Footings for 800mm garden retaining wall - on Sandstone!

[Jonsend]

Hello all,

Just registered but have visited often over the last 1.5 years since we bought our house. Anyway, on to my question...

The garden is sloped upwards away from the back of the house and has a number of rough sandstone retaining walls. They all need rebuilding and I am starting with the one nearest to the house. We decided to move the wall back to leave more room for decking so I dismantled the existing dry stacked wall (garden neglected for decades so I was surprised it was still standing) and started digging back a few feet. I found though that there was a fairly sturdy sandstone step base a few inches from the surface (I guess this is why the wall was still standing)(the house is also built on sandstone).

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• Jonsend
• 25 Apr 2011
• 1

I can break up the sandstone with a pickaxe but does my concrete footing need to be as deep as it would on soil?

Cheers,

Jon

 

[r896neo]

If it truely is the case that under the top 18 inches of soil you come to solid rock, sandstone or not, then a retaining wall can be substantially under engineered in comparison to a normal scenario. In fact you would be building a wall to stop erosion rather than hold back the earth as the pressure will be minimal because the rock will not move.

However to go down that route you would need to thoroughly investigate that this is the case along the whole length of the proposed wall.

In your case it will probably be best to dig out the lower level as far back as required and then assess the ground because this will give you a perfect cross section of the soil conditions.

If that is what you have already done then it might simply be a case of digging/ chiselling into the rock by twice the depth of your footing in order to give it a good catch.

 

[Jonsend]

Thanks for your reply. I doubt I will be so lucky with the higher walls