a deeply fjord-indented coastline, with an archipelago of offshore islands whose inhabitants need contact with the mainland, communications are obviously difficult.

Nordoyvegen is currently the largest country road project in Norway. It is an impressive one. Five islands off the westernmost coast will be joined by road to each other and to the mainland. North to south they are Haroya, Fjortofta, Skuloya, Haramsoya and Lepsoya. Islets and rocks play their part as well.

Around 2,900 people on the islands at present rely on a farfrom- straightforward network of ferries between the different islands and the mainland, with extra high-speed vessels and ambulance boats when necessary. This is in latitude 63 degrees north, some 200 miles further north than the Shetlands, and winter seas can be rough.

In future, transport will be by road. Three subsea tunnels, and one land tunnel (to preserve a small island’s environment and give a wildlife corridor) totalling 13km will link the chain of islands; three bridges will join the first main island, Lepsoya, via the much smaller Hestoya, to the mainland. It is an ambitious project in wild and beautiful land- and sea-scape, and it is easy to see why it is regarded as spectacular.

The logistics alone are daunting. “You could call them quite challenging” says Lars Erik Skjolden – with some understatement. Skjolden is chief engineer for Skanska, the project’s contractor. “We are building tunnels on five different islands, and the bridges are built from a site on the mainland.

To get to the islands today you need two different ferry routes from the mainland.

There is one northern route based in Brattvag that takes you to Fjortofta and Haroya islands; we are building the Fjortoftfjordtunnel, 3.6km, to join them. The Nogvafjordtunnel is 5.7km and goes between Fjortofta and Skuloya. But to get to Skuloya you need to take an altogether different ferry that starts from a different port on the mainland.

“That is also the ferry we take to get to the site of the northern part of the third major tunnel, Haramsfjordtunnel, which is based at Haramsoya. But to get to the southern end of the tunnel there are no ferry routes at all. We have had to build our own temporary quay and dock.

To get people, equipment, machines and deliveries out to Hestoya we have a subcontractor with his own boat. The boat is called the ‘BB Lifter’ and it is an old 1970s first-generation supply boat from the oil business.

Because of the project’s size and the distances involved, Skanska has set up one main office on the mainland and two forward offices on the islands.

All work on the bridges and at sea is administered from the mainland office. Each island office has 60 rooms to accommodate the workers.

Skjolden explains: “Tunnellers working on Hestoya have to be transported from the mainland for each shift. Also, we have concrete factories established at Skuloya and Fjortofta to provide the tunnels with shotcrete and other constructions. Shotcrete for Hestoya is transported from Skuloya by offshore supply ship BB Lifter. For deliveries we have good communication with our different suppliers, so there is not much trouble with getting what we need, but we have to have more parts and wares in stock than normal to make sure we don’t run out of anything. Deliveries need a couple more days than if the project was in Oslo.”

The sub-sea tunnels are all more than 100m below the water surface. The tunnel at Hestoya has a notable feature: its entrance is offshore from the island and is eight meters below sea level.

The portal was originally designed to be on the island itself, with the tunnel inclining downwards at a gradient of 10%; but several tunnel fires in Norway led to a re-design. It was realised that steep inclines into or out of tunnels give increased risk of mechanical problems in heavier vehicles, such as overheating brakes and transmissions, and is the main cause of fires in such tunnels.

The Norwegian Centre for Transport Research found that 40% of the fires in tunnels happen with inclines steeper than 5%. The risk increases when, as at Nordoyvegen, three tunnels come after each other in close succession. That increases the strain on large vehicles several-fold, which therefore leads to higher risk of overheating and fires.

Consequently, the Nordoyvegen gradients were reduced from 10% to around 4% where possible, but in some cases to around 7% or 8%. That is still steep, and will need special attention paid to fire-safety equipment and procedures. But a consequence of the change was that the entrance to the Hestoya tunnel is now not only offshore of the island but is also below sea level.

Cars do not have to be sub-aquatic, however. To keep the sea out, the road to the entrance will be within a purposebuilt dyke, rising up on either side of the road. The dyke has a waterproof core of asphalt, similar to those used on hydro powerplant dams. To build it, a temporary cofferdam has been constructed.

“The temporary dam gives us a dry construction pit to start the tunnelling” says Skjolden. “We will be constructing the permanent dykes at the same time as we are doing the tunnelling. Then the temporary dam will be removed.”

The finished tunnels will be to a standard Norwegian profile, originating from the national road administration and known as T8,5. This sets widths and profiles. The roadway – one lane in each direction – will be set within a near-semi-circular arch of about 10m diameter; there will be no overtaking lanes, but emergency stop and breakdown niches every 500m, a fire water system permanently installed, and niches wide enough for U-turns. In addition, there will also be extra-long emergency stop/breakdown ‘pockets’ outside the tunnel entrances.

“At the bottom of each tunnel there is a large excavated cavern, 100m long and 20m deep, that acts as a sump for storing, cleaning, and pumping out water that leaks into the tunnel” says Skjolden. The sub-sea tunnels are all more than 100m below the sea surface.

