At twice the height of Nelson’s Column and taller than Big Ben’s clock tower, lifting the £118m New Wear Crossing’s steel pylon into place has required Farrans and Victor Buyck to push innovation to the limit.
Project: New Wear Crossing, Sunderland
Client: Sunderland City Council
Contract value: £117.6m
Main contractor: FVB JV – Farrans / Victor Buyck joint venture
Start date: May 2015
Completion date: Spring 2018
If you’d arrived at Sunderland’s Pallion station before February this year, there wouldn’t have been much to grab your attention.
It sits opposite housing on one side and a small retail park on the other, which backs onto a derelict brownfield site along the southern bank of the River Wear.
The former industrial area is the historical home of shipbuilding along the river, but with industry now long gone, it has been marked by the council as ripe for a revamp.
If you arrive to the very same station today, you’ll see one structure that acts as a symbol of that regeneration.
The New Wear Crossing’s central pylon now looms over the area; a steel structure that stands at twice the height of Nelson’s Column and taller than Big Ben’s clock tower.
The 100 m-tall pylon forms just one part of the £117.6m bridge, which will link the south of the river to the north. It will not only improve links to Sunderland city centre, but breathe life into the local area as the first new bridge over the Wear for 40 years.
The project is being tackled by FVB, a joint venture of Farrans and steel fabricators Victor Buyck, and the team has found that bridging the gap over the river has presented immense technical challenges.
A catalyst for regeneration
Standing on the bridge’s precast concrete deck and looking up at the mammoth steel pylon puts in perspective what a huge task this project has been for the joint venture.
FVB project director Stephen McCaffrey explains some of the numbers behind the pylon: over 1,000 tonnes of steel and 550 tonnes of concrete have gone into the structure, which is held in position by 40 6 m-long bolts.
The massive scale of the pylon was a conscious decision by client Sunderland City Council to make the scheme stand out as a symbol of the regeneration the bridge can bring about.
“If the council had wanted to do it cheap, they could’ve gone for a much more conventional design, but a big part of their drive was to have a landmark structure,” Mr McCaffrey says. “It’s planned to put the area on the map and drive regeneration.”
The bridge forms part of a five-phase investment into the city’s local infrastructure, with the first phase of the infrastructure-specific works already completed. Farrans and Victor Buyck’s £117.8m bridge is part of the second phase, which will also see the JV improve local road links on both the north and south banks of the river.
Such is the scale of the pylon that it was lifted into place over a 15-and-a-half-hour period earlier this year.
But before it could be put in place, the team had to tackle the challenge of how to support such a huge structure.
Piling on the river
FVB came up with an unorthodox solution that entailed constructing a special cofferdam to allow the pylon’s foundation piles to be installed.
“Conventionally, you would use jack-up barges to float plant in and install piles from there,” Mr McCaffrey says. However, this method threw up a number of challenges.
“If the council had wanted to do it cheap, they could’ve gone for a much more conventional design”
Stephen McCaffrey, Farrans
“First, how do we know the piles are in place before we concrete them? There’s also no way of preventing muck that would arise from the top of the piling rig flowing into the river,” he explains.
“We decided to construct a heavy frame on top of the cofferdam and have mobilised a piling rig from there, which let us install the piles off the frame.
“That had a significant number of advantages for us: it meant we could put in the piles in a dry environment, and it meant we could use a conventional piling rig rather than a pile top driller.”
This method was also environmentally friendly, as any arisings from the piling works could be caught in the cofferdam and removed, rather than spilt into the river.
Mr McCaffrey says the team came up with a meticulous step-by-step procedure that would allow it to build the pylon’s base both efficiently and safely.
First, the team dredged the river to make a berthing pocket for the crane barge, which was needed to insert the cofferdam’s sheet piles.
FVB New Wear Crossing 8 Cofferdam landscape copy
The barge crane installed these in early 2016, with the cofferdam left open until the top frame was installed. Site workers could then drain it, allowing a dry environment for the follow-on work.
Rigs working inside the cofferdam installed passive de-watering wells to release any build-up of pressure in the ground beneath the surface of the now empty enclosure.
A layer of blinding concrete was then placed on the floor of the cofferdam, followed by a steel-framed piling platform on top, which acted as the base for a 150-tonne piling rig.
This built 10 huge foundation piles, measuring 25 m long and 1.5 m in diameter each, with the piles bored 15 m to found in the bedrock below.
With these installed, the team removed the piling rig before casting the pylon’s 3 m-deep reinforced concrete pile cap. This entailed a 24-hour, 1,450 cu m pour that completed in August last year.
The steel piling frame at the top of the cofferdam was then removed to allow the construction of reinforced concrete tusks, which form the first 8 m of the pylon’s structure to support the massive steel frame. These tusks take the structure above water level, where the steelwork is then joined on.
Raising the pylon
Installing these piles and the concrete tusks was the first step to raising the pylon, which was one of the largest technical challenges of the job and the culmination of two years of planning.
The pylon started its life in Belgium at Victor Buyck’s manufacturing facility alongside a canal. Mr McCaffrey points out that at 100 m tall and 36 m wide, it was “just a bit wider than Victor Buyck’s biggest fabrication shed” – meaning that it had to be built in two halves and then joined together outside.
In a project that has seen its fair share of technical innovation to increase the efficiency and speed of the job, the process of actually getting the pylon onto its transport barges to have it shipped across to Sunderland was a slow one.
