The Autobahn GmbH’s Southwest branch is undertaking a major structural and operational renovation of the Engelberg Tunnel on the A81 motorway near Leonberg in Baden-Württemberg, Germany. This busy transport artery — carrying around 120,000 vehicles per day — is being strengthened using cutting-edge robotic drilling solutions, demonstrating a new frontier in tunnel construction automation.
The Engelberg Tunnel comprises two 2,530-metre twin tubes on one of southern Germany’s most critical motorway links, each accommodating three traffic lanes plus a hard shoulder. Originally constructed from 1995 to 1999 as a replacement for an older 1938 structure, the tunnel has over time suffered deformation due to swelling anhydrite rock in the surrounding geology. This type of rock expands significantly upon contact with moisture, exerting pressure on the tunnel lining and creating structural risks. Roughly 180 m of the west tube and 170 m of the east tube exhibit damage attributable to these geological forces.
Repair works began in April 2019 and are scheduled to continue through 2026, with all lanes maintained during construction via a carefully managed traffic plan. Closures are limited to periods of low traffic volumes to minimise disruption.
Advanced Structural Reinforcement Strategy
To address the deformation issues, engineers are implementing a suite of reinforcement measures:
- Installation of a reinforced concrete facing shell supported by steel girders to enhance vault stability.
- Addition of an intermediate ceiling to improve load distribution.
- Reinforcement of the existing roadway slab to function as a transverse stiffener.
- Complete renewal of all safety and operating technology systems along the tunnel.
These measures together will ensure the long-term functionality of the tunnel as a vital transport corridor.
A core innovation in this project has been the deployment of three fischer BauBot construction robots on behalf of the tunnelling contractor Baresel. These high-precision, robot-assisted drilling systems have dramatically increased efficiency and safety in preparing anchor points for anchors and fasteners in reinforced concrete.
Across the course of the project:
- The BauBots fully automatically drilled over 9,000 holes in the concrete lining.
- Each hole measured 20 mm in diameter and 240 mm deep, positioned at heights up to 7.5 m above the tunnel floor.
- Integrated dust extraction systems maintained a clean and healthy working environment compliant with safety standards.
Robotic operation replaced work that traditionally involved larger human crews, reducing manual drilling risks such as vibration and airborne dust exposure, while
The robotic drilling process was supported by a digital construction plan specifying exact drilling locations and parameters. BauBot Services GmbH coordinated the planning, execution, and automatic documentation of each borehole, capturing important metrics such as depth and reinforcement hits without the need for manual logs. Backup robots, end effectors, and trained operators were available to eliminate downtime.
According to Emil Kral, Managing Director of BauBot Services GmbH, the use of these construction robots “significantly increased efficiency and improved quality” during the tunnel renovation — underscoring the value of automation in large-scale infrastructure works.
As the Engelberg Tunnel upgrade progresses toward completion in 2026, this project serves as a pioneering example of how advanced robotics and digital workflows are reshaping tunnel repair and reinforcement — improving productivity, worker safety, and structural outcomes across heavy civil engineering projects.
