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Borough Viaduct and London Bridge: The keys to opening capacity

The key to fulfilling the full potential of the Thameslink project involves a massive rebuilding project at London Bridge.

In simple terms the Thameslink project is about delivering two things: longer trains, and more of them. The work being done at Blackfriars, Farringdon and the outer stations is mainly designed to facilitate the arrival of the longer, 12-car trains. But there is one big hurdle to overcome before trains can run at the desired frequency - London Bridge station, which represents a major bottleneck in the system.

At the moment, London Bridge, the capital’s oldest railway terminus, has 15 platforms and handles 250,000 commuters a day, with three different train operating companies (TOCs) bringing them in from Kent, Sussex and outer London. Of those 15 platforms, nine terminate at the station, while six of the lines continue through the station to Cannon Street, Charing Cross or Blackfriars.

In the peak rush hours, 86 trains an hour in each direction stop at or pass through London Bridge, but only one of these is a Thameslink train, indicating the scale of the problem Network Rail has if it is to meet its challenge of 18 trains an hour in each direction stopping at the station.

“There is only one Thameslink train per hour in each direction because of competition for space and train paths with all the other trains coming in and out,” explains Network Rail project director for KO2 developments Martin Jurkowski, adding that the route the Thameslink trains currently have to take crosses the path of many of the other trains causing delays outside the station.

“This is a very challenging location to work in, and to actually do what we’re proposing to do there is extremely testing.”

Martin Jurkowski, Network Rail

The solution is to provide two dedicated tracks for Thameslink trains, so they can stop at London Bridge and then continue onto Blackfriars and through London, a proposal that involves building a new grade separated crossing south of the station.

Furthermore, it involves constructing a new 300m long viaduct through Borough Market to create the space for two more tracks; and completely reconstructing London Bridge station in an entirely new configuration - all without unduly inconveniencing the commuters and train operators that use this section of the line.

Work is already under way to build the new Borough Viaduct, but it will be 2012 before construction starts at London Bridge station itself. “This is a very sensitive location to work in, and to actually do what we’re proposing to do there is extremely testing,” says Jurkowski.

The station scheme involves totally remodelling the station so that it will have nine through lines and six terminating platforms. Two of these through platforms will service the Thameslink trains, four will be for the Charing Cross trains and three for Cannon Street.

The platforms themselves will also be widened as much as possible because, as Jurkowski explains, the new layout is not being built purely to improve Thameslink services. “One of the challenges we’re facing is that passenger growth is increasing year on year at London Bridge - even during the recession - and the station is close to not being able to cope with the number of passengers.”

The site at Borough Market

Construction is well underway on site

Numbers are currently increasing at a rate of about 4% a year, and the other two TOCs at the station - Southern and Southeastern Trains - are also planning to introduce 12-car trains, capable of bringing in even more passengers to London Bridge. Network Rail’s plans should be able to accommodate growth of about 50% on today’s numbers, mainly by creating the new concourse area and widening platforms.

But space is extremely limited, and the work must be done within the existing station footprint, hence the location of the new 70m wide concourse underneath the rail lines themselves. It will be formed by opening up the vaults that support the entire station and its rail lines at the moment, some of which date back to the station’s original construction in 1836.

The biggest challenge is how to totally reconstruct the station - and the associated rail infrastructure - while keeping trains running in and out of London Bridge. It has been described at Network Rail as “like performing open heart surgery while the patient’s awake”.

“We know that what we do has an impact on the railway network in the South East,” Jurkowski adds. “If we shut London Bridge, London would notice and the economy would notice, so we’re devising approaches that will still allow all of these commuters to access London.

“There has to be a trade-off between value for money construction and maintaining capacity on the railway through the worksites,” explains Jurkowski. “We’ve spent 12 months working with the train operating companies and the Department for Transport to develop an appropriate approach.”

The proposed new track layout at London Bridge

The proposed new track layout at London Bridge

Since planning started for London Bridge reconstruction, a new neighbour has arrived in the area in the form of the Shard development, London’s latest iconic tower, which is currently under construction on a site adjacent to the station.

With work at London Bridge station not set to start until after the Olympics in 2012, the timing has been fortuitous, as it would have been impossible for both projects to be under way at the same time. But the Shard has influenced the station’s conceptual design resulting in some changes.

However, Network Rail is working closely with the Shard project team, and learning from its experience of building in such a tight, congested part of London, especially when it comes to the logistics of getting materials in and out.

With work set to start on the station design in the next few months, and a contractor due to be appointed at the end of 2011, Network Rail plans to hit the ground running on the scheme straight after the Olympics.

Once completed and the bottleneck is finally opened up, Network Rail will be able to deliver the full benefits of all its investment in the Thameslink project.

The current signalling system around London Bridge will have to be replaced by 2021 and other renewal work is desperately needed. As Network Rail investment projects director Simon Kirby explains: “We’re talking about a once in a generation opportunity. Network Rail’s plans will transform London Bridge station and remove the bottlenecks around it once and for all - within the agreed budget.

