Hi and welcome to Failurology; a podcast about engineering failures. I’m your host, Nicole, and I’m from Calgary, Alberta.
This week’s failure is the Malahide Viaduct, north of Dublin, Ireland. The failure blocked the only train route between Dublin and Belfast for 3 months. Water is a beauty and it can be a real pain. I’ve seen water destroy buildings, degrade pipes and in episode two I talked about the impact of water on the City of New Orleans during Hurricane Katrina. And similar to that episode, I came into researching the Malahide viaduct thinking I knew what I was going to find. But what I uncovered was so much more interesting.
But before I get into that, the news.
This week in engineering news; the UKs first electric only charging station opened for business in early December.
The charging station, located in Braintree, Essex, has 36 electric vehicle chargers delivering up to 350 kw of power. The chargers can provide over 300 kilometers of range in 20 minutes for a cost of roughly 10 euro (or $15 CAD).
The chargers are powered by solar panels on that station's roof and a network of hybrid solar and wind farms. There is also a 6 megawatt-hour battery at the station to balance power supply.
Several countries, cities and territories have implemented or proposed bans on the sale or registration of new gas or diesel vehicles. The UK joined this list in 2030 with a proposal to ban the sale of new combustion engine vehicles by 2030. Canada’s goal is to ban the sale of combustion engine vehicles by 2040; with British Columbia banning by 2025, Vancouver by 2030 and Quebec by 2035. Alberta is a bit behind the 8 ball on renewable energy as of late. We have plenty of solar and wind farms, but we also have a government and several citizens obsessed with reinvigorating the oil and gas industry in Alberta. I personally think that it’s a dying industry and we should re-diversify into other industries before we get left behind. But that’s just me.
If you want to read more on the charging station, check out the website page, link in shown notes, for this episode. I will also include a link to a Wikipedia page with lists of the phase out of fossil fuel vehicles.
Now on to this week’s engineering failure; the Malahide Viaduct Collapse in Ireland. On Friday August 21, 2009 at around 630pm – pier 4 and 20 meters of post tension concrete beams between piers 4 and 5 of the Malahide viaduct collapsed into the water.
Irish Rail is a network of over 1900km of railway with seven routes radiating from two main terminals in Dublin; Connolly and Heuston station.
I visited Ireland in 2019 and Irish Rail was a great way to travel around the country. We took the train from Dublin to Galaway and then down to Cork and Cohn and back up to Dublin. It was a really easy and rather cost effective way to travel. The Canadian equivalent, Via Rail, is not as accessible. It doesn’t even come to Calgary. And there is no train between Calgary and Edmonton or Calgary and Vancouver. We either have car, bus or air travel for options. I would much rather travel by train, and would probably travel to these cities more if a train was available.
The Irish Rail network contains 780 viaducts.
Viaduct, is derived from the latin word via meaning road and ducere(do-chair-eh) meaning to lead. A viaduct is a type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. They are usually used to connect two areas of similar elevation across a river valley or other low lying feature.
The Malahide viaduct, also referred to as the Broadmeadow viaduct, is located about 15 kilometers north of downtown Dublin, north of a small settlement called Malahide.
If you’ve ever ridden Irish Rail between Dublin and Belfast, you have crossed this viaduct as it’s the sole train route between the two.
82 passenger trains and 6 freight trains pass over the Malahide Viaduct every weekday.
The track of the Viaduct is a double track, continuous weld rail on concrete sleepers. The maximum speed over the viaduct is 145 kilometers per hour. And due to tight clearances there are permanent speed restrictions between Malahide station and the viaduct.
The viaduct is 180 meters long, but forms part of a longer causeway across the Broadmeadow Estuary. As we know from the levee failures in episode two, an estuary is where a stream or river meets the sea. The water is brackish, meaning a mix of fresh and salt water. The total crossing is about 1200 metres in length.
The first structure to cross the Estuary was built in 1844 by the Dublin and Drogheda (dro-ee-da) Railway. It was a 175m timber structure with 10 timber piles spaced 15.85m apart.
The original structure was replaced in 1860 with wrought iron lattice girder beams and masonry piers.
Due to sea air, frequency of use, and weight of locomotives, a more robust structure was required. The current structure has been in place since 1968 and is made up of prestressed concrete spans and 11 stone piers with gravel ballasts.
As the tide rose and fell, water traveled through the viaduct, resulting in scouring. Scour erosion is the removal of sediment such as sand or gravel from around bridge piers. It’s caused by fast moving water that travels around the pier and scours or scoops out sediment on the opposite side of the pier.
