A record-breaking tunnel is being built under the Baltic Sea between Denmark and Germany, slashing travel times and improving Scandinavia’s links with the rest of Europe.
A record-breaking tunnel is being built under the Baltic Sea between Denmark and Germany, slashing travel times and improving Scandinavia’s links with the rest of Europe. The 18km-long Fehmarnbelt tunnel will be the world’s longest pre-fabricated road and rail tunnel, comprising five parallel tubes.
The Fehmarnbelt is a proposed undersea tunnel connecting Germany and Denmark, set to revolutionize transportation between Europe's largest markets.
Spanning approximately 18 kilometers, it will reduce travel time between Puttgarden, Germany, and Rødbyhavn, Denmark, from an hour by ferry to just 10 minutes.
The project aims to enhance economic integration, boost trade, and improve connectivity in the region.
With a projected cost of around €7 billion, the Fehmarnbelt tunnel is expected to become one of Europe's most significant infrastructure projects.
Engineering Marvel
Running for 18km, the Fehmarnbelt will see segments of the tunnel placed on top of the seafloor, and then joined together. The project’s main construction site is located at the northern entrance to the tunnel, on the coast of Lolland island in the south east of Denmark. The facility spans more than 500 hectares (1,235 acres), and includes a harbour and a factory that manufactures the tunnel sections, called ‘elements’.
‘It’s a huge facility here,’ says Henrik Vincentsen, chief executive of Femern, the state-owned Danish company building the tunnel. To make each 217m-long and 42m-wide element reinforced steel is cast with concrete.
Immersed Tunnel Technology
Most underwater tunnels burrow through bedrock beneath the seafloor. Instead, 90 individual elements will be linked up, piece by piece, like Lego bricks. The 18km long rail and road tunnel between Denmark and Germany will comprise five parallel tubes, each weighing over 73,000 tonnes.
Immersed tunnel technology involves building tunnels underwater using a prefabricated structure, often in the form of a steel or concrete tube.
This method allows for faster and more efficient construction compared to traditional tunnel-building methods.
The immersed tube is designed to float on water during transport and then sunk into place using ballast.
Once settled, the tube is sealed and connected to other sections to form a continuous tunnel.
Immersed tunnels have been used in various projects worldwide, including the Channel Tunnel between England and France.
‘We are breaking records with this project,’ says Mr Vincentsen. ‘Immersed tunnels have been built before, but never on this scale.’
Construction Process
The construction process is complex and painstakingly precise. The elements are lowered into a trench dug out on the seafloor, using underwater cameras and GPS-guided equipment, to line it up with 15mm precision.
‘We have to be very, very careful,’ emphasises Anders Gert Wede, senior construction manager at Femern. ‘We use a system called ‘pin and catch’ where you have a V-shaped structure and some arms grabbing onto the element, dragging it slowly into place.’
Environmental Concerns
Denmark and Germany signed an agreement to build the tunnel back in 2008, but the scheme was delayed by opposition from ferry operators and German conservation groups concerned about the ecological impact. However, their legal challenge was dismissed by a federal court in Germany, green-lighting construction to go ahead.
‘We have done a lot of initiatives to make sure that the impact of this project is as small as possible,’ says Mr Vincentsen, pointing to a 300-hectare wetland nature and recreational area planned on reclaimed land, which has been built from the dredged up sand and rock.
