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Open and shut case

Rail Underground

The £3M cost of a complete shutdown of the Waterloo & City line is paying dividends, as Ruby Kitching discovers.

One problem with the Tube upgrade taking place under the Public Private partnership between London Underground (LU) and contractors Metronet and Tube Lines is that much of the work is tucked into the five hour slots when the service shuts down every night. This means that it will be years before passengers experience a marked improvement.

However, on the 2.4km long Waterloo & City line, a consolidated engineering programme is fast forwarding nearly two years' worth of night engineering work.

The line, which runs between Waterloo and Bank, has been closed since April to allow contractor Metronet and subcontractor Balfour Beatty Rail to spruce it up over a five-month closure (NCE 9 March). Metronet has paid London Underground £3M for the privilege of closing the entire line down, and for £40M will replace and realign the two running rails and conductor rail in both directions to improve the ride quality, particularly on curved sections of track.

'Only the central section [under the river] is straight - the rest is like a dog's back leg, ' explains Balfour Beatty Rail project director Adam Stuart (pictured below).

'The line was built after the City had sprung up so the only clear route avoiding services was to follow the road network between Bank and Waterloo. This means sharp curves.'

Stuart adds that Victorian engineers paid little attention to smoothing out the transition between straight and curved sections of track. It is here that trains have to travel at restricted speeds. There are also some sections where the rails are mounted on longitudinal timber sleepers, which are relatively unstable having been strengthened with tie rods to ensure they remain rigid under the forces imposed by the trains.

The timber sleepers are being replaced with concrete, allowing speed restrictions along these stretches to also be lifted. By the end of this month, almost all the track will have been replaced, allowing the line speed to lift from 16km/h at worst, to a constant 55km/h.

Stuart has worked on aboveground railway lines before and admits that the constraints of working underground with access only from Waterloo via an access shaft directly onto the line has made the job tougher.

'We originally went for making up the concrete [on site for the tunnel invert] because there's a water main running through the tunnels. But with hindsight it was the wrong decision, ' he says, pointing out that in the hot tunnels, even the simple task of mixing concrete becomes difficult.

A few weeks into the construction programme, Stuart decided to source concrete from a nearby batching plant.

The concrete is quick-setting, 'but costs 10 times the price of normal concrete', says Stuart.

But by far the most arduous job is realigning the track where the cast iron tunnel lining ribs clash with sleeper fixings. Here the lining is nibbled back so that sufficient concrete can be placed between it and the sleeper fixing.

Other work involves installing CCTV and modifying the signalling system. This will allow a quicker turnaround of trains at Waterloo, allow trains to travel across the Bank crossover at higher speed and allow a fifth train to run on the line to increase capacity.

A final deep clean of the stations and introduction of a completely reconditioned fleet will complete the makeover so that by 1 September, the new look Waterloo & City line will show off what the Underground is really capable of.

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