To overcome this problem, a stone weir was constructed from 90,000 tonnes of stone along the length of the viaduct in 1846 to protect the piers from scour and maintain a constant level of water in the estuary (reducing the volume of tidal flow). This meant that the piers were not founded on bedrock; they sat on top of the weir. The integrity of the piers relies on the integrity of the weir.
Stones had to be replaced regularly to maintain the weirs' integrity. The bridge design has easily removable handrails to allow stone discharge along the weir. Between 2000 and 6000 tons of stone were regularly discharged from 1922, with the last documented time before the 2009 collapse being in 1996.
There is evidence of complaints from locals in 1957, 72, 92, 95, 96, & 97 that discharging stones impacted the water level in the estuary and impacted their livelihood or recreation. This may have contributed to a stop in stone discharge after 1996; although this is speculation on my part.
The construction of the viaduct allowed for even flow through all twelve spans of the viaduct. This is important so that one area does not wear or erode faster than other areas. In addition, the stone weir impacted velocity through the viaduct.
During ebb tide, which occurs between high and low tide, where water flows back to the sea, the step up to the weir from the bottom of the estuary, reduces flow through the viaduct, causing a drop in pressure and an increase in velocity and scour potential.
During flood tide, which occurs between low and high tide, where the water flows into the estuary, the weir acts as a step down, increasing flow through the viaduct, increasing pressure and decreasing water flow.
To recap, we have ebb tide, water flowing out to sea, which has an increase in velocity, and flood tide, water flowing into the estuary which has a decrease in velocity.
When the tide switches from ebb tide to flood tide, it does so smoothly. But the change from flood tide to ebb tide, when flow changes from into the estuary to out to sea, causes a vigorous turbulent mixing action which creates scour erosion.
As the erosion occurred over several years, the width of the weir expanded as stone was pushed outwards with each tidal change. This also removed stone from around the piers, exposing them to erosion and risking their structural integrity.
In 1967 and 1968, in an attempt to stabilize and minimize erosion of the weir, the weir crest was grouted to form a grout rock armour. It proved successful after storms in 1969. However, over time, it too started to erode.
On Friday August 21, 2009 at around 630pm – pier 4 and 20 metres of post tension concrete beams between piers 4 and 5 collapsed into the water. Pier 4 was the fourth pier from the north end of the viaduct.
At 6:20, the eight car 5:50 train from Pearse to Dundalk passed over the Viaduct in the down direction, north towards Belfast.
At 6:22 the four car 6:07 train from Balbriggan to Pearse approached the viaduct in the up direction, towards Dublin, and observed water splashing up over the viaduct as the eight car Pearse to Dundalk train had passed over it. As the four car 6:07 train from Balbriggan to Pearse train passed over the viaduct, the driver witnessed a section beginning to collapse. The four car train made it safely across and the driver raised the alarm when he arrived in Malahide. The signalman set all signals to danger, ensuring no trains crossed the viaduct. The driver of the four car train made an unscheduled stop at Malahide Station and de-trained all passengers. He walked back along the track to the viaduct and observed that pier 4 had collapsed and the post-tensioned concrete beams of span 4 and 5 had collapsed into the estuary.
The weather conditions at the time of the accident were dry with good visibility. The accident occurred close to the time of the second low tide of the day. The morning low tide that day was the lowest tide for that month and the tidal range was also one of the largest for the month of august.
A canoeist on the estuary noted that some stones at the base of Pier 4 had washed away. This was four days before the collapse.
An assistant engineer investigated the next day, three days before the collapse, and noted missing or cracked stones, but no structural defects. From what I’ve read, the assistant engineer was not familiar with the structural or tidal conditions of the estuary; the area in question was not within their division. They also incorrectly assumed that the piers were on bedrock, rather than sitting on the weir. This was a missed opportunity to correct the bridge before failure and indicates poor training and record keeping within the Irish Rail maintenance system.
A passenger travelling over the viaduct at 9:35am and again at 5:55pm on the day of the collapse, noticed a 3m diameter whirlpool on the west side of the viaduct.
Over time, due to lack of maintenance to mitigate erosion, a channel formed between piers 4 and 5. The water was no longer evenly distributed through all twelve spans. For days, months, maybe even years, leading up to the collapse, during the end of the ebb tide cycle, with water flowing out to sea, the majority of water flowed between piers 4 and 5 and increased erosion through this section. The erosion around pier 4 ultimately led to a phenomenon called piping, which is a subsurface formation of a continuous pipe-like tunnel. Meaning that the water eroded the material underneath pier 4 until it eventually gave way.
