Our Take
Norway's subsea tunnel method works because it treats geology as variable, not fixed: different rock types get different support strategies, leaks are managed not stopped, and two teams tunnel inward to meet with centimeter precision by 2029.
Why it matters
Nations including Japan, Spain, Morocco, and US states are studying Rogfast's approach because subsea infrastructure reduces ferry dependency and travel times. Norway has already built over 1,000 kilometers of tunnels; this project proves the method scales to depths and distances competitors haven't attempted.
Do this week
Infrastructure planners: Request core samples and seismic surveys of your planned subsea route before committing to tunnel method, because rock type (granite vs. phyllite vs. class-5 unstable rock) determines blasting intensity, grouting volume, and schedule variance (10 to 30 meters per week per the Skanska side).
A 26.7-kilometer tunnel taking shape under the North Sea
Rogfast, short for Rogaland Fixed Link, will become the world's longest and deepest subsea road tunnel when completed in 2033. The tunnel descends 390 meters (1,280 feet) at its deepest point beneath the fjords of Boknafjord and Kvitsøyfjord on Norway's west coast. Two construction teams are tunneling inward from opposite ends: Skanska from the north (Vestre Bokn) and Implenia with Stangeland from the south (Randaberg). They expect to meet in 2029 with no more than a few centimeters of deviation, using multiple daily laser scans to verify alignment.
The project will eliminate two ferry routes and cut the five-hour journey between Stavanger and Bergen by 40 minutes. Four lanes of traffic will run through the tunnel, with two undersea roundabouts located 220 meters below sea level. At one section, just 50 meters of rock will separate drivers from the bottom of the North Sea.
Norway has constructed more than 1,000 kilometers of tunnels over the past several decades, more than any other nation attempting subsea infrastructure at scale. The Rogfast method has already attracted inspection visits from representatives of Japan, Spain, Morocco, and multiple US states seeking to replicate the approach.
Drill-and-blast beats tunnel boring machines for complexity
Norway favors the drill-and-blast method over tunnel-boring machines because geology is unpredictable and variable. Each 80 meters, engineers send sound waves through the rock face to grade its stability on a scale of 1 to 5. The rock type determines everything: how much explosive per blast (phyllite requires more; it's compact), what structural supports to install (steel rods for strong rock, reinforced concrete arches for weak), and how much grouting is needed to manage seawater seepage.
The seabed around Norway was shaped by glaciers during the Ice Age. As ice retreated, it dragged softer rock away, leaving behind hard granite, gneiss, and other challenging formations. One section contains phyllite, a compact rock formed from shale and siltstone that releases toxic quartz dust during blasting. Workers monitor exposure and water curtains spray the blast face to control drift.
Water is the constant adversary. Subsea tunneling is defined by an "ultimately unwinnable battle with the ocean." Before blasting, engineers drill probe holes 25 to 30 meters ahead to measure water flow. Even a small hole can unleash a torrent within seconds. If leakage exceeds about four liters per hole per minute, the team groutes by pumping cement-like sludge through fan-shaped holes in the ceiling and walls. Stopping the water entirely is impossible; the game is to slow it. Once open, the tunnel will have mini reservoirs throughout to catch trickling water and pump it back out.
This variability means progress is unpredictable. On the Skanska side, some weeks the face advances 30 meters; others, as few as 10. Each blast adds about five to six meters. Workers cycle 12 days on, 16 days off, in 12-hour shifts deep underground where no natural light reaches.
Managing water, rock grade, and team rotation
Subsea tunnel projects require three parallel disciplines to execute. First, geological survey and staging: core samples and seismic data from the ocean surface must precede any construction to identify rock types and fracture patterns. Grouting specialists must be embedded early to design ahead-of-face leak management, not remediation behind the face (which is "a lot more difficult," per project leader Ole Magne Rønning).
Second, adaptive structural support tied to real-time rock grading. The team applies different reinforcement for each rock class: umbrellas of steel rods for stable granite, reinforced concrete arches for weaker sections, and sprayed shotcrete (liquid concrete with steel fibers) to seal all walls. This requires on-site engineers capable of rapid assessment and material switching.
Third, ventilation planning that begins during excavation. Rogfast will feature two nine-meter-wide ventilation shafts (one intake, one exhaust) boring down 210 meters from the surface to handle exhaust from four lanes of road traffic. These shafts are drilled from surface, then widened vertically by pulling up a drill rig from below, then enlarged by surface-detonated explosives. This is distinct from rail tunnels, which require less complex air management.