Explosions, fire and overload the biggest challenges as Norway builds the world's first floating tunnel across the fjords

Norway´s west coast is lined by more than 1,000 fjords, making the journey both long and difficult. A new road system of bridges floating tunnels could cut their drive time in half.

For drivers on Highway E39 from Trondheim in the north to Kristiansand in the south, the journey involves 21 hours of commute, which is slowed down by seven ferry crossings.

However, the government of Norway has come up with a plan that could cut the driving time in a half and make the commute ‘ferry free’ by building the world’s first submerged floating tunnel.

Currently the largest risk to the innovation could be explosions, fire and overloading, according to Arianna Minoretti, chief engineer at Norway’s Public Roads Administration.

The Norwegian Public Roads Administration (NPRA) are working with the Norwegian University of Science and Technology’s Center for Advanced Structural Analysis (CASA) to use live explosives to “investigate how tubular concrete structures behave when subjected to internal blast loads,” CASA researcher Martin Kristoffersen told the CNN.

The tests will help the team to understand what would happen to the tunnel’s structure if, for example, a truck carrying dangerous goods exploded inside: -  However results so far show that the water pressure surrounding the tunnels would reduce the damage caused by explosions.

The map above shows the HIghway E39, to be reconstructed bridges and tunnels. Illustration by The Norwegian Public Roads Administration.

This $40-billion dollar infrastructure project will build a series of bridges over the fjords, and a world record for a 27 km-long, 400 meter-deep rock tunnel, drilled right into the sea bed.

“Route E39 is a key route for Norway,” Kjersti Kvalheim Dunham, a project manager overseeing the revamping of the E39 route, told ABC News. “Improved transport will improve welfare for the local population, open up to more exports and increase tourism.”

The floating tunnel however, will be built within a fjord over 1400-m deep, too deep to drill into the sea bed. The plan is to build it deep enough under the surface so as to allow the biggest ships to safely pass over but also ensure that there is enough room underneath to accommodate submarine passage.

This illustration shows the view of a potential submerged floating tunnel as seen above water. Illustration by The Norwegian Public Roads Administration

The depth of the tunnel will also keep it away from the ‘influence’ of winds, waves and currents, making for smooth driving underwater.

Currently 50 international experts are “doing detailed simulations and detailed measurements of wind speed, current, undersea landslides, bedrock geology, etc.” to make sure the plans, as well as the tunnel, is rooted in “the real-world environment,” says Arianna Minoretti, chief engineer at Norway’s Public Roads Administration.

According to ABC News, the two concrete tubes of the tunnel — one for traffic headed in each direction — will be firmly fixed in position and attached to floating pontoons, spaced 820 feet apart to allow sea vessels to pass through.

This illustration shows a potential submerged floating tunnel in one of the Norwegian’s fjords. Illustration by The Norwegian Public Roads Administration

Currently only 10 per cent of the project has been completed. The whole route won’t be completely finished until 2025.

The government has also unveiled plans to build the world’s first sea tunnel for ships to bypass the storm-battered Stan peninsula in Norway. The project, estimated to cost $314 million will begin in 2019 and take about three to four years to complete.