Technology

Norway’s floating tunnel

 By Chris Dalby

In 2016, the World Economic Forum got an exciting tidbit of news. Norway, which has 1,190 fjords along its west coast, was planning to pioneer an underwater, floating tunnel that would allow drivers to stop relying on a network of slow ferries. The stretch chosen for this experiment is the drive from Kristiansand to Trondheim, which currently takes 21 hours and seven ferries

The tunnel, once built for an estimated $25 billion, would see two tubes of around 1,200 meters each submerged 20 meters beneath the Norwegian Sea. In order to give drivers the feeling of being in any other tunnel, the tubes will be attached to the bedrock of each fjord and then attached to pillars floating on top of the sea. Another design option would see a bridge built on top of the tunnel for stability.
The idea picked up speed when Norway’s public roads body approved the building of these tunnels along E39, the highway along its western coastline that has the most ferries for a single road in Europe.
According to the government, the tubes would sit “65-100 feet beneath the water’s surface, tethered to floating pontoons and seabed anchors.”

Perspective section of the floating tunnel's project (vegvesen.no)

The tunnel is far off from completion, set to be inaugurated in 2035. However, early testing is proving the project’s potential. The Norwegian University of Science and Technology’s (NTNU) Centre for Advanced Structural Analysis has been stress-testing concrete to be used on the tunnel and has found that it could resist far more pressure than previously thought, up to an explosion inside the tunnel with walls 80-100 cm thick.
Furthermore, this new science rests on existing technologies. Offshore drilling platforms have become increasingly sophisticated at being anchored to the seabed, allowing them to resist gale-strength winds and huge waves. Floating bridges, such as the 2.3-kilometer example in Lake Washington, offer the technology that could see the tunnel accompanied by its own bridge.
“This idea of Norway’s is sort of an intermediate technology of things that have been done before,” says Henry Petroski, a Duke University civil engineer who specializes in bridges.
There are also concerns about this project. While it might increase commuter ease and reduce journey times, these underwater tunnels could wreak havoc with shipping and military operations. The government has already acknowledged the tunnels could pose a problem for Norway’s submarine fleet.

Underwater digital rendering view of the floating tunnel (vegvesen.no)

Another concern is that any infrastructure in the fjords would mar their beauty and put their pristine environment at risk. To this, Norway has said that a floating tunnel would be less likely to cause these problems than a series of bridges.
The key will be balance. The project mulled by Norway is to have two floating tunnels at key locations along with conventional bridges and tunnels, including Rogfast, which if it materializes, would be the world’s longest road subsea tunnel at 392 meters deep.
The project has seen a lot of interest from countries struggling with road infrastructure between islands, including China, Japan, Denmark, Singapore and Turkey.
Efforts at similar technology have been tried in the past without going anywhere. Back in 2007, China even began work on an underwater bridge, dubbed an “Archimedes Bridge.” One hundred meters long, the bridge prototype was to be built across Qiandao Lake, with one-lane motorways running through it. Its buoyancy was to keep it submerged while cables anchored it to the lake bed. While a flurry of press greeted the start of the project, it quickly petered out.

Digital rendering view from above (vegvesen.no)

As early as 2004, Indonesia considered a submerged tunnel as an option to connect the islands of Sumatra and Java, with a budget rumored at $15 billion. While a bridge was later favored, before being cancelled itself, experts have continued to point at how submerged tunnels could be vastly beneficial to Indonesia, a country with over 13,000 islands.
In the recent past, technology made floating tunnels imaginable but not ultimately feasible. The tipping point has still not yet been reached. However, engineers and bureaucrats seem to agree that this elegant solution offers answers to specific problems, such as that of Norwegian fjords. A proof of concept is needed. But in decades to come, the floating tunnel idea may become a global standard.

READ MORE: Is Norway’s oil wealth stifling innovation? by Nicholas Newman

about the author
Chris Dalby
Journalist. Editor. China, Mexico, Latin America, Asia, place branding, Olympics, oil and gas, mining, renewable energy, international politics.