The pylon is the largest structure Victor Buyck has ever transported by river”
Stephen McCaffrey, Farrans
With the help of lifting specialist Sarens, which oversaw its transport and lifting, the steel frame was edged onto transport barges over the course of two days. It then travelled to the port of Ghent, where it was then shipped across to Sunderland.
“It’s not the tallest, or the widest structure that Victor Buyck has made,” Mr McCaffrey says. “But when you put its height and width together it’s the largest structure they’ve ever transported by river.”
The pylon arrived at the Port of Sunderland in January and was transported up the river Wear to site.
FVB New Wear Crossing 1
It is the largest steel structure to be lifted vertically into place since the London Eye in 1999 – but Mr McCaffrey argues the pylon required more innovation. “The London Eye was built in place; it was all assembled on site. But the pylon here was fabricated offsite, brought to site and connected up as one element.”
On arrival, the first thing the team had to do was to move the pylon into its lifting position – no mean feat considering its height and weight.
“We had to lift the pylon and rotate it 90 degrees, meaning we had to put a lot of planning into where the centre of gravity would be and the position of the barge,” Mr McCaffrey says. “We spent an awful lot of time looking at the connection details, and the biggest challenge was actually getting the rigging and lifting system right.”
Two-year plan, two-day lift
Again, much like the construction of the cofferdam, the team laid out a detailed process of how they would lift the pylon into position.
Once it was turned around it rested on two temporary supports while the lifting equipment was rigged up either side of the river.
To prepare for the mammoth lift, site workers fitted hinges to attach the pylon to each of the concrete tusks built into the riverbed.
FVB New Wear Crossing 2
A 50 m-high crane boom, taken from Sarens’ SGC-120 crane – one of the largest in the world – was also fitted to the pylon for the raising operation
This created an angle between the lifting cables and the top of the pylon to allow it to be pulled upwards.
“In-situ poured concrete was never an option for the bridge deck”
Stephen McCaffrey, Farrans
The lifting cables were passed through four hydraulic strand jacks, anchored 30 m into the ground on the south side of the river, while two hydraulic jacks located on the northern bank acted to counter the tension of those on the southern bank.
The cables were then drawn through the jacks to pull the pylon into a vertical position.
Although the planning took two years, the strand jacks and the crane boom raised the pylon to an angle of 70 degrees in just under 16 hours.
At this point, the crane boom was disconnected from the cables, while the strand jacks pulled the pylon the rest of the way to its eventual 90-degree angle, where it is held in place by tensioned cables on both sides of the river.
Mr McCaffrey says the two years of planning might have seemed like a lot for something that was over in less than two days, but it allowed everything to go smoothly.
“We expect challenges like that when we do this type of work, but we had the right people in place to overcome that,” he says.
“Once we started the lift, everything went pretty much as predicted by our designers, [but that was because] we’d put a lot of time into modelling how the concrete tusks would react, and what type of movements we would expect to see while we were lifting.”
After fixing the pylon in place, the base of each leg received reinforced concrete, allowing the rigging cables to be removed, leaving the huge structure freestanding in the middle of the river.
Launching the deck
But at the time of Construction News’ visit in May, the pylon is no longer alone, with the 300 m-long bridge deck making its way across the river from the south side to the north.
The team largely built the deck on the southern bank, which is made up of offsite fabricated steel and precast concrete panels, as Mr McCaffrey explains.
“In-situ poured concrete was never an option as the bridge deck needed to remain flexible during the launch stage,” he says.
FVB New Wear Crossing 11
The 20-hour launch programme took place in March this year, which saw the team gradually slide the bridge deck into position over the river using hydraulic lifters. This was not without its challenges, particularly at the design stage.
“One of the criteria that we had to balance at the design stage was how many [precast units] we could put on the deck before the launch; the more you put on [from the back], the closer you get to the front, and the heavier it becomes,” Mr McCaffrey explains.
“As a result we’ve tried to put on as many as possible before we launch.”
The team installed a temporary blue steel nose (see box) to link the southern side of the river to the north, which will then be removed, allowing the team to install the final 40 m of bridge deck to be built in-situ.
The launch of the bridge deck was a particularly symbolic moment for the team, marking the first connection between the south and the north bank of the river since the project started two years ago.
But Mr McCaffrey says that while the pylon and the bridge deck might be coming along at speed, the hard graft isn’t over yet.
“There’s still a lot of work to do – we want to keep people focused until the end of the job and get it finished to a high standard.”
As the final stages of the bridge deck are put in place, the team now has to put the finishing touches on what will not only be a landmark for Sunderland, but a catalyst for the city’s growth.
Looking at aerial photographs of the job, one thing that’s striking is the massive amount of blue steelwork used across the length of the bridge.
Mr McCaffrey explains that this is all temporary works, and says the team has probably built just as much temporary works as it has permanent since starting on site two years ago.
These have included a temporary launch nose fitted to the front of the bridge deck to assist with its launching, as well as temporary steel supports for the pylon.
The temporary supports either side of the pylon are due to be removed once the bridge’s cables have been installed and stressed – which takes the load off the bridge deck – later this year.
But Mr McCaffrey says a massive amount of planning has gone into the role of temporary works on the job, and how it can all be safely removed as the project progresses.
“The temporary works that have been used to deliver the bridge have been a massive feature of the job, and that’s taken a lot of time for us to sit down and develop the construction methodology.
“We’ve got an international team of people based in Dublin, London, Belgium, and the construction team based in Sunderland, making it a challenge to get everyone together. But it had to happen; it’s important that people get together around the table to plan for it.”