The tunnel is laid in a trench on the sea bed

The immersed tunnel will be laid securely just below the seabed, where the environmental impact is minimal.

The 89 elements that comprise the Fehmarnbelt tunnel will be built on land and towed out to sea, where they will be lowered down into an excavated trench in the seabed and assembled. The tunnel is subsequently covered with a layer of sand, gravel and stone, broadly aligned with the seabed.

An approximately 17.6 km long trench has to be dug at the bottom of the Fehmarnbelt and will be up to about 90 metres wide by 16 metres deep. The alignment of the tunnel trench runs from just east of Rødbyhavn to just east of Puttgarden on the German side. The tunnel elements will be lowered into the trench and assembled, hence the designation as an immersed tunnel. The trench is then refilled. 

The work will only have a temporary impact on the marine environment. In general, the excavation techniques are also selected in order to reduce sediment spill as much as possible. Among other things, this is to prevent the amount of light reaching the plants on the seabed being reduced. The trench will be excavated from both sides of the belt and is planned so that the effect on the surroundings and environment remains within an acceptable level. There are particularly strict requirements on how much material may be spilled during the excavation.

Once the tunnel is complete, a layer will cover it to make it flush with seabed.

The proposed alignment of the immersed tunnel route. Right: Lolland, left: Fehmarn.


Did you know that ...

... a 10 to 16 metre deep trench will have to be dug in the seabed along nearly 18 kilometres, with the consequent removal of 15 million cubic metres of material. This is nearly seven times greater than the volume of the Great Pyramid in Egypt.

The trench will be filled with stone, sand and gravel

  • The elements will rest on an up to one metre thick foundation of fist-sized stones and gravel that will to be laid on the floor of the trench.
  • A layer of coarse gravel helps to keep the tunnel elements in place.
  • Sand is laid on top of the gravel layer.
  • An approximately 1 metre thick layer of large and small stones is laid on the top of the gravel. The sand spreads gradually, so the seabed will be as it was before over most of the tunnel section.
  • The many tonnes of soil from the excavation will be used to build new coastal areas near Rødbyhavn and, to a lesser extent, near Puttgarden.
  • To reduce the risk of ship collisions during the construction phase, a VTS system (Vessel Traffic Service) will be set up to direct and inform shipping. This will significantly improve the safety of shipping in the Fehmarnbelt during the construction phase.