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Working the West Coast

WCML - Logistics pose the main challenge to contractors working to widen the West Coast Main Line's Trent Valley bottleneck, John McKenna discovers.

In December it became possible for the first time to travel the West Coast Main Line (WCML) from London to Glasgow at 125mph (200km/h), making a journey time of four and half hours.

Achieving real high speed rail travel over the entire length of the WCML is the most significant milestone in the route's ongoing £8bn modernisation.

However, the upgrade is far from over, with £1bn of work still to be done.

A major element of the final spend is the £300M Trent Valley four tracking project, due to be completed by August 2008.

This will remove a bottleneck on the 19km route north east of Birmingham that goes through Tamworth, Lichfield and Armitage. At either end of this section the WCML has four tracks, with the two inside tracks acting as express lanes for the tilting Pendolino trains.

But through the Trent Valley there are twin tracks only - one in either direction. Once the trains heading north from London to Manchester and Glasgow reach Tamworth, they have to share the line with freight and commuter trains.

As a result, delays and congestion are common phenomena in the Trent Valley area, and work to widen the route to four lanes began in earnest in May last year. Network Rail senior project manager Keith Riley says it is generally fairly simple in engineering terms.

Civil works on are budgeted at £160M, with the remainder of the budget to be spent on resignalling.

Construction involves widening cuttings and embankments, relaying tracks and upgrading or replacing 45 bridges and culverts. Riley says much of the Trent Valley project has been a battle of logistics rather than anything else: He singles out the widening of a road over rail bridge in Tamworth as an example.

'Upper Gungate Bridge is a hub right in the middle of town with traffic in every direction, ' he says. 'Our biggest challenge is to rebuild while keeping traffic flowing under the bridge.' The Trent Valley scheme has been divided into a series of individual contracts and Norwest Holst was appointed as main contractor for the widening of Upper Gungate Bridge.

Due to its location on the main arterial route into Tamworth town centre, the contractor has had to widen the bridge while ensuring the road remains open at all times. It consists of two separate two-lane decks with a sizeable gap between them.

This enables the existing bridge to be replaced with a longer deck in three stages, allowing the original alignment to be maintained while keeping one lane of traffic open in either direction.

Traffic has initially been restricted to the outer edges of each deck, enabling Norwest Holst to work safely on the inside lanes and in the gap. The middle sections of new abutments for the longer deck have been constructed - 'abutments both consist of 1,050mm diameter bored piles with reinforced concrete capping beams', says Network Rail senior civil engineer for Trent Valley Roger Colton.

With the central section of the abutment work nearly complete, the next stage of the operation will be to demolish the decks' inside lanes and install new precast, prestressed concrete beams. These will be topped with concrete planks and normal road construction.

'Once this is done, ' continues Colton 'we can move traffic from the eastern side of the bridge onto the central portion and demolish that side of the structure.' Then, with the eastern side rebuilt, traffic will be diverted again, enabling the western side to be knocked down and rebuilt.

The three-step method has kept the road open, but it has nearly trebled construction time, Colton says. 'If we could come in here and build this bridge straight off with no traffic restrictions at all we could probably do it in nine or 10 months. Dealing with the traffic has stretched it out to two years.' Upper Gungate Bridge reconstruction is programmed to finish in January next year.

Up the line north of Tamworth, contractors working in wide open green fields by the River Tame have an entirely different logistical challenge. Birse Civils won the £10M contract to build two parallel railway viaducts without causing disruption to the Pendolino trains that whiz past every five minutes.

Across e rent alley scheme, keeping disruption to train services to a minimum has been a key priority. To that end 70% of the structures on the scheme have been built off site.

Tame river's two viaducts are no exception.

These are identical structures, each measuring 92m long and 12m wide. The three girders making up the first viaduct were lifted into place in February with the aid of a 1,000t capacity mobile crane. Birse is now adding secondary steelwork, ready for a composite reinforced concrete deck.

Once this work has been completed, contractor Carillion will slew the route's existing two tracks onto the new bridge. 'That will then enable us to take out the old bridge and build a second structure identical to this one in its place, ' says Colton.

While the work is carried out, the original, 100 year old Tame crossing is being closely monitored by Network Rail. 'It's basically falling apart, ' says Colton. 'We've got instruments on it monitoring it continuously for movement and stress in the main members. If we didn't take it out this year as part of the project we would almost certainly have had to take it out anyway.

If we weren't carrying out this widening work, rebuilding that bridge insitu and keeping the line open would have been an absolute nightmare. I'm not quite sure how we would have done it.' Birse is also widening two flood water culverts either side of the river, to ensure that when in spate it will not erode the bridge abutments and railway embankments. And the contractor is widening the WCML embankment itself. To minimise earthworks and associated land take along the Trent Valley section, only the east side of the embankment is being widened.

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