HomeInfrastructureChristmas under London: TfL's festive engineering work

Christmas under London: TfL’s festive engineering work

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London Underground, like it’s Network Rail cousin, took advantage of the Christmas closedown, and the opportunity to take longer possessions over the holiday period, to undertake two major pieces of work.

The first was on the Northern Line Extension. This deep-tube line is being extended to Battersea as part of plans to help regenerate the Vauxhall, Nine Elms and Battersea areas, supporting 25,000 new jobs and more than 20,000 new homes. Two new stations are being built, at Nine Elms and Battersea Power Station, and are targeted for completion in 2020.

A significant stage in the creation of the project was achieved over the Christmas and New Year period, with work taking place from the night of 22 December right through until New Year’s Day.

Connecting the extension

The new 3.2km tunnels from Battersea to Kennington having been completed on 8 November, both the northbound and southbound tunnels for the extension branch were connected to the existing Kennington Loop running tunnel via newly-constructed step-plate junctions.

The larger diameter tunnels had been constructed in the months leading up to the recent closure. These tunnels were effectively “wrapped around” the old tunnel in readiness for connection.

The old 1920s loop line tunnel is formed of cast-iron segments and the new one is, throughout the majority of its extent, formed of precast concrete segments. However, to make the connection to the original loop line tunnel, the new tunnel transitions through a section with a sprayed-concrete lining to a final steel-segment section, enabling it to be step-plate connected to the cast-iron segments.

Ferrovial/Agroman/Laing O’Rourke Joint Venture is the main contractor for the work. Mark Thompson, TfL project manager, told Rail Engineer that the final removal of the old cast-iron sections in the connecting locations proved to be a very challenging part of the work. Diamond sawing alone was insufficient, as the arch compression forces tended to jam the saw when only two-thirds of any cut had been made. Therefore, it was necessary to resort to piecemeal fracturing to complete the removal.

An additional obstacle was the volume of mass concrete embedded at the back of the cast-iron segments. This had to be broken out, with all spoil being removed through new access shafts.

This was a complex piece of work, benefiting from the closure period of 10 days to couple up the new tunnels. Because the connections are on the Kennington Loop, there was no need for a complete Northern Line closure, merely a reduction in the train service frequency, as a consequence of the loss of the Loop facility. Once the civils work was complete, sub-contractor Rhomberg Sersa installed the low-vibration track and turnouts, concreted it all in position and restored the railway ready for the first train on New Year’s Day.

Completing Earls Court

London Underground’s other major closure over the Christmas period, which was also very successful, was for the renewal of three crossovers just to the east of Earls Court station.

The closure of all the District line routes around the immediate station area took place from Christmas Eve until the night of 30 December. It was critical that the District line would be fully available for the New Year’s Eve celebrations and this was achieved.

The three crossovers were nearing the end of their maintainability. Their renewal formed one of the last remaining stages of the progressive replacement of all the trackwork in the Earls Court area. The previous bullhead material has been replaced with flatbottom rail on concrete bearers.

An option for the work to have been undertaken in many small stages within normal 52-hour possessions over many months would not have been feasible. Such an approach would have meant the temporary loss of some train routings whilst the pointwork was being replaced piecemeal. So the chosen method of doing all the work in one major possession gave the most economic and beneficial solution at the expense of a short period of disruption during a less busy commuting period.

The LU/Balfour Beatty Track Partnership carried out the work in-house with around 200 staff overall, split between three shifts per day throughout the closure. Although installing the new trackwork in modules would have been desirable, restrictions on the handling space available made this impractical. All the new components were therefore installed individually, using RRVs for the mechanised moving and lifting, but with the work overall being essentially heavily manual. The switch and crossing work was pre-assembled, checked and marked up by the manufacturer, Progress Rail, at its premises prior to delivery in component form. Approximately 500 concrete bearers were installed overall in the new layouts.

John Lambert, head of track programme (renewals and enhancements) for LU, told Rail Engineer that he was particularly satisfied regarding two aspects of the project, namely safety and planning.

So far as safety was concerned, there was only one minor injury throughout the whole closure. This was a bruised thumb as a result of carrying a Fastclip tool in the wrong manner. Refresher training has already been carried out. John commented: “This impressive safety record is a direct consequence of putting safety at the heart of everything we do.”

Excellent planning gave the opportunity to achieve significant extra work beyond that minimum which was strictly essential for timely reopening. For example, contained within the base plan was the making of 20 out of the overall 129 welds needed in the layout. In fact, thanks to good progress with the works, it became possible to complete 59 welds, leaving a lot less to be done in follow up possessions. Also, scrap materials were cleared from a previous ballasted track renewal and some follow up tamping carried out.

The new crossovers and associated works will provide improved reliability and lower maintenance costs for many years ahead. Specifically, 30A/B crossover has been lengthened, changing from C switches to a D/E layout. This will enable enhanced speed through the crossover, which will in turn, when the new signalling under the Four Lines Modernisation project is installed, allow an increased train frequency.

And there’s more…

In addition to these two major projects, other work was carried out during the closure period.

As part of the 4LM project (four lines modernisation) cabling was installed along over 3.5km of track. This will support the new Wi-Fi-based signalling system, allowing trains to run closer together resulting in a more frequent service and shorter waiting times for customers.

Passengers will benefit from this huge amount of work and investment later this year when the first section of the new signalling system goes live between Hammersmith and Latimer Road and when the new Hammersmith Control Centre opens. While service frequencies cannot change until the whole line has been upgraded, reliability should certainly improve once the new system is introduced over the first sections.

Engineers were also out at Wimbledon and Wimbledon Park stations, refurbishing junctions to again make services more reliable.

Meanwhile, the ‘clean-up gang’ was out in force, recovering scrap materials from around the network and removing vegetation from areas where it was out of control. Overall, 100 tonnes of waste was removed over the Christmas period.

As services resumed in the New Year, Mark Wild, TfL’s managing director of London Underground, said: “The work we completed over the festive period was incredibly complex and I thank customers for their patience whilst our engineers worked around the clock to carry it out.

“This work is part of our record investment in the Tube, which will see over forty per cent of the network radically improved with more frequent trains, quicker journeys and better reliability and the first major extension to the Tube network since the 1990s.”

This article was written by Mark Phillips.

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