Groundbreaking tunnelling for fast connections

The "Stuttgart - Ulm rail project" is located on the European east-west main line from Paris to Budapest and is divided into the two major projects "S21 – reorganization of the Stuttgart rail hub", with the construction of the new, lowered main station, and the "New Wendlingen–Ulm line". The conversion of the main station into a through station and its connection to the European high-speed network will significantly reduce journey times on regional and long-distance mainline services.

Several tunnels have been built along the new line using Herrenknecht tunnelling technology. Over a distance of nearly 50 kilometers, a total of four tunnel boring machines dug their way through the underground for the Filder Tunnel, Bossler Tunnel and Albvorland Tunnel projects on the planned new train line. As a result of the railway project, journey times between Stuttgart and Ulm will be almost halved in future. Around ten million passengers a year will benefit from the project.

Challenging geology

This was because of the varying layers of rock: the machine had to penetrate sandstone with marls and clays and nodular marl as well as unleached gypsum keuper. Thanks to its convertibility, the Multi-Mode TBM passed through the different geological formations with maximum safety.

Along the tunnel alignment, the machine overcame a height difference of 155 meters in total with a gradient or incline of up to 2.5 percent. Only in the geological transition zone on about half of the route was the machine not used. There miners removed the material from the rock using diggers and loosening blasting. Due to these complex project requirements, initially no mechanized tunnelling was planned for the Filder Tunnel. However, the particularly flexible and convertible Multi-Mode TBM machine type from Herrenknecht convinced the client to use mechanized tunnelling on a large part of the tunnel section.

After the traditional christening of the machine in July 2014 with the name SUSE (German acronym for "Stuttgart-Ulm reached faster"), in November 2014 the drive toward the main station began. After a good 4 kilometers of tunnelling to the beginning of the geological transition zone, in November 2015 the TBM successfully completed the first construction phase in the eastern tube. While the tunnelling work was in progress, the complex logistics were handled via the launch portal. This solution saved the city of Stuttgart thousands of truck journeys in the valley basin with dust and noise pollution. The machine was then disassembled in the tunnel. It was made ready for the second of a total of four drives in the parallel western tube leading back toward the main station.

Millimeter precision: underground TBM disassembly

Fast, safe completion of the complex construction process, including disassembling the TBM inside the bored tunnel, called for close cooperation between all project participants as well as individual detailed solutions right from the start. With a shield diameter of 10.82 meters and an inner diameter of the tunnel of 9.6 meters, disassembly and transport back to the launch portal was only possible in the given time frame because all mechanical and logistical requirements were precisely planned in advance and then implemented on the jobsite. The Herrenknecht teams were already involved early in the planning phase.

In June 2016 the Multi-Mode TBM then began tackling the second tunnelling section from the Filder portal toward the main station. A year later, in July 2017, it reached the geological transition zone in the western tube, through which it was then pulled. From November 2017 to July 2018, SUSE successfully completed the third drive for the Filder Tunnel and reached the cavern where it was turned 180° for the final drive in the eastern tube back toward the Filder.

Bossler Tunnel

With overburdens of up to 250 meters, a Herrenknecht EPB Shield (Ø 11.34 meters) was used to build the 8.8 kilometer long twin-tube Bossler Tunnel under the Swabian Alb in the direction of Ulm. It is the railway tunnel with the largest diameter ever excavated by machine in Germany and is due to go into operation in 2022.

From Ulm to Stuttgart in no time

In November 2014, TBM "Käthchen" was christened at the launch portal near Aichelberg and in April 2015 the giant worm set off. In June 2015 already, the thousandth meter of tunnel was bored and lined with segments produced in moulds from Herrenknecht Formwork in a purpose-built factory close to the Aichelberg tunnel portal. A total of 60,000 segments were installed in the Bossler Tunnel.

Tunnelling progressed so quickly and safely that the decision was made to use the TBM to excavate further sections that were originally to be built conventionally. In early November 2016 already, the proud miners celebrated their final breakthrough after 8.8 kilometers in the eastern tube. In mid-April 2017, "Käthchen" began driving the western tube, successfully completing it in early June 2018 after weekly top performances of up to 214 meters of tunnelling per week. In total, the Herrenknecht TBM drove almost 7.8 kilometers in the first tube as well as 8.8 kilometers in the second tube – that is almost the entire tunnel.

Albvorland Tunnel

The approximately 8 kilometer long Albvorland Tunnel is the third tunnel structure on the new line between Stuttgart and Ulm for which Herrenknecht supplied mechanized tunnelling technology. Here the contractor used two tunnel boring machines in parallel, each driving – from east to west – 7.5 and just under 8 kilometers of single-track tunnel tubes respectively. The tunnelling experience gained from the neighboring lots of the Filder and Bossler helped, among other things, to optimize the design of the cutting wheels for the Albvorland Tunnel machines. Furthermore, the peculiarities of the assembly and start-up situation at the Albvorland Tunnel had to be taken into account when designing the shield and the back-up.

After both machines, designed as EPB Shields (Ø 10,820 mm), successfully passed acceptance by the customer at the Schwanau plant in March 2017, a crew of 20 specialized Herrenknecht experts carried out the assembly at the eastern portal near Kirchheim unter Teck. In doing so they followed a sophisticated plan, according to which assemblies were gradually assembled in the site equipment area and lowered into the narrow launch shaft.

In October 2017 an official ceremony signaled the start of construction. With peak performances of up to 200 meters per week, from January 2018 to early August 2019 the Herrenknecht EPB Shield Sibylle (named after the legendary figure Sibylle von der Teck), excavated 7.6 kilometers of the northern tube of the Albvorland Tunnel. WANDA covered the 8 kilometers in the parallel southern tube between November 2017 and the breakthrough in October 2019 at up to 186 meters per week. For the Herrenknecht tunnel boring quartet, this final breakthrough marked the end of their work for the key Filder, Albvorland and Bossler tunnels.

Stuttgart – Ulm railway project