By order of the Stockholm City Council, Sweco together with the Spanish company TYPSA is designing an 11-kilometre section of the new underground line from Kungsträdgården station to Nacka and Gullmarsplan stations. The task includes building seven new stations.
The project is conducted by the international team, including the employees of different Sweco offices (Sweden, Finland, Poland) and the TYPSA company from Spain. As a part of the project there are six basic trade blocks; geotechnics and mechanics of rocks, track systems, networks and appliances, architecture and constructions and the environmental protection. The underground tunnel and the seven stations constitute “separate” tasks realised as a part of the main project.
With regard to the increasing number of inhabitants and the plans of creating new living estates in the Stockholm metropolitan area, there is a need to expand the existing commuting connections. These connections are to facilitate fast and comfortable communication between different parts of the city for the increasing numbers of passengers. Therefore, it is planned, inter alia, that until 2025 four new underground lines will be built, which will constitute an extension of the existing lines or the new arms of the Stockholm underground stellar system.
Img 1. Underground network in Stockholm, the segments which are to be put in service are marked in the dashed line
One of the segments which is to be built is the extension of the blue line in the East direction (Nacka Centrum) and the South direction (Hagstöra). Sweco together with the Spanish company TYPSA will design the segment from the Kungsträdgården station to Nacka Centrum and Gullmarsplan stations (crossroads with the green line).
The length of the designed segment, on which seven new stations will be built, is 11 kilometres. Due to the lay of land, the existing obstacles and the depth of the ground depression, the underground station is situated 80-90 meters below the ground level or the water surface. It can be seen on the long sections shown below.
Img 2. Long section of the designed underground line to Nacka Centrum station
Img 3. Long section of the designed underground line to Gullmarsplan station
Arriving at the solution for this part of the project was preceded by much analysis. For example, as alternative solutions to the passage through Saltsjön (Salt Lake) the tunnels were analysed and described as: sunk in water or “shallow” in the non-rocky grounds below the lake bed. Finally, taking into consideration the costs and risks linked with the construction and the future use; for instance, the possibility of the ship sinking with heavy displacement was taken into account, the variant of the "deep" rock passage. As a consequence, there is an allowance of over 90-meter ground depression below the level of the Sofia station. It will probably be the first Stockholm underground station where the whole vertical transport will be carried out exclusively by the use of lifts.
The deep location of the station under ground level makes the descent to the platform level a relatively long time. Additionally, the standard narrow escalator tunnels limit the visibility of the platform to which they lead. To increase the sense of space in the station it was generally agreed that the descent to the platform level will lead through the intermediate gallery, from which the whole platform can be seen.
Img 4. Underground station, standard solution
Apart from the transport and communication function, the Stockholm underground also plays a role in the public space. It is sometimes called the longest public gallery. For example, the stations which are designed in a ‘cave’ type appearance provides a pleasant surprise for commuters.
Photo 1. Kungsträdgården station (Ulrik Samuelson’s design, 1977)
Stations on the new segments are inspired by the “artistic” station ideas. In order to implement this, conducting of an international contest is planned. The aim of this contest will be to “recreate the new stations into works of art”.
The past and present
The beginnings of the underground transport in Stockholm historically begins in the 1930s. At that time, the first underground railway segments were put to work, including the oldest tunnel segment between Slussen and Skanstull (1933). In 1941 the decision was made about the underground construction in the present shape. In 1951-1960 new segments of the green line were constructed. The blues line was built in 1964-1978 and the currently last (third) stage of its development took place between 1975 and 1994, when the Skarpnäck station was opened. For this reason, the currently realised underground development plan is called “the fourth” construction.
The underground network consists of three lines (green, blue and red) in the stellar system shape. The total number of stations is 100, from which approximately half are underground stations, and the total length of lines is approximately 106 kilometers.
The anticipated finish of the design works is 2019, whereas the planned realisation (construction) plan is 2018-2025. The estimated cost of the project is 500-600 million SEK (220-260 million PLN), and the cost of the realisation of the venture, including the stations but without the rolling stock, is 12.5 billion SEK.
Sweco plans and designs tomorrow’s communities and cities. Our work produces sustainable buildings, efficient infrastructure and access to electricity and clean water. With 14,500 employees in Europe, we offer our customers the right expertise for every situation. We carry out projects in 70 countries annually throughout the world. Sweco is Europe’s leading engineering and architecture consultancy, with sales of approximately SEK 16.5 billion (EUR 1.7 billion). The company is listed on Nasdaq Stockholm. www.swecogroup.se