Preserving Manchester’s heritage while upgrading its railway has been among the mammoth challenges faced by Skanska and Bam on their major overhaul of one of the city’s most iconic sites.
Project: Ordsall Chord
Client: Network Rail
Contract value: £140m
Main contractor: Bam Nuttall
Main contractor: Skanska
Steelwork subcontractor: Severfield
Piling subcontractor: Dawson Wam
Engineering consultant: WSP
Start date: October 2015
Completion date: December 2017
On 15 September 1830, Manchester’s Liverpool Road station was opened to the public.
Acting as the terminus for the world’s first inter-city passenger railway, running between Liverpool and Manchester, it cemented Manchester’s status as one of the North’s most important industrial hubs.
Although the station closed to passenger traffic in 1844, heritage trains have been running into and out of Liverpool Road, which is now Grade I-listed and part of the city’s Museum of Science and Industry, for more than 180 years.
However, the infrastructure surrounding this historic station is now at the heart of Network Rail’s critical programme of upgrades aimed at improving rail links across the city centre.
To achieve this, a Skanska/Bam Nuttall joint venture has been tackling one of the most complex – not to mention controversial – challenges in Manchester’s recent history: the Ordsall Chord.
Protecting Manchester’s heritage
The 380 m viaduct forms part of Network Rail’s Northern Hub investment programme, which aims to boost connectivity across the region, from Hull in the North-east to Blackpool and Liverpool in the North-west.
In Manchester, the Chord will link Victoria station – which serves the North – directly with Piccadilly station, which serves the South as well as the city’s airport. Once the Chord is built, alongside improvements to Victoria, Oxford Road and Piccadilly stations, the programme will allow an additional 700 trains to travel through the city each day.
Ordsall Chord Skanska Bam Nuttall CGI 1
But the viaduct, which will span the River Irwell between Salford and Manchester, almost never happened, after a judicial review into the project was brought by former ICE president Mark Whitby.
A year ago, Mr Whitby told Construction News the proposed bridge would “substantially harm the city’s heritage” and destroy an area of “international importance”.
Although his claim was rejected in March this year, the scheme’s importance and its heritage is not lost on Skanska project director Keith Gardner. “The project had to be something that had to be sold to the council as well as the locals in terms of what we’re producing here,” he explains.
The heritage assets, which sit in and around the entire site, have made the construction process much more “intense”, he says, with rigorous processes put in place to ensure all listed structures are properly managed.
“The project had to be sold to the council as well as the locals”
Keith Gardner, Skanska
Walking Construction News around the site, Mr Gardner points out a large number of listed structures, both Grade I and Grade II, including Stephenson’s Bridge, which carried the world’s first intercity railway passengers in 1830. “All those years ago when they did these arches, they got the masonry and the mortar from anywhere they could,” he says.
The arches are being repaired and renovated as part of the project, with a large steel girder removed to provide views of the Grade I-listed arches for the first time since the 1860s.
CREDIT Matthew Nichol Photography_Ordsall Chord_River Irwell Pedestrian Bridge_Skanska Bam Nuttall_Aug 2016 1
Source: Matthew Nichol Photography
There are various different colours of stonework – “pinks and yellows and all sorts” – which Mr Gardner says has to be reflected in the team’s repair work. It’s an approach that has fed into everything the team has done across the project, he explains, with archaeologists from Salford University on site from day one with a watching brief over the works.
The Ordsall Chord in numbers
Throughout the civil engineering part of the project, the team will:
- Pour 14,399 cu m of concrete
- Install 632 piles
- Build 12 signal gantries
- Lift and install 4,378 tonnes of steelwork
“The amount of consents and planning conditions that have to be discharged before we can do anything – it’s quite intense.”
One example is a Grade II-listed structure on the Manchester side of the Irwell, which Mr Gardner calls “the zig-zag arches”, some of which have had to be demolished carefully so the team could build the viaduct’s south abutments. “It took us something like nine months in terms of design and consent, and about three hours to knock them down,” he says.
The heritage of the site even plays into the viaduct’s design from architects BDP, who have included an ash-struck finish on the concrete and a rusted look to the arch. “It’s the first time I’ve ever had a concrete shutter inspected by an architect before I’ve put it up. It’s part of the quality procedure, signing everything off as we go,” Mr Gardner says.
A UK first
The architect’s design for the viaduct itself has been one of the most challenging parts of the job – not least due to its status as a world-first.
