Network Rail has said that remote instrumentation and monitoring installed at the Barnehurst landslip site provided early warning of the failure and reduced risk to the travelling public.
Network Rail south east route asset manager for geotechnical engineer Derek Butcher said that the ground movement occurred at 3.30am on Monday and the monitoring provided the alert to the large ground movements.
“The monitoring meant that we were able to close the line as soon as the movement was detected and allowed us to keep passengers safe,” said Butcher.
The instrumentation system at the site was formed of 250 sensors and 10 cameras was installed at the site in 2016 by Senceive and GE understands that the system is set to be supplemented with further instrumentation shortly.
“This section of the railway was opened in 1895 and cost pressures to minimise the land take led to the steep cuttings and left us with a legacy of unstable earthworks,” said Butcher. “There have been four failures in this area in the last 10 years, however, we didn’t have any advance warning of the failures which is why we installed the remote monitoring system.”
Repairs to the failed section will copy previous H piles retaining walls used on other sections of the Barneshurst cutting with H piles drive 6m into the ground with a 2m upstand left to allow concrete planks to be fitted to form the retaining wall.
According to Butcher, various options were considered, including a temporary repair to allow one rail line to be reopened but he said that this would have taken eight weeks to complete. “The permanent repair solution we are undertaking requires both lines to be closed but can be fully completed within seven days,” he said.