CROSS Safety Report
Hidden defects in railway masonry arch viaducts
This report is over 2 years old
Overview
A reporter raises concern about the sell-off of spaces under railway arches, as it may become difficult to carry out future inspections and maintenance.
Key Learning Outcomes
For asset owners and managers:
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Regular inspections and maintenance can help keep a structure safe before it deteriorates beyond repair
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Be aware that safety critical defects may be hidden behind linings
For all built environment professionals:
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Network Rail have published a challenge statement on tenanted arches and are inviting the supply chain to help with research and development activity
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A reporter is concerned about the sell-off of spaces under railway arches. This was brought to their attention by an article in Issue 852 of the Rail Magazine. If space under railway arches is sold off, then it becomes almost impossible for inspection and maintenance to be carried out. The article says ‘the risks of something really disastrous resulting from this sale cannot be discounted’.
Selling off the leasehold for 125 years is likely to lead to some major difficulties in a few years, according to the reporter, since there may be defects already hidden behind linings. The reporter is aware that many inner-city arch viaducts, where the space below the arch is used for small businesses, have not been inspected for years. For those few that have been inspected, defects have been found that have required immediate remedial action. In some cases that has not always been successful.
The freight loading on some of these structures is such that the joints between the bricks open and close repeatedly as the train passes over. Small amounts of mortar are lost occasionally, leading to greater movement over time.
The freight loading on some of these structures is such that the joints between the bricks open and close repeatedly as the train passes over. Small amounts of mortar are lost occasionally, leading to greater movement over time
The reporter believes that this problem needs to be addressed if a potential collapse is to be averted and thinks that the process could best be started by raising this issue with CROSS.
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Feedback
I recently read with interest the Report 764 Hidden defects in railway masonry arch viaducts on this Structural-Safety website. My intention with this feedback is mainly to add detail to the following statement in the aforementioned report: "It is understood that the railway arch sell-off is supported by robust measures to ensure that the asset management inspection and assessment requirements for the loadbearing railway arch structures can be met. The new regime will of course need to demonstrate this will remain the case."
Upon reading the report, and the quoted statement above in particular, I was rather surprised. To my knowledge there is no explicitly "new regime" for the safety-related management of property sales to third parties, or of third party access, or of structures that are wholly or partly owned or managed by a third party.
Rather, my experience is that the means and methods by which Network Rail manage these risks are not new, but have been in place for many years, all under the scrutiny of the Office of Rail Regulation (now Office of Rail and Road). Network Rail have the power under the Railways Regulation Act 1842 to a enter third party premises if required following an emergency or in order to prevent an emergency developing. The right of access granted by the 1842 Act is also highlighted on Network Rail's webpage Buying a property next to the Railway.
The 1842 Act guarantees that Network Rail has a means of obtaining access to ensure the safe operation of its infrastructure. There is therefore no realistic prospect, for example, that a 125 lease could prevent Network Rail from performing essential structural examinations. Nevertheless, use of the 1842 Act is rare as it is usually unnecessary.
Instead, access for examination is routinely arranged with the cooperation of third parties, as part of Network Rail's standard infrastructure management regime. For the masonry arches noted in the aforementioned report, the relevant Network Rail standard is NR/L1/CIV/032 The Management of Structures. This standard, the current issue of which has been in place since 2009, has clear provisions and robust infrastructure management requirements for both Outside Party structures (wholly owned by another organisation, for example road overbridges) and Shared Structures (where ownership and/or responsibility is shared between Network Rail and a third party, for example occupied viaduct arches).
NR/L1/CIV/032 also requires up-to-date information on ownership of property close to the railway be maintained, for use in routine management or emergency. In addition, Network Rail property sales are subject to a comprehensive Property Clearance Process under standard NR/L2/PRO/001, which has also been in place since 2009. Prior to authorisation of any property sale, asset and maintenance protection engineers will undertake a technical and safety review to ensure that a proposed sale will not prejudice Network Rail's ability to safely operate and maintain the railway. This will include having a clear plan in place for the management of any infrastructure assets that remain relevant to railway operation, regardless of their ownership or occupancy.
My view is therefore that the existing systems and processes for managing risks related to third party access are well-established and robust, provided they are followed properly and good records and communication between the relevant parties is maintained throughout the life of the assets. I hope you find this information to be of interest and relevance.
Expert Panel Comments
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Railway engineers have a long tradition of monitoring, maintaining and keeping safe old masonry bridges. There is also a long tradition of business premises being located underneath bridge arches and rail authorities have powers to access these as they require. There are occasions when defects are discovered during inspections so the ability to gain access for visual sightings to look for problems and precursors of failure is important.
The reporter is right to raise a concern and the matter has been considered by the railway authorities. An article in Railway Technology from September 2018 states ‘Network Rail has sold the sites on a leasehold basis with plans to retain access rights for using the property for railway operations in future’.
Can the inspection and assessment requirements be met?
It is understood that the railway arch sell-off is supported by robust measures to ensure that the asset management inspection and assessment requirements for the loadbearing railway arch structures can be met. The new regime will of course need to demonstrate this will remain the case.
A more recent approach is to install long-term monitoring systems in old bridges to evaluate the deterioration of the structure and to determine the effectiveness of previous maintenance measures. This may include the following measures:
Sensors to measure distributed deformation
Acoustic emission sensors at specific damaged locations
High sensitivity accelerometers to measure the dynamic response of the structure due to vibration caused by trains passing over
The sensing data is then interpreted remotely. However, concerns have been expressed to CROSS about the ability of even the most advanced accelerometers to measure critical movements for masonry bridges. In long viaducts, where there can be many tenanted arches, an additional challenge is to decide which arches to monitor.
Network Rail’s challenge statement on tenanted arches
As part of Network Rail’s research and development (R&D) programme, they publish challenge statements to raise industry awareness of their priority challenges and to promote research and development into new ideas and technologies to solve them. They have published a challenge statement on tenanted arches and are inviting the supply chain to help with R&D activity for remote condition monitoring, hidden inspection techniques and improved detection of defects by way of example.