According to Skanska, the unique design for the viaduct makes it the first asymmetrical network arch bridge in the world – and the first network arch in the UK. “The biggest technical challenge was: can you actually manufacture steel like that, and can you make the shape the architect wants?” Mr Gardner explains.
The architect wanted a “flowing ribbon effect” across the bridge, he says, which includes a dip in the steelwork that the team affectionately calls “the swoosh”.
“The way a network arch is built is different to a typical bowstring,” he says. “The hangers that hold the arch together are diagonal and cross each other at least twice. They’ve not been built [before] because the software hasn’t been out there to examine a structure of this type in the past.”
“The amount of consents and planning conditions that have to be discharged before we can do anything is quite intense”
Keith Gardner, Skanska
The design also incorporates a change in steel, with the steelwork entering one side of the bridge as an I-section beam, but transitioning through ‘the swoosh’ into coffin-shaped beams.
Mr Gardner says Skanska had built a similar structure in Norway, the experience of which the team used early on in the tender process, but made the most of its steelwork contractor’s skillset to help tackle the technical challenges of the design.
CREDIT Matthew Nichol Photography_Ordsall Chord_Skanska Bam Nuttall_Aug 2016 4
Source: Matthew Nichol Photography
“Early on, we said that if we’re going to succeed here, steelwork will be a big part of that,” he explains. “We engaged Severfield, who were brought into the alliance on the basis of behaviour, as opposed to money.
“It was about who fits into our behaviours and our values for the alliance. We tried to avoid this main contractor being in the middle between client and supplier – we put Severfield in the design office with the designer.”
Piling in the river
Severfield also worked closely with the alliance on the removal and upgrade of Princes’ Bridge, an 1800s footbridge which originally linked the Salford and Manchester banks of the Irwell.
The footbridge will be replaced by a new structure, but before the old one was demolished, the team took a unique approach to temporary works to smooth both the demolition and construction of the new bridge.
Mr Gardner explains that the team made use of the old footbridge as part of a complex system of temporary works. Skanska and Bam piled through the river using the footbridge as a platform to avoid using gates across the river.
The team pre-augured into the sandstone in the river through the bridge before installing the temporary works, which then supported the demolition of the existing bridge using a crane. The temporary works, which were left in place, now take the load of the new structure as it is installed.
“It’s not just about civil engineering – a railway bridge is no good unless a train runs over it”
Keith Gardner, Skanska
“The big risk of the project was whether we got the piles in the right place through the river,” Mr Gardner says. “The worst out of alignment was 100 mm, which was exceptional, especially when you’re driving them almost ‘freehand’.”
The collaborative approach to these piling works saw input from Skanska, Bam, Cementation Skanska, Aecom-Mott MacDonald, Severfield and piling contractor Dawson Wam.
Piles were also used on the south side of the viaduct, which has 155 CFA piles each 600 mm in diameter, socketed 3 m into the sandstone. “Manchester sandstone is relatively weak so you can get quite a way into the ground,” Mr Gardner says.
On the north side, however, that same weakness in the sandstone proved a curse rather than a blessing. “We’ve dug a 25 m by 15 m by 9 m cofferdam and mass-filled it on to the sandstone – we couldn’t get [piles] deep enough and didn’t have enough space,” he adds.
The intense scrutiny the project is under even extends to its concrete, with the finish having to be exact. This also meant the team could not use self-compacting concrete for each of the viaduct’s piers, which include around 600 cu m of the material.
“The problem you have with a self-compacting concrete is that the temperature it raises to exceeds our specification, meaning we’d end up with cracks,” Mr Gardner explains.
The ash-struck finish of the concrete, as well as the rusted look of the arch itself, has to be examined by both the architect and the council. “We’re not actually working to a standard civil engineering specification on this job – the standard that we’re working to is what the council say and agree to,” he says.
Ordsall Chord Skanska Bam Nuttall CGI 2
The alliance has had to take that approach – keeping stakeholders happy while tackling an immense civil engineering project – not just with the heritage assets but across the entire project. “It’s not just about civil engineering; a railway bridge is no good unless a train runs over it,” Mr Gardner says.
Despite the scepticism, this immensely challenging project will improve Manchester’s connectivity while revealing some of the city’s heritage assets for the first time in more than 150 years.
With a world-first network arch still to be installed over Christmas, the team’s challenges aren’t over yet.
But once complete, the Ordsall Chord will be a feat of engineering that Stephenson himself would likely have been proud of.