Transport & Immersion

Towing of tunnel elements
Each tunnel element will be towed from the production site to a holding area near the tunnel trench in the Fehmarnbelt by four tugboats. Before towing, the elements will be fitted with ballast tanks. At the holding area, they are hooked up with the immersion pontoons.

A tunnel element is towed into position by tugboats. Photo from the construction of the Øresund tunnel.

Immersing the tunnel elements and closing the trench
When a tunnel element is ready for immersion, the ballast tanks are filled with water. The tunnel element slowly sinks and will be positioned as required. The elements will be immersed from both sides – Germany and Denmark, just as the trench is dredged from both sides.

Once a tunnel element has been positioned on the foundation bed, it is connected to the previous one by means of rubber seals (Gina gasket) and the water pressure acting on the seaward end of the element. The trench is backfilled and covered with a protective layer. The fill along both sides of the tunnel element is a combination of gravel as a retaining measure (locking fill) and general sand fill. The gravel is designed to keep the tunnel element in the trench and prevent any movement occurring during the backfilling with sand. The cover layer, which is about 1.2 metres thick, will protect the immersed tunnel from damage caused by ships running aground or dragging anchors. The backfill and cover layers will not extend above the existing level of the sea bed, except for the very nearshore areas.

 
The immersed tunnel inside trench dredged into the sea bed and covered with a protective layer of rock, gravel and sand.