The first tunnel segment of the Fehmarn Belt Tunnel has been successfully immersed. This marks an important milestone in the European mega-project connecting continental Europe and Scandinavia.

With a length of 18 kilometres, the Fehmarnbelt Tunnel is set to be the longest immersed tunnel in the world – over three times as long as the current frontrunner the 5.8-kilometre Transbay Tube in San Francisco.The immersion of the first tunnel element on the Danish side of the Fehmarnbelt Tunnel is an enormous operation that has been prepared in detail and requires extensive expert knowledge.   

Engineers from several European countries are working closely together through the RAT Joint Venture of technical consultants, bringing together the complementary expertise of Ramboll, Arup and TEC. The RAT Joint Venture has been working with the client Sund & Bælt since 2008, providing expert advice in a range of technical disciplines. 

The 18-kilometre-long Fehmarnbelt Tunnel provides commuters with a much faster and weather-independent journey. The tunnel is designed as a highway and a double railway, making the switch from freight lorries to environmentally–friendly trains much more attractive. 

The Fehmarnbelt Tunnel will complete the high-speed rail connection between Stockholm and Hamburg. 

There are three important civil engineering contracts for the Fehmarnbelt Tunnel, each to be considered a separate project.

The TPR contract (Tunnel Portal and Ramps) focuses on the tunnel entrances and approach structures. It includes the cut‑and‑cover sections, the portal buildings, and the access ramps, forming the crucial transition between land and water in the polder area.  

The TDR contract (Tunnel Dredging and Reclamation) covers the preparation of the site. This included dredging the tunnel trench—now completed—as well as creating land reclamations, building temporary working ports, and rerouting the sea dike to make construction possible.  

The TUX contract (Tunnel) involves the immersed tunnel itself. Tunnel elements are constructed in factories on land by contractor Femern Link Contractors (FLC), then transported via basins to the working port. From there, the elements are towed to their final position and carefully lowered into the prepared trench.  

The numbers 

• 18-kilometre tunnel
• 79 Standard Tunnel Elements
• 10 Special Tunnel Elements
• Each Standard Tunnel Element is 217 meters long and the Special Tunnel Elements are 39 meters long
• A total of 90 (79+10+1) immersion operations will be carried out: 79 Standard Tunnel Elements, 10 Special Tunnel Elements, and 1 closing joint
• The deepest point of the trench is 45 meters below sea level
• The deepest point of the track is about 40 meters below sea level
• 2 x 2-lane highway there and back and 2 x 1 railway line there and back
• One Standard Tunnel Element contains 33,000 m3 of concrete
• One Standard Tunnel Element displaces 75,000 tons of seawater when it is set in place