How long will it be? And how deep? We give you all the numbers on the construction of the world’s longest and deepest road tunnel under water.
Driving under the fjords
A tunnel under water – how can that be done? With more than 40 years of experience of constructing tunnels, Knut Storli, Foreman at contractor NCC, is one of Norway’s tunnel experts. Here are the challenges of building tunnels under the sea.
History holds several examples of tunnel constructions under water. The first, The Thames Tunnel in London, was inaugurated in 1843 and considered a civil engineering success. Since then, Norway has picked up the mantle as the world’s foremost tunnel builders. The country holds examples of several spectacular tunnel constructions. One of them being the Laerdal Tunnel, the world’s longest road tunnel. Now, Norway is planning the world’s longest and deepest underwater road tunnel.
Knut Storli, Foreman at NCC, is one of the experts working on the first phase of the tunnel.
How do you start with a project such as an underwater tunnel?
When constructing a megaproject such as Rogfast, you need to take it in several steps. The first thing you do when starting a project is a thorough geological and seismological investigation of the area to get a proper picture of the rock mechanics you are going to work in. Then, we will start by constructing two parallel cross-cut tunnels that will be used for transport of excavated materials during the construction of the two main tubes. When Rogfast opens, the cross-cut tunnels will be used as ventilation shafts.
How do you tackle the challenges of building a tunnel under water?
To make sure we don’t run into any water or softer layer of rock that is difficult to work through, we drill probe holes with the tunnel rig, normally
24 to 27 meters in front of the tunnel. If we discover any leakage, we seal the tunnel by drilling several holes around the tunnel profile and pump a water cement mix with high pressure into the rock cracks. Another challenge is the risk of salt water that can seep through and cause damage to the equipment.
From an environmental point of view, there are very strict rules for what we can dump back into the sea. The water and mud from the drill and blast construction must be decontaminated and cleared of any oil remnants or other impurities. Once the construction is complete, ventilation is a major issue. The cross-cut tunnels we are building will be used for this purpose. In case of a fire, controlling the air currents in the tunnel are of vital importance to the rescue work.
What kind of equipment is needed?
We use a mix of Norwegian and Swedish tunnel rigs. We also use wheel loaders, articulated haulers and trucks that move the blasted rocks out of the tunnel.
Why are Norwegians so good at building tunnels?
We’ve been doing this for a very long time, so we have highly developed competence and techniques. Also, we have a lot of experience in building underwater tunnels for hydro power. I have just left a project on the Faroe Islands which was one of the most exciting projects I’ve done, with an underwater roundabout near the city of Torshavn.
What makes the Rogfast tunnel special?
It will be the deepest and longest underwater tunnel in the world. But constructing it will need the same equipment and the same expertise as for any other underwater tunnel. You always need to be 110 percent safe when working on such a project.
Norway embarks on the country’s biggest infrastructure project in modern history. Here is the story on how the contemporary Vikings are shaping a new future under water.