Promoter Femern has decided to resurrect the possibility of a bored tunnel for its Fehmarnbelt road and rail crossing between Denmark and Germany following a public consultation.
A technical report into four possible solutions — a cable-stayed bridge, a suspension bridge, immersed tunnel or bored tunnel — for the planned Fehmarnbelt fixed link between Denmark and Germany was published today, which reveals designs for a bored tunnel that was previously considered too technically challenging.
Femern announced a year ago that its preferred option was an immersed tunnel for the four lane motorway and dual track rail link. The bored option had been previously rejected due to difficult geological conditions, which in combination with the need for a large diameter and long boring drives would “be pushing the boundaries of what is considered proven construction technology”, Femern had said.
The outline design for the bored solution calls for six slurry shield tunnel boring machine to each drive 10km from the land end of the tunnels to a central connection point. The relatively short drives reflect the high level of wear expected on the cutter heads and the challenges of tunnelling with face pressures of up to 600kPa. The costs of the bored solution are also 25% higher at €6.8bn (£5.7bn) at 2008 prices than the immersed tube design, according to the report. The report was prepared by Femern based on conceptual designs from consultants Rambøll, Arup and Tunnel Engineering Consultants; and Cowi and Obermeyer.
“The results of our investigations into a bored tunnel solution do not change our preference solution from the technical point of view,” said Femern technical director Steen Lykke. “On the contrary, they have confirmed that an immersed tunnel has a number of advantages within a range of parameters. This applies to technical risks, construction time, construction costs as well as operation and maintenance costs.” The final approval of the project in Denmark will be in the form of a construction act passed by the Danish Parliament. In Germany the final approval will be made by the competent authority Landesbetrieb für Straßenbau und Verkehr Schleswig-Holstein in Kiel.
The approvals are expected in 2013/2014 with construction expected to start in the summer of 2014. The Fehmarnbelt crossing is expected to open in 2020.