CROSS Safety Report
Vegetation damage to railway arches
Lack of clarity as to maintenance responsibilities leads to degradation of railway arches.
Key Learning Outcomes
For owners, leaseholders, asset managers and tenants of railway arches and other masonry structures:
- Structures may fail if maintenance is neglected
- There should be clarity as to who is responsible for maintenance
- The boundaries and scope of maintenance should be defined
- Access for inspections and maintenance should be defined
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A reporter has confirmed that vegetation growth in the outer brickwork of railway arches is damaging the integrity of the arch. The reporter cites a number of examples including figure 1 below and believes the problem may be widespread and that essential maintenance of the arches is being missed.
In some cases, the arch has been infilled under with a facing wall to form workshops, offices, or other premises under the railway arch. However, the brickwork or stone forming the arch is usually still the primary structure supporting the fabric of the viaduct over. The reporter has observed vegetation that is rooted deeply into the arch and is concerned that the strength of the arch is affected through the degradation of the masonry and the effects of water penetration and weathering.
The reporter believes that there may be a lack of understanding as to responsibility for maintaining occupied railway arches.
Expert Panel Comments
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The growth of vegetation on structures is a ticking timebomb. There have been some notable failures of structures resulting directly from debonding caused by such growth, leading to harm or the potential for harm.
Importantly, it is necessary to prevent growth by adequate maintenance. Prevention, for example by repointing and crack stitching or other means, will prevent growth in the first instance. However, when vegetation has established, it is not satisfactory to cut it off at the face and leave the remainder with the unbonded masonry, as the vegetation will re-establish and there is a path for continued weathering. What lies behind, out of sight, could be a network of roots that has disrupted materials and caused major structural damage, all of which is not evident, until whole panels fall off, putting lives at risk.
out of sight, could be disrupted materials causing major structural damage...putting lives at risk
Unfortunately, this is an increasingly common problem and not just with brick arch structures. The lack of regular maintenance, as well as leading to unseen deterioration, can inhibit inspection, increase the lack of functionality of the structure (e.g., the capacity of culverts), and ultimately increase safety risks and impairment. These risks build up day by day if not addressed. Garden and boundary walls are very susceptible to damage from trees and other vegetation and can fail because of root damage. Unstable boundary walls have resulted in fatalities.
Lack of clarity over boundaries, maintenance liabilities and interfaces can be behind neglected routine maintenance. The example given is occupied arches, but it applies everywhere there is an interface between an infrastructure owner and another party. The lack of clarity can lead to uninspected structural assets, missed defects, and unactioned maintenance. There have been cases where there has been subsequent reputational damage and adverse publicity.
lack of clarity can lead to uninspected structural assets, missed defects, and unactioned maintenance
Access for inspections must be considered. A previous CROSS report - Hidden defects in railway masonry arch viaducts – concerned the potential difficulty in undertaking inspections and maintenance of railway arches that are occupied. The report included reference to a Network Rail challenge statement on tenanted arches.
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