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A joint venture between Rambøll, Arup and Dutch firm TEC will deliver a remarkable new tunnel between German and Danish islands.
In September 2008 Denmark and Germany signed a treaty for the establishment of a fixed link across the Fehmarnbelt between Lolland (Demark) and Fehmarn (Germany). The Fehmarnbelt Fixed Link will connect Scandinavia and continental Europe with a combined double track rail and four-lane motorway.
Denmark assumed sole responsibility for the financing, implementation and future operation of the link and for this purpose a state owned organisation Femern A/S has been established. A feasibility study looked into a number of possible solutions, including bridge and tunnel (immersed and bored) options. In April 2009 Femern A/S selected the Rambøll-Arup-TEC Joint Venture for the design of the tunnel alternative. Following the competition between the bridge and tunnel solutions, an immersed tunnel was identified as the preferred solution by the Danish politicians in February 2011. The final decision on the type of construction will be taken within the framework of the approval procedures in Germany and Denmark.
The immersed tunnel solution is of a unique scale and will set a new record in terms of dimensions. With a length of 18km and foundation depths reaching more than 40m under the sea surface, it will be one of the deepest and by far the longest tunnel of this type ever built. The Rambøll-Arup-TEC joint venture has developed a concept for a potential solution that forms the basis for the following description. However, the project is foreseen as a design and construct contract and detailed design and the construction methods will be selected by the contractors.
Design focus
The length of the tunnel is the most important factor in the design and the main driver in cost. The Fehmarnbelt Fixed Link tunnel would be five times longer than the world’s longest existing concrete immersed tunnel (the Øresund Link between Denmark and Sweden). The length of the tunnel will not only affect the production, but will also influence safety, operation and maintenance.
General description
The Link replaces the existing ferry service between Denmark and Germany and is located close to the ferry crossing corridor. The motorway will be connected in Denmark and Germany to the existing E47 motorway. The railway will become part of the existing railway between Hamburg in Germany and Copenhagen in Denmark, part of the European transport network (TEN). The total length of the project measures approximately 25km of motorway and 26km of railway. The coast-to-coast connection is 17.6km in length.
Alignment
The horizontal alignment is designed to limit environmental impact. This has been achieved by positioning the alignment as close as possible to the existing infrastructure corridor with the proposed offshore alignment virtually straight. The vertical alignment of the tunnel is defined by the existing levels on the landsides and the depth of the tunnel protection layer below the sea bed within the marine section. A protection layer ensures that the tunnel is sufficiently buried to avoid sustaining any damage from anchors or from stranded ships.
Rail
The rail tubes provide for a rail design speed of 200km/h rail connection through the fixed link with a cross section designed to the UIC GC kinematic profile with a height of 4.9m above rail. The rail cross section includes emergency walkways on both sides of the tube with the width of the track of 3.50m. In the approach areas ballasted track will be used with slab track for the ramp and tunnel areas
A traction power system of 25kV and 50Hz will be installed on the project. The system separation section to change the German 15kV/16.7Hz to the Danish 25kV/50Hz energy system is located on Fehmarn. The project will implement the European Rail Traffic Management System, Level 2 (ERTMS) with the two main systems, the European Train Control System (ETCS) and the Global System for Mobile Communications – Railway (GSM-R). For interoperability in the European network the track from Lübeck to Denmark will be equipped with this system.
Tunnel cross section
The tunnel cross section consists of two tubes for road and two for rail. Both road tubes accommodate two traffic lanes and an emergency lane. A service and refuge gallery is provided between the two road tubes with escape from the train tubes via the road tube which is considered an improvement compared to normal practice in stand-alone railway tunnels.
Immersed tunnel
The coast-to-coast part of the tunnel will consist of 79 standard elements, each approximately 217m long and 10 special elements, each approximately 45m long, making up the 17.6km long immersed tunnel section. The elements contain all standard functions for road and rail traffic, escape and installations. In every element a niche is placed above the road to allow space for the ventilation jet fans with special rubber seals between the elements providing a water tight connection.
