The engineer in charge of delivering the £1.6bn A303 Stonehenge Tunnel has said that potential contractors are nervous about the risk of tunnelling at a World Heritage Site (WHS).
Speaking at the New Civil Engineer Tunnelling Summit 2017, Highways England programme director A303 Stonehenge Derek Parody said that while there had been a strong appetite from some contractors, the issue of risk allocation was one of the sticking points.
“It’s fair to say it varies [on the interest from contractors],” he said. “There is quite a strong appetite from certain parts of the contracting community. The things still being addressed that are perhaps making people slightly restless is say, the risk allocation. For example the archelogy where does the archology risk sit?
“I didn’t list archaeology as a challenge as the archaeology of the WHS is really well understood. We know what’s there, so it’s about developing a strategy to get to the point where archaeology is no longer an issue for the people building it.”
Parody also detailed the challenges of building a road and tunnel through the WHS.
The scheme involves building a 2.9km long twin-bore tunnel through the World Heritage Site with portals inside its boundaries.
To build the scheme, Parody said the road and tunnel would have to be “invisible” in both the permanent condition and during construction.
During construction, water would present a significant issue as there was a significant aquifer underneath the WHS and water levels in the ground changed rapidly between the seasons. He said the contractor would have to choose whether to dewater or not, but there would have to be a clever solution to not pumping “millions of gallons of water” on to the surface.
He also said the logistics of getting the tunnel boring machine, equipment, plant into the tunnel and in excess of 1M.m3 spoil out of the tunnel down the single carriage way road while keeping it open would be significant.
Lighting the road in the dark skies environment would need a clever solution to keep road users safe, especially at junctions.
“How do you make the existing road safe without all of the paraphernalia which goes with a site,” he asked. “All the signage, the lighting at the entrance to the tunnel which usually goes with it. They need to be resolved within the context of a WHS.
“The people behind the WHS, they want something that is invisible. You don’t realise you’re building a road when you’re building it.
“The concept of building a road which looks like a road now is unacceptable.”
Around 60 previous schemes have previously been put forward to try to solve the problem, however the current scheme had the required funding to allow it to go ahead.
“One of the key issues which makes it deliverable is there is now a budget which is commensurate with what is required to solve the problem,” he said. “There is a considerable amount of money being made available to solve the problem.”
Parody reiterated that it was looking for innovative solutions to solve the problems. In November this year, he said the project was reaching as much as government was prepared to spend on the scheme. This meant it was looking at value engineering some of the components out of the scheme.
It is also looking at ways of privately financing the project.