Local communities around Stavanger, in southwest Norway, are to vote early June on the latest plan and budget – including a large loan guarantee by them – for the world recording-breaking 26.7km long, Rogfast twin tube undersea road tunnel which could start specified drill & blast excavation as early as next year.

Statens Vegvesen Rogfast project video

The latest 2015 cost estimate for Rogfast is NOK14.2 billion (US$1.87 billion). The project has been under intense design development over the last few years, and approval by the local communities would pave the way for the project to be finalised and put to the Norwegian Parliament in 2016.

Pending parliamentary approval, contract award and construction could commence also in 2016, towards the end of the year, confirms the national roads authority, Statens Vegvesen. The latest construction schedule anticipates completion in 2024.

The tunnel route lays north of Stavanger, running between portals at Harestad (nearest Stavanger) and Laupland, on the opposite side of the Bokna fjord. E39 Rogfast is being developed as a mostly toll-financed road tunnel scheme by Statens Vegvesen. A special purpose toll road company is to be set up for the project.

The proposed funding structure for the fixed link includes NOK2.83 billion (US$373 million) – about 20% of the cost – from the national government. But the funding plan mostly rests on the local region agreeing to guarantee the bulk of the funding for the project, which would be debt taken on by the toll road company.

Statens Vegvesen believes the toll structure and demand forecast would enable the project debt to be paid off by toll revenues over 20 years. The toll fee structure being presented to the local communities as part of the funding proposal is NOK300 (US$40) for cars and NOK900 (US$120) for heavy vehicles. The tolls would end after the debt is repaid.

More than 60km of tunnelling is specified for yet another world record subsea highway in Norway. As Statens Vegvesen (the Norwegian Highways Authority) prepares to tender for detailed engineering design of the 27km-long twin tube connection between Arsvågen and Harestad, Peter Kenyon talks to Project Manager Tor Geir Espedal about the extreme technical and physical challenges presented by Rogfast, and the likely plan of attack for excavating at depths of up to 392m below sea level.

Preparations are underway in Norway to tender for detailed final engineering design of the extreme Rogfast project - a 27km subsea highway connection which most recent estimates cost at NOK13.4 billion (US$2.2 billion).

Fig 1. Rogfast will be 5km longer than the nearby Ryfast tunnels

The new connection is part of a nationwide program to improve journey times on Norway's strategically important E39 Coastal Highway and, ultimately, to make redundant all eight fjord ferry crossings along this vital road corridor. The Rogfast Project is even more extreme than its nearby Ryfast sister project, where contractors have just broken ground on a separate 22km subsea connection (Fig 1).

Current design for Rogfast, based on geological surveys completed by Cowi and Sintef, comprises parallel 10.5m wide x 27km long two-lane unidirectional tunnels, a single a 9m x 4km bi-directional entry/exit ramp system at the small island of Kvitsøy, and a longitudinal ventilation system that calls for construction of three double shaft ventilation stations. Design also includes three vehicular crossover points to allow emergency access to the opposite tube. This will enable each tube the potential to switch to bi-directional operation in the event of an accident, emergency, or during localised maintenance, thereby maintaining traffic flow. Additionally, emergency pedestrian cross passages will be constructed every 250m, and every 125m where the alignment slopes at gradients of 5%, a total of more than 130.

Rogfast tunnel enables E39 to bypass 8km ferry connection and the Rennesøy tunnels

Excavation method for the main tunnel is not yet determined, but TBMs have not been ruled out and it is possible that during the construction tendering phase project owner Statens Vegvesen will make the choice open to contractors. A study has been completed that highlights a number of key benefits for mechanised tunnelling, and during the land planning stage provision is made for the location of infrastructure that would be necessary for TBM operations.

"In the detailed planning phase of the project it will be considered whether TBM excavation is feasible," Rogfast Project Manager Tor Geir Espedal told TunnelTalk. "If it is, alternative bidding documents will be developed that will make it possible to have TBM as an alternative to the traditional drill+blast method. Price and quality will then be the factors that decide which method will be preferred." Either way, tendering will be on a construction-only basis, and according to Espedal the tunnelling works will be split into three lots.

Should TBM excavation be selected the design will call for a cutterhead diameter in the 11.5 - 12.5m range, and ultimately this may be considered too great a risk given the prevailing geological conditions, some of which are not yet known and are currently the subject of a seaborne program of core drilling and seismic surveys. "Although the decision is not made yet, I believe that the tunnel will be excavated by drill+blast," said Espedal.

Complex geology and the unsurveyed "white zone"

Geology
Unsurprisingly for such a long alignment geology is expected to be a complex mix, although an analysis of the many tunnels in the nearby region demonstrates that water ingress is not likely to be a serious problem except for 7% of the Rogfast alignment. Along two-thirds of the tunnel length there is anticipated to be little or no need for injection waterproofing methods, but moderate need for waterproofing is expected to be required along 27%. A "great to very great need" for injection waterproofing will be required along 7% (2km) of the tunnel's length.

