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

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


 

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

Project

Between 2013 and 2018, MH Poly contributed to the realization and immersion of the Marieholm tunnel in Göteborg, Sweden. MH Poly was involved from the tendering phase to the immersion of the third and last tunnel element.

Project description

The Marieholm tunnel is part of the larger Marieholm Connection Project, in which both a bridge and immersion tunnel are built to improve the connection between Tingstad and Marieholm. The 500 meter long immersion tunnel consists of three elements and a cut-and-cover section. The tunnel is designed to house three traffic lanes in each direction, and a total traffic capacity of 90.000 vehicles per day. Construction of the tunnel started in 2014 and is expected to be completed in 2020.

MH Poly had already been involved in the project as part of a consortium during the tender in 2013. During the tendering process, MH Poly contributed ideas about the various immersion methods. After awarding the project, MH Poly focused on designing the temporary structures required to enable the immersion of the three tunnel elements. Additionally, interfaces between other temporary and permanent constructions were considered by MH Poly. Lastly, MH Poly advised and supported the consortium on-site during the immersion.

Project activities

  • Design Basis for the immersion of the tunnel elements;
  • Preliminary design and detailed design of immersion related structures 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;
  • Advise 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.

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 presence of a 100mm soft clay layer, it was not possible to use this solution. Instead the secondary support had 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.

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