Expanding Stockholm's Railway Network
The technically demanding immersed tunnel section was constructed by the Pihl and Züblin joint venture on behalf of Trafikverket, the Swedish Transport Administration. The tunnel consists of three immersed tunnel elements, each approximately 100 metres long. After immersion, the elements were connected monolithically and are locally supported by pile bents.
MH Poly was appointed as a specialist engineering consultant, providing expertise in immersed tunnel technology and construction engineering throughout the project.
Specialist in Immersed Tunnel Engineering
MH Poly supported the project team during the preparation, detailed engineering and execution phases of the immersion works. Our scope focused on developing, reviewing and optimising a wide range of immersion-related systems and temporary structures.
A key part of the assignment was the design of the immersion pontoons, including the complete winching and positioning system used for the controlled lowering and accurate positioning of the tunnel elements.
In addition, MH Poly delivered engineering, technical advice and construction support for various execution aspects, including monitoring systems, control equipment, support structures and temporary works.
Scope of work
Preparation and Support of the Immersion Team
- On-site support for the immersion team during project execution
- Review and finalisation of immersion design memoranda and design assumptions
- Assessment of immersion-related design documentation
- Technical advice and coaching in the development of construction methodologies and operational checklists
- Active participation during the immersion operations
Design and Engineering
- Design and engineering of the immersion monitoring system
- Design and engineering of the winching system
- Design of immersion pontoons and supporting steel frame structures
- Design of connection points for Combifloat pontoons
- Design of spreader beams, support frames and winch frames
- Design of roller guides and winch support structures
- Design of monitoring and control systems, including load cells
- Design of deck layouts and container arrangements
Structural Engineering and Technical Drawings
- Detailed construction design of pontoons, steel frames, welded connections, brackets, winches and bolted connections
- Structural verification of temporary works and auxiliary structures
- Preparation of structural calculations and technical reports
- Production of AutoCAD and Autodesk Inventor engineering drawings
Technical challenges
The Citybanan immersed tunnel is located in a highly complex urban environment where precision, safety and constructability were critical. The controlled immersion of the tunnel elements required advanced engineering, continuous monitoring and carefully designed temporary structures to ensure accurate positioning and safe execution under demanding site conditions.
