Construction firm Carillion’s failure to construct a drainage system correctly in accordance with the designer’s requirements has been identified as the main cause of a passenger train derailment at Carmont, Aberdeenshire in 2020, the Rail Accident Investigation Board (RAIB) has found.
The Aberdeen-bound train derailed on 12 August 2020 after it had collided with debris washed out of a drainage trench onto the railway track. The train deviated to the left before striking a bridge parapet causing the vehicles to scatter.
Three people died in the rail crash – the train’s driver Brett McCullough, the conductor Donald Dinnie and passenger Christopher Stuchbury – while the remaining six people onboard were injured.
The RAIB’s report into the accident, published last week (10 March), has also been critical of Network Rail’s processes and its failure to recognise the risk presented by Carillion’s construction work, which if identified could have led to remedial actions.
According to the RAIB investigation, the 06.38am service from Aberdeen to Glasgow was returning to Aberdeen after a blockage had been reported on the line ahead when the train derailed at around 09.37am. The train had been travelling at 73 mph (117 km/h), which was just under the normal speed for the line.
There had been near-continuous heavy rain that morning but the 51.5 mm of rain that fell at the accident site, the RAIB reported.
The main cause of the derailment was debris that had been washed out of a drainage trench, which had been constructed by Carillion between 2011 and 2012. The ‘french drain’ contained a 450 mm diameter perforated pipe that had been installed as part of a wider project to resolve a known problem with the stability of the earthworks in this area, the RAIB noted.
The pipe had been buried in a gravel-filled trench that ran for 306m along the edge of a field at the top of a slope that ran down to the railway. The report notes that the drain then sloped down relatively steeply (at an inclination of 1 in 3) for 53m to track level.
The RAIB investigation found, however, that Carillion’s drainage system and associated earthworks had not been installed in accordance with the original design.
Carillion, which ceased operations on 15 January 2018 after going into compulsory liquidation, had constructed a low earth bund (artificial ridge), which was not part of the design, outside Network Rail’s land.
RAIB noted in its report that there was no evidence to suggest that Carillion had notified either Network Rail or Arup, the designer, about the bund’s construction.
Its investigators concluded that the use of gravel in such a steeply sloping trench increased the likelihood of the stony material being washed away should the water reach the drain as a concentrated flow. They added that the bund had the effect of diverting a large amount of water into a gully so that it all reached the drain at the same location, which increased the propensity for washout of the gravel infill.
‘This report makes clear that there are fundamental lessons to be learned by Network Rail and the wider industry'
The report said that Network Rail and Carillion’s contractual arrangements stipulated that Carillion was responsible for the works’ delivery in accordance with the designs approved by Network Rail. Any amendments to the design should have been dealt with as part of the formal processes in place during the scheme’s construction phase. However, the RAIB found no evidence that changes were dealt with as part of this process nor that any reference was made to Arup.
In addition, Network Rail’s audit regime at the time of the drain’s construction did not include audits likely to detect design modifications implemented onsite without proper change control, the investigation found.
The report noted that, ‘although Network Rail had a project team, they were not required by Network Rail business processes to check that the drain was being installed in accordance with the design. They therefore relied on a contractual assurance process that required Carillion to refer proposed changes to the designer, Arup, for approval.’
RAIB also found no evidence of any ‘as-built’ drawings being submitted to Arup or Network Rail. These drawings are required to assist future asset maintenance and, according to the investigation, they can provide an opportunity for the designer to recognise inappropriate design modifications.
The RAIB’s report makes 20 recommendations to improve safety, which cover how the railway manages extreme events; the management of civil engineering construction activities; management assurance of railway control functions; train design; and applying learning from previous events.
Significantly, it calls on Network Rail and its contractors to improve their management of civil engineering construction activities to prevent an incident like this happening again. In relation to this, Network Rail needs to ensure that all new works are incorporated into inspection and maintenance regimes.
The RAIB also recommends that Network Rail extends its assurance regime so that it covers route control offices as well as enhance the capability of route control offices to effectively manage complex events.
One of its findings was that the ‘route controllers’ responsible for the operational management of Scotland’s railway network ‘had not been given the information, procedures or training that they needed to effectively manage complex situations of the type encountered’ that morning.
As there had been no written processes in place that required route control or the signaler to instruct the train driver to run at a lower speed on its journey between Carmont and Stonehaven, the RAIB noted that the train was able to travel at just under the normal speed for the line despite the poor weather conditions.
In line with this, the RAIB recommends improving the operational response to extreme rainfall events, using modern technology and making sure there is a detailed understanding of the risk associated with extreme rainfall.
The report also calls for additional standards and guidance on the safe design of drainage systems.
Commenting on the report’s findings, Andrew Haines, Network Rail’s chief executive, said: ‘This report makes clear that there are fundamental lessons to be learned by Network Rail and the wider industry. As well as expressing our deep sorrow and regret at the loss of the lives of Christopher Stuchbury, Donald Dinnie and Brett McCullough, it’s important that we acknowledge it should not have taken this tragic accident to highlight those lessons. We must do better and we are utterly committed to that.’
