TunnelTalk was able to take exclusive pictures of that machine in the Herrenknecht factory in Germany prior to its official handover a few days later to project owner Deutsche Bahn.

The €6 billion Stuttgart-21 project comprises a 57km stretch of new high speed rail line around the German city of Stuttgart, which links with a new 60km stretch linking the towns of Wendlingen and Ulm. Almost half of the 117km of high speed line is in 21 twin running tunnels of 500m or more. The improvements will see journey times between Stuttgart and Ulm cut from 54 to 28 minutes, and will also reduce longer-distance national and trans-European journeys on both east-west and north-south routes.

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