The third and final concrete element for the Marieholm immersed tube tunnel project in Gothenburg is complete and ready to be floated out from the dry dock to await sinking into position later this month (September 2018).

Last float-out begins for Marieholm highway

Preparations for sinking the element underway

Contractor Züblin has completed casting all three 100m long x 10m high x 32m wide concrete elements in the dry dock that will become the transition ramp for the road tunnel on the north side of the Gota River waterway and link the immersed tunnel to the Gothenburg road network.

With steel bulkheads on the end of the concrete element, the contractor flooded the dry dock last week as planned. Stein Kleiven, Project Manager with transport authority Trafikverket, told TunnelTalk that the first stage of the final element float-out went well. “The second part of the float-out to be immersed into the bed on the Gota River will begin next week and take a week to complete,” he added.

In preparation, key tasks have been underway for installing the survey tower and access shaft, attaching pontoons over the concrete element, and testing towing winches and sinking ballast tanks said Kleiven. During the towing and sinking process, the project area in the Gota River will be closed to all sea traffic.

Design of the immersed tube was underway in 2015 when the dry dock in the tunnel alignment was under construction in challenging deep clay ground conditions. Despite the complexity of the task, the first two elements for the 500m long immersed tube tunnel were cast consecutively in the transition ramp dry dock during 2017 and sunk into position in December 2017 and February 2018. Casting of the third and final 25,000 tonne element started in Spring 2018.

Road ramp will be built next on dry dock site

Each element is formed of five segments and a three-stage casting process was employed for each segment. “For all works there has been a lessons-learned list to take care of improvements to be implemented in the next sequence of work,” said Kleiven. “These helped improve efficiency with each round of works on the same design and in the same site on the dry dock.”

Specialist firms Strukton and MH Poly have supported Züblin on the project and Trelleborg supplied Gina and Omega gaskets and seals.

“The project is currently on schedule and on budget,” said Kleiven. “Once this final element is in place, there are a lot of works left to be done before the link is ready to open to traffic in in late 2020.”

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.