CROSS Safety Report
Incomplete casting of composite brick/concrete parapets
This report is over 2 years old
A reporter states that during a parapet raising scheme over a mainline railway, a void up to 300mm deep was identified below existing coping bed level.
Key Learning Outcomes
For construction professionals:
Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design
Effective communication of essential design information in an accessible form to tradespeople working on site can also ensure the works are in accordance with the design intent
For client organisations:
Consider introducing a technical assurance regime to provide additional independent assurance that the requirements of specifications for workmanship, materials, drawings, inspection and test plans are being complied with
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During a parapet raising scheme over a mainline railway, holes for new connecting dowels were drilled vertically through the coping stone of the existing high containment parapet. During this activity, a void up to 300mm deep was identified below existing coping bed level. The existing parapet wall was designed in accordance with BS6779-4 which comprises brick-clad external faces and an inner reinforced concrete core; construction was circa 2012.
The original copings are also reinforced concrete and were detailed to be robustly connected to the inner core with high yield dowel bars. The core of concrete in the wall should therefore be flush to the underside of the coping. On identifying the void, the contractor responsible for the parapet raising scheme undertook some further local intrusive investigations at the client's request. The investigations confirmed that the top lift of concrete was absent from within the core of the wall, through most of the length of the parapet.
This meant that most of the original copings were not anchored to the wall as per the intention of the BS Code of Practice and original scheme designer (it should be noted that the original contractor and the contractor responsible for the parapet raising scheme are separate organisations). The support to the copings from the original wall construction is negligible and therefore posed a significant risk to safety from being struck by vehicles prior to corrective temporary and permanent remedial works.
This meant that most of the original copings were not anchored to the wall as per the intention of the BS Code of Practice and original scheme designer
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This too is a situation envisaged by the Construction Industry Research and Information Association (CIRIA) Report Guidance on catastrophic events in construction (C699) about failure of one structure impacting on another nearby. In this case had the coping become dislodged, perhaps by a vehicle strike, and fallen on an operational railway line the consequences could have been catastrophic.
In 2015 a heavy goods vehicle (HGV) tried to reverse back over the Froxfield railway bridge and pushed over the brick parapet onto the track below. Although a passenger train struck and ran over part of the fallen masonry parapet, the train did not derail. In 2001 a vehicle veered off the M62 onto the East Coast main line and caused the Selby rail crash. A London express train and a freight train collided, killing six passengers, four railway staff and injuring more than 80 others.
Construction works not in accordance with the design
As in report 693 which discusses the stability of existing structures impacting construction sites
and in numerous previous CROSS reports, many instances are still emerging of construction not being in accordance with design intent. It is of little comfort to public safety (after a failure) if the party with responsibility can be identified.
There are too many instances of poor and dangerous construction which put innocent parties at risk. These all suggest more supervision and inspection are required. The Report of the Independent Inquiry into the Construction of Edinburgh Schools February 2017 and the summarised Standing Committee on Structural Safety (SCOSS) alert on Inquiry into the construction of Edinburgh Schools state that public sector clients should engage individuals or organisations with the necessary professional expertise to undertake on their behalf an appropriate level of ongoing inspection.
There are too many instances of poor and dangerous construction which put innocent parties at risk. These all suggest more supervision and inspection are required
Effective communication of design information
It is critical that there is effective communication of essential design information in an accessible form to the tradespeople such as bricklayers working on site. Client organisations could revisit the robustness of their technical assurance regimes to provide additional independent assurance that the requirements of specifications for workmanship and materials, drawings, inspection and test plans and other design documents, are being complied with.