Norway is drilling the world’s longest and deepest undersea road tunnel, cutting through fault zones and rocks that keep seawater seeping in | World News
While much of the coverage of Norway’s Rogfast Tunnel has focused on the record it will hold as the world’s longest and deepest undersea road tunnel, the real story engineers are dealing with lies underground, where rocks have been squeezed, fractured and folded over millions of years to create some of the most unpredictable terrain along the entire Norwegian coast. Stretching nearly 27 kilometers below the Boknafjord and reaching a depth of nearly 400 meters below sea level, Rogfast is more than just a длинный tunnel; it is a direct battle with unstable geology, constant salt water pressure and forces that engineers cannot always predict in advance to create a fjord.
Why the Bockner Fjord presents such a difficult engineering problem
Boknarfjord is one of Norway’s largest fjords, extending 45 kilometers inland and reaching a depth of several hundred meters, directly through an area where the country’s fishing, oil and gas industries have a large presence. For decades, crossing the fjord meant relying on a chain of tunnels, bridges, ferries and islands, a route that became increasingly inadequate as truck traffic through the area climbed well above the national average. Rather than adding another ferry line, Norway has chosen to cut right through the rocks beneath the fjord.
Drill through fault zones and unstable rock
What makes the Rogfast particularly demanding is not only its length, but also what’s beneath it. The tunnel route passes through several different rock bands, between which sit fault zones where millions of years of geological movement have crushed and cracked the ground. Some sections, such as the dense phyllite found at the southern end, are relatively easy to excavate. Other sections proved much less predictable, forcing engineering teams to continually adapt their methods as subsurface conditions changed.
Fighting a saltwater leak nearly 300 meters deep
Working this deep under the sea presents a problem unrelated to drilling itself: keeping salt water out. Rogfast project manager Anne Brit Moen said crews arrived about 300 meters below sea level and immediately began dealing with a large brine leak that had seeped into the tunnel system. To solve the problem, engineers relied on specialized grouting and sealing methods designed specifically for deep-sea geology, injecting material into the surrounding rock to seal out the water before construction could safely continue. As Oddvar Kaarmo, project manager at the Norwegian Public Roads Administration explains european newsNorwegian regulations require at least 50 meters of solid rock between the tunnel and the sea, a safety margin engineers rely on to maintain durability under such pressures.
Build from solid bedrock rather than prefabricated sections
Unlike similar undersea tunnels elsewhere in Europe, such as the Fehmarn Belt Tunnel currently being built between Germany and Denmark using prefabricated modular sections, Rogfast is drilled and blasted directly through solid bedrock. This method takes longer and is more demanding, but it is a method that Norway has perfected over decades of tunneling, giving the country truly world-leading expertise in this specific type of underground engineering. Construction is taking place simultaneously from three separate access points, with teams working simultaneously from the north, south and center of the route to speed up an already lengthy project.
An underground roundabout unlike anything built before
About halfway along the route, engineers are building something that has never been attempted before, a junction that connects the main tunnel with a branch line to Kvetsoy, Norway’s smallest city. The connection consists of two roundabouts located approximately 260 meters below sea level and is designed to allow traffic to continue flowing through one of the tunnel tubes even if the other tunnel tube needs to be closed for maintenance or emergencies. Making this interchange work reliably at such depths while still meeting strict safety standards would require its own dedicated engineering solution, separate from the rest of the tunnel.
A project has been reinvented once by its own complexity
Logfast’s difficulties have left their mark on its history. Work first began in 2018 but was halted at the end of 2019 after projected cost overruns forced planners to redesign the project, ultimately adding approximately NOK 8 billion to the total budget. according to Nuo ConsultingEngineering companies involved in the design of the project will resume construction in 2021, and signed contracts for the northern, southern and central sections of the tunnel between 2022 and 2024, giving the project a new, more realistic foundation after early setbacks.
What Rogfast means for future engineers
Norway still has dozens of fjord-crossing projects to complete on its wider E39 coastal highway, some with engineering issues that remain unresolved even on paper, including a proposed floating tunnel that would be suspended below the water elsewhere along the route. Whatever solution ends up being built there, it’s likely to be influenced by the lessons learned from Rogfast in the first place. For a country whose relationship with its coastline has always meant negotiating difficult terrain rather than simply overcoming it, Rogfast is the latest and most technically demanding chapter in the long relationship between Norwegian engineers and the land beneath their feet.
