ANALYSIS:The collapse of a troublesome viaduct has created a logistical nightmare for Iarnród Éireann, writes FRANK McDONALD,Environment Editor.
THE VIADUCT over Broadmeadow Estuary has given trouble since it was first built by the Dublin and Drogheda Railway in 1844, mainly due to tidal scouring of its support piers. Indeed, the first structure – made entirely of timber – had to be replaced by wrought iron superstructure on stone piers as early as 1860.
As engineer Niall Torpey recounted in the Irish Railway Record Society’s journal, the superstructure had to be strengthened to carry heavier locomotives on the Dublin-Belfast line in 1932. The stone piers also needed regular attention because of Broadmeadow’s tidal scouring and were repointed in the 1960s.
“Finally, following the observed deterioration in the wrought iron in this marine environment, it was further replaced in the period 1966-1968 with the current prestressed concrete structure”, Mr Torpey wrote. Since then, no further major works were carried out on the viaduct, which is 180m (594ft) long.
In 1998, as Fine Gael transport spokesman Fergus O’Dowd recalled yesterday, International Risk Management Services (IRMS) identified sections of the viaduct as being among the most unsafe stretches of rail track in the country, assigning it a 60 per cent security risk on a scale where 5 per cent is “best practice”.
The IRMS report led to a major improvement in railway standards, including relaying track on precast concrete rather than wooden sleepers. Two follow-up reports, also by IRMS, in 2001 and 2003 monitored the progress on what Barry Kenny, spokesman for Iarnród Éireann, called “this massive investment programme”.
In 2003, the derailment of a freight train hauling cement wagons from Limerick Junction to Rosslare caused a section of the Cahir viaduct in Co Tipperary to collapse. But there was a major difference between that accident and the one that took place near Malahide on Friday, in that none of the Cahir bridge piers crumbled.
An investigation by the Railway Safety Commission of the Cahir derailment found “serious deficiencies” in Iarnród Éireann’s management of its infrastructure, and concluded that these critical shortcomings in the company’s inspection and maintenance regime “were principally responsible for the accident”.
According to Mr Kenny, every bridge on the rail network is thoroughly inspected at two-yearly intervals. The inspection of the Broadmeadow viaduct that was carried out last Tuesday – just three days before the collapse – was clearly not in this category; it was a purely visual inspection of the bridge deck and its support piers.
The Broadmeadow viaduct has 11 piers, one of which collapsed, bringing two of the deck spans with it.
The last full inspection of the structure was carried out in 2006, Mr Kenny said, and it paid particular attention to the effects of tidal scouring.
“No scouring issues were found at that time,” he told The Irish Times.
Local sources, say tides in the estuary were up to 4.5m (15ft high, which is stronger than usual. High tide was at about 1pm and low tide was shortly after the collapse at about 6pm.
A team of railway engineers, supported by divers, is now examining the viaduct’s stability to determine what needs to be done.
“We have to assess whether there is damage to the remaining sections of the viaduct,” Mr Kenny said. “The view at the moment would be to replace the damaged section with a single span, strengthening the adjacent piers to carry it.” However, he conceded that complete replacement cannot be ruled out.
It took 11 months to repair the damage to the Cahir viaduct, even though none of its piers needed to be replaced. The line it serves is one of the most underused in the rail network, with just two passenger trains a day, whereas the line severed by the latest viaduct collapse carried 10,000 passengers a day in each direction.
“If the whole viaduct is going to have to be rebuilt, it could be massive undertaking,” one railway engineering source said. “If one of the piers collapsed, there is a danger of this happening with others, because of the difficult conditions you encounter in a tidal environment with a lot of scouring of these structures over the years.”
Iarnród Éireann is fortunate that the collapse happened during the evening peak period, with no loss of life. Had it occurred at night, the company would now be faced with a severe logistical problem as nearly all of the suburban commuter trains are housed in the new maintenance depot at Drogheda station.
“We have 44 carriages there that can’t now be used on the rest of the network,” Mr Kenny said. “That’s 44 out of a total of 180, so it means that other services can be met” – on the Maynooth, Kildare and Gorey lines. Two of the four Belfast Enterprise trains were north of Malahide, which means they can be run to and from Drogheda.
As for the cost, Iarnród Éireann is certain to lose revenue from passenger fares as well as having to pay for replacement bus services. The physical work of repairing the damage will be considerable – a lot more than the €3 million bill that had to be met from reinstating the viaduct over the river Suir at Cahir.