Gothenburg immersed tube highway 25 May 2017

Contractor Züblin has floated out the first 100m long immersed tube element for its design-build Marieholm road tunnel contract in Gothenburg, Sweden.

Float-out of first immersed tube element of Marieholm road tunnel, Sweden
Photos courtesy Trafikverket/Kasper Dudzik

The 25,000 tonne concrete element took seven months to construct in dry dock. The next two are expected to take five months each, following the initial learning curve, Swedish transport authority Trafikverket told TunnelTalk.

“The launching is an important milestone in the project,” said Trafikverket Project Manager, Stein Kleiven. “We are pleased that so far everything has gone according to plan.”

The three 100m long immersed tube elements are 32m wide x 10m high and form the key part of the 500m long road tunnel below the Gota River, in Gothenburg. The first element will remain floating outside the dry dock, until it is lowered into position towards the end of this year, Trafikverket told TunnelTalk.

“A major challenge has been construction of the dry dock in the special ground conditions we have here, with 100m depth of clay,” Kleiven told TunnelTalk. “It feels good to know that the dry dock works as planned, and we all look forward to construction of the remaining elements.”

Construction of the dry dock, which is located in the tunnel alignment, started in mid-2015 and each element is being cast one at a time. Trafikverket explained that each element is formed of five concrete segments, joined together with special joints. They are then tensioned together with cables, which remain in place until cut after the element is placed in the dredged channel on the sea bed.

Züblin is supported by Dutch firms Strukton and MH Poly, including assistance with placement of the elements on the sea bed. COWI prepared the tender documents for Trafikverket.

The two final elements are due to be placed into position early and after mid-year in 2018. Trafikverket expects that the Marieholm Tunnel will be commissioned by the end of 2020.

Gothenburg and west Sweden have other key tunnel projects underway, particularly the West Link rail which is being developed below the city also by Trafikverket. Bids have been received for the first of three large tunnelling lots, as reported in late April 2018 by TunnelTalk.