A lapsed system to monitor scour risk on more than 100 at-risk rail bridges across Scotland has been identified, following an investigation into why trains were allowed to cross a viaduct damaged by storms.
The Rail Accident Investigation Branch (RAIB) launched an investigation into the Lamington Viaduct on the West Coast Main Line after a train driver reported a “rough ride” on 31 December last year. The viaduct spans a bend on the River Clyde between Lockerbie and Carstairs.
A maintenance team was deployed but initially found no significant track defects and trains were allowed to cross. A short time later, the team found the viaduct’s central river pier had been partially undermined by scour following high river flow velocity the previous day and trains were stopped from crossing.
The Victorian-built viaduct had been hit by Storm Frank, causing damage to the second pier’s steel bearings, which support the bridge-deck and track above the pier, a non-load-bearing section of the viaduct’s third pier and the structure’s north abutment.
The investigation into the incident found that a process devised by Network Rail to mitigate scour risk on 100 vulnerable structures across Scotland had lapsed due, in part, to “organisational changes” within Network Rail. RAIB said this led to the “loss of knowledge and ownership of some structures issues”. The “lapsed” system had special precautions for at-risk structures during flood conditions, including monitoring river levels and closing the line if a pre-determened level was exceeded.
The RAIB investigation found that the viaduct was identified as being at high risk of scour in 2005. Construction of a scour protection scheme for the viaduct’s piers and abutments had been deferred until mid-2016 because a necessary environmental approval had not been obtained. RAIB said that defects in the central river pier had not been fully addressed by planned maintenance work.
There were no effective scour mitigation measures in place for over 100 of the most vulnerable structures across Scotland.
“It is of particular concern to me that the vulnerability of this structure to scour had been identified at least 10 years previously. Despite this, insufficient action had been taken to protect the piers from scour, or to monitor the integrity of the viaduct at times of high water flow. The continued operation of trains over this high risk structure, despite a previous report from a driver of a rough ride, provides vivid evidence that the risk of scour was not generally appreciated by those involved,” said rail accidents chief inspector Simon French.
“Of even more concern was our finding that there were no effective scour mitigation measures in place for over 100 of the most vulnerable structures across Scotland. We discovered that a previous process for managing scour risk on Scotland Route had fallen into disuse, at least in part due to organisational change, and that this had not been recognised by Network Rail.”
French said it is vital that the railway industry improves its historical knowledge of its assets and associated management systems.
“It is my view that the safety of assets can only be assured if those responsible clearly identify the control measures that are in place, how they contribute to safety and what must be done to keep them in place into the future,” said French.
“I hope that the future will see a much greater use of remote sensing equipment to monitor the condition of structures (and earthworks). Recent advances in technology make this easier to do, and I am encouraged that Network Rail is already working towards extending the use of such equipment.”
Network Rail said all of its structures were getting their routine inspections at the time of the incident and Lamington had been inspected at the start of December 2015.
It admitted, however, that shortcomings in how it monitors live flooding events have been highlighted by the report, adding that since the incident processes have been changed to ensure all at-risk structures are subject to additional inspections in the event of forecast flooding.
“We worked closely with RAIB as it completed this report and will carefully review the findings. The safety of passengers, and rail workers, is of vital importance to Network Rail and we have already made significant changes to our management and maintenance of scour-risk structures in Scotland since Lamington,” said a Network Rail spokeswoman.
“We have invested over £3M so far this year to reduce scour-risk at high priority structures and have carried out 277 specialist underwater examinations to assess the foundations of bridges ahead of this winter. We have also identified 50 bridge sites where we will roll-out telemetry equipment, to help monitor the impact of flooding on the network and to improve early identification of potential issues.”