When the Blue Line is extended from Kungsträdgården, the first stop will be Sofia in East Södermalm. The tunnels will go through rock, on a straight course under Saltsjön.
That is one of the explanations why the station will be so deep - 100 metres below the surface.
"Under Saltsjön there is a weakness zone in the rock that we need to go beneath. Södermalm is also at a high level, so overall it will be this deep,” says Andreas Burghauser, project director for the Blue Line to Södermalm.
The station itself, with the platforms underground and the ticket hall in Stigbergsparken 100 metres above, will be built both from below and from above.
"We will build a very large shaft and then fill it with content. You could compare it with building a high-rise, but downwards instead of upwards,” says Andreas Burghauser.
The deepest station in the world today is 105.5 metres below the ground, in Ukraine's capital Kiev. But Region Stockholm has no ambition to beat the record.
"We are building as deep as we need to and we have a responsibility to look after the taxpayers' money. Building the deepest in the world is not a goal for us,” says Andreas Burghauser.
New conditions and requirements
The last major expansion of the Metro took place around 40 years ago, when the Blue Line was built. Now another annual ring is being added to Stockholm’s Metro network and this time there are new rules, requirements and construction methods.
What is new at Sofia Stations is that passengers can take lifts instead of escalators up to street level.
“As a passenger, it is hard to tell if the platform you are standing on is 10 or 100 metres below the surface, but taking the lift up will certainly be a novelty for many. There will be eight lifts with space for 30 people in each. There is nothing like that on the Metro today,” says Andreas Burghauser.
Going up in the lift will take about 30 seconds, a lot faster than it would have been with escalators and a faster trip up to ground level than at many of today's stations.
The first part of Sofia Station to be built is a work tunnel from ground level at Londonviadukten, where machinery, personnel, building materials and rock spoil will be transported throughout the construction period.
If all necessary permits are in place, work will begin in autumn 2019.