would allow commuter services to be diverted underground and release much-needed capacity on the existing surface line.


Stockholm SL Odenplan Karlberg Trafikverket


Existing lines Planned lines


Metro lines open


The plan was formally adopted in 2005, but the following year a coalition government was elected which felt the City Line was too costly and too complex. A public inquiry was subsequently launched, but this concluded a tunnel was the most practical and economic option for solving Stockholm’s rail capacity problems. In May 2007 the government finally authorised Banverket to proceed with the project, clearing the way for construction to start in January 2009.


City T-Centralen Central Old Town Slussen


The SKr 16.8bn (SUS 2.58bn) tunnel is being financed jointly by the Swedish government through Trafikverket (SKr 10bn), the city of Stockholm (SKr 1bn) the region of Stockholm SKr 3.8bn), and the regions of Mälardalen and Östergötland (SKr 2bn). “It was not easy to get the


South Arstaberg.. N IRJ


project accepted, and it was discussed at length by politicians for a long time before the government decided to go ahead,” explains City Line project director Mr Kjell-Åke Averstad. “There are a lot of technical challenges in this project. If you look at the layout of the city on the surface, you can see there is a lot of water and a lot of old buildings. Things are just as complicated below the surface, because the


Proposals for engineering solutions to this pinch point go back decades, including adding a third track and tunnels on various alignments. In the 1990s work started on the construction of a third track, but it was soon decided the project would not offer sufficient additional capacity and it was subsequently abandoned. In 2000 the Swedish government asked Banverket (now Trafikverket) to study a permanent solution to the problem and in 2002 a feasibility study was completed on what would become the City Line, a 6km double-track tunnel beneath the city centre which


IRJ February 2013


tunnel has to pass between a lot of existing tunnels. It’s very difficult to drive the line through all of this while providing good connections to the metro and bus routes from the new stations.” Construction of the running tunnels and service tunnels was tendered as seven sectional contracts, which vary in their value (SKr 250m to SKr 1.5bn), complexity, and tunnelling method. “We wanted to offer the market a variety of contracts, firstly to ensure competition, but also because we have some specialised works which are new in Sweden, where we needed to bring in experience from abroad,” says Averstad. “There is a lot of flexibility in the contracts. For example, one contractor can take on tunnelling work


in the adjacent section if he reaches the border first. This means that if one contractor experiences delays it won’t necessarily hit the project schedule.” The northern portal section at


Tomteboda and the southern portal near Stockholm South are lined concrete tunnels, while four of the five intermediate sections are blasted straight through the bedrock. South of Stockholm Central the tunnel encounters its biggest obstacle, the Riddarfjärden, and this requires the construction of a 300m-long immersed precast concrete box supported by steel- reinforced piles to carry the line under the channel between Södermälarstrand and Riddarholmen. This was the only one of the seven tunnelling contracts to be let on a design-and-build basis, and the tunnel is being constructed by a consortium of Züblin, Germany, and Pihl & Son, Denmark, which were involved in building a similar structure on the Øresund Link, while the design work was carried out by engineers from Cowi and Züblin. The three tunnel sections, which are each 100m long, 21m wide and 10m tall were cast in two stages in large steel cradles. The first stage was carried out at Södertälje on Lake Mälaren, where the lower part of each section was cast. All three sections were then towed by a tugboat to the construction site, where the remaining concrete was added. The first section will be lowered into position in the spring, and the remaining two will be sunk during the summer. Beyond the southern portal a 1.4km flyover is being constructed between Årsta and Älvsjö to carry the City Line over the northbound track of the existing line from Stockholm Central.


New stations


The project involves the construction of two new stations, the first mainline stations in Sweden to be equipped with platform screen doors. At the northern end of the new line, Odenplan will replace the existing Karlberg station with a single island platform and two tracks, although it has been designed to allow expansion to four tracks in future when required.


Situated just east of Stockholm Central, Stockholm City will be located directly below T-Centralen metro station and will have two island platforms from the outset. The station’s two underground concourses will have direct escalator links to T-Centralen, the hub of the metro network, significantly improving links between metro and


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