Railway Accident Investigation Unit (RAIU) – But how could this have happened? Well, following the collapse, the Railway Accident Investigation unit investigated the failure, and shed light on several issues.
The scope of their investigation is as follows.
Establish the sequence of events that led to the collapse
Establish the immediate cause, contributing factors and underlying causes that led to the failure
Review the management of inspections and maintenance of the viaduct
Review historical documents related to the viaduct
And review the role of the Railway Safety Commission in relation to enforcing safety recommendations.
3D and 2D models of the viaduct were created, as well as mathematical and hybrid models to simulate hydraulic mechanisms involved in the collapse
A post accident survey found an asymmetrical scour hole under pier 4 that was roughly 4m deeper than the base of piers 3 and 5.
The live load, or dynamic load of train cars passing over the viaduct, is believed to be a contributing factor in the undermined pier 4 collapse.
The concrete beams were removed from the viaduct and tested at an offsite facility. The beams passed the required loading for the structure and did not contribute to the failure.
The tracks are regularly inspected by patrol gangers. The viaduct section was from the 7-1/4 milepost to the 9-1/2 milepost in division 1 and the 9-1/2 milepost to the 13-3/4 milepost in division 5. This meant the patrol ganger reported to two separate divisions and two separate permanent way inspectors, requiring two separate log books. The last patrol of the Malahide Viaduct was carried out on August 10th, which noted no faults in relation to the structure. There should have been a more recent patrol, but the patrol ganger was on vacation and no one was assigned to relieve his duties. Likely because each division thought the other was looking after it.
Patrolling standards stated that the underneath of bridges be checked at least once a year for scour. But there is no record of any scour check of the viaduct by a patrol ganger. Identification of scour would have required access under the bridge as well as specialized training; which the patrol gangers do not receive. In other words, while the standards stated that scour inspections were required, Irish Rail did not provide the patrol gangers with the tools or skill set to do so. This type of thing is actually pretty common. And there could be a variety of reasons this was not corrected. It’s possible the patrol gangers weren’t aware this requirement was in the standard since it appears it was not closely monitored. It’s possible the patrol gangers knew about the requirement and that they couldn’t complete the task, they raised the concern to their superiors but nothing was done. Or it’s possible that no one understood the risk of scouring and didn’t think the inspection was required. I don’t really know what happened here. But I do know that it takes participation from all levels to adequately implement a standard or policy.
A track recording vehicle travelled over the viaduct on August 20th, the day before the collapse, and noted no defects in vertical or horizontal alignment, cross level or twisting which would have indicated the crossing was close to failure.
Ground level inspections were recommended every two years and thorough inspections every six years
There were some conflicting requirements on when inspections were needed; Irish Rail was in the process of switching their inspection system over to a new protocol. The last Bridge Inspection card retrieved for the Viaduct, prior to the 2009 collapse was dated January 30th 1998; thorough bridge inspections were recommended to be completed every 6 years, but it appears that recommendation was not fully implemented. It’s also possible that some engineers were not even familiar with the inspection requirements. The next bridge inspection was scheduled for 2011.
All engineers complete a Civil Engineering and Earthworks Structures: Guidance Notes on Inspections course. The course is intended to
Give further knowledge of inspection procedures
Describe the types of structures to be inspected
Describe typical defects
Guidance on how to assign condition ratings.
The course was stand-alone with no follow up training and the course didn’t include any field instruction. It was also likely given to engineers at the start of their employment. I personally do training at the start of employment, and then follow up a few weeks later once they have settled in and have a better understanding of procedures and systems. There is so much going on at the beginning of employment, it’s impossible to retain everything. Also, they likely wouldn’t have understood the importance of everything they were taught until they got out into the field. As a manager, its your job to make sure your staff are successful; not only does it make your job easier, but it also makes you successful.
There was a Bridge Scour inspection carried out in 2006 by a third party; Collins engineers.
Overall, they found the viaduct in fair condition
But the inspection scope did not include a report on foundations. If it had, it may have noted that the foundations were not on bedrock, but on the weir. This would have highlighted that the integrity of the weir was integral to the viaduct and that there was a high risk of scouring.
The last ground level inspection of the viaduct, prior to the 2009 collapse, was dated October 5th, 2007. The card was incomplete
condition ratings were only provided for the handrail nothing else
no photos were taken
no comments were made on the structure even though the 2005 inspection card suggested a check for scour
the inspector's name was not on the card and it was not signed off by a superior.
