World's deepest underwater tunnel takes cues from Norway

Spain and Morocco are looking to the Norwegian Public Roads Administration as they plan a 40-kilometer railway tunnel beneath the Strait of Gibraltar—set to become the world’s deepest subsea tunnel.

Last week, senior management from Morocco’s SNED and Spain’s SECEGSA visited the Rogfast construction site north of Stavanger, accompanied by Morocco’s ambassador to Norway. Project managers Kjell Håvard Belsvik and Anne Merete Gilje briefed the delegation on planning and constructing the world’s longest and deepest subsea road tunnel.

Learning from Rogfast

The Gibraltar project specifically requested to visit Stavanger, viewing Rogfast as the tunnel project under construction with the greatest transfer value to their plans.

While the Strait of Gibraltar is just 15 kilometers wide at its narrowest point, challenging geology and water depth mean the 40-kilometer rail tunnel is planned slightly further west. The tunnel will run 28 kilometers underwater, reaching depths of 400-450 meters below sea level.

Unlike Rogfast, which uses ventilation towers on Kvitsøy for its 27-kilometer road tunnel, the Gibraltar project cannot use this solution. Instead, planners are developing a twin-bore railway tunnel.

Geological challenges

“The rock is of varying quality. The tunnel will pass through two geological plates between Africa and Europe,” says Jose Luis Goberna, director of Spain’s SECEGSA. “It can be solved. You have an easier job here on the West Coast, although it’s challenging enough.”

Surveys using seismic methods and drilling have been conducted. The project has also collaborated with the Norwegian Geotechnical Institute.

Renewed momentum

In 2023, Spain and Morocco resumed tunnel cooperation after years of stagnation. The planning is financed by both countries’ transport ministries and has received EU funding.

“It’s great that the Norwegian Public Roads Administration shares its tunnel expertise,” says Moroccan ambassador Nabila Freidji.

Construction director Kjell Inge Davik says the international interest is exciting: “These are historic dimensions when Spain and Morocco want to connect two continents across the Mediterranean. We’re happy to share our expertise in tunnel construction.”

Rogfast has hosted delegations from Canada, Serbia, France, Germany, and the USA, with a Japanese delegation scheduled for November.