IARNRÓD Éireann staff maintaining a viaduct in north Dublin did not “appreciate” that the structure was sitting on a man-made causeway instead of being sunk into the bedrock, a report carried out by the rail company has found.
A major accident was narrowly avoided last August when a section of the Broadmeadow Viaduct which crosses the Malahide Estuary collapsed moments after a commuter train passed over it. The line, which links Dublin to Belfast, was closed for three months and cost €4 million to repair.
The report, which was independently chaired by John Buxton, a chartered civil engineer, also said an engineer sent to examine the viaduct a week before the collapse misunderstood the concerns raised by the Malahide Sea Scouts.
The report said the structure of the viaduct was unusual because the piers holding it up did not extend down into the bedrock of the sea. Instead, they sat into a manmade causeway made of large stone blocks which rested on the bed of the estuary. This made the piers vulnerable to erosion.
It said in 1967 grouting was carried out on the causeway and it was believed this would reduce the need for ongoing maintenance.
Since then, engineers had focused on the foundations of the piers, replacing stone blocks to protect the piers, but not the entire causeway.
“It was no longer appreciated that the structure as a whole comprised two separate components: a causeway/weir and a viaduct,” the report said.
The importance of maintaining the causeway “was no longer fully appreciated”. In the months prior to the collapse, the channel between pier 4 and pier 5 deepened and the flow became ever stronger with standing waves, the report found. Eventually, pier 4 became undermined and collapsed.
On August 17th, the week before the collapse, a group leader of Malahide Sea Scouts noticed a rock at the base of pier 4 had been washed away and contacted Iarnród Éireann.
But “a misunderstanding appears to have developed” so that the engineer looked primarily for cracks or missing stones in the pier structure rather than in its foundations, the report said. He found some faults in stonework, but none were of a serious structural nature.
The report also found climatic, oceanographic and hydrological changes over recent decades contributed to the erosion. It commended the actions of the train driver, Keith Farrelly, for his quick thinking in placing his power controller into the “coast” setting, which reduced the force acting on the collapsing viaduct as the train passed over it. The signalman was also commended.
The report made a number of recommendations, including that a handover process be put in place to ensure knowledge is not lost when staff move or retire. Yesterday, Iarnród Éireann denied suggestions it had been warned in a report in 2006 that the estuary was prone to serious erosion.
The report, carried out by independent specialist divers, did not state that there was any reason for concern about scour at that time, but did recommend underwater examinations be carried out every six years, a spokesman said. He added the divers could not have known the piers were not sunk into the bedrock because Iarnród Éireann had not told them.
The organisation has said it has carried out a number of improvements recommended in the report including replacing pier 4 and retro-fitting other piers with piled foundations; installing a bridge monitoring system on the viaduct and reviewing other bridges susceptible to scour, including the Rogerstown Viaduct, on the same line.
Opposition spokesmen on transport, Fine Gael TD Fergus O’Dowd and Labour Party TD Tommy Broughan, called on Iarnród Éireann and the Minister for Transport to come before the Oireachtas transport committee.
“A culture of secrecy and complacency has flourished in Iarnród Éireann for far too long,” Mr O’Dowd said.
