The world’s longest submerged tunnel is already under construction in the Baltic Sea

An ambitious undersea road and rail tunnel is currently being built in Europe that will link Germany and Denmark. Called Fehmarnbelt tunnelspans an 18-kilometre stretch under the Baltic Sea, making it the longest underwater tunnel in the world. It is expected to open in 2029 and remain in operation for at least 120 years.

The Fehmarnbelt tunnel is being built by the business association Femern A/S, Rambøll, Arup and TEC, who are carrying out this work. submerged tunnelBut what is this exactly? Well, a tunnel built in another place and then sunk in the place where cars and trains will travel. The submerged term is important since there are longer underwater tunnels, such as the Channel Tunnel, for example, but it is still an extraordinary task.

Once completed, it will connect Rødbyhavn in Denmark with Fehmarn in Germany to create the shortest route between Scandinavia and the rest of Europe. It takes just seven minutes by train or 10 minutes by car to cross the Fehmarn Belt – instead of the current 45 minutes by ferry.

To put its size in perspective, construction of the tunnel will require 360,000 tons of rebar, which is equivalent to almost 50 times the weight of the metal structure of the Eiffel Tower. The construction zone on the Danish side is the size of 373 football fields. Up to 70 ships are involved in dredging the tunnel trench, also 18 km long. In total, about 12 million cubic meters of soil have been dredged from the seabed.

The submerged tunnel consists of 79 standard sections and 10 special sections. Each of the standard sections weighs around 73,000 tonnes and is 217 m long, 42 m wide and 10 m high. The smaller special sections are less than half the length, but are slightly wider and higher. The tunnel sections are built on land and then floated to their final position using a barge, before being submerged and sealed on the seabed at a depth of 40 metres.

Yes, it is a very expensive work. The budget for the Fehmarnbelt tunnel is around 8.4 billion Danish crowns (approximately 1.2 billion US dollars). King Frederick X of Denmark recently opened the first section of the tunnel during a special ceremony and it will be sunk in the coming weeks. In this video you can better understand the entire assembly process:

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