In 2011, an immersed tunnel was chosen as the preferred technical solution for the Fehmarnbelt fixed link. The 19 km long tunnel will comprise a four lane motorway and dual track railway. The owner is the Danish state and Femern A/S is the client.
In many ways, building the Fehmarnbelt fixed link will be a unique engineering achievement. The tunnel will be the longest of its type in the world and Denmark’s largest construction project. The tunnel will be located at depths of 30m to 40m under water and up to 3,000 people will work at the complex construction site.
Although the Fehmarnbelt tunnel will be constructed in line with the same principles as the 3.4 km Øresund tunnel, it will also embrace new and innovative initiatives. For example, the tunnel will be equipped with ten “basements”, which is the first time for such a concept to be used in tunnel construction.
Tunnel elements to be immersed on the seabed
The tunnel will comprise 89 tunnel elements and two portal buildings, connecting it with land in Denmark and German. 79 of the elements are 217m long, 42m wide and 9m high. The remaining 10 elements are so-called special elements with a special ”basement” for machinery. They are 39m long, 45m wide and 13m high.
The tunnel elements will be cast in concrete and steel on land. The elements will then be transported out to the Fehmarnbelt and immersed in an excavated trench in the seabed, where they will be joined together one by one and covered.
The tunnel will be about three times longer than the world’s longest immersed tunnel, which is an older rail tunnel under San Francisco Bay. It will also be five times as long as the immersed tunnel under Øresund.
The volume of material to be dredged from the seabed corresponds to the volume of seven Egyptian Cheops pyramids. And there will be room for 10 tennis courts on top of just one of the elements, which each weighs around 73,500 tonnes – around the same as 4,500 crowded buses.
At its deepest point, the road tunnel will be almost 39m below sea level. The dredged tunnel will be covered with a metre layer of stone, which, over time, will sand over. For most of the tunnel section, the stone layer will be flush with the sea bed.
3.2 million cubic metres of concrete and 360,000 tonnes of reinforced steel will be needed for the construction. One million cubic metres of concrete and 200,000 tonnes steel were used for the Øresund fixed link.
Read more on Fehmarnbelt’s website.