Saint-Louis: Two tunnels, zero disruption to rail traffic

Full timetable, underground construction

The location was highly sensitive: an international railway line between France and Switzerland. Shutting it down was not an option. Instead, a tight phasing plan was developed in which three of the four tracks were temporarily taken out of service, while the fourth remained operational.

The tunnel was built in two sections, with an intermediate phase to switch the tracks. This way, rail traffic kept moving above ground, while construction continued beneath it.

Two tunnels, seamless connection

The first tunnel weighed 1,760 tons and was slid 33 meters into position. The second, slightly lighter at 1,100 tons, had to be moved 39 meters.

The sliding itself was carried out on a specially prepared system of steel tracks (SB300) with load distribution on Azobé planks. Each tunnel had its own computer-controlled jacking groups to ensure precise and controlled movement.

The biggest challenge? Making sure the two tunnel sections connected perfectly. A job of millimeters. For this project, we developed a special method to allow the second tunnel to be shifted sideways by 5 centimeters. That margin turned out to be exactly what was needed for a seamless fit.

Fast where possible, slow where necessary

Most of the sliding was carried out at a speed of 26 meters per hour — a solid pace. But during the final connection phase, we deliberately slowed down. Where precision is key, control outweighs speed. In the end, the two tunnel sections fit together perfectly — without delay and without damage.

What this project demonstrates

For Civiele Technieken deBoer, this project was a textbook example of working at the very edge of what is possible: time constraints, complex phasing, and zero tolerance for error. We combine heavy equipment with smart engineering and precise execution. Not to make headlines, but to ensure the work goes unnoticed — while the trains above keep running as if nothing happened.