Project - Marieholm Tunnel Göteborg – ‘A design for immersion of the tunnel elements’

Marieholm Tunnel Göteborg – ‘A design for immersion of the tunnel elements’

Project description

The project ‘Marieholmstunneln’, situated in Göteborg, is an approximately 500 meter long immersed tunnel project, which includes a cut-and-cover part at both the Tingstad and Marieholm side of the river. This project is part of a connection project of Trafikverket, The Swedish Transport Administration. The tunnel is designed for a traffic flow of 90.000 vehicles per day; three traffic lanes will be constructed in each direction. The construction started in 2014 and is planned to finish in 2020. At this moment the cut & covers are being constructed.

For MH Poly the project started in 2013 by advising in the tender phase. After winning of the tender, by the Joint venture Zublin Boskalis, MH Poly has been involved in basic and executional design of the temporary constructions which are needed for immersion of three tunnel elements. MH Poly was involved during the immersion process by on-site supporting the immersion team.

Project scoped

In this project, MH Poly has used his expertise to advice on immersion related matters. Considering the challenging boundaries in this project, MH Poly has also been using his broad knowledge to immerse the tunnel elements in the most effective manner without exceeding the client’s restrictions. During the tender phase MH Poly also indicated the interfaces between the immersed tunnel and other (temporary and permanent) constructions.

Project activities

- Design Basis for immersion of the tunnel elements.
- Preliminary design and detailed design on immersion engineering items such as: immersion pontoon, access shaft, bulkheads, anchor points, sandflow system and a closing seal between the immersed tunnel part and the cut and cover.
- Advice on immersion and construction sequence of the immersed tunnel
- Illustration of the immersed tunnel both in 2D and 3D.
- On site consultancy during the immersion operations.

Soil conditions

One of the challenges in the project is the presence of soft clay with the maximum layer thickness of 100 meters. The soil conditions had a major influence on both the permanent and the temporary design where the sand flow and the temporary supports are a part of it.

Tunnel foundation

The foundation method of the immersed elements is the conventional sand flow method. The sand flow usually consists of a 1 meter thick sand layer which is pumped from a storage area, usually located on shore, through a pipe line to the outflow points underneath the tunnel element.

In order to be able to install the sand foundation the tunnel element needs to be immersed on the temporary supports leaving a gap between the underside of the element and the soil. Conventionally, the temporary (secondary) supports consist of concrete foundation pads located at the secondary side of the tunnel element. Due to the soft clay it was not possible to use this solution. Instead the secondary support has been executed as a piled foundation, where one support point consists of three piles. During the immersion process the temporary supports were constantly monitored. As soon as the sandflow process is completed the tunnel element can be released on the sand foundation.

The Port Authority of Rotterdam has awarded the design with 9 out of 10 score, the highest score of all competitors. At the end of March 2016, the Factory Acceptance Test (FAT) will be started and soon after, the construction will start.

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