Retaining wall foundations on a slope

[Jellybellyjim]

Ok, so I'm pretty confident after a load of research I know how to build a hollow block retaining wall for my garden. My problem is down one side of my future garden is an access track that will slope down from level with the garden at the far end to about 1.2 metres at the house end. (Hence the need for retaining as the garden runs with the track at the moment) I understand how to go about the foundations and wall that will go across the back of the house as that will be level but what do I do at the side? Do I step the foundation like you would fenceposts?? The problem with this being i want a white rendered slick look not a stepped one. Or do i run the foundations on a slope with the track and take up the slope by cutting the first couple of courses to get the blocks level??

 

[Halitosis]

I recommend stepped foundations. Did something similar in my own garden and built some shuttering from wood to enable a single pour of concrete (mustn't be too wet). Although a bit of a faf at the preparation stage, it makes the blockwork easy and the foundations are hidden below final ground/path level

 

[Jellybellyjim]

Ah, brilliant! I thought that was how it must be done! Great work on your project by the way!! How deep were your foundations? What was the overlap on the steps and how far below the final level was the shallowest part ? Oh and did you tie the steps together with rebar?

 

[Halitosis]

I went 12-15 inches deep with my foundations (though that was probably more than necessary) and tried to ensure the overlap at the steps was about the same. Doing a single pour rather than each step individually make for a much stronger bond - only consider a little vertical rebar if pouring separately. 3 years later and nothing's moved so I think it'll last the duration. Just make sure you consider drainage as apparently water is the main cause of retaining wall failures.

 

[Jellybellyjim]

I did hear that about the drainage, the bit I can't work out is when putting the membrane on the inside of the wall does the drainage sit inside or outside the membrain?

 

[Halitosis]

Your blockwork wall will presumably be mortared, and therefore effectively watertight and will act like a dam with water building up behind and ultimately causing the wall to fail unless you provide it with an outlet (drain or at minimium weep-holes). I ran a flexible field drain (embedded in pea gravel) along the length behind my wall, with a drainpipe running under the wall and away to a rainwater drain beside the house. Depending on the size and location of your retaining wall you may get away with the drain running off to a lawn or soak-away, but it cant be allowed to run towards a building or across a boundary to a neighbour's property.
I found the pavingexpert website brilliant with all sorts of advice, and for what its worth, some photos of my project are here