Shallow foundations and high velocity flows led to structural failure caused by scour at Lamington viaduct, South Lanarkshire 31 December 2015.
Earlier this week the RAIB released its report looking into the factors which gave rise to this incident which fortunately led only to the closure of the line for some weeks rather than any loss of life.
It is noted in the report that the incident followed a period of heavy rainfall and that the River Clyde was flowing into the sea at a rate that was 249% of the December average measured between 1971 and 2000. Furthermore for many Scottish regions, this was the wettest calendar month since records began in 1910. However the flows were not considered unprecedented.
The viaduct was considered vulnerable to scour due to a number of factors including its location on a bend in the river and was due in 2015 to benefit from the construction of scour protection but these works were deferred as the 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. However, due in part, to changes within Network Rail and loss of knowledge these mitigations processes were no longer in use.
It was also concerning that those sent out to inspect the track, when a train driver reported a dip defect in the track, did not consider that the defect might be related to failure of the underlying structure rather than simply a track defect; particularly, as a previous RAIB report ‘Failure of the River Crane railway bridge near Feltham, West London, 14 November 2009,’had already recommended that:
“Network Rail should review the guidance provided for non-specialist staff who may be required to assess the failure of track support in the vicinity of a structure, and determine whether it is safe for trains to run over that structure.”
In this report the RAIB has made three recommendations to Network Rail covering the management of scour risk, the response to defect reports affecting structures over water, and the management of control centre procedures. The report also contains five learning points related to effective management of scour risk. If you are responsible for inspecting or maintaining bridge foundations crossing main river channels then reading this report is a must.
Whilst this report concentrates on defects caused by scour there may be other hidden defects in infrastructure assets and CIRIA have a project underway to produce good practice guidance by collating current research, experience, innovation and future proposed innovations to help manage risk where bridges structures are concerned. If you want to know more about this project please click
here or contact Lee Kelly, CIRIA’s Project Manager (firstname.lastname@example.org)