A damning investigation on a partial collapse at Balcombe Tunnel has revealed a catalogue of errors that could have resulted in “severe consequences” for rail passengers.
A recently published report by the Rail Accident Investigation Branch (RAIB) into a potentially life-threatening incident on Friday, September 23, 2011, has revealed 18 missing bolts or studs and three sagging steel beams, and highlighted the absence of regular, detailed examination work in the tunnel due to “insufficient access” on a busy line with “no alternative, diversionary route”.
The investigation concluded that if a large beam suspended over the rails had struck a train travelling at a typical speed of 90mph, a bolt hitting the windscreen would have risked “severe consequences for the driver”. Network Rail has apologised for the problems and reviewed the way incidents are communicated and reported. Steel beams inside the tunnel have been provided with extra support and other tunnels have been examined to make sure similar problems do not exist.
The Balcombe Tunnel incident closed part of the Brighton line for 24 hours, effectively severing the main rail route to London from the Sussex coast.
The crew of an engineering train passing through the tunnel at about 5.24am noticed that part of a large steel tray for catching water that was mounted into the underside of the roof, was “sagging”.
Network Rail carried out an emergency inspection which revealed that three steel beams had become detached from the tunnel lining on one side, leaving 12 metres of tray “partially supported”.
The tray is one of six in the tunnel supported by transverse beams and fixed by large bolts that are referred to as “studs” in the RAIB report. Each bolt, measuring up to about 15 inches long, is glued into holes in the tunnel’s lining.
Eighteen bolts were found to be missing, a further five were loose and 28 had loose or missing nuts.
The investigation identified that the polyester glue or resin used to fix the bolts was incompatible with the type of brickwork in the tunnel lining and could have been softened by the damp conditions.
Witness statements indicate there was “no on-site testing” during the design stage to assess compatibility.
According to the RAIB report, “some railway staff were aware” that bolts “had fallen on more than one occasion since 2008” but appropriate action was not taken to mitigate the risk.
Information about the missing bolts was “not passed on” to new contractors employed by Network Rail from April 2009 onwards.
A new member of staff responsible for managing some of the tunnel maintenance had limited experience, “did not recognise” the significance of the missing bolts and needed mentoring.
For eight years between April 2003 and the date of the incident in September 2011, a detailed examination of the tunnel was recorded on only four occasions “as against the eight required by Network Rail standards”.
Access to the tunnel for inspections was limited due to “an intensive daily train service” and the work of track and signalling maintenance teams. Engineers had also expressed concerns about going onto the trays to inspect them, fearing they might collapse.
The RAIB has made nine recommendations that focus on: confirming the compatibility of materials, effective responses to defects and abnormal events, and the “competency of staff monitoring and inspection records”.
Network Rail has apologised for the inconvenience to passengers and has undertaken extensive remedial work inside the tunnel as well as improving the way problems are communicated and logged.
The company has also ensured - in response to and Enforcement Notice issued by the Office of Rail Regulation in May 2011 - that engineers are given enough time to carry out detailed maintenence examinations.
For the full response from Network Rail and more on this story, see page three of the Middy, published on Thursday, September 19.