“The alternative is to spend £1bn anyway, only to lock commuters into another 40 years of congestion.”

Borough Viaduct

Key to unlocking capacity at London Bridge is the project to widen Borough Viaduct, which takes trains west of the station towards both Charing Cross and Blackfriars. “If you get one train stuck on that, everything backs up all the way down to Kent,” says Network Rail senior programme manager Graeme Campbell. “We’re taking out a massive, massive pinch point.”

The widening will double capacity on the viaduct from two to four tracks, allowing the original tracks to be dedicated to Thameslink trains and the new pair to carry the Kent trains into Charing Cross.

Borough is a historic area of south London that is home to many businesses and attracts large numbers of visitors, not least to its renowned food market. Threading a new 300m long rail viaduct through and above existing buildings is far from easy, but Network Rail has been keen to keep disruption to an absolute minimum.

Right from the start the company adopted a targeted demolition policy, so that only buildings that were right in the path of the new structure have been taken down. And when the viaduct is complete, new buildings are to go back into the vacant spaces, so there will be no unsightly gaps in the urban landscape.

Negotiating with the traders at Borough Market has been an important aspect of the job, as a 120m section of the new viaduct runs right through the area used by traders. They have been temporarily relocated, and the original Victorian cast iron and glass market roof has been taken down, stored and refurbished.

The eye-catching new Borough viaduct

The eye-catching new Borough viaduct

“In the new design the roof will go back in a slightly different place,” explains Campbell. “We have spent a lot of money trying to retain the cultural identity of this place.”

The market section of the viaduct is one of four distinct elements that make up the new structure. From the west they are the Park Street/Hop Exchange, where the new viaduct ties in to the existing structure; the market viaduct; Borough High Street bridge;and the railway approach, where it heads into London Bridge station.

Of these, the most eye-catching element is the Borough High Street bridge, a trapezoidal girder bridge that will span 70m over the busy main road.

“We were originally going to build it in our yard and take it down the road,” says Campbell, adding that shallow services and Jubilee Line Tube infrastructure beneath the road made this option impractical.

Instead, the team will build the 1,200t bridge on top of the market viaduct, which is currently under construction. It will then be pushed out over the road, and supported by transporters at road level as it is manoeuvred into position. “Our expectation is that it will go across the highway in one weekend and then be jacked down into position the next weekend,” explains Campbell.

Piling for the market viaduct has just finished and the 1.8m diameter circular columns that will support the new steel girders and precast concrete deck are currently being built.

The bridge over Bedale Street

The bridge over Bedale Street

Exciting though Borough High Street bridge will be, it is not necessarily the biggest challenge on the job, according to Skanska project manager Susan Fitzpatrick. “The bridge is the glamorous, big section that will grab everybody’s attention,” she says. “I’m very excited by it and I’m looking forward to it, but what will keep me awake at night is the cantilever section,” she says.

This is a small, tricky piece of the job that is all but hidden from view, but enables the new viaduct to tie into the existing structure at the west end of the job. Here the contractor has only the tightest of spaces in which to build a wedge shaped section of deck, and must build suspended falsework out over the roof of an existing property in order to be able to cast the concrete.

The other section likely to cause sleepless nights is the railway approach, where the new viaduct will link into the new infrastructure that will eventually be built at London Bridge.

Here piles must be sunk through a double layer of vaults that currently support the road to the station, many of which have been filled or part-filled with everything from rubble to solid concrete in the intervening years.

Like many other sections of the job, the railway approach is bound to be of interest to the 30 archaeologists from the Museum of London who have been active on the site since work began. “This area is very important historically, because for centuries London Bridge was the only bridge over the river,” says Campbell. “Anywhere we’re putting in a pile the archaeologists will do an investigation.”

The newly designed Stoney Street

The newly designed Stoney Street

Important finds on the job so far include some distinctive 17th century Southwark delftware pottery and 300 skeletons from a burial ground, which are being re-interred under the guidance of nearby Southwark Cathedral.

History aside, Fitzpatrick says the biggest challenge on the job is not the complex engineering but “constructing a major building and civil engineering project in this area without anyone really knowing we’re here”. Ten years ago local residents and traders had to put up with years of disruption while the Jubilee Line was being built in the area, so it is not surprising that they may have been wary when the Thameslink work started.

“I think we’re growing on them now, and I think people recognise that we’re trying really, really hard,” says Fitzpatrick, explaining that Borough Market is a thriving wholesale market at night, attracting up to 40 articulated lorries between 2am and 8am.

“We know that if we shut a road off overnight and their customers can’t get in, then they won’t come back, so we try to work around them,” she says.

Despite these complications, Fitzpatrick says she prefers this job to building on a greenfield site. “This will look amazing. You can really see it coming up and fitting together like a jigsaw,” she says.

“Everyone’s engaging with the project and at some stage we all have our moments of feeling like a little kid and remembering why we joined the industry.”

London Bridge and Borough in figures

70m

wide new concourse

40%

passenger growth accomodated in the new station and platforms

9

through lines

2

dedicated Thameslink lines

6

terminating platforms

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