Team is tunnelling beneath a station on the historic Manchester-Liverpool line while pulling out all the stops to keep the trains above on a level track.
Project: Newton-Le-Willows station enhancement programme
Client: Network Rail
Funder: Local Growth Fund and Merseytravel – part of a three-year £340m investment by Liverpool City Region and Network Rail
Main contractor: Galliford Try
Structural engineer: Tony Gee & Partners
Start date: January 2017
Completion date: Easter 2018
In 1830, the first railway line exclusively for steam trains opened in the UK.
It linked Manchester and Liverpool together, increasing productivity and boosting the economy. These trains heaved trade across the region faster and more efficiently than any canal boat or horse could and played a vital role in developing the North-west.
Parts of the original 187-year-old railway line are still in use today. But time is a great leveller and has worn parts of it down, with one particular station halfway along the rail in need of major redevelopment.
Newton-Le-Willows station near Warrington was built in 1845 and is undergoing an £18m revamp. The original 1845 ticket office, which is a listed building, will close to the public and a new ticket office is being built. A subway is also being dug to link the station to the platform on the other side of the tracks.
But this is far from straightforward, as Galliford Try is employing a construction method never before attempted in the UK.
The team is mining underneath the tracks to create the subway, while trains continue to rattle above them. The line has been kept fully operational while works are ongoing and has required the team to do some complex engineering in order to ensure no damage is done to the historic route or the original listed ticket office.
A floating rail line
The team is tunnelling under the tracks to create a new subway, but the line is still open to the public and trains still carry passengers to and from the station in an effort to reduce costs.
The railway is constantly moving, according to senior project manager Ian Woodall. And as the team continues to tunnel and move material out from underneath the tracks, it is essential that the line does not fall below 22 mm, as this could stop the trains running.
As the team tunnels through an embankment – on top of which the listed ticket office building and tracks sits – huge 27 m-long tubes are pushed through to form a tunnel canopy. Thirty tubes are stacked adjacent to one another vertically to form tunnel walls, and horizontally to form a tunnel soffit (see picture below). This allows an enclosed space for material to be excavated, with the tubes providing support to prevent the embankment from collapsing.
Galliford Try Newton-le-Willows 6
However, enough material needs to be taken out to ensure a bulb effect is not created as the ground is pushed up by the tunnelling process. This will push the tracks and make for a bumpy rise as trains pass over this area. But if too much material is taken out, the track will fall, creating voids.
“We’ve pulled out between 400 and 500 cu m of material underneath a live railway without affecting the trains or platforms,” Mr Woodall says. “We drive big hollow tubes underneath the railway line, and you have to constantly balance the material you are taking out with the material you are pushing through.”
To master this equilibrium, the track is monitored twice a day and readings are taken from hundreds of survey points located along the track. The data is sent back to the team to see whether too much movement has occured. If it has, Network Rail track maintainers will come in to pack in material to lift up the tracks.
In addition, black boxes – electronic void detectors – are connected to the lines, identifying dips in the ground that might appear along the line as a result of the tunnelling process and constantly sending out real-time data for the team to use.
The ‘ugly beam’
“The temporary works have been a monumental part of the job,” Mr Woodall says.
Because the listed station building and embankment – along which the railway line runs – would not pass current building standards, the team had to make sure construction works would not further compromise the stability of the line, according to Mr Woodall.
Galliford Try Newton-le-Willows 13
One major aspect of these temporary works was to install a 16-tonne torsion beam – known as the “ugly beam” among the team – to hold up the embankment wall as the team tunnel through it.
“We’ve pulled out between 400 and 500 cu m of material underneath a live railway without affecting the trains or platforms”
Ian Woodall, Galliford Try
Installing it was a “feat of engineering”, according to Mr Woodall: “Essentially, a massive letterbox has been cut out of the retaining wall and the torsion beam is holding up the wall, part of the railway and platform,” he says. “It’s like a big wedge – it’s a fair piece of temporary works we had to do.”
Another vital piece of temporary works is the construction of the steel subway envelope. “This is capable of taking the full load of the railway,” Mr Woodall says. “But it is not able to last for 120 years. We need to put another layer of reinforced concrete inside too.”
To assess the impact of driving through the 27 m-long tubes to construct the tunnel canopy, 3D modelling was used to ensure the canopy’s construction would not damage the track.
Tight spot for a crane
Sandwiched between residential housing and local businesses, the team are delivering the station upgrade in a very tight site.
“This is a heavy construction site in a residential area and there’s no room to move,” Mr Woodall says. And this lack of space was especially challenging when the team was adding a crane into the mix.
“There is a 70-tonne crawler and a 27 m jib on site and we had to demonstrate through engineering assurance that this won’t topple over,” he says. “It is key to protect the public and the railway.”
Galliford Try Newton-le-Willows 3
The tubes being driven into the embankment to create the tunnel canopy also had to be taken on site in parts: two 12 m-long tubes and one 3 m-long tube are welded together and then used for the excavation.
“There are the technical constraints of having to erect a steel structure,” Mr Woodall says. “We need to put up waiting shelters and canopies, up on the platform adjacent to 25,000-volt lines, which we’ll only do during isolation – when the power is turned off from 2am to 5am on a Sunday morning.”
However, there have been no complaints so far about the works, and Mr Woodall is hoping to get the green light to tunnel underneath the railway line 24 hours a day. “Mining under the live railway is the key risk in this job,” he explains. “As it’s a process of mining and framing – we have intermediate frames to put in every metre – we want to keep that process rolling along and get the railway supported as soon as we can.”
Undoubtedly the new station will look different from when it was first built in the 19th century. But what won’t change is the importance of this nearly 200-year-old route to link the local community to Manchester and Liverpool.