concrete slab under drainage area of retaining wall

30 Sep 2010
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United Kingdom
Hi. I am building a one meter high retaining wall where a brick garage used to be which also acted as a retaining wall. my plan is to keep the back wall of the garage to retain the soil while I build a new retaining block wall. The back wall of the garage is only one skin thick with just soil behind and is failing as a retaining wall.
The main question is if I build my new block wall in front of the failing brick wall with a space for a land drain and hardcore drainage between the old and new walls there will be a solid foundation beneath that drainage cavity. Is this ok. I understand you normally build the wall to the back edge of the foundation or slab so drainage goes behind. Obviously with my proposal the drainage will be on the slab. I would also put holes in the base of both walls for extra drainage. Does any one forsee any problems with my idea. Cheers :confused:
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Does any one forsee any problems with my idea. Cheers :confused:

If you want water on the garage floor, no. Can't you put a perforated pipe in and lead it to the side?
You're building a gravity retaining wall so you need to use an adequate block thickness and suitable foundation.
Please scan a sketch of a plan view and a section view of whats existing and what you propose.
Yes, there will be a french drain/land drain put in. The garage has been already knocked down with only a meter high wall left at the back which is also retaining a bank of soil. so imagine the slab is now effectively a over wide foundation. Normally the drainage (pea gravel and french drain) would be behind the foundation/slab. In my case it would be on the founadtion. I will see if I can do a picture
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