Several years of preparatory work were required prior to the construction of the Fehmarnbelt tunnel. The preparatory work included the most comprehensive EIA survey in Danish history. Marine and land flora and fauna were extensively mapped in order to minimise the impact on the environment. The subsoil in the Fehmarnbelt was analysed through hundreds of drilling samples to ensure a completely accurate understanding of its properties and composition.
Over the same period, a range of potential technical solutions for the link were studied in depth. Bridges and both immersed and bored tunnels were assessed on price, risk, environmental impacts and a range of other criteria.
An immersed tunnel was the optimal solution
In 2011, it was decided that the Fehmarnbelt link should be built as an 18 km immersed tunnel. The reasons for this included the good experiences from the immersed tunnel on the Øresund link, and because this type of tunnel has a number of advantages over a bridge.
Unlike a bridge, a tunnel is not affected by wind and weather, and it does not adversely impact the surrounding environment when completed. A bored tunnel would have proved to be a very expensive and risky solution since the seabed is not suitable for drilling. In terms of finance, environmental considerations and risk, the immersed tunnel was therefore the optimal solution.
Contractors are responsible for design
The Fehmarnbelt tunnel is being constructed on the basis of a design philosophy called "design and build". As the client, Femern A/S set overall requirements, including the size of the tunnel, where it should be located and what it should be able to do. It was then up to the bidding contractors to tender on both price and a detailed technical solution.
The desired outcome of this approach is that the companies that design the tunnel would ultimately construct and then operate it for the first few years after opening – thus ensuring smooth and phased transitions from design to construction and finally to operation.