Sockenplan, Sweden

The project is part of a major expansion of Stockholm’s metro system. Over the next 10 years, Region Stockholm will expand the metro system with 18 new stations and approximately 30 kilometres of new track. The expansion plan covers almost 30 separate contracts, and the value of the total investment is approximately EUR 2 billion. Sockenplan is the southernmost part of the new blue line towards Söderort, which will ultimately connect the existing Hagsätra line and the new blue line from Södermalm at Sockenplan.

Requirements for high competence and good planning

YIT has pervious experience of similar work in Finland and elsewhere. In the ongoing major expansion to Helsinki's metro system, YIT has been one of the main contractors since 2009 and is thus has a lot of up-to-date experience and knowledge from a major metro project. However, despite relevant experience of similar methods, the Sockenplan project is an demading project. The short construction period means that technical solutions and working methods that use the time more efficiently need to be found. Parts of the contract are designed by the client, while other parts are carried out by the contractor, which requires a clear demarcation. Other challenges that affect the project are strict noise and vibration requirements.

“The noise and vibration requirements affect at what times we can work, as well as what methods and machines we can use. Investigations need to be carried out in order to ensure that we can use the method we planned for,” says Mikael Porsbratt, project manager.

A breadth of working methods

A large part of the project includes the support construction, which shall be designed and then carried out in order to realize the large shaft. The support construction will consist of RD pile walls, Berlin-type retaining walls, polyurethane retaining walls and shoring that crosses the large shaft. This requires specialists in geotechnics, hydrology, support construction and grouting. The rock tunnel that will be built at a later stage of the project will be carried out with the help of wire sawing.

“The support construction is complex, and it is vital that the potential environmental impact is monitored, such as subsidence of the existing buildings and the impact on groundwater. But thanks to our experienced specialists, we will succeed,” concludes Mikael Porsbratt.

Environmental construction

The work involves some novel, environmentally-friendly working methods.

As underground demolitions are performed, one has to drill several holes into the rock for the explosives. In this effort, electro hydraulic “jumbo” drills are used – but the challenge with work this intense is that massive volumes of clear water are needed to rince the holes during drilling and to cool machinery down. Finally, all the process water must be pumped upp to communal sewage network which causes costs.

Environmental Manager Johanna Weckström says that with this project they wanted to see if they can develop a new kind of concept for recyckling the water on site.

“This way, we can use the same water over and over again.”

The Sockenplan metro project also uses BREEAM Infrastructure (formerly CEEQUAL) system to ensure that the Region Stockholm's strategic environmental and responsibility work is integrated as seamlessly as possible into the practical planning and implementation of each subcontract of the project.

Water treatment and environmental construction | YIT.fi