At 08:40 hrs on Thursday 31 December 2015, subsidence of Lamington viaduct resulted in serious deformation of the track as the 05:57 hrs Crewe to Glasgow passenger service passed over at a speed of about 110 mph (177 km/h). The viaduct spans the River Clyde between Lockerbie and Carstairs. Subsequent investigation showed that the viaduct’s central river pier had been partially undermined by scour following high river flow velocity the previous day. The line was closed for over seven weeks until Monday 22 February 2016 while emergency stabilisation works were completed.
The driver of an earlier train had reported a track defect on the viaduct at 07:28 hrs on the same morning, and following trains crossed the viaduct at low speed while a Network Rail track maintenance team was deployed to the site. The team found no significant track defects and normal running was resumed with the 05:57 hrs service being the first train to pass on the down line. Immediately after this occurred at 08:40 hrs, large track movements were noticed by the team, who immediately imposed an emergency speed restriction before closing the line after finding that the central pier was damaged.
The viaduct spans a river bend which causes water to wash against the sides of the piers. It was also known to have shallow foundations. These were among the factors that resulted in it being identified as being at high risk of scour in 2005. A scheme to provide permanent scour protection to the piers and abutments was due to be constructed during 2015, but this project was deferred until mid-2016 because a necessary environmental approval had not been obtained.
To mitigate the risk of scour, the viaduct was included on a list of vulnerable bridges for which special precautions were required during flood conditions. These precautions included monitoring of river levels and closing the line if a pre determined water level was exceeded. However, this process was no longer in use and there was no effective scour risk mitigation for over 100 of the most vulnerable structures across Scotland. This had occurred, in part, because organisational changes within Network Rail had led to the loss of knowledge and ownership of some structures issues.
Although unrelated to the incident, the RAIB found that defects in the central river pier had not been fully addressed by planned maintenance work. There was also no datum level marked on the structure which meant that survey information from different sources could not easily be compared to identify change.
As a result of this investigation, RAIB has made three recommendations to Network Rail relating to:
- the management of scour risk
- the response to defect reports affecting structures over water
- the management of control centre procedures.
Five learning points are also noted relating to effective management of scour risk.
Simon French, Chief Inspector of Rail Accidents said:
It was 29 years ago that four people lost their lives when a train fell from a collapsed bridge at Glanrhyd in Carmarthenshire. The investigation that followed recommended improved procedures for checking the integrity of bridges over rivers, especially at times of flood, and more effective management of the risk of scour.
Our recent investigation into the partial failure of the viaduct at Lamington, in South Lanarkshire, serves as a reminder that, under certain circumstances, the scouring effect of a swollen river can undermine bridge piers to the point where the structure above starts to fail. The risk of scour is often higher for older bridges, particularly those with shallow foundations.
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.
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.
The railway has seen numerous organisational changes over recent decades. Although change is inevitable, and often for the better, it is vital that the railway industry finds ways to retain its corporate memory of its own assets and the 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.
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.
I hope, and believe, that Network Rail will think carefully about what it needs to do to assure itself that any emerging gaps in its asset management regime are detected, and then corrected, long before there is a risk to the travelling public.
Notes to editors
- The sole purpose of RAIB investigations is to prevent future accidents and incidents and improve railway safety. RAIB does not establish blame, liability or carry out prosecutions.
- RAIB operates, as far as possible, in an open and transparent manner. While our investigations are completely independent of the railway industry, we do maintain close liaison with railway companies and if we discover matters that may affect the safety of the railway, we make sure that information about them is circulated to the right people as soon as possible, and certainly long before publication of our final report.
- For media enquiries, please call 01932 440015.
Newsdate: 14 November 2016