JerryD
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My garage is built as a retaining wall, it retains 7 feet at the rear and from 7 feet down to 4 feet down one side, (We live on the side of a hill)
We built these two walls from 9" hollow concrete blocks, threaded over 25mm h/t bars cast into the foundation concrete. The hollows in the blocks were filled as work progressed with strong, wet concrete (5:1) which totally encased