Tunnels will be excavated using drill and blast, Skjolden explains. “The blasting patterns are of a Norwegian standard for tunnelling. We drill from 100 to 115 holes which are charged with bulk explosives. The holes range from 48mm-64mm in diameter, and the number and size vary depending on whether we are using non-electronic or electronic blasting systems. For the standard cross-sections we drill the holes about 5.8m into the rockface and use about 800kg of bulk explosives. A lot of the rock mass that is hauled out of the tunnel is taken by barges and tugboats to make foundations for the three bridges that are being built between the mainland and the first islands. All the rock mass that is dumped at sea is blasted with electronic systems to reduce the amount of plastic going into the sea. The electronic blasting systems is based on copper wires, debris from which will not float up and pollute the ocean. “Our projected rate of advance is 40m per week per site,” explains Skjolden.

“That is an average based on geological reports of how much good and how much poor geology we meet. Some sites go as planned but as of today we have had a larger amount than expected of poor geology on some sites, meaning we haven’t been able to live up to our projected advance rate. We vary from 6m to 65m per week, depending on rock quality and water leaks. If the rock mass is very poor, we often reduce the length of the blast to 3-4m and we secure the contour with 32mm steel spiling bolts 6m long. If it is even poorer, we build up steel-reinforced shotcrete ‘bows’ from the floor over the contour. Poor rock quality combined with water leaks reduce our weekly advance rate very considerably. That is why we have sometimes achieved under 20m a week.

“The geology reports are based on some preliminary investigations of the rock quality, done by drilling core holes and by seismic refraction. That tells us where to expect zones with poor rock. But as well as the preliminary tests we have it written into the contract that when we are under sea and less than 40m below the sea bed, or if we have seismic refraction results of less than 3000m/s, we must drill a core hole in the tunnel past the expected poor zones.

This is to check what kind of geology we will meet. We have built our own rig for this, based on a Sandvik core drilling machine. We also have to have preparations in place in the case of a tunnel collapse. For that purpose, we have built a hydraulic steel shield on a Cat772 truck. If there is danger of collapse, we can close off the tunnel to isolate the area and fill beyond the closure with concrete to stop the collapse from expanding.

The construction team is working on all the tunnels simultaneously; it presently has five tunnel rigs working at five different sites. Four new AMV rigs were delivered from the factory at the start of 2019. The fifth rig is an Atlas Epiroc. All rigs have 20-feet guides. That means they can drill up to 6m per blast if the rock mass quality allows it.

“We have wheel loaders and semitrucks to load and haul the muck out of the tunnel. The wheel loaders are either Cat 980s or Cat 988s. Early in 2020 we brought in three AMV hybrid front loaders to replace three of the wheel loaders. These new machines load up by electric power in the tunnel, which is positive for the environment globally and good also for the work environment in the tunnel. The new machines also perform scaling during the loading cycles, which removes the need for a separate machine do to that. We intend to certify Nordoyvegen as environmentally sustainable, with CEEQUAL certification; the hybrids will contribute to that.

Skjolden continues: “We also have three injection rigs from Epiroc that cover all five different sites when they need injection because of water leaks in the tunnel. We systematically drill four 25-30m-long holes to check for water in front of us. These long holes have to overlap by at least 8m. Normally we do three or four blasts between each long hole-drilling session. If we have more than 10L/min leakage over all four holes combined we need to drill a screen around the tunnel and begin injection. We normally have 35- 40 screen holes for this. The water that leaks into the sub-sea tunnels is mostly saltwater, not fresh, and it is not good for our machines. This means we have to clean and maintain them constantly to make sure they are in shape. At each site we have established halls for maintenance and we have own mechanics at each shift.

With five sites in production, there are 15 teams working in rotation, three at each site. One is on day shift, one is on night shift and one shift is at home. The teams work two weeks on and one week off. Each team has three workers doing the tunnelling, one mechanic and one electrician, making around 70 tunnel workers in all. Some shifts also have young apprentices working their two years to get their certificate, after which they can start as tunnel workers. There are also three shotcrete rigs on the project, one for Haramsoya and Skuloya, and one that is shared between Fjortofta and Hestoya. Those are provided by Entreprenorservice, which is a company owned by Skanska.

Work started in January 2019 and so far, as of the end of April, around 45% of the tunnelling has been completed, with overall completion planned for the summer of 2022.

Nordøyvegen project

  • A permanent connection to the mainland for a population of around 2,900 on islands in the Haram and Sandøy area of coastal Norway
  • Three subsea tunnels, one land tunnel, three bridges and 10km of roadworks replace two ferry routes
  • 13 km of tunnels in all: Haramsfjord Tunnels, 3,500 m, 112m below sea level Nogvafjordtunnel, 5,730 m, 134m below sea level Fjørtoftfjord Tunnel, 3,680 m, 118m below sea level Burberg Tunnel, 170m – land tunnel, to give wildlife corridor bridge.
  • Blast rock from tunnels is used to form bridge foundations and rock-dumped causeways: 800,000 pam3
  • Soil excavation and transport: 200 000 pfm3
  • Dredging:35 000 pfm3
  • Tunnel Portals: 360m (eight in total)
  • Tunnel bolts: 56,000 pcs

Bridges:

  • Lepsøy Bridge, 800m
  • Lauke Bridge, 110m
  • Hamnaskjersund Bridge, 200m
  • 2.7 km landfill in the sea – 800,000 m3

Asphalt core dyke formed around the Hestøya tunnel portal