Project - The Söderströmstunneln; An immersed tunnel in the heart of the centre of Stockholm

The Söderströmstunneln; An immersed tunnel in the heart of the centre of Stockholm

Project description

For the north – south extension of the underground Citybanan, the underground commuter railway system through the centre of Stockholm, the mainly drill and blast tunnel faces a challenge at the over 300 m wide fjord, Ridderfjärden, where it has to cross the water through very soft clay.

An immersed tunnel was chosen to solve this problem. The client, Trafikverket awarded this project to the joint venture Pihl en Züblin. Three tunnel elements of approx. 100 m each were immersed on to pile groups and later structurally connected with post tensioning. A special design in a very complex environment.
MH Poly has been involved as a consultant for the immersion system and has designed the immersion pontoons and warping/ mooring spread as well as on site assistance in the preparation of the immersion.

Project activities

- Support and preparation of an immersion team on site;
- Completion and check on Design Basis for immersion;
- Completion and check on immersion related engineering items;
- Design and advise on the immersion survey system;
- Design and advise on winching and warping system;
- Advise and coaching in the drawing up the necessary method statements and checklists for execution;
- Active participation in the immersion team during immersion;
- On site engineering, advice and guidance of the works;
- Design and detailed design of specific immersion related items, such as immersion pontoons and corresponding frames;
- Detailed structural calculation reports with the following components: immersion pontoon, frames, brackets, winched, welds, bolts etc;
- Detailed design on fixing points on Combi floats;
- Detailed design of crossbeam construction, support frames, winch frames;
- Detailed design of mooring / warping winches and fairleads;
- Detailed design of control system (incl. load cells);
- Detailed design of deck layout and containers;
- Shop drawings Autocad / Inventor.