CASE STUDY
Constructing the world’s longest, deepest subsea road tunnel with precision technology
The Rogfast tunnel is a groundbreaking infrastructure project that will significantly cut travelling time between Stavanger and Bergen in Norway. As the world's longest and deepest subsea road tunnel, its construction demands extraordinary precision. Even minor deviations in drilling and blasting could have significant cost, environmental, and logistical consequences.
Norway is known for its natural beauty, with fjords and scattered islands shaping its landscape. But the same features that carve out stunning coastlines often create logistical challenges. For example, traversing the western region from Stavanger to Bergen today means relying on ferries, extra travel time, and vulnerability to adverse weather conditions.
Spanning 27 km, the Rogfast tunnel will connect the municipalities Randaberg and Bokn. It will be the longest and deepest subsea road tunnel in the world, transforming travel and connectivity to benefit commuters, industry, and tourism. Scheduled to open in 2033, this four-lane roadway will include a roundabout junction, service tunnels, ventilation towers, and drainage systems – all built underwater through bedrock.
Skanska, one of the leading global construction and development companies, is responsible for 9.3 kilometres of the project. For this complex engineering task, they use Hexagon’s measurement technology to ensure reliable accuracy and precision.
Spanning
the Rogfast tunnel will connect the municipalities Randaberg and Bokn
Unique challenges under the fjords
Building the Rogfast tunnel demands extraordinary accuracy beneath tonnes of rock and sea. Skanska’s project manager Anne Brit Moen explains just how unique and difficult this endeavour is:
“Project Rogfast is really special,” says Moen. “Two teams are drilling towards each other, and we’ll meet underneath the fjord at 392 metres below sea level. We are used to building undersea tunnels, but since Rogfast is very long and deep, it’s more unpredictable and challenging than usual.”
The team is navigating intense water pressure and persistent leakage, all while working in a harsh underground environment. Crews contend with dirt, mud, water, and vibrations from heavy machinery. Additionally, the geological composition of the rock necessitates drilling and blasting rather than using a tunnel boring machine, introducing the added complexity of controlled explosions to carve out the tunnel.
To reach the requisite 5 centimetre accuracy amidst these conditions, Skanska must establish positioning truth to guide them deep underground.
“Two teams are drilling towards each other, and we’ll meet underneath the fjord at
below sea level. We are used to building undersea tunnels, but since Rogfast is very long and deep, it’s more unpredictable and challenging than usual.”
Surveying: the foundation of precision engineering
Surveying is more than just a technical step in the Rogfast – it’s the foundation upon which the entire endeavor is built. From establishing initial reference points to ensuring ongoing alignment, surveyors drive the precision required for a project of this scale. Even the smallest deviation in measurements can cascade into costly delays and rework, underscoring the importance of accuracy from the very beginning.
“The project starts and ends with surveying – it sets the baseline for everything. Without it, the production teams can’t do their job,” says Rolf Christian Kværnæs, head of geomatics at Skanska.
In a project as ambitious as Rogfast, where the tunnel descends beneath the fjord and GNSS signals are unavailable, surveyors face unique challenges. Maintaining the accuracy of the reference network in such conditions demands both skill and cutting-edge technology.
The Leica MS60 MultiStation combines the highest-accuracy robotic total station functionality with advanced scanning and imaging capabilities. The MS60’s capabilities go beyond traditional surveying. Its reliable positioning ensures seamless integration with machine control systems, enabling accurate leveling, compaction, and excavation. This ensures that every cut, layer, and adjustment aligns perfectly with the project’s design.
To further support surveyors, the Leica AP20 AutoPole enhances efficiency and flexibility. By allowing surveyors to tilt the pole for measurements and stakeout, the AP20 enables access to difficult-to-reach points and smooth navigation around obstructions like heavy machinery.
As Kværnæs emphasizes, “There is no room for error in a project like this, and Hexagon’s technology allows us to deliver accuracy.”
Building with insight
The ability to collect, interpret, and act on data on-site is crucial for maintaining quality and efficiency in the project. Skanska leverages advanced sensors and software to ensure that construction is guided by precise, actionable insights.
For instance, Leica Captivate field software acts as a digital bridge between data collection, design execution, and decision-making. Whether running onboard the MS60 or on a controller tablet, Captivate facilitates tasks such as staking out designs and verifying as-built conditions through its specialised tunnelling app. By allowing surveyors to view data in both 2D and 3D, Captivate ensures that design information is clear and accessible.
When Skanska’s surveyors use the MS60 to scan profiles of freshly blasted areas or surfaces layered with shotcrete, Captivate generates 3D point cloud results that can be viewed and analysed directly on-site. This immediate access to detailed data empowers crews to quickly identify issues or proceed confidently, ensuring that each step aligns with the project's specifications.
The impact of accuracy
Precision is not just a technical requirement for the Rogfast project – it is the backbone of its success. A deviation of even a few centimetres could result in costly delays, environmental disruption, and logistical challenges.
“When we drill and blast, precision has a big impact not only on costs but also on our environmental footprint,” says Moen.
For example, a deviation of 10 centimetres during drilling and blasting would result in an additional cubic metre of rock per metre of tunnel.
a deviation of
during drilling and blasting would result in an additional cubic metre of rock per metre of tunnel.
This means more energy-intensive blasting, increased debris removal, and additional truck hauls. Minimising unnecessary excavation directly reduces fuel consumption, carbon emissions, and wear on equipment.
Precision also ensures the teams stay on track to meet at the designated point beneath the fjord and within tolerance. Hexagon’s solutions help prevent errors that can accumulate and allow Skanska to consistently validate accuracy across construction stages.
Once a phase is complete, Skanska uses the Leica RTC360 laser scanner to create high-resolution, as-built scans of the area and its features. These scans, which capture High-Dynamic Range (HDR) imagery and two million points per second with LiDAR, confirm the reality matches the design. They also provide a way to reliably validate and report on progress.
A partnership driving progress
The collaboration between Skanska and Hexagon demonstrates how strategic partnerships and shared innovation can overcome complex engineering challenges.
“The collaboration with Hexagon allows us to be at the forefront of innovation,”
says Kværnæs.
The Rogfast tunnel is an extraordinary engineering ambition. It highlights Skanska’s expertise and the trust placed in them to deliver one of the most ambitious infrastructure projects in history. Faced with immense technical challenges and the highest demands for precision, Skanska relies on reliable measurements, advanced technology, and close collaboration to ensure every step of the project stays on track.
