Working out on Bokna fjord in south west Norway, on the small windswept and exposed island of Kvitsøy, which rests slightly north of the oil and gas town of Stavanger, tunnellers are steadily making their way underground to prepare for the main excavations of what is to be the world’s longest and deepest undersea road tunnel.

Out in the middle of the fjord, surrounded by deep waters, Kvitsøy is leading the early tunnelling works for the 26.7km-long, twin-tube Rogfast road project. These latest early excavations call for a spiral access adit to descend from Kvitsøy island down to the level of the main tunnels. Two large ventilation shafts, approximately 230m deep and approaching 10m in diameter, will also be sunk from the island, soon.

Rogfast is a strategic lynchpin in the country’s constantly developing E39 West Coastal highway, which has been underway for years and still has some decades to go. The coastal road is an inter-generational asset that uses the many subsea tunnels and bridges over fjords to thread together faster transport links and, progressively, replace many of the ferry crossings over the exposed waters along the rugged and mountainous west coast.

The E39 West Coast Highway is being developed by Statens Vegvesen, the Norwegian national roads authority (NPRA), and Rogfast is by far its longest subsea tunnel project although it has built many. The Rogfast project is to be a toll tunnel, which is to help cover approximately 40% of the budget, the balance to be supplied by state funding. The latest budget reference for the roads authority is NOK20.6 billion (US$2 billion), at 2020 prices.

NPRA already has significant subsea tunnelling experience locally, in the Rogaland region, primarily in recent years with the Ryfast fixed crossing which passes below a different fjord beside Stavanger on the Randaberg peninsula. It is also a toll tunnel and has already come into service.

The roads authority is also looking at a missing link between the network of Stavanger tunnels and Rogfast, slightly to the north. The gap may be filled by a shallow stretch of works, possibly cut and cover, on the relatively short E39 Smiene – Harestad project.

Stavanger’s place as a northern tunnelling hotspot will continue as more underground construction in the area takes hold and continues for the rest of the decade. The current schedule is for Rogfast to open to traffic in the middle of 2033, says NPRA.

GEOLOGY AND EXCAVATION METHOD

The geology below the Bokna fjord is varied, including along the alignment of the Rogfast tunnel, explains NPRA’s project manager for Rogfast, Oddvar Kaarmo. The geological profile was developed over some years with drilling campaigns from ships and also geophysical measurements, spread over the broadly south to north alignment that stretches from near Stavanger, on Randaberg peninsula, over to Bokn, on Laupland region, at the north side.

Along that broadly south to north path, with its curving horizontal alignment, the subsea tunnelling works are to blast through varied, clearly separated, zones of rock below the fjord, starting with phyllite before changing to gabbro, greenstone and slate, then some granitic gneiss, and finally a long stretch of bedrock gneiss/granite. A number of weak zones have been identified along the route.

The vertical alignment of the subsea road tunnel follows fairly the undulating sea bed profile but its changes in the tunnel grade also correspond, to some degree, to where changes in the rock types occur.

On the south to north path, Rogfast road tunnel’s vertical alignment:

  • descends from the south portal on Randaberg peninsula to run at maximum incline of 5% passing through phyllite, by when the tunnel will have reached depths approaching 300m;
  • then the alignment rises about 60m over about 4.5km through gabbro;
  • the alignment then crests in greenstone and slate, then dip a little where the main tunnels will pass under island of Kvitsøy and then run deeper again;
  • the deepest part of the tunnel will be approaching almost 400m in depth shortly after the alignment enters the long stretch of bedrock gneiss/granite, and from there it climbs up at 5% grade toward the surface, reaching the north portal on Laupland.

While drill and blast is an area of long-time expertise in Norwegian tunnelling, recent years saw a return of tunnel boring machines (TBMs) to underground projects in the country, notably for large rail tunnel projects, such as in Oslo and Bergen. Some decades ago, prior experience with TBMs in Norway was primarily in hydropower development, for headrace and tailrace water conduit tunnels.

After assessing the alternatives, NPRA has chosen for a combination of reasons to have all major tunnelling for Rogfast undertaken – as done on the nearby Ryfast tunnels – by drill and blast. Given the geology, it is anticipated that extensive use will be made of pre-excavation grouting (PEG) of the rock ahead of the advancing faces. PEG is another area of strength for the Norwegian and Scandinavian tunnelling markets and capabilities with the approach are also growing internationally.

