Ensuring quality in the world's deepest road tunnel
392 meters below sea level, crews are blasting what will become the world's longest and deepest undersea road tunnel. Statens vegvesen has engaged NGI to conduct independent quality control throughout the construction of the massive tunnel project.
This is how the tunnel entrance at Kvitsøy will look when the Rogfast project is completed. ( Illustration: Norwegian Public Roads Administration / Norconsult)
The E39 Rogfast project will connect Stavanger and Bergen without a ferry crossing. A 27-kilometer tunnel beneath Boknafjorden, complete with a full road junction blasted out of the rock beneath the island of Kvitsøy. When the tunnel opens as planned in 2033, it will cut travel time by 40 minutes.
– NGI holds the contract for extended independent control of excavation and rock support on the E39 Rogfast tunnel, says Arnstein Aarset, who heads the engineering geology and rock engineering section at NGI.
The control contract covers four major tunnel contracts: the Kvitsøy Tunnel and the three sections of the Boknafjord Tunnel – central, south, and north. NGI's job is to verify that everything carried out beneath the seabed meets the specified requirements.
A future tunnel bore (left) and exit ramp (right) beneath Kvitsøy. ( Photo: Ø. Dammyr)
An underground road junction
What sets Rogfast apart as an extraordinary tunnel project is the combination of extreme depth and demanding geology. Beneath Kvitsøy, crews are building a complex network of tunnels, exit ramps, rock caverns, and vertical shafts that reach almost 400 meters below the sea surface. The entire system must handle fresh-air supply and fire ventilation to function as a safe driving route.
– It is a complete system of tunnels, shafts, and rock caverns, all blasted out of rock that has never previously been mapped in detail, says Aarset.
The tunnel is built with two separate bores with escape connections between them. This allows traffic to be evacuated rapidly when needed and ensures vehicles can get through, even in the event of an accident or maintenance work.
Demanding geology
The rock masses beneath Boknafjorden carry a long geological history. Volcanic activity, tectonic movements, and millions of years of transformation have produced a rock foundation that varies considerably along the tunnel alignment.
– The geology at Rogfast ranges across rock masses of sedimentary, volcanic, and igneous origin, with varying degrees of metamorphism. The rocks also bear the marks of past crustal movements, which have created fractures, faults, and zones of weakness, explains Aarset.
The preliminary investigations identified several critical weakness zones. Particularly challenging are the graphite-rich black shales near Kvitsøy – a rock type that becomes unstable when exposed to air and water.
– These zones demand extra attention in terms of waterproofing solutions, tunnel driving, and management of rock mass stability, he says.
Control built for the long term
NGI's control assignment is not just about ensuring the tunnel is built correctly today – it is about ensuring it will function safely for decades to come.
To achieve this, the NGI team closely monitors whether actual rock conditions match the design assumptions, particularly regarding waterproofing, rock support, and documentation. All the technical work serves one overarching goal: to ensure the tunnel can withstand the stresses it will face in the future.
– We need to know with certainty that the support will hold. That is the difference between a tunnel that is safe today and one that is still safe in fifty years, concludes Arnstein Aarset.
Arnstein Aarset
Head of Section Rock Engineering Rock Engineering arnstein.aarset@ngi.no+47 976 00 103