World’s longest subsea tunnel gathers pace

The E39 coastal highway, or Rogfast, will begin north of Stavanger, cross the Boknafjord and the Kvitsøyfjord and end in Bergen.

“With its 26.7 kilometres, Rogfast will be the world’s longest subsea road tunnel, and also the deepest (392 metres),” says the Statens Vegvesen (the Norwegian Public Roads Administration). “Construction is scheduled to be completed in 2033.”

Implenia, the Swiss construction company, has formed a joint venture with Norwegian contractor Stangeland Maskin, and has been contracted to build one of the tunnel sections.

The most complex part of the project, it says, is the EO2 Kvitsøy exit, which has 8.8km of double-tube, two-lane tunnel with a cross section of 10.5 metres and a two-level ramp inside a mountain.

”Approximately two million cubic metres of rock from the tunnel will be filled in two sea fills and the largest sea fill will become commercial land on Kvitsøy,” Implenia says. “The high water pressures and some areas with poor rock conditions pose a particular challenge and require complex sealing measures through injections.”

Implenia and Stangeland Maskin are contracted to do about 70% of the entire project.

Swedish company Skansa was contracted for the northern part, where it will build a large part of the Boknafjord tunnel, taking up 18.5 kilometres of the total route. 

Among the challenges of subsea tunnelling is the geological nature of Norway’s fjords, and with a road in place, the Norwegian Public Roads Administration believes the journey time from the north of Norway to the south will be halved from 21 hours due to the elimination of ferry crossings.

Norway already has the record for the longest subsea road tunnel in the world. Its 14.3km Ryfast Tunnel, east of Stavanger, claimed the title when it opened in 2019, but will lose its crown with a tunnel almost twice as long.