PLANS AND PROCUREMENT

The journey of project development has been long one for Rogfast but this often happens with many planned major infrastructure projects, including tunnels, in Norway and elsewhere. Rogfast plans to take twin, large, T10.5 profile (10.5m wide at road level) tunnels undersea. Time timetable for Rogfast has been pushed back, and back again.

Procurement first got underway shortly after the national Parliament approved the project plan in 2017 and budget was also in place, anticipating then an opening by 2024. Bid levels came in too high from the construction market at that time, busting budgets. Some rethinking and potential for procurement changes were examined, and market consultations undertaken – all before the covid pandemic.

For all those reasons, the procurement plans and schedules, and the opening date of Rogfast, were progressively pushed back. The overall plan to have three major contract lots to execute the tunnelling works, though, has broadly remained in place over recent years.

The main lots on Rogfast have been as follows, from south to north:

  • Harestad lot (E03), at the south end of the project, coming off the mainland from near Stavanger and running north but not quite as far as the island of Kvitsøy;
  • Kvitsøy Lot (contract E02), located out in the middle of the open fjord, to create a maze of deep construction access and ventilation structures as well as its own stretch of main tunnels plus an underground interchange; and,
  • Laupland lot (E04), completing the northern end of the tunnel route.

However, the sequencing did shift for the main lots. Kvitsøy lot (E02) had always been the front runner of the three packages in preparing for procurement, and it accounted for about a third of total tunnelling on the project. Most recent plans for the works on and under the island, however, split that original package of access and main works.

Additionally, procurement for Harestad (E03) and Laupland (E04) lots, each containing long runs of main twin tubes only, plus cross passages spaced at 250m intervals, have taken the lead in the procurement schedule. They are expected to be awarded first – later this year, potentially.

Each lot has already had NPRA going through some rounds of negotiating procedures with prospective contractors, after each stage of which further revised prices offers are put forward. With the processes well advanced, the lots are approaching their final stages towards contract awards, pending as ever that they satisfy budget ceilings.

PREPARING FOR MAIN TUNNELLING

The tunnel packages are mostly the same, except for a split between the access and main works in the original Kvitsøy lot (E02).

A long access adit ramp, a pair of deep shafts, main tunnels plus a complex network of tunnels for an undersea interchange, and also technical rooms, were all originally part of the Kvitsøy lot (E02).

NPRA’s project manager for Rogfast, Oddvar Kaarmo, tells T&T that the earlier plan to have all of the Kvitsøy work in lot E02 “was terminated.” It was decided to carve out a smaller package of works that would allow the key site and construction access infrastructure to get established first out in the middle of the fjord. This plan was achieved by carving out a package of access works to form a new lot, named E15, which was then put out to procurement.

Kaarmo says E15 took about a quarter of the construction works originally planned for E02 lot. He adds that having smaller contracts has helped competition. Meanwhile, the new, slightly smaller, E02 lot which is minus the access works is still in the procurement pipeline.

The E15 package is dominated by construction of the main access tunnel – a 3.75km-long ramp to spiral down from the island surface to reach the level of the main and interchange tunnels. Works on the lot also include establishing the initial site works on the island as well as associated surface structures, such as bridges and roads, adds Kaarmo.

Contractor on lot E15 is Hæhre/Risa. The JV is blasting the spiral adit on a 7% incline and progress has been going well, the client reports. More than 1km, or over a quarter, of the length of the access ramp has been completed already. The adit is expected to be finished by mid-2023.

The two deep ventilation shafts at Kvitsøy remain part of the reduced E02 main works package, which it is anticipated could start rounds of competitive procurement negotiations in 2023, possibly after the adit tunnel is approaching finish or is sufficiently well advanced.

Kaarmo says: “The final details regarding the execution of these two shafts will be described in the competition basis” with evolving competitive contract negotiations including developing design and construction proposals as well as price levels.

The shafts work as a couple in the ventilation system, one as intake for fresh aid and the other exhausting the air from underground, and both powered by fans, and electrical and mechanical equipment, in the technical rooms in blasted cavern rooms, down among the interchange tunnels. The rooms will also hold equipment to power lighting and drainage needs.

