Our infrastructure specialists are involved in the Femern Tunnel project, which will run under the Baltic Sea for 18 km. We are supervising the design of the temporary factory that will produce the 200 m and 17,000-ton caissons.

Key information

Project name: Femern Underwater Tunnel in the Baltic Sea

Date: 2020-2021

Client: Femern Link Contractors

Size: 18km under the Baltic Sea

Location: Denmark, Germany

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François RIQUET

Business Development Manager, Europe

Business Development Manager, Europe



Operational Director of SOCOTEC Civil Engineering

Operational Director of SOCOTEC Civil Engineering


Project details

The Femern tunnel will link Germany and Denmark by passing under the Baltic Sea. The aim is to open up Copenhagen, making the journey from Hamburg much more direct (2.5 hours by car instead of 4.5 hours). This 18 km immersed tunnel will be both road, with 2x2 lanes for vehicles, and rail, with 2 train tracks.

This exceptional structure, which will be the longest in its category, is being carried out by the FLC (Femern Link Contractors) consortium. At its peak, the site will employ no less than 2,000 workers.

The tunnel will consist of 89 concrete caissons, each 200 m long. These 73,000-ton caissons are prefabricated in a specially built factory at the entrance to the future tunnel. They are immersed in a trench before being transported by ship to their assembly site 40 metres under the sea!

Production of the caissons is scheduled to begin in 2023, with delivery scheduled for 2029.

Description of the missions entrusted

In this first phase of the project, our teams are involved in preparing the construction of the purpose built temporary caisson factory. The factory itself is a gigantic building, very long in order to produce the caissons. To immerse the caissons before transporting them, each unit of the factory must be able to be flooded thanks to a complex system of locks.

  • Independent design checking of the works, category 3 inspections, the most complex requiring a high level of expertise
  • Verification of all studies on all technical aspects of the design carried out by the design office
  • Counter-calculations
  • Modelling when necessary

Photos Credit: Femern A/S.

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