The Marieholms Tunnel, scheduled to be complete in 2020, will serve as a vital transportation link, under the Göta Älv River in Gothenburg, Sweden, an important industrial center. © Trafikverket
A new $500-million project will provide better access across the Göta Älv River in Sweden’s second largest city.
March 25, 2014—Construction has begun on a $500-million project to construct a tunnel beneath the the Göta Älv River in Gothenburg, the second largest city in Sweden. The tunnel is being developed by Trafikverket, the Swedish Transport Administration, to serve as a vital link between the city, the island of Hisingen, and the Port of Gothenburg.
Gothenburg is an important industrial city with approximately 550,000 residents. Gothenburg’s port is the largest shipping destination in the Scandinavian region. The city’s thriving manufacturing sector includes such major corporations as automaker Volvo, communications specialist Ericsson, and bearing producer SKF.
The tunnel will comprise three lanes in each direction, connecting three busy highways: the E6, the E45, and the E20. It is expected to carry approximately 50,000 vehicles per weekday, according to Erik Bengtsson, a chief project manager for COWI AB, in Gothenburg.
Trafikverket selected COWI to review and update previous studies of such a project, to develop a preliminary design, tender documents, risk assessments, and conduct tender evaluations. During construction COWI will assist Trafikverket with technical support, said Bengtsson, who provided written answers to questions posed by Civil Engineering online. Ramboll, in Orestad, Denmark, is developing two complex interchanges for the project, one on either side of the river.
The new tunnel will be constructed about 600 m north of the existing Tingstads Tunnel, which has been at capacity for years, creating traffic delays during peak traffic periods. The Tingstads Tunnel will remain in operation when the new tunnel is complete in 2020, serving as an alternative route.
Bengtsson said the heavy traffic of large ships on the river was the key factor in the choice to build a tunnel rather than a bridge.
“The alternatives were a high bridge or a drawbridge,” Bengtsson said. “A drawbridge will affect the traffic capacity too much. And between a high bridge or a tunnel, the tunnel was the most cost-effective.”
The plans call for a mix of tunneling methods—cut and cover for some sections and immersed tunnel for others. The tunnel sections will each be 30 m wide and 10 m high. The immersed tunnel sections will be joined with Gina gaskets and Omega seals. Geotechnical conditions at the site are varied, with a layer of gravel topping approximately 100 m of clay. The construction firm, which will be selected later this year, will have some flexibility in deciding the exact balance of tunneling methods used.
The project features several design, engineering, and construction challenges, most of which derive from the heavily developed nature of the area surrounding the river. For example, the soft soils dictate deep pile foundations for the interchanges. But the danger of ground motion will require careful monitoring of surrounding structures, Bengtsson said.
The industrial history of the river also means that some of the work will take place in brownfield areas. Contaminated soil will require proper disposal. Another environmental concern is the wildlife in and around the river. That has resulted in strict turbidity measures. Dredging will be permitted only during the winter months.
“I think the most challenging aspect both [from a] design and construction standpoint will be how to make the immersed tunnel elements,” Bengtsson said. “[The] workplace area is small, so it will be difficult to build immersed tunnel elements on the site. You cannot transport finished tunnel elements in Göta Älv because it is too shallow.”
A likely solution will be a hybrid approach in which steel shells of the immersed tunnel sections are fabricated off-site and delivered finished via ship on the river. The shells would then be offloaded and completed with cast in place concrete.
“The contractor will decide how to do it,” Bengtsson said. “I hope that the contractor will find great innovations to solve the problem.”