All the E15 and E02 underground works – the ramp, shafts, the stretch of main tunnels plus the ‘pit bottom’ interchange junction, and technical rooms, are all located in geology comprising mainly greenstone and slate, with some gabbro.

“We know for sure that the shafts and the intersection area are buildable,” says Kaarmo. He adds, “The contract will describe any other details,” such as particular options for construction methods.

But he adds: “The shafts at Kvitsøy will, in general, be produced with ‘core drilling’ from the top, and then drilled upward, in some degree or distance. The raise boring approach will be up to the contractor, in some measure, for Kaarmo adds further that the shafts would be extended by sequenced traditional drill and blast method.

Consultants working for NPRA on the Kvitsøy works, across both lots, are Norconsult for tunnel design and Multiconsult for environmental matters on the island, says Kaarmo. Other consultants take on some tasks, he says, and yet other work is handled internally by NPRA.

In future, perhaps around 2026-27, NPRA aims to is contract notices for the mechanical and electrical fit-out packages, covering technical rooms and buildings, pump stations, electrical substations and transformer rooms, emergency call points for road users, impulse fans for tunnels, shafts ventilators, and also creation of a ventilation hall (60m x 19m x 14m).

During the operational life of the Rogfast crossing, the access spiral tunnel will function as an intermediate, local access to the undersea crossing, further opening up the transport and commuting possibilities in the region.

PROGRESS AT KVITSØY ADIT

The entrance portal to the Kvitsøy tunnel adit is approached in an excavated trench and was blasted open to have a road approximately 1.6m below sea level at the start, about 100m from the sea, NPRA’s construction manager for E15, Sveinung Brude, tell T&T.

“So, we are under the groundwater level,” says Brude. He adds, of the advancing drill and blast works and water ingress, “We had fresh water over about 500m before we have seawater.”

Progress has gone fine.

Speaking to T&T in late August, he said, “We are 1100m inside the tunnel now with no big challenges. We have just three rounds of grouting.”

Brude says: “We have a good geological report, we find what we expected.” He adds that seismic checks ahead of the face are being used.

The E15 tunnelling works will go as far as the first roundabout at the interchange zone under the island, at the level of the main tunnels, and this marks the boundary of the start of main works package E02. Another branch of the E15 tunnel will go, though, “to the first ventilation cavern, by the bottom of the future shafts,” says Brude.

Brude reports that others can learn from the experience so far that “The geology is fairly good.”

OTHER ADITS AND SHAFTS

A further deep shaft, potentially for ventilation purposes in future operations – or at least for use during the construction stage, is to be constructed below the southern, mainland, end of the Rogfast crossing, at Tungenes on the Randaberg peninsula. The site will have one shaft only. The large shaft is expected to be more than 140m deep and built as part of the E03 lot. Geology in that area is principally phyllite.

The other excavations to reach down to the main tunnel levels are a number of large access adits, including: the spiral ramp at Kvitsøy; a relatively short tunnel already built at Mekjarvik (Lot E11), closest to the southern portal – “where it is possible to walk down to the main tunnel” already, says Kaarmo.

Also already built is a longer tunnel, near the northern end of Rogfast’s alignment, near Bokn. It is the Arsvågen adit (Lot E13) which might double-up as a ventilation conduit in future, eliminating the need for a separate vertical shaft. But, again, it might only be principally used for the construction stage.

Kaarmo says, though, that the Arsvågen adit and the Tungenes shaft might not be key parts of the eventual, final, ventilation design, depending on how that develops along with take up of new transport technology.

“More use of electrical vehicles in society in general will most likely reduce the need for fresh added air to the tunnel,” he says.

However, air quality needs during construction stages is vital, adds Kaarmo. He says of the length and depth of the tunnelling works that they “will probably challenge the contractor.”

Kaarmo says: “The contractors have to be careful while producing the tunnel, and thereafter excavating blasted rocks from the tunnel and transporting them up to the surface. Which means not a higher activity in the tunnel than what the air quality allows.”

Should Tungenes shaft not be required in future it is expected then to be filled or closed off.