Immersed tube recommended for Femern link Nov 2010
Femern A/S New Release
- Fewer risks, all told, in both the construction and operational phases than a cable-stayed bridge is how project leaders of the Femern fixed link project between Denmark and Germany have arrived at a recommendation to select the immersed tunnel option and take it forward into detailed design.
Bridge or tunnel? Tunnel or bridge? The comparisons are completed and the tunnel is recommended
- This conclusion places special emphasis on the technical risks of executing the two projects; environmental impact factors; the potential impacts on navigation safety and construction cost. It must be emphasised that the recommendation remains provisional pending the Environmental Impact Assessment (EIA).
- A political decision on which of the two outline proposals is to constitute the preferred solution in respect of the process going forward, including the forthcoming EIA report, is expected in early 2011. It is anticipated that the preferred solution will form the basis for the project application to be submitted to the German authorities.
- The final decision on which solution is to be built will be made pursuant to a specially enacted construction act in Denmark and subject to approval by the German authorities.
- It is expected that the contracts with the contracting firms who will be undertaking the construction project will be signed in 2014. It will be up to the contracting firms to organise the work, including the location of the large production sites for manufacturing bridge or tunnel components.
- Femern A/S is working on the assumption that a large proportion of the steel structures for a bridge would be constructed in the Far East, e.g. China, while tunnel components would be produced locally owing to their great weight. On account of the risks entailed by sea transportation of such large components, Femern A/S has previously concluded that production of concrete components should ideally be sited up to 120 km from the route corridor. A more distant siting may also be considered if the contracting firms conclude that this would be more financially competitive overall.
A cable-stayed bridge across the Fehmarnbelt, with two free spans of 724 m each, would be the largest spans ever constructed for either road or rail traffic. Compounded by the high shipping traffic in the area, this would pose significant risks in the construction phase in terms of cost overruns, delays and industrial accidents.
Cable-stayed bridge option
- An immersed tunnel will also present considerable technical challenges during the construction phase, as a result of the intensive shipping traffic in the Fehmarnbelt. However, unlike a bridge, an immersed tunnel will not entail as many technical operations which push the limits of what has been done before. Essentially, the procedure will be the same as it was for construction of the Øresund Fixed Link's immersed tunnel under the Drogden Channel, only many more times over and at far greater depths, i.e. up to 30-40 m in the Fehmarnbelt against approximately 10 m in the Øresund. The Fehmarnbelt tunnel will be just under 18 km long, while the Øresund Tunnel is approx. 4 km long.
One of the key parameters for the choice of technical solution is the environmental impact of the projects.
Immersed tube tunnel option
- Both a cable-stayed bridge and an immersed tunnel would impact the marine environment in the Fehmarnbelt. The preliminary conclusion is that a bridge would have slightly more significant permanent environmental impacts than an immersed tunnel. However, the nature of these impacts does not, from a purely environmental perspective, preclude a bridge.
- A number of the environmental impacts of a fixed link would be on Natura 2000 sites. In such instances, EU legislation prescribes that the least intrusive alternative must be selected.
In the interests of navigation safety, a tunnel clearly poses fewer risks than a bridge. The Fehmarnbelt is a heavily trafficked stretch of water with 47,000 vessel transits per annum (2006), including many tank vessels. In the coming years, shipping traffic in the Fehmarnbelt is expected to increase substantially to approximately 90,000 vessel transits in 2030.
- However, risk analyses for a bridge show that, from a vessel perspective, navigation safety would be improved in relation to a situation with no bridge and continued ferry crossings. This would require a cable-stayed bridge with two navigational spans of at least 724m each, and the implementation of permanent, radar-based vessel monitoring in the form of a Vessel Traffic Service (VTS) system covering a range from the south end of the Great Belt to the Cadet Channel.
Femern Fixed Link
In financial terms, there is very little difference between the two projects. The construction estimate (2008 price level) for an immersed tunnel is EUR 5.1 billion and for a cable-stayed bridge, EUR 5.2 billion.
- Assessment of the overall cost of each of the two projects must also take into account the construction time and the cost of operation and maintenance. The construction time for the tunnel is estimated at 6½ years, and for the bridge, 6 years. The cost of operation and maintenance is slightly higher for a tunnel than for a bridge.
- All told, the payback time for the two projects would be essentially the same: approximately 30 years for the coast-to-coast project. This means that, from an overall financial perspective, there is no difference between bridge and tunnel.
- A full description of the respective cable-stayed bridge and immersed tunnel proposals is available on Femern A/S's website.
Cost comparison for Femarnbelt link options - TunnelTalk, Nov 2010
Innovations for the Fehmarnbelt tunnel option - TunnelTalk, May 2010
Femern Bælt fixed link options - TunnelTalk, Jun 2009
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