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Removing the risk: Polhill Cutting near Halstead

Rail passengers in Kent no longer need to pack a red flannel petticoat after the cutting that may have inspired The Railway Children story has been stabilised.

Recessions are rarely good news for anyone, but for the rail network it gave rise to some extra funding that has been used to reduce the potential for failures at high-risk sites. For one particular site in Kent this opportunity has resolved a problem that has been an iconic part of many childhoods for more than a century.

It is believed that the slope stability problems at the Polhill Cutting near Halstead inspired Edith Nesbit, who grew up nearby, to write The Railway Children. While the steam train that the Waterbury family saved from disaster may be a thing of the past, until recently the rock fall issues at Polhill Cutting were not. Nonetheless, a recently completed scheme means that passengers should no longer feel the need to pack a red flannel petticoat in case of a landslide.

Polhill Cutting is believed to have inspired Edith Nesbit’s book The Railway Children

Polhill Cutting is believed to have inspired Edith Nesbit’s book The Railway Children

“Many of the Victorian era cuttings were very steep and most suffered from failures during or soon after construction,” says Network Rail geotechnical route asset manager for the south east Derek Butcher. “It is believed that Nesbit took inspiration from watching these problems when she wrote The Railway Children, which was first serialised in The London Magazine in 1905 before being published in book form in 1906.”

Polhill Cutting lies to the south of Knockholt station and leads to the northern portal of the Polhill Tunnel, which opened on 3 March 1868 and carries the Charing Cross to Dover rail line under the North Downs.

“The station was originally called Halstead but travellers confused it with another town of the same name in Essex so the railway company renamed the station Knockholt, which is a few miles west of Halstead,” explains Butcher.

Halstead was the childhood home of Nesbit in the 1870s and it is known that she used to enjoy walking over to the railway line to watch construction and repair work there.

“The cutting has had instability issues since it was built as a result of spalling caused by the freeze/thaw action on the weak chalk,” says Butcher. “Tree roots have become more of an issue here since the line moved from steam power to diesel and electric trains too. The heat and smoke from the steam trains meant that very little vegetation thrived in cuttings but quickly became established once steam stopped being used.”

Nonetheless, Butcher believes these risks have been removed following completion of a stabilisation scheme by Murphy. The work involved securing the weak chalk in the 600m long, 20m deep cutting using anchors and rock netting.

The scheme is actually a beneficiary of the recent recession as it was not part of Network Rail’s Control Period 4 (CP4) funding and was not thought to be enough of a problem to come under CP5 funding, which covers the period from this year until 2019.

Work included rock fall netting

Work included rock fall netting

“The Office of Rail Regulation (ORR) and government offered a £250M pot of funding to create a fiscal stimulus for the contracting industry by bringing forward work that focused on specific areas of the railway network,” explains Butcher.

“The Enhanced Spend Project (ESP) was for use on five streams of work: bridge painting, spandrel wall stabilisation, hidden critical elements, scour protection and earthwork cuttings risk reduction.

“The aim was to use the funding for schemes that was to reduce the risk of failure at high risk locations such as on high speed lines, on curves and the approaches to tunnels. In these situations a train driver has less visibility of the track ahead or there is a potential for something to fall from a great height.”

Network Rail’s operations in the south east bid for £41M of funding for projects it believed it could deliver quickly and with minimal impact on rail services. Butcher’s team was successful in applying for £19M of funding which mostly targeted rock cuttings that were suffering from similar problems to those at Polhill.

Work on the projects started in August 2012 and Polhill was one of the last to be delivered under the ESP scheme. In total, the £19M ESP funding in Kent enabled 13km of rock cutting to be stabilised with 166,000m2 of rock faces treated.

Butcher says the funding was spread as wide as possible by minimising the design work before moving onto site by using Network Rail’s standard detailing, which includes a suite of designs for rock fall netting. “Murphy installed trial anchors and carried out pull out tests on site while the vegetation was being cleared from the rest of the site,” he explains.

Rail passengers in Kent no longer need to pack a red flannel petticoat after the cutting that may have inspired The Railway Children story has been stabilised.

Rail passengers in Kent no longer need to pack a red flannel petticoat after the cutting that may have inspired The Railway Children story has been stabilised.

Work on Polhill - and all the projects funded through ESP - has now finished. “These were high risk sites so it is good to have them fixed,” says Butcher. “Especially as, although they were high risk and deteriorating, they could not be included in CP5 because there had been no significant problems at the site.”

Butcher believes that without the ESP funding, there would have been issues at a number of the sites treated during the last winter due to the heavy rain. “Several small failures that were captured in solutions deployed under ESP could have resulted in multiple large failures causing high levels of disruption if they had not already been stabilised,” he adds.

What is clear is that while these rock faces may not have failed this winter, they were at risk of causing disruption during the upcoming winters of CP5. Remediation of the slopes under ESP means that CP6 funding has now been freed up and will be available to further reduce the risks in other areas.

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