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CROSS Safety Report

Deadly retaining wall

Report ID: 134 Published: 1 July 2009 Region: CROSS-UK

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Overview

A blockwork retaining wall, about 2.5 metres high suddenly collapsed causing a fatality.

Key Learning Outcomes

For homeowners and the construction team:

  • Masonry walls should be designed and assessed by a suitably qualified and experienced engineer

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An engineer is concerned about the dangers from inadequately constructed brickwork and blockwork. They cite the case of a blockwork retaining wall, about 2.5 metres high. It was built around the mid 1990s and consisted of hollow 200 mm blockwork, which was partially filled with concrete, but had no reinforcement. This of course was not readily apparent. Backfill behind the wall was poorly placed and for this reason did not put sufficient load on the wall to cause it to collapse, though there was a certain amount of cracking.

Shortly after a contractor started work adjacent to it the wall suddenly collapsed causing a fatality. The reporter cannot conceive that an engineer had anything to do with the original construction. To them it emphasises the need to get across to the general public, including in particular small relatively unskilled contractors, the importance of proper professional involvement in work of this nature.

The reporter’s own very strongly held view is that except perhaps where specifically engineered, and where high quality workmanship can be ensured, no masonry wall should be built 100mm thick to any height greater than 450mm. They think the ODPM (now Communities and Local Government) leaflet is along the right lines and free copies of this or a similar leaflet should be readily available in all DIY stores and garden centres. Whatever is produced their view is that it should contain, in large red letters, the message that walls are potentially dangerous, and that for any wall higher than say 1m, or any wall retaining more than say 300mm of backfill, professional engineering advice should be obtained.

Expert Panel Comments

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This tragic case follows earlier reports about fatalities and injuries from the collapse of free-standing walls and boundary walls. It is difficult, if not impossible, for most people to see whether a wall is fundamentally defective and hence dangerous. Nor is it easy to comprehend that a low wall can become a deadly instrument. A long-term campaign will be needed to inform and educate those who build such walls without engineering advice.

The subject has been drawn to the attention of CLG with a view to issuing revised guidance. Even if the wall is engineered, such walls do degrade either due to environmental actions or tree roots etc., such that a wall which is safe as constructed eventually becomes unsafe. This message needs to be put over, particularly for those carrying out modifications or work adjacent to such walls.

References giving guidance on good practice include:

  • Design of Free Standing Walls - Brick Development Association

  • A Reinforced Brickwork Freestanding Boundary Wall - Brick Development Association

  • Building brick or blockwork freestanding walls - Building Research Establishment, Good Building Guide - GBG 14

  • Surveying brick or blockwork freestanding walls - Building Research Establishment GBG 13

 

This report has been re-published to clarify the Key Learning Outcomes regarding the design of masonry walls.

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