Seabed erosion is suspected of being behind the collapse of a railway viaduct on one of State’s busiest lines, it was revealed today.
Initial tests on the Malahide estuary crossing on the main Dublin to Belfast track suggest recent low tides and heavy rains also combined to play a part in the collapse.
The bridge, which carries more than 90 trains a day, fell into the sea on Friday moments after rush hour commuter services carrying hundreds of passengers passed over it.
Iarnród Éireann said a preliminary examination showed a small breach occurred in the seabed, possibly in recent weeks, which changed the flow and pressure of the water around the viaduct piers.
“Recent low tides, coupled with major rainfall on Wednesday, would have seen the volume and speed of water flowing out of the estuary increasing, causing water pressures to increase, with ultimately the forces of water pressure widening the breach quickly,” said Barry Kenny, Iarnród Éireann spokesman.
“The effect on the causeway plateau and sea-bed would ultimately result in the sudden and catastrophic undermining of the pier supports from below water level, resulting in the collapse of the pier on Friday evening.”
The company said this was the primary line of inquiry while its investigation was ongoing, but stressed other factors or possibilities have not been ruled out.
Other issues being examined include tides, rainfall and climatic issues, inspection and maintenance reports and procedures as well as the role of Iarnród Éireann staff.
The collapse of the railway bridge has caused travel chaos and uncertainty for thousands of commuters.
The affected section of track is expected to be closed for at least three months.
Passenger organisation Rail Users Ireland (RUI), which said it was a miracle people weren’t killed, has demanded urgent tests on all railway bridges around the country.
Iarnród Éireann said an inspection team is being set up to carry out detailed inspections of bridges and viaducts over water across its network.
The company also vowed to establish a committee, including independent advisors, to oversee the investigation.
An engineer who carried out an inspection of the viaduct only last Tuesday was charged with examining the condition of the piers as visible above water.
Iarnród Éireann said they were satisfied the tests, which found any markings on the bridge were cosmetic and not structural, was “thorough, professional and accurate.” The last full inspection of the viaduct was carried out in October 2007, with the next inspection due in October.
The crossing collapsed into the estuary just after the 6.07pm service from Balbriggan, in north county Dublin, to Pearse station, in the centre of the capital, passed over it.
The southbound train was carrying around 60 passengers at the time while a packed northbound train carrying several hundred commuters had also passed over the bridge minutes beforehand.
A number of bus transfers and alternative arrangements have been put in place to cope with the passenger disruption.
Speaking this morning, Myles McHugh, service manager with Iarnród Éireann, said an extra 15 to 16 buses were being placed on the Dublin Bus 33 route to service commuters in the Balbriggan, Skerries, Rush, and Donabate areas.
Mr McHugh said on Morning Irelandthat consultations with local schools would be taking place today and tomorrow to discuss travel arrangements for children from next week when schools return.
Those travelling should check www.irishrail.ie for further details on alternative services.
Repairs to the collapsed viaduct are likely to be disrupted for much longer than the three months estimated by the company, following the viaduct incident.
Up to 20,000 rail journeys a day, split evenly in and out of the city centre, are to be replaced by road transport over the next three months, the shortest period within which Iarnród Éireann says it envisages the viaduct can be repaired.
Over the weekend, engineers and railway safety inspectors, supported by divers, examined the collapsed section of the viaduct and the remaining 10 piers.