Investigation Report No. R2010 – 004: Malahide Viaduct Collapse on the Dublin to Belfast Line, on the 21st August 2009

"On the 21st August 2009 as an Iarnród Éireann passenger service, travelling from Balbriggan to Pearse, passed over the Malahide Viaduct the driver witnessed a section of the viaduct beginning to collapse into Broadmeadow Estuary. The driver reported this to the controlling signalman who immediately set all relevant signals to danger ensuring no trains travelled over the viaduct. Within minutes of the report of the accident, by the driver, Pier 4 of the Malahide Viaduct had collapsed into the Broadmeadow Estuary. All post accident emergency procedures were properly employed by the operating staff resulting in no fatalities or injuries to any members of the public or staff.

At the time of the accident, the Malahide Viaduct piers were formed on a grouted rock armour weir, with stones intermittently discharged along this weir to maintain its profile. The immediate cause of the collapse of Pier 4 was as a result of the undermining of the weir that surrounds and supports Pier 4 through the action of scouring. This was as a result of a combination of factors:

- An inspection carried out on the Malahide Viaduct three days before the accident did not identify the scouring defects visible at the time;

- A scour inspection undertaken in 2006 did not identify the Malahide Viaduct as a high-risk structure to the effects of scouring;

- Iarnród Éireanns likely failure to take any action after an independent inspection carried out on the Malahide Viaduct in 1997 identified that scouring had started at the base of Pier 4 and that the rock armour weir was too light for the job”;

- The historic maintenance regime for the discharge of stones along the Malahide Viaduct appears to have ceased in 1996, resulting in the deterioration of the weir which was protecting the structure against scouring."

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