Three major key structures of the rail project were built in difficult Swabian ground conditions in Baden with the final act the completion of the Albvorland Tunnel in late October 2019 by the tunnel boring machine (TBM) S-1024 (EPB Shield, diameter 10,820mm), which bore the name of Wanda (the German acronym for Wendlingen on the Neckar through the Alb foothills).

This was the fourth and last successful project completion by the Herrenknecht tunnel boring quartet for the key structures Filder, Albvorland and Bossler tunnels. The machines bored a total of almost 50km of modern and efficient tunnel infrastructure with precision and speed. The TBM mastered their underground mission under the guidance of the experienced tunnelling experts and engineers of the three construction consortia and the overall direction of client Deutsche Bahn.

The Stuttgart-Ulm rail project is located on the European east-west mainline from Paris to Bratislava and is divided into two major projects, Stuttgart 21, with the construction of the new main train station and the reorganization of the Stuttgart rail hub, as well as the new Wendlingen-Ulm line. With the construction of the main station as a through station and the connection to the European high-speed network, the travel times in regional and mainline services will be shortened significantly.

The twin-tube Filder Tunnel measures 9.5km, making it the longest tunnel structure between Stuttgart and Ulm. Herrenknecht supplied a high-tech convertible Multi-Mode TBM type (diameter 10,820mm) for the Filder Tunnel. In the fall of 2014, TBM Suse (the German acronym for Stuttgart-Ulm reached faster) began excavating the tunnel from the Filder Plain down towards the Stuttgart main station.

In the upper section of the Filder Tunnel, Suse worked in closed mode with screw conveyor muck removal, in the lower Filder Tunnel in open mode with belt conveyor discharge. With this convertibility of the TBM, designed and implemented by Herrenknecht engineers, the tunnelling crews mastered the different geological formations along the tunnel alignment with maximum safety.

For precise tunnelling control, the miners of the contracting joint venture Arge Atcost 21 relied on a navigation system from the Herrenknecht Group Brands company VMT GmbH based in Bruchsal.

The large-scale project between Stuttgart city centre and the Filder Plain was divided into four TBM tunnelling sections: eastern and western tubes, each with Upper and Lower Filder Tunnel. Sophisticated overall logistical planning, a multitude of individual detailed solutions and partnerships between the project players laid the foundations for success. The Herrenknecht teams were involved early on in the planning phase and later during implementation - for example when disassembling or converting a TBM. Herrenknecht's expertise from a large number of pioneering large-scale projects over the past four decades made a significant contribution to the rapid and safe progress of the project.

Richard Lutz, CEO of Deutsche Bahn AG, said on the occasion of Suse's final breakthrough in September 2019: "As a hinge between valley basin, airport and new line, the Filder Tunnel is an essential part of the project. I thank all the miners and engineers for their work on the tunnel. Construction and engineering skill have done extraordinary things here."

For the Albvorland Tunnel between Kirchheim unter Teck and Wendlingen am Neckar with two EPB shields, the Herrenknecht specialists, together with the contractor crew, met the first challenges even before the huge cutting wheel began to turn.

In order to keep to the schedule for the Albvorland Tunnel, Implenia Construction GmbH ordered two identical machines from Herrenknecht - one for each of the two tubes. The schedule for jobsite assembly stipulated that both machines should be assembled in the narrow launch shaft at the same time. With a diameter of 10.82m and only a few metres between the machines, this was an extremely tricky job. A crew of 20 specialised Herrenknecht experts assembled both TBM at the tunnel's eastern portal near Kirchheim unter Teck.

With peak performances of up to 200m per week, from January 2018 to early August 2019 the Herrenknecht EPB Shield Sibylle (named after Sibylle von der Teck), excavated 7.6km of the northern tube of the Albvorland Tunnel. Wanda covered the 8km in the parallel southern tube between November 2017 and the breakthrough in October 2019 at up to 186m per week.

The 8.8km long twin-tube Bossler Tunnel is the third tunnel structure on the new line between Stuttgart and Ulm for which Herrenknecht supplied mechanised tunnelling technology, alongside the Filder Tunnel and the Albvorland Tunnel.

At the launch portal near Aichelberg, the TBM (the 11,340mm diameter Käthchen) began tunnelling in April 2015. The miners continuously raised the daily advance rates and after just two months, the 1,000m mark was passed.

Tunnelling progressed so quickly and safely that the decision was made to use the TBM to excavate further sections of the tunnel that were originally to be built conventionally rather than with precast concrete parts for the tunnel lining produced by Herrenknecht Formwork.

In early November 2016 after 8.8km the miners of the contracting joint venture Arge Ata Tunnel Albaufstieg celebrated the breakthrough in the first, eastern tube. In mid-April 2017, Käthchen took on the second, western tube, which she had already successfully driven by early June 2018 after best performances of up to 214m of tunnel construction per week.

In late July 2018, coming from the Filder Plain in the western tube, shortly before the new underground Stuttgart main station TBM Suse had reached an underground cavern. Here the 120m long TBM had to be turned 180 degrees for the subsequent excavation of the eastern tube of the lower Filder Tunnel. Oliver Boiger, head of Field Service at Herrenknecht, and his team first placed the 1,400t shield machine with the cutting wheel on a kind of sled on cushions filled with nitrogen. Using steel plates laid out in the cavern, they manoeuvred the shield around the tight bend, at the same time with exact precision in the smallest of spaces and without losing any time.

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