Kent rail routes have suffered 40 earthworks failures in the last two months following five months’ worth of rain in the same period.
“We normally expect two to three landslips a year but we have recorded 40 since December and we estimate that the cost of repairing these will be in the region of £10M to £15M,” said Network Rail Kent route managing director Fiona Taylor. “Ten of the failures have been on the Tonbridge to Hastings line and we have been forced to close the line while we repair three of these.”
Taylor said that the works underway on the landslips at Marley Lane and Whatlington near Battle and at Stonegate are permanent engineering solutions rather than emergency repairs. All three landslips have been caused by deep seated failures in the Wadhurst Clay.
Both the Whatlington and Stonegate failures occurred at sites known to Network Rail, which were due to be repaired under CP5 and Geotechnical Engineering was on site carrying out ground investigation work for the planned repairs at Stonegate at the time of the failure. The site at Marley Lane was being monitored to assess the risk but was not part of planned CP5 works.
“If the level of rainfall we have seen since December continues throughout February, we will have received the equivalent of eight months of rain in just three,” said Network Rail Kent route asset manager Derek Butcher.
Taylor added that conditions are the wettest in 250 years. She said that as a result they are the most extreme conditions experienced since the Victorian-are structures were first built so while the failures could not be predicted, they were not unexpected.
Work by Murphy to repair the failure at Marley Lane is well progressed with a 60m length of sheet pile wall already installed by U-Pac and backfilling with 4,000t of aggregate already underway.
“The aggregate has been brought in from the south by freight train,” said Butcher. “We had originally planned to bring in the 10,000t of stone needed by Volker Fitzpatrick to repair the failure at Whatlington from the north but the failure at Stonegate has prevented this. The plan now is to complete repairs at Marley Lane to enable the freight train to deliver the aggregate to Whatlington from the south.”
Piling work is already underway at Whatlington and haul road construction at Stonegate was expected to be completed by Dyer and Butler to enable Aspen Piling to start work there today.
“The failure at Stonegate, which happened last Monday, is more serious because it has affected the embankment under the rail line. The other two failures only affect the shoulder of the embankment,” said Butcher.
According to Butcher, the situation at Stonegate could have been much more serious if the contractor had not reacted quickly and used pipework to extend a culvert below the failed embankment. “The toe bulge of the deep seated failure would have engulfed the culvert without extension and turned the embankment into a dam,” he said. “If that had failed then repairs would have taken three to four months to complete.”
Taylor has said that she hopes the repairs at all three sites will be completed in early March. Nonetheless, she stressed that although additional surveying work is being undertaken elsewhere on the rail line further failures could not be ruled out because of the weather conditions.