CROSS Safety Report
Retaining wall collapse
This report is over 2 years old
A retaining wall is reported to have collapsed four times during the course of its life.
Key Learning Outcomes
For civil and structural design engineers:
Adding to the height of cantilever walls should be carried out with care. If the additional load added is a UDL (like wind), then the bending moment at the base is proportional to the square of the height
Consider what reasonably foreseeable loads could be applied beyond the code minimum values on elements such as freestanding walls
A design check should be carried out on an existing wall or parapet that have attachments added to them
For construction professionals:
Alterations should not be made to masonry retaining wall without approval or an assessment being carried out by a suitably qualified engineer
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A retaining wall is reported to have collapsed four times during the course of its life says a reporter. The wall was approximately 1.7m high and built on a strip footing with steel rods (starter bars) protruding out approximately 300mm here and there.
Square mesh fabric reinforcement dropped in the cavity of the wall. There is apparently very little provision for drainage behind the wall and a fence was bolted to the top block course which may have contributed to the latest collapse which occurred during high winds.
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A retaining wall 1.7 m high with a fence on top is a significant structure which demands proper design and construction.
References giving guidance on good practice include:
Design of free standing walls by the Brick Development Association, February 1984
A reinforced brickwork freestanding boundary wall, Brick Development Association, January 1988 (BDA Engineers File Note 7)
BRE Good Building Guide - Building simple plan brick or blockwork freestanding walls GBG 14 (&19), May 1994
BRE Good Building Guide - Surveying brick or blockwork freestanding walls GBG 13, April 1992
BRE Good Building Guide - Building brickwork or blockwork retaining walls (up to 1,7m) GBG 27, 1996
This report has been re-published to clarify the Key Learning Outcomes regarding the design of masonry walls.