Project Citybanan I Stockholm – Immersion of the tunnel elements for the Söderströmstunneln

09 July 2013

The Söderströmstunneln is one of the most challenging parts of the new Citybanan, a 6 km long railway tunnel crossing the centre of Stockholm. Major parts of this underground link can be executed using the common drill and blast method. That is not applicable to the 450m long Söderströmstunnel crossing the Söderström, connecting the islands Riddarholmen and Södermalm.

JVS - Stockholm TE1 TE2 

The immersed tunnel comprises three prefabricated elements of about 100m length. Since the soft subsoil does not allow the bedding directly on the seabed the tunnel will be founded on four piled and one raft foundation. Once the construction is completed the tunnel will form an underwater bridge with a loose end in the so called joint house and a fixed restraint at the other end formed by massive rock anchoring.

Unique in the immersion operation is the use of external temporary jack supports on the piled and raft foundations and sliding plates underneath the tunnel elements, to support and slide the elements to their final position. Other aspects are the temporary underwater parking of the Riddarholmen element inside the joint house, to create space for the immersion operation of the centre element, and the usage of two different immersion pontoons, to deal with the different lengths of the elements and the reduced space around the abutments of the tunnel.

The Design and Build contract for the tunnel is carried out by a Joint Venture consisting of the German contractor Züblin Ground Engineering, part of the Strabag SE Group, and the Danish E. Pihl & Søn A.S. Stukton Immersion Projects contribution to the project is the supply of equipment, e.g. the cross beams of the immersion pontoon, and personnel in command of the immersion operation.

Immersion of the tunnel elements takes place in April – August 2013.