Taking forward its expansive, longterm transport plans, Denmark has a fresh surge of tunnelling-related activity underway with more metro to be built in the capital and a possible undersea road and rail link to Germany.

The metro project – Cityringen – will add a 15.5km long underground loop to Copenhagen’s existing Y-shaped network by 2018. Due to start construction this year, the project to build a twin-bore line got underway in earnest three years ago, soon after studies were completed during construction and initial completions of the first metro lines.

Long before the metro studies, though, and even discussed back when plans were being developed for the country’s first major projects involving significant large tunnels – the Great Belt (‘Storebaelt’) and Oresund crossings, both long since opened – was the prospect of a fixed link across the Fehmarn Belt, or channel, to Germany. Since last year consultants have been working to refine potential options for a tunnel across the 19km wide relatively shallow channel.

Both immersed tube and bored tunnel are being considered for the Fehmarn road and rail link, and so is having a ventilation island along the route. However, prior studies priced a tunnel crossing to be more expensive than a bridge alternative. At present both alternatives are being explored for construction of a link to start by 2013 for, again, completion by 2018.

Cityringen – set for build
While the decisions on whether a tunnel or a bridge will be chosen for the Fehmarn link and the route alignment are about a year away, this month should see the next milestone in development of Cityringen when bids are due for the tunnelling packages.

Four JVs were prequalified to bid for the tunnelling packages, and received the tender documents last October. The JVs are:

• Alpine Bau with FCC Construccion;
• MT Hogaard with Hochtief, Ed Zublin and E Pihl & Son;
• Salini Costruttori with Tecnimont and Seli,
• Bilfinger Berger with Vinci Construction Grands Projets and Per Aarsleff;

However, in February, the latter JV dropped out and as T&TI went to press the client still anticipated bids from the three remaining consortia.

Tenders for each of the two running tunnel and station construction packages are to be submitted by 4 May. The client, Metroselskabet, has said it expects to make the awards soon after, possibly in June.

Cityringen – the works
Copenhagen has a high groundwater level and extremely strict environmental controls. Geology along the alignment of the twin tubes comprises glacial moraine over limestone, and there are some sand beds.

Metroselskabet has organised the tunnel works to be undertaken in two packages – North and South – covering construction of 17 underground box stations and TBM excavation of approximately 14.9km, or almost all, of the loop. The tunnels are to be driven at depths of approximately 15m-35m.

The boundaries between the packages are at Aksel Mollers Have station, in the west of the loop, and between Trianglen and Osterport stations – at Oster Sogade lake – in the east.

The project also calls for five construction and ventilation shafts to be sunk and four crossovers constructed, to be done by sequential excavation and sprayed concrete lining (SCL). Design development radically reduced the number of shafts from an initial plan of about 20, and also changed a few of the 62m long, standard length stations to be built at shallower depths.

Consultancy support on the civils works was given to the client by a JV of Cowi, Arup and Systra.

The metro network may spread farther. The current project work on development of Cityringen includes an element, funded by Copenhagen Municipality, to study branch lines off the loop and provide for such with construction of stub tunnels.

Fehmarn – rival concepts
While the design stage is giving way to construction for Cityringen it is only half way through the refinement process in the conceptual stage on the Fehmarn scheme – at least to determine which is the best tunnel option to square off against the bridge alternative.

The tunnel option is chasing behind the cheaper bridge, which has been estimated to cost EUR 4.5bn (USD 6.1bn) against EUR 5.5bn (USD 7.4bn) for the subsea solution. But that margin was not enough to terminate the tunnel option when the figures were given in 2008, and it is to survive at least until 2011 while parallel, but separate, conceptual studies are performed to refine the tunnel and bridge options.

The studies were launched a year ago with the appointment of two teams of JV consultants by the project developer – Femern A/S, a subsidiary of Sund & Baelt A/S, which has experience from the construction and operation of the fixed links across the Storebaelt and Oresund.

The tunnel analyses being taken forward by a consortium of Ramboll Danmark, Arup and Tunnel Engineering Consultant (TEC). The JV is supported by a rake of subconsultants – WTM Engineers, HTG Ingenieurburo fur Bauwesen, Wilkinson Eyre Architects, Schonherr Landskab and Oriental Consultants.

