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NOSING AHEAD

The bridge that will tie the whole of the upgraded East London Line together is now being assembled just off Brick Lane. John McKenna reports from Shoreditch.

Brick Lane. Where the towering glass and steel structures of the City of London make way for the little brick buildings of the East End. If you avoid the temptation to enter one of its many curry houses or the growing number of modern art galleries, you will stumble upon some blue hoardings by what was once Shoreditch Underground station.

Rising up from behind these is a structure destined to have as great an impact on the local landscape as the soon to be completed Broadgate Tower by Liverpool Street Station.

GE19, an 84m span steel warren truss bridge, is currently being erected by fabricator Fairfield Mabey on a site adjacent to the six national rail lines it must eventually cross.

It is one of three new bridges being built by Balfour Beatty/Carillion joint venture as part of its £336M main works package on Transport for London's (TfL) £1bn East London Line project. The East London Line, which previously ran from New Cross Gate in south London to Shoreditch, is being extended south on existing suburban rail routes to Crystal Palace and West Croydon. Northwards it will eventually to run to Dalston on the Victorian Kingsland Viaduct, restored by contractor Taylor Woodrow and consultant Faber Maunsell as part of a £36M enabling works package completed in December 2006.

GE19, along with a new viaduct in Bishopsgate Goods Yard and a crossing over Shoreditch High Street, will link the existing line from Whitechapel to the Kingsland Viaduct and its three new stations at Hoxton, Haggerston and Dalston Junction.

Of the three bridges GE19 is the biggest and the only one that requires two possessions of major national rail routes.

Before the structure could be built, the existing GE19 structure had to be demolished by Network Rail during a nine day possession over Christmas. Once this was completed, Fairfield Mabey moved in to begin assembling the new structure, ready to be launched during a 50 hour possession over the May Bank Holiday weekend.

GE19 is a steel structure designed by Benaim on behalf of main project consultant Scott Wilson. It has an 8m deep warren truss, an 84m span and contains 812t of steelwork. It will be launched at a 600 skew to the rail lines it crosses on a 1:30 gradient.

During the launch it will have an additional 300t of temporary steel work including its temporary nose and trestles. The various steel elements of the permanent structure, fabricated by Fairfield Mabey in Chepstow, are currently being fitted together using 30,000, 24mm and 30mm high strength friction grip bolts and 2,100 connection plates.

Precast concrete Omnia planks will be placed on the bridge's steel girders, allowing a cast-insitu 250mm thick reinforced concrete base to be poured on top. However, only the rear 45% of the deck will be in place before the launch. This will act as a 500t counterweight together with 320t of steel kentledge placed on the back of the bridge during the launch (see diagram).

The counterweight will prevent the bridge from falling on to the tracks during the launch. Once the temporary steel nose is over the western abutment, the kentledge will be removed, lowering the nose and reducing the stresses on the structure. The remainder of the concrete deck will be put in place after the possession.

While Marriott watches the weather forecasts praying for dry sunny days, Balfour Beatty/Carillion GE19 section manager Phil Wharton will hope for anything but wind during the launch – if it gets up above 12m per second the launch will have to be suspended until the wind dies down.

"The weather and plant failure – for example one of the strand jacks braking down – are the two biggest risks to the launch," says Wharton.
While there will be plenty of spares on site to cover mechanical failures, the weather is less easy to control, even for a joint venture of Balfour Beatty and Carillion's might.

However, Wharton is confident that there is plenty of contingency within the contractor's allotted 35 hours (the amount of time remaining in the 50 hour possession after allowing for Network Rail's closing and opening of the six rail lines) to cover any disturbances.

For Balfour Beatty/Carillion East London Line construction manager Adam Stuart, the success or otherwise of the GE19 launch will determine the success of the whole main works contract.

"It's the lynchpin," says Stuart.

"All the new track and rail systems are being done in a southerly direction from Whitechapel station. Once that is done they will move north from Whitechapel, and without GE19 in place we won't be able to run the rail systems on the northern section of the line."

Balfour Beatty/Carillion's 50 hour possession on the national rail lines to launch GE19 starts on 4 May. Stuart says all heavy civils work should be finished by the Autumn, with the line ready for dynamic testing in 2009 and handed over to TfL for trial operations by September 2009.EAST LONDON LINE: MAIN WORKS

The original GE19 bridge was a long-redundant brick jack arch structure built in 1880. It was on the wrong alignment for the East London Line and its steel beams had corroded.

The bridge was demolished by Network Rail during a nine day possession of the lines running into Liverpool Street.

Main contractor Murphy and demolition specialist Gregory carried out the job, with Colas responsible for the safe removal and installation of overhead electrification lines.

Rather than remove the rail lines, the contractors protected the track underneath the bridge by creating a temporary crash mat. Murphy put down a TRRAM geotechnical surface over the tracks then 200mm polystyrene blocks were placed in the spaces between the running rails on top of the sleepers. On top of this a 300mm timber crash mat was bolted together in panels and placed on top of the polystyrene.

Gregory's plant sat on top of the bridge and jack hammered down removing steel beams and allowing brickwork to fall on the crash mat, gradually retreating to the side as the machines removed more the bridge.

The brickwork was crushed and turned into hard core fill, and the steel sold. In total the demolition cost Ł2M, carried out by Network Rail but paid for by TfL.

GE19 BRIDGE LAUNCH

The warren truss will be hauled across the railway during a 50
hour possession starting on 4 May.

35 hours
Time allotted for jacking

812t
Amount of steel in the truss

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