"In the Cowi and Sintef geological report summary, it is stated that the Rogfast tunnel goes through an area of complicated geology in the form of several thrust nappes and faults, where many types of rock are represented," said Espedal. "Four thrust nappes, consisting mainly of granitic and dioritic gneisses, have been defined over the bedrock."

To make matters more complicated the alignment passes a so-called "white zone" in the area just north of the staging island of Kvitsøy, for which there is no reliable geological and seismic data. Sea-based core drilling is in progress here to confirm conditions more accurately here.

"The distribution of rock types between Kvitsøy and Bokn is very uncertain but it is expected that the tunnel will go through a large fault zone just a kilometre north of Kvitsøy, and thereafter into a thin layer of nappes to eventually enter bedrock gneisses," said Espedal. "We have revealed several zones with low seismic velocities, as one could expect, but our expert geologists do not think that this makes it impossible to build the tunnel."

Ventilation station on the tiny island of Kråga

Ventilation
A longitudinal ventilation system is selected, with three stations along the alignment each featuring a double shaft, one for extraction of polluted air, the other for intake of fresh air.

"There will be one ventilation station on the mainland in Randaberg, one on the island of Kvitsøy, just beside the start of the tunnel ramp to the island, and one on a small island called Kråga just before the mainland at the northern end of the tunnel alignment at Arsvågen," said Espedal. The shafts will be 160m, 260m and 200m deep, two at each location, all with a diameter of approximately 6m, implying a total vertical shaft length of 1,250m.

"The shafts will probably be constructed by drilling a small-diameter hole from above, followed by drill+blast also from above. Blasted rock will then fall down into the tunnel and be transported out from below," said Espedal.

Three vehicle crossover passages are included in the design

Fire and safety
A major element of concern, and one of the most complex aspects of the project, is the access ramp that enables entry and exit to the main tunnel at the half-way point along the alignment: the island of Kvitsøy. The interchange of Rogfast with the tunnel arm to Kvitsøy is planned to be of a two-level design with four ramps, a design not permitted under European safety directives for Trans European Road Network (TERN) routes. This has required special dispensation to be granted, but there is still a fire safety problem concerning regulations that specify the tubes along the main tunnel must be kept as separate fire cells; one possible solution that has been suggested is to install fire doors to separate the ramps to Kvitsøy.

Fig 2. Complex Kvitsøy access ramp system

Aerial view of Kvitsøy entry/exit portal

The highly complex design effectively means that the four one-way entry and exit ramps will be run underground and connect with two underground roundabouts that will allow the crossover of north and southbound traffic in a bi-directional tube just above the main tunnel (Fig 2). All traffic will enter or exit this below-ground roundabout system via a single tube 9m x 4km gyratory "arm" that will afford bi-directional access to and from Kvitsøy into and out of the main Rogfast tunnel. The need to maintain slope below 5% necessitates the circular alignment of the Kvitsøy tunnel at this point.

Originally designed with a maximum slope of 7%, the 6km section of tunnel at the northern end of the alignment has been flattened to 5%, extending by 1.5km the original 25.5km length of the tunnel. "This summer (2013) we had to change the plans for the tunnel, and adjust the incline in the northern part of the tunnel due to European regulations, and so we have had to start all over again with a new zoning plan for the road in the north," said Espedal. "This takes time, approximately two years of extra time, but we hope to make some shortcuts, and run some processes in parallel, so that we can have approval from the Norwegian Parliament in 2015."

Procurement and funding
"At this point we do not exactly know when the construction procurement can start, but a normal procedure would suggest 2016. We are hoping to make it earlier, 2015, but this depends on the Government's willingness to make some shortcuts in the approval procedure," said Espedal. "As with the nearby Ryfast project, it will be construction-only contracts. The funding of Rogfast is similar to Ryfast, although with a slightly larger amount of money from the state; at the moment the funding is based on approximately 20% state funding and 80% tolls."

Tunnel construction will be broken down into three lots – the northern section of twin tube main tunnel between Kvitsøy and Arsvågen, the southern section of main tunnel between Harestad and Kvitsøy, and a third lot that will comprise construction of access ramps and the gyratory access tunnel system at Kvitsøy. The process to engage a design consultancy to perform detailed engineering designs is expected to begin "before Christmas" (2013), said Espedal, and with a 7-8 year construction period completion is targeted for 2022-2023.

References

Norway begins Ryfast tunnel construction - TunnelTalk, October 2013
Tendering for world-longest subsea road tunnel - TunnelTalk, January 2013
New undersea mega-project for Norway - TunnelTalk, May 2012
Links across the waters: Straits Crossings conference report - TunnelTalk, January 2010

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