Lack of flood risk impact on an embankment in Leicestershire led to its failure under loading from a freight train which subsequently derailed in December 2012, according to a report from the Rail Accident Investigation Branch (RAIB).
RAIB reports that the incident close to the banks of the River Soar near Barrow upon Soar on 27 December occurred when one of the rails on which the train was travelling dipped due to failure of the embankment resulting in the 11th and 12th wagons on the 13 car train derailing.
Investigations into the embankment after the incident by Network Rail showed that it suffered a single rotational failure where a layer of ash underlay the clay embankment. The investigation found that flooding in the days before the incident had saturated the ash material and caused softening in the lower 400mm of clay material.
The report states: “The investigation found the embankment failed under the weight of the passing train because water within the embankment had reduced its stability and none of Network Rail’s processes had identified this. It is possible that an evaluation of the embankment could have identified the reduced stability, but the circumstances for triggering an evaluation were unclear, and there was no defined process for reporting trigger events.
“The investigation also observed that the evaluation process did not make use of rainfall data, or data that showed how the geometry of the track on top of the embankment was changing over time. An additional inspection during flooding could possibly have identified the embankment’s reduced stability. However, none was required at this location as Network Rail did not consider how the embankment was constructed when assessing the risk of an earthwork failure due to water.
“It is also possible that the embankment’s reduced stability could have been identified by a routine examination, but none was due. A basic visual track inspection had been planned for three days before the accident but it was not completed. It is possible that this planned inspection would have found a track defect which could have led to the discovery of the embankment’s reduced stability.”
RAIB has called for track maintenance staff to directly notify the route geotechnical team if the foot of an embankment floods and changes in track geometry are noticed. The organisation also called for Network Rail to amend its processes so that when assessing whether an embankment should be included in the flood warning database, the assessment should include additional factors which are relevant to its stability such as how the embankment was constructed.