Bressay tunnel in three years, say engineers behind project
By ROSALIND GRIFFITHS
THE FIRST vehicles could be making the 85-second journey through a tunnel to Bressay within just over three years if it wins approval, it emerged this week as fuller details of the project were unveiled by engineers.
Provisional plans show a 1,200 metre long tunnel, only 350 metres of which would be under water, with a gentle gradient, two lanes for vehicle traffic and a narrow hard shoulder for safety but no walkways or cycle lanes.
The tunnel, which would be the first subsea hard rock construction for road of its kind in the UK (others such as the Clyde, Tyne and Mersey tunnels are under rivers or river estuaries) would be built by drilling and blasting through the sandstone conglomerate rock, with an automated machine with robotic arms at the heart of the process.
The new details emerged this week during two roadshows hosted by the Bressay Tunnel Project Team, which comprises ZetTrans, Shetland Islands Council and Glasgow-based engineers Donaldson Associates. In June this year, the council decided to explore the tunnel option further following a Stag (Scottish Transport Appraisal Guidance) study which found that it best answered the needs of businesses and the community.
The early plans have been drawn up by Donaldson Associates and the team is likely to go to the council for a decision on whether to proceed in April of next year. Planning permission would be sought after this decision.
According to the plans, the entrance to the tunnel on the Lerwick side would be near the existing Gremista road. It would then head out under Shetland Catch, under the sea and emerge at Heogan. Only 350 metres of the journey would be under water, with the length of the tunnel meaning a very gradual gradient. The whole journey from portal to portal is expected to take a minute and 25 seconds.
Lead official of ZetTrans Michael Craigie said that a specialist contractor would be needed for the tunnelling work but Shetland companies would be employed in ancillary works, such as road infrastructure and removal of spoil. He estimated construction could start in March 2010 “with a fair wind” and take about 20 months, with the first vehicles travelling through in January 2012.
Mr Craigie said of the trail-blazing nature of the project: “Attention would be paid to this tunnel at national level because it would be the first sub-sea tunnel, and there could be attention from other Scottish islands.”
He said that although the “base cost” of the tunnel was £26.5 million, a sum of £46 million has been suggested to include “contingencies”. By April there will be a better idea of the total cost. If the council gives the go-ahead the project would then enter the “consent and procurement” stage, involving serious spending.
But at the moment work is going on to involve businesses and communities, with planning being the key. Transport strategy officer Emma Perring said: “We have a good process in place. Making sure everyone’s involved puts the project on a good foundation.”
In engineering terms the tunnel would be relatively simple to build, according to Donaldson Associates director Andrew Sloan, thanks to the shallow waters of Bressay Sound, only nine metres below chart datum.
The drill and blast tunnel would go through the sandstone conglomerate rock, with an automated machine with four or five spider-like robotic arms doing the tunnelling. One man would sit in the machine and could override the computer-controlled arms, if necessary.
At each stage the rock would be injected with cement grout before blasting to reduce water ingress and the tunnel would be lined with sprayed concrete.
Mr Sloan described the construction system as “highly automated and sophisticated”.
The tunnel, which would be underneath 25 metres of solid rock, would have many safety features.
Mr Sloan said: “There will be a narrow hard shoulder for safety and CCTV and smoke detectors in the internal controls. And management of the tunnel would be easier and safer because of the low number of users. The key is planning and ZetTrans are doing it very well. We are now furnishing data so that an informed decision can be made in April.”
Between now and April there are many issues to explore. These are consent options (permission to build under a legal framework), procurement options (how best to appoint advisers and specialist contractors), funding options and engineering studies, which include topographical and bathymetric (sea bed) surveys.
Then there will have to be an Environmental Impact Assessment (EIA) without which planning consent cannot be given. It will go out to tender.
Environmental consultant Annie Say, who helped with the Stag process, said the study would consider land use, flora and fauna, flood risks, crofting interests and Lerwick Port Authority interests, the appropriate use of the tunnel spoil and whether existing buildings such as Shetland Catch would experience noise or vibration.
At the moment, said Dr Say, there do not appear to be any “show stoppers”. She said: “At this stage there are no apparent issues of particular concern although all issues need to be investigated. If we do this well it could have relevance for other peripheral communities.”
Mr Craigie said he had been encouraged by the large public turnout to the roadshows, with 40 or 50 folk at Bressay and a steady stream in Lerwick. “What’s impressed me is people’s curiosity, not just in the link but in the technology.”
If the project were a success, the next “obvious” tunnel to build would be Bluemull Sound. Yell Sound would be more difficult and could be 15 years into the future. Whalsay’s infrastructure needs attention soon and cannot wait for a tunnel option there to be considered.
Meanwhile, the team suggested the tunnel could lead to an improvement in the Bressay infrastructure. There would be work done on the Heogan road and walking and cycling would be encouraged to and from the tunnel as there would be 11 buses per day to take walkers and cyclists through it.