CROSS Safety Report
Stability of brick walls
This report is over 2 years old
A 230mm cantilevered brick wall approximately 1.6m high failed after backfill material was placed behind it, which was not the design intent.
Key Learning Outcomes
For construction professionals:
Be aware that backfilling small gaps can generate enough pressure to destabilise walls as demonstrated in this report
There has been numerous failures associated with freestanding masonry walls and a previous Alert was issued by the Standing Committee on Structural Safety (SCOSS) – Preventing the collapse of freestanding masonry walls
For structural design engineers:
Careful consideration is required for the design of cantilevered brick walls, particularly in the temporary stage because there is no redundancy and relatively small loads at the tip can precipitate failure
Consider what reasonably foreseeable loads could be applied beyond the code minimum values on elements such as freestanding walls
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A 230mm cantilevered brick wall approximately 1.6m high was built roughly 300 to 400mm in front of a rock face. The space between the wall and rock face was backfilled (which was not the design intent) and it pushed the wall over.
It was surprising that so little soil could generate sufficient pressure to topple the wall. However, the backfill was recently excavated clay that expanded after placement and created pressure between the rock and the wall.
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Expert Panel Comments
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The water pressure generated in a 100mm gap is just the same as if the gap were 1 km. If the designer of the wall was aware of its location it would be a reasonable expectation that he/she would highlight the risk of backfilling.