From a blank piece of paper, to a world icon, the £1.35bn, 2.7km Queensferry Crossing took 10 years to complete, with just six for construction.
When New Civil Engineer visited, a week before the Queen opened the bridge last month, the gleaming cable stays in the mist looked majestic. Closer up one could see the temporary works, cranes and workers carrying out final snagging and commissioning. Some items, such as the deck dehumidification system and smart motorway signs, were to be to be switched on after opening.
It all makes for a stressful scramble to the finish line, before traffic, pedestrians and the Queen arrive. “People tell me ‘oh you must be enormously proud of it’ but at this point in time I don’t have time to be proud of it. I’ve lost a lot of sleep on this job,” says Michael Martin, project director for principal contractors Forth Crossing Bridge Constructors FCBC. “It’s very challenging, I knew it would be when I took it over. But it has been a lot more challenging than I thought it would be.”
FCBC represents an international effort, bringing together Hochtief Construction of Germany, Dragados of Spain, United States contractor American Bridge International and Morrison Construction – none of which have worked together before. The overall scheme is 22km long, which includes three other contracts and major motorway upgrades to the north and south of the bridge. No less than 24 languages have been spoken on site which has employed more than 10,000 people.
The materials spend is split between Scotland and overseas. The prefabricated steel deck segments arrived on massive ships from China, but Martin says that most orders for the bridge have been placed with Scottish suppliers and subcontractors.
Martin goes on to say that, weather-wise, the bridge was not built in Scotland, but rather in the North Sea. “Another way to explain it would be: you don’t hear about cars blowing over on the streets of Edinburgh, you do hear about it on the Forth Road Bridge.”
A mild breeze in the car park, or even at sea level will be a howling gale 210m up on one of the towers. Sequential cantilever construction has been done plenty of times around the world, but only a few times to this scale, in these offshore-like conditions.
Due purely to the wind, tower cranes that should take 12 days to dismantle, took 63. Multiple examples like these, and their knock-on consequences, made the job a day-to-day, hand-to-mouth exercise.
The “target completion date” of December 2016 was missed, as was the contractual finish in May 2017. But calling the project “late” is a sore point with Martin. “The fact we didn’t meet a non-contractual completion date [December], and that is given so much prominence, and is constantly referred to, whenever anyone speaks about the project, I have to say is a constant irritation to me.
“I’m enormously proud of the effort put in on what was a very tight timescale considering its size and complexity.”
Project director and client’s representative David Climie agrees, saying in retrospect the early target date should never have been released. “To be fair we were all pretty confident that we could hit the end of 2016,” he says.
As it was the project fell behind the contractual deadline. “We’ve gone 10 weeks over [the contractual May date] on a six year project, so that’s less than 3% in terms of time.” FCBC has applied for a time extension for the contract because of the amount of delay caused by the weather. Discussions are ongoing.
Something to note is that this largest ever spend from the Scottish Government’s capital budget has come in under budget. The Scottish National Party has certainly noted it, particularly after the Scottish Parliament building and Edinburgh Trams projects went years late and were hundreds of millions over budget.
Climie says the cost saving came from economic design – directing public transport to the Forth Road Bridge allowed the Crossing to be narrowed. Another factor was lower-than-expected inflation, and fortunate timing: “We were fortunate… after 2008, much of the private finance had dried up and most of the contractors were looking for the next big job. We expected the principal contract would be between £900M and £1.2bn as part of the £1.7bn to £2.3bn envelope. The tender from FCBC came in at £790M, and the other contracts alongside came in similarly lower.”
The crossing took the record for largest free standing balanced cantilever in the world during construction, stretching 322m in each direction from the central tower. At one point this tower was rocking on the bedrock, pushed around by a one-in-500 year storm. But in February the last of the 750t deck segments was safely hoisted into place.
It helps when you have the latest in bridge building technology to provide assurance, including real time loadings, stresses, orientation and global positioning surveys. And the ongoing monitoring regime on the structure means that repairs and maintenance can be planned and carried out in a timely way, so the bridge could last well into the 22nd century.
Tallest bridge in the UK
The Queensferry Crossing is now the tallest bridge in the UK and longest three-tower, cable-stayed structure anywhere in the world.
The south tower boasts the world record for longest and largest marine supplied underwater concrete pour – 16,689m3 was placed in 15.2 days, with work taking place 24 hours a day, up to 40m below the surface.
Steel caissons 30m in diameter, and more than 30m tall were sunk down through 20m of soil to rock head to create a dry workspace, with the rock then cleaned before the concrete plug was poured. At the height of production, the concrete batching plant at nearby Rosyth docks was producing 120m3 of concrete every hour.
At its highest point the deck is 80m above the water, with 19 deck segments extending from each tower. Each segment is attached to a pair of cables, each made up of 30 to 100 tendons, and each tendon made up of seven strands of high tensile steel wire. Each tendon is galvanised and waxed and two cable stays can be taken out at any one time for maintenance.
Caisson excavation in progress nov 12
When the Queen opened the Queensferry Crossing on 4 September it was 53 years to the day after she opened the Forth Road Bridge. And with the Forth Rail Bridge, a World Heritage site, a stone’s throw away, three centuries of bridge engineering can be seen at a glance.
“It is in its own right, put anywhere in the world, one of the world’s major bridges. But put in this location, in Scotland, next to the Forth Road Bridge and the Forth Rail Bridge, it’s unique,” says Martin. It is a genuine tourism attraction and a view that will no doubt produce a new legion of inspired bridge builders.
In the crowd at the bridge’s opening was the family of John Cousin the only worker who died worki ng on the project. The 62-year-old from Northumberland, known as “Generator John” around site, was hit by a moving boom on a crane on the deck of the north tower.
“I’ll never forget it,” says an emotional Martin, who came out of retirement to work on this project. “I would have done anything to prevent it happening. But I can’t turn the clock back.”
At the end of the Forth Rail Bridge there is a plaque with the names of 74 people killed during its construction. Many more off site deaths went unrecorded on that project. Seven died during construction of the Forth Road Bridge.
“The performance of the construction industry is improving all the time,” says Martin. “But the phrase I use here is ‘safety has no finishing line’. You’re never good enough.”