The next recommended ground inspection was expected in October 2009; although based on record keeping from the 2007 card, I doubt the 2009 inspection record would have offered much. That said, it’s important to note that the level of scouring present wouldn’t have been visible from a ground level inspection; divers were required to carry out a proper inspection. Even though this was known to Irish Rail, no formal approach was taken to carry out these inspections.
Reminder that the viaduct fell between two divisions; division 1 and division 5. The investigation following the collapse found that the engineers responsible for carrying out these inspections each have approximately 800 inspections, 130 of those bridge inspections, to carry out each year. Assuming approximately 250 working days per year, each engineer would have to complete 3.2 inspections per day. Even if that was possible, I doubt the inspection or report would have been thorough.
Irish Rail had been aware of requests for a scour/flood management plan since 2001, but nothing was ever produced.
A 1997 inspection came to light during the investigation, when a diver inspected the piers following removal of an abandoned barge. They noted the following.
Scouring had started at the base of pier 4
The rock armour grout had diminished by 80% on the west side and 70% on the east side of the viaduct. As well as that the grout was too light for the intended purpose.
Undermining of concrete was present at pier 7
There was evidence of cracking of spalling of the concrete deck
No evidence of remedial action by Irish rail was discovered.
There was no requirement for Irish Rail staff to upload information into the database. And there was no formal process for sharing information when someone left the division. This is often referred to as corporate memory loss.
In summary, the inspection process was a mess. When internal inspections occurred, they were incomplete. When external inspections occurred, the recommendations don’t appear to have been implemented. And a lot of this is due to Irish Rail not setting their staff up for success by developing policies and procedures to carry out proper inspections and share information. Over time, this led to significant scouring to go unnoticed, undermining of pier 4 and collapse of the viaduct.
After the collapse
The repairs took three months and cost roughly 4 million euros
Pier 4 was rebuilt with a concrete base and 20m steel piles. The other piers were strengthened with fifteen additional piles at every pier. All stonework was re-pointed and reinforcing rods were used to strengthen each pier.
The Railway Accident Investigation Unit provided recommendations to Irish Rail that were then implemented.
A technical manager was appointed who is responsible for developing, owning and implementing all technical standards. The technical manager is also responsible for verifying engineering compliance through checks to ensure that line managers are adhering to the technical standards, completing inspections on schedule, and entering information into the infrastructure asset management system. This includes accountability for investigation of reports from members of the public.
Within the infrastructure asset management system, an inspection regime was implemented for all bridge structures according to frequency as per the structural inspection standard. This will assist in the scheduling of inspections, as well as organizing the required resources.
A Coastal Defense inspector was appointed to specifically review scour inspection information as well as develop and coordinate scour action plans.
Irish Rail identified 105 bridge structures that are susceptible to scouring and conducted detailed surveys on each using a risk-based condition rating system. These bridges require inspections every three years, unless emerging risks dictate more frequent inspections.
A flood and scour management system was developed to deal with risk ratings on structures, frequency of inspections, use of measurement sensors to provide pre-cursor warnings, the use of visual and underwater examinations and remedial action plans.
Paper-based information, and previous reports were entered into the infrastructure asset management system.
The employee guidance program was revised to manage training and competency as well as include field mentorship.
The division 1 and 5 overlap on the viaduct was removed. It was the only such overlap across Irish Rail. As per standard practice, when a track patroller is on vacation, a supervisor will assign a relief track patroller.
So there you have it, the Malahide viaduct collapse. It reminds me of the Ford Pinto in episode 5. In the case of the Pinto and the Malahide viaduct, things happened in the way a large bureaucracy proceeds. I’m not saying it's ok that the viaduct collapsed, but I’m also not surprised that it did. It’s really easy for things to get lost and tied up in red tape. It seems like the larger the organization the greater the disconnect between those making the policies and those fulfilling them. As much as the Malahide Viaduct collapse shouldn’t have happened and could have been prevented, it seems to have shed light on some significant operational issues within Irish Rail which led to a significant organizational restructure. Hopefully they remain vigilant and don’t let complacency set in.
Check out the podcast page, link in show notes, for photos from this week’s episode. If you’re enjoying what you’re hearing, please rate, review and subscribe to failurology, so more people can find it. And if you want to chat with me, my twitter handle is @failurology or you can email me at firstname.lastname@example.org.
Thanks everyone for listening. And tune in next week to hear about Air France flight 447, which crashed into the Atlantic in June 2009 on its way to Paris from Rio de Janeiro, Brazil. But more on that next week. Bye everyone, talk soon!