The JV is working alongside the client’s own tunnel team, under Steen Lykke, which most recently worked in Istanbul, leading the Marmaray project. The scheme is centred on an immersed tube tunnel under the Bosphorus but includes significant other bored tunnel and station works, at grade infrastructure and rolling stock.

Lykke says: ‘We are now well into the process of optimising the different tunnel solutions.’

Fehmarn – tunnel studies
As the design studies for Fehmarn commenced, the prime focus for the tunnel option was a 18,565m long immersed tube tunnel – favoured as being a more robust solution than a bored tunnel as found in a feasibility study completed in 1999.

The immersed tube tunnel concept had a cross section comprising two 10m wide cells for road traffic and a pair of 6.37m wide cells for single-track rail lines. A ventilation island in the middle of the strait was also planned for the link between Rodbyhavn, Denmark and Puttgarden, Germany.

The study has been investigating ‘a relatively high number’ of cross section layouts, says Lykke – more than 10 for the immersed tube tunnel and more than five for bored tunnel solutions. These are to be compared on a range of parameters, such as robustness, environment, possibilities for arranging safety features and ventilation, construction time and risks, constructability, cost and connections of the alignment into the shore and beyond.

He adds that the process is more of a de-selection of candidates to arrive at the potentially best tunnel solution, and that will compete against what emerges from the bridge studies, also undergoing conceptual refinement.

While the process has not been finalised – and so bored tunnel options have not been ruled out – Lykke says it’s believed that a solution with both road and rail tubes together, side by side, in the same structure would be superior on many of the assessment parameters. The indicative size of the tunnel cross section would then be approximately 40m wide by 9m high – “close to what was shown in the original feasibility study,” he adds.

The layout is for an immersed tube and initial planning has considered production yards able to cast 200m long elements weighing approximately 70,000t.

Lykke also says ‘one of our main focus points during the development phase so far has been to optimise the use of space inside the immersed tunnel’, and a key aspect of that work involves a wider scope of potential ventilation systems.

The 1999 feasibility study had considered cross or semi-cross flow ventilation systems as the best options, and these are among those now being studied but do require substantial space for ducts in the running tunnels. But longitudinal ventilation systems are also being considered due to improved vehicle emission standards since the earlier study.

Other key areas being addressed included taking advantage of the tunnel length to possibly concentrate the mechanical and electrical installations in special, dedicated standardised elements to be installed at intervals.

A further possibility being analysed is to omit the need to build a ventilation island in the middle of the strait, with consequent benefits for construction costs and navigation.

Meanwhile, out in the strait, environmental surveys and site investigation work have been underway since mid-2009. The work is to be completed by late 2011 with approximately 25t of samples to be cored from pairs of 100m deep boreholes.

International perspective
When the field data are collected and the tunnel and bridge conceptual studies completed, the client will pass over the findings on the Fehmarn project – on the best tunnel and best bridge conceptual designs – to the Danish Minister for Transport to choose which of the alternatives to build. Once legally authorised, the client’s procurement plans call for award of a design and build contract for the civil works.

Construction of the Fehmarn link was previously anticipated to begin in 2012 and this is now expected to be in 2013, still for completion in 2018 – the same year as Cityringen is due to come into service.

Offshore and onshore, Denmark has projects underway that hold challenges for tunnellers that draw global attention. In Copenhagen, the metro will be enlarged with an entirely underground loop that is a significant addition for any world capital, and vital to the city as it becomes an increasingly strategic transport hub between Europe and Scandinavia, already bolstered by the Oresund link.

Oresund, at 4km, is the longest immersed tube built and if the Fehmarn strait was to be crossed by such a tunnel then it would be the world’s longest – even with an island in the middle, notes Lykke. It would also be the deepest road and rail tunnel as a single structure immersed tube, he adds.

Denmark may not have many tunnels but those that have been built, and are planned, are major structures that more than make their mark internationally.


Cityringen will add a 15.5km underground loop to Copenhagen’s existing y-shape network by 2018 Map of Copenhagen’s metro and proposed route Denmark’s tunnelling projects Cross section of the proposed rail/road tunnel to Germany