[Colm Moore]

.

Continued


Iarnród Éireann investigation into the Malahide Viaduct collapse

Iarnród Éireann’s investigation was independently chaired by John Buxton, Chartered Civil Engineer, and was also advised by a panel of experts led by Dr Eamon McKeogh of University College Cork in relation to the complex hydraulic and environmental issues involves. The Iarnród Éireann report will also be considered by the Rail Accident Investigation Unit in the preparation of their independent investigation into the accident.

The report found:

- Works undertaken in 1967 on the superstructure of the viaduct also included significant grouting work, to a depth of 2 metres, to the causeway/weir. These works, it was believed, would generally reduce the need for ongoing maintenance, particularly the unloading of “rip-rap” stone (large stone blocks) which had been regularly carried out to maintain the causeway/weir profile by replacing stones washed away by the tides. Since this time, the placing of rip-rap was more limited and appeared to be carried out only to protect the piers.

- Over time, erosion of a section of the causeway/weir between Piers 4 and 5 caused changes to the water flow under the structure, resulting in the majority of the water flowing in a deepened channel between these two piers, further increasing erosion. In a relatively short period of time, the weir “crest” receded from the seaward side of these piers to beneath the span between them and, subsequently, onto the other (estuary) side of the viaduct. In the months prior to the collapse, the channel deepened further and the flow became ever stronger with standing waves and, latterly, a “piping” mechanism causing further “scour” action. Eventually Pier 4 became undermined and collapsed.

- A key finding of the investigation is that since grouting works were undertaken on the causeway/weir in 1967, the engineering emphasis has been focused on the maintenance of the viaduct structure itself. However, the condition of the grouting in the causeway/weir required maintenance. By this time, although protection of the pier foundations was still being undertaken, the importance of maintaining the weir profile was no longer fully appreciated. Prior to the collapse, therefore, it was no longer appreciated that the structure as a whole comprised two separate components: a causeway/weir and a viaduct. The structure is unusual in that the piers did not extend down to the “bedrock”, but are instead founded within the manmade causeway/weir formed of large rip-rap resting on the bed of the estuary, making the piers prone to erosion or “scour” damage.

- Climatic, oceanographic and hydrological changes over recent decades have increased the hydraulic “head” and hence the erosive effect of the water flowing into and, more especially, out of the Broadmeadow Estuary over the causeway/weir.

- During the week before the collapse, a group leader of Malahide Sea Scouts observed that a rock at the base of pier 4 had been washed away and contacted Iarnród Éireann on 17th August to report this. The information reported by this member of the public was dealt with in a professional manner by Iarnród Éireann staff. However a misunderstanding appears to have developed so that the engineer delegated to inspect the viaduct on 18th August was looking primarily for cracks or missing stones in the pier structure rather than in its foundations. He found the “dressed” stonework of the viaduct to be in need of pointing and there were some cracked stones on a number of piers. Whilst none of these faults were of a serious structural nature, their presence appeared to him to explain the reason for the report from the canoeist. Therefore this visual inspection did not lead engineers to question the stability or the structural integrity of the viaduct.



A series of actions have already taken place or are underway arising from the accident.

- The replacement Pier 4 is founded on piles and all the remaining existing piers have been retro-fitted with piled foundations. A bridge monitoring system has been installed on the Malahide Viaduct

- The list of structures susceptible to scour has been reviewed and is now more comprehensive. Pier and abutment depths are being established for all bridges on the scour list wherever practicable. Where this is not possible, other mitigating measures will be implemented.

- There is one other structure on the IÉ network that has similar foundations to Malahide, Rogerstown Viaduct. This is on the same route as the Malahide Viaduct. Pier and abutment depths have been established for this structure and found to be deeper than for Malahide and are secure.

- The Acting Chief Civil Engineer has initiated a full review of the systems in place for monitoring structures subject to scour and has commissioned consultants to look at international best practice for this with a view to implementing system improvements.

- The driver of the 18.07hrs Balbriggan to Pearse train has been commended for his quick thinking in placing his power controller into the ‘coast’ setting which reduced the forces acting on the collapsing viaduct as the train passed over it. His actions to protect the line after the incident were also exemplary as were those of the CTC Signalman who has also been commended.

- The need to maintain the causeway/weir of the Malahide Viaduct to an acceptable profile is now clearly understood. The weir has been reconstructed to its original profile. Furthermore an improved weir profile is being developed, in line with the outcome of the studies undertaken by UCC.

- Information on the viaduct that is currently known, or can reasonably be collected including archived materials, is being assembled and will be made available through IAMS (Infrastructure Asset Management System). Thus in future, IAMS will form the basis of the required inspection and maintenance process and staff will be better equipped to undertake these duties. Similar information will also be added, on a risk prioritised basis, for all other structures on Iarnród Éireann.

- Most of the bridges on the “scour inspection list” have been inspected (by engineer divers) and this work will be completed by April 2010. Following on from these inspections each structure will be given a risk rating and the inspection frequency will be based on this rating. Trigger levels will be defined for special additional inspections of the structure as required (e.g. exceptional tides) and/or its closure when conditions deteriorate. A re-opening process for each structure is also to be documented.



The investigation also makes a series of recommendations.

- Recommendation 1: Complete all of the above actions.

- Recommendation 2: The structures standard should be revised to include more information on ‘scour’, the erosive effects of different water conditions (e.g. standing waves), particularly in the context of the design of remedial measures.

- Recommendation 3: The introduction of the revised structures standard should be supported by the running of a series of Structures Inspection Training Courses. The training should incorporate ‘follow up’ mentoring in the field by experienced, competent staff.

- Recommendation 4: Roles and reporting lines for structures and track patrolling inspections should be reviewed and a ‘handover’ process should be put in place to ensure knowledge is not lost on staff movements within the organisation or when staff leave the service.

- Recommendation 5: Flood and tidal warning arrangements, using information from Met Éireann and the Coast Guard, should be formalised throughout Iarnród Éireann.

- Recommendation 6: Consideration should be given to extending the installation of monitoring/warning equipment to structures susceptible to scour so that changing conditions at sites during adverse conditions can be monitored.

- Recommendation 7: The bridge card system of monitoring the condition of structures should be expanded to incorporate all relevant information that needs to be recorded during an inspection. The records should cover each span or relevant element of the structure and these should be incorporated into an enhanced IAMS based system supported by photographs.

- Recommendation 8: The process for dealing with reports from the public should be documented and unified across the organisation.

- Recommendation 9: The effects of climate change, land and leisure developments in the Broadmeadow catchment area should be kept under review by IÉ so that the organisation is well placed to take informed action to mitigate any potential future adverse effects on the railway. In particular, it is recommended that dialogue is initiated with the relevant state agencies accordingly.

Iarnród Éireann assures customers that these recommendations will be fully implemented, as will any and all recommendations arising from the investigation of the Rail Accident Investigation Unit.

The investigation also states that the public spiritedness of third parties who contacted Iarnród Éireann prior to and subsequent to the incident should be commended.


Malahide Viaduct Summary and Conclusions http://www.irishrail.ie/upload/malahideviaduct.pdf