THE NEW £1.6 billion Forth bridge could be finished a year earlier than planned, if construction is not hit by bad weather or other delays, project chiefs have revealed.
The Forth Replacement Crossing is due to open at the end of 2016, but contractors are so concerned about potential disruption from high winds and severe winters they have allowed for 20 per cent more time to complete the job within their five-year contract.
Strong winds could delay the year-long work on the foundations of the bridge’s three massive towers – the most critical part of the project – which is already under way.
Gusts would prevent cranes moving giant caissons – steel tubes – into place, on which the towers will sit.
The arrival in May from Poland of the first caisson – the height of a six-storey building – will be the first substantial part of the bridge to appear.
High winds could also disrupt cranes that are due to start assembling the bridge’s 700ft (207m) towers – 166ft (50m) higher than those of the adjacent Forth Road Bridge – next year.
Freezing temperatures also pose a threat to progress, potentially preventing concrete from setting on the towers and deck.
A spokesman for the Scottish Government’s Transport Scotland agency, which is in charge of the project, said: “The bridge is scheduled to be completed by the end of 2016. It could be delivered earlier than that.”
However, he said it would also depend on no delays from construction problems or materials being delivered late.
Transport Scotland project director David Climie told a media briefing in Rosyth yesterday called to give details of progress made and the challenges ahead: “So far, things are progressing extremely well. We are still on schedule and within budget and are determined to keep it way.”
The £790 million principal contract was won by the Forth Crossing Bridge Constructors consortium, comprising Spanish firm Dragados, Hochtief of Germany, American Bridge International, with Scottish company Morrison Construction,
Carlo Germani, the principal contract project director for the consortium, said work this year would focus on the foundations.
This will involve excavating the riverbed down to rock for the north and south towers, while the top 15ft (4.5m) of Beamer Rock – about 3ft (1m) of which was above the water – has been blasted away for the centre tower to rest on.
The rock will be reused in a new stretch of the M90 on to the bridge from the north.
The river is so shallow in places that channels around the other tower sites are having to be dredged by up to 16ft (5m) to make them deep enough for construction barges.
Mr Germani said of the foundations work: “This is the most critical operation because of the geological risk. If we get this right, we will be on our way.
“The arrival of the caissons will be the most significant construction milestone yet.”
He added that using caissons would significantly reduce the cost compared with the traditional piling method of digging foundations, which was favoured by the unsuccessful rival bidder. The caissons, up to 53ft (16m) high, which comprise welded steel sections, will take some three months to install.
They will be floated into position and lowered by pumping in water and concrete.
This will be followed by construction of the towers, until late 2014, followed by a further 18 months to complete the deck.
The deck is being built in 149 segments, 40ft (12m) long and 13ft (40m) wide, in China and Spain. They arrive by sea from October next year and moved by barge to be fixed to the bridge using cranes, beginning with those closest to the towers.
The shape of the cable-stayed bridge will then start to take shape, with cables fanning out between the tops of the towers and the bridge deck in a Christmas tree pattern.
However, the bridge approach viaducts – between the shore and outer towers – will be pushed into place from either end, in a similar way to Clackmannanshire Bridge.
Also unlike the early bridge, the carriageways will provide a smooth surface for drivers, with just two “bumps” as they cross expansion joints.
A separate £25m contract is under way to upgrade junction 1a of the M9, south of the bridge, to enable motorway traffic to and from the west to access the bridge via the M9 spur.
Mr Climie said it was hoped this would reduce rat-running by Forth Road Bridge drivers taking a short cut via the A904 through Newton, but the village will get traffic-calming measures.
A third, £12.9 million contract, by Graham Construction, to install electronic traffic control signs on the M90 approach to the new bridge from Halbeath is also due to be finished this summer.
It will feature Scotland’s first compulsory variable speed limits, to keep traffic flowing at busy times by lowering speeds.
The normal 70mph limit may be cut to 40-50mph – or even 30mph – to cut congestion, with speeds shown on 18 “goalpost”- shaped gantries over the motorway and one L-shaped “football rattle” one.