In Lincoln a new footbridge alongside one of the most dangerous level crossings in the UK will help pedestrians cross the railway safely throughout the day.
Project: Lincoln High Street Footbridge
Client: Network Rail Infrastructure
Contract value: £4.3m
Contract type: Design and build
Region: East Midlands
Main contractor: Galliford Try
Start date: March 2015
Completion date: July 2015
The cathedral city of Lincoln doesn’t look like one of the most dangerous places on the rail network – far from it, in fact.
With its spires visible for miles around, the cathedral cuts an impressive sight – dominating the landscape as it has since the first building was completed in 1092.
Historically rich, the city can also boast a bustling population, boosted by students studying at its two busy universities.
But Lincoln’s success has brought its own issues.
Trains run through its centre, controlled by two level crossings as they pass over main roads. These crossings can cause road traffic to back up throughout the city centre and pedestrians have to wait while the trains pass on their way to and from Lincoln Central station.
City centre danger
The crossings, one at High Street and another at Brayford Wharf East, are recognised as being among the most dangerous on the rail network and now contractor Galliford Try is in the process of trying to eliminate that danger.
“Both the High Street and Brayford Wharf level crossings have been identified by the Office of Rail and Road as ‘significant safety risks’ and we are working with Network Rail to provide a scheme that helps mitigate some of the risk”
James Boyes, Galliford Try
It is constructing a new footbridge with lift access over the railway line alongside the High Street level crossing just metres from the end of the platform at Lincoln Central, in a move designed to improve safety levels.
“Both the High Street and Brayford Wharf level crossings have been identified by the Office of Rail and Road as ‘significant safety risks’ and we are working with Network Rail to provide a scheme that helps mitigate some of the risk,” says Galliford Try project manager James Boyes.
“Somewhere in the region of 1,200 people per hour normally use the crossing, but at peak times numbers can be significantly greater and there can be large crowds of pedestrians waiting for trains to cross.”
Upgrade increases risk
The recent completion of the Great Northern Great Eastern project, a line upgrade to help deliver more freight and passenger services and faster journeys throughout the region, has seen an increase in the number of trains using the line through Lincoln, increasing the number of times the crossing barriers are deployed.
Lincoln footbridge Galliford Try DSC 2149
“That can lead to frustration for some people and at peak times there is concern that that frustration leads to people taking risks across the crossings,” says Phil Crosby, Network Rail’s project manager on the scheme.
To alleviate these issues, the team at Lincoln has developed a scheme that will provide a permanent, safe crossing point with both stair and lift access. This will help reduce crowding and prevent some of the huge risks taken by some to get across the railway.
The steel-framed bridge runs adjacent to the High Street and spans 21 m across the railway to the abutments on the north and south side of the railway.
To accommodate the southern abutment, the Galliford Try team needed to carry out some demolition work to an existing building (see box) as well as excavate lift pits and install piles across both the north and south abutments.
Asbestos legacy for Lincoln bridge team
One issue for the Galliford Try team has been the location of an existing building within the footprint of the proposed bridge. To accommodate the project, part of the building – a three-storey 1970s reinforced concrete structure – has been broken away.
With asbestos found across the concrete roof structure beneath the bitumen coating, initial plans had been to use a scraping technique to clear the material. But air tests soon found that safety limits were being reached, with work called to an immediate halt.
Instead, after conducting research and consulting with the Health and Safety Executive, a second method of removal was used.
The roof beams containing the asbestos, each weighing in at 25 tonnes, were sprayed with a glue material and covered in a plaster of Paris wrap. They were then lifted out of position using a 250-tonne mobile crane and lowered down to ground level.
Being too large to remove directly from site, they were cut into two within an encapsulation tent and then carried off site. The remaining section of the building was then broken out using remote-controlled robots working from the third floor down to ground level.
“The building had been a shop and offices,” Mr Crosby says. “We had to take out the front bay to accommodate the bridge. Everything was done under a series of possessions and road closures.”
Around 40 bottom-driven 273 mm-diameter piles have been placed to depths of 8 m, with ground beams measuring 600 mm deep, 450 mm wide and 8 m long helping support the structure.
Lift pits have been excavated to a depth of 2.5 m and cast using waterproof concrete, as a result of the high water table in the area.
The bridge itself is a single-span steel-frame lattice-girder bridge, fabricated off site by Doncaster-based specialist Carver Engineering Services and brought to site in seven different sections.
Lincoln footbridge Galliford Try IMG 8393
These were lifted into position over three separate nights during January, with the lower lift shaft towers being lifted into position first before the main and back spans of the bridge, followed by the steel stairs and landings, as well as the upper towers.
“You have to take advantage of the speed and simplicity that steel offers in these situations,” Mr Boyes says. “When we went into the design of the bridge, we recognised that having it fabricated off site would be the way.
“But there are other constraints that can affect the design, such as the availability of possessions, the space in which you have to work, and the size of the crane you will need to lift the different sections into position.”
The logistics of building on city centre sites is always tricky and this project is no different (see box).
Lincoln footbridge Galliford Try DSC 7967
But being so close to a live railway and in the centre of a bustling city, the site team has had to work closely with Network Rail and the local authority to gain permissions for work, track possessions and road closures.
Installing the stone composite cladding for the two lift towers and the unusual glass balustrade to the deck walkway has been carried out under normal working hours, although there are sections on the northern side of the bridge that will need to be completed during track possessions.
“The glass balustrade is a requirement of the planning process,” Mr Boyes explains. “Normally these would be solid steel, but Lincoln City Council didn’t want the bridge to be dark and foreboding. They didn’t want anything that might put people off using it.”
With the team putting the finishing touches to the bridge before it is handed over to the client, it will soon be helping make Lincoln city centre a safer place for pedestrians.
Access adds difficulties to logistics
City centre projects are always difficult to service and the new Lincoln High Street footbridge is no different. Bounded by a busy railway and a bustling High Street, the only access to the site is off the Brayford Wharf side of the scheme.
For the smaller-scale work this has not been too much of an issue, but bringing a prefabricated steel lattice girder bridge in sections through the narrow streets of Lincoln and erecting them on site has necessitated a number of road closures and track possessions.
The business of getting those possessions from Network Rail can be long and laborious. Quite rightly, the operator needs to see planning for every point in detail before it can be satisfied that the risk of overrun and consequent disruption is minimised. Sixteen weeks has been the lead-in time for any proposals, with possessions needing to be booked eight weeks in advance of any work.
Likewise, the practicalities of transporting steel bridge sections has had to be agreed between the local authority and police, with routes planned weeks ahead along with secondary routes and hold points set up outside the city.
“The planning and the execution of the works has been complicated and thorough,” Mr Crosby says. “But it is better to make sure these operations are planned carefully to get them right.”