The special elements are different from the standard elements and provide space for tunnel technical installations such as transformers and pump sumps. In addition, the special elements provide: parking for maintenance vehicles; easy access to tunnel installations; and transverse underpass to access the longitudinal gallery between the roads as well as the railway tubes.
Approach structures
The approach structures for both road and rail consist of the open ramp, the portal building and cut and cover sections. The approach structures create the transition zone between the landside rail and road and the immersed tunnel section of the link.
Tunnel installation
The tunnel installations support the safe passage of vehicle and train users through the tunnel and safe working conditions for maintenance staff in the tunnel and while supporting emergency operations.
Special design issues
Owing to the extreme length of the tunnel a number of design issues require special attention, including the safety of users, the ventilation system and fire suppression.
Driver’s perception
Although a vehicle trip through the tunnel will take about 10 minutes it is important for safety reasons to ensure that driver awareness is maintained for the full length of the tunnel. This is achieved by improving driver’s perception in the tunnel by making the journey comfortable and memorable. The design incorporates several features to support this including a climate controlled environment with no weather-related impact. An uninterrupted emergency lane provides comfort by the awareness that in the event of an incident one can park outside the normal traffic lanes. Artificial light is used to create coloured light portals and moving light images to maintain driver awareness and interest and develop a sense of progression through the tunnel. Furthermore a high performance traffic management system will guide drivers during their journey and will take control in the event of an incident.
Safety
Safety and self rescue are more prominent when tunnel length increases. The safety level is higher compared to when travelling on a motorway or railway due to the absence of adverse weather conditions, turn outs, crossings and the constant light level in the tunnel. In addition to this a great number of provisions are implemented to manage incidents in a manner that provides adequate safety. The safety strategy has been based on three key objectives: accident prevention; control and self rescue; and emergency response.
Longitudinal ventilation
Tunnel ventilation is designed as a longitudinal system. For the day-to-day operation the ventilation design of the road tubes takes into account the low number of vehicles in the opening year, the expected traffic growth in the coming years and reduced car emissions from improvement in technology. The system is capable of keeping conditions in the tunnel below internationally recognised threshold values throughout the lifetime of the tunnel. The longitudinal ventilation concept eliminates the need for ducts and an intermediate ventilation island, which reduces the navigational risk in the strait and the cost of the project.
Fire suppression
For a long tunnel it is essential to create optimum conditions for self rescue and control of a fire. The response time of emergency services is relatively long and asset protection is also relevant. For these reasons it has been decided to install a deluge suppression system in both road and rail tunnels. The objective is to limit the fire size and control the fire growth. The suppression system controls any fire rather than suppressing or extinguishing it. By controlling the fire, the development of a catastrophic fire can be avoided and the tunnel structure protected, minimising damage and repair time. If the fire is controlled, the chances of a successful evacuation will increase whilst aiding the emergency services’ ability to control the situation. The “risk to life” safety is drastically reduced and furthermore the downtime as a result of a fire is minimised.
Conclusion
That the tunnel has become the preferred solution is a result of a cost reduction, due to the introduction of longitudinal ventilation and the omission of the ventilation island, the industrial element production method and the introduction of special tunnel elements. In addition, the immersed tunnel has a number of advantages: maintaining the openness of the Fehmarn; no restriction to water exchange through the Fehmarn Belt; no impact on ship traffic; no ship collision risk; and low environmental impacts.
JV Partners
Rambøll (Denmark), Arup (UK), and TEC, Tunnel Engineering Consultants (The Netherlands) have joined forces to form a joint venture partnership investigating the tunnel solutions for the Fehmarnbelt Fixed Link. The partners have access to over 30,000 highly qualified specialists from around the world and have many years experience working on major, multidiscipline, multinational infrastructure projects.
Issues related to the companies in the joint venture:
Please contact:
Ramboll – Klavs Munch Koefoed mailto:kmk@ramboll.dk - +45 5161 6260
Arup – David Edwards - mailto:david.edwards@arup.com - +44 782 5057 428
TEC - Wim Janssen - mailto:w.janssen@TEC-tunnel.com- +31 6533 88922
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