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Low retaining wall concrete foundation depth

Postby CSTB » Wed May 26, 2021 1:09 pm


I'm building a low retaining wall. Over the length of the wall (17m), the height I'm retaining goes from 550mm down to zero. I have plenty of 7n 100mm dense concrete blocks, and I'm planning on 3 courses above ground.

What depth of concrete foundation would you recommend? The soil is clay, but doesn't hold too much water. It's also at the top of a hill so unlikely to get too saturated. I've read anywhere been 100mm and 1000mm, but looking for more specific advice for my situation.

Is any reinforcement needed, like rebar or fibres? The concrete will be C25 delivered and mixed on site by a volumetric truck.

I was also planning on painting the back side of the wall with bitumen paint, but should I be using a tanking slurry instead? The front of the wall will be rendered and painted, so I'm trying to avoid water penetration.

Many thanks,

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Simply Build It

Postby stoneyboy » Thu May 27, 2021 9:50 pm

Hi cstb
I assume the top of the wall will be level and the varying height is due to sloping ground.
Where you have nearly 700mm above ground level suggest you build in some piers on the reverse side.
Your question re depth of foundations presumably refers to how far in the ground you should go? This will depend on soil conditions - more important is the width which should be wider the higher the wall.
Regarding water penetration suggest you use 1000g polythene behind the wall and into your foundation trench.
Regards S
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