Autobahn GmbH's Southwest branch is currently carrying out extensive structural and operational upgrades to the Engelberg Tunnel in Leonberg, located in the southwest German state of Baden-Württemberg. Three fischer BauBots were used for this project. The construction robots fully automatically drilled more than 9,000 holes — each with a diameter of 20 mm and a depth of 240 mm — at heights of up to 7.5 m. This improved efficiency and precision during fastening tasks.

The Engelberg Tunnel is part of the important A81 federal highway and runs beneath the eponymous Engelberg mountain, north of the Leonberg interchange. With around 120,000 vehicles passing through every day, it is one of the busiest highway tunnels in southern Germany. The two tunnel tubes are each 2,530 m long and feature three lanes plus a hard shoulder in the westbound tube towards Karlsruhe/Munich and three lanes plus a hard shoulder in the eastbound tube towards Heilbronn. The current tunnel was originally built between 1995 and 1999 as a replacement for the old Engelberg Tunnel, which dated back to 1938.

Over the years, pressure from the surrounding rock has caused damage to approximately 180 m of the westbound tunnel and about 170 m of the eastbound tunnel. Geological challenges include anhydrite rock, which swells when it comes into contact with moisture, deforming the tunnel walls and endangering the structure. The complex upgrade is being carried out while traffic continues to flow, with all lanes remaining open, and therefore in a very confined space — made possible by a sophisticated construction site traffic management plan. Closures occur only during periods of low traffic volume. The construction work also involves the complete renewal of the operating technology, while still maintaining 100 percent safety. The all-round renovation began in April 2019 and is scheduled for completion in 2026. The client is the Federal Republic of Germany, represented by Autobahn GmbH’s Southwest Branch.

The measures to reinforce the tunnel lining in the sections damaged by anhydrite include the installation of a reinforced concrete facing shell with steel girders for static to brace the vaults, as well as the installation of a suspended ceiling. In addition, the road deck, which serves as transverse bracing, is being reinforced. At the same time, the safety and operating technology systems are renewed along the entire length of the tunnel.

Innovative construction robotics from fischer in action
On behalf of the renowned tunnel construction company Baresel, the project stakeholders used three fischer BauBot construction robots. The robot-assisted, high-precision drilling technology enabled fast, safe, and accurate preparation of anchorage points — particularly in high-to-reach areas of the tunnel vault. The BauBots automatically drilled more than 9,000 hammer-drilled holes in concrete, each with a diameter of 20 mm and a drilling depth of 240 mm, at heights of up to 7.5 m.

BauBot Services GmbH — the central point of contact for all aspects of planning and implementing fischer robotics applications on construction sites — coordinated and supervised the use of the construction robots, from planning and execution to documentation.

fischer's services ranged from creating the digital construction plan, which specified the exact drilling points for the BauBots, to supporting on-site execution by operators, and right through to successful completion. The robots' integrated dust extraction system ensured a clean and healthy working environment, as well as approval-compliant installation of fasteners in the cleaned boreholes. Drills and consumables were included in the service package. To minimize downtime, additional robots, end effectors, and operators were also available as replacements. Each borehole was automatically documented with relevant process parameters such as borehole depth, reinforcement encounters, and other important data — eliminating the need for manual logs.

“The use of our three fischer BauBots significantly increased efficiency and improving quality during the renovation of the Engelberg Tunnel,” emphasizes Emil Kral, Managing Director of BauBot Services GmbH. “This project highlights the enormous potential of modern automation solutions in infrastructure construction.”

The comprehensive structural upgrade and technical modernization of the Engelberg Tunnel ensures the long-term functionality of a key traffic axis. The combination of well-thought-out planning, expert execution, and innovative technology — such as the use of the three fischer BauBots — makes this project a pioneering example in the field of tunnel construction and renovation.