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Sandstone Retaining Wall - Storm Water Pipe

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  1. #1
    Join Date
    Oct 2014
    Sunshine Coast

    Default Sandstone Retaining Wall - Storm Water Pipe


    I am looking to build a small retaining wall out of 400x400x1000 sandstone block - 2 rows high and about 7m long. The blocks will sit a little below ground level and will retain only about 600mm of soil.

    I was digging out the area yesterday and i came across a number of pipes coming from the house - most of them are far enough away, but a stormwater pipe will run directly under the blocks.

    My question is what is the minimum depth that the pipe needs to be below the base of the blocks to disperse the weight? I would normally expects stormwater to be 600 below ground level but this one would be only about 200.

    I will probably use sand or road base as a base for the blocks and each one weighs about 370kg.



    *edit added some photos

    Ignore the broken pipe and the one at ground level - i am concerned about the one below that is between 200 and 300mm below the top of the concrete. You can just see it where i've scraped a bit of dirt away.

  2. #2
    Golden Member manofaus's Avatar
    Join Date
    Oct 2007


    The recommended foundation for retaining walls at that height is 100mm compacted material with a bearing pressure of 50kpa. This is about 7 and a bit psi, or 5t per m2. You could just re-route it behind with a couple of 45 degree bends. Depending if it is a charged line you could dump your retaining wall surcharge in it too.
    sorry for the ramble.

  3. #3
    3K Club Member johnc's Avatar
    Join Date
    Jul 2004


    Is it possible to simply move the storm water pipe away from the foundation? that would at least move it away from the footing. We have a bluestone retaining wall, made of 400 x 400 blocks some 1.2m in length and some 2.4, three rows. They sit on a solid reinforced concrete footing which is 400mm square. Sizes are approx, nothing has shifted and block drainage links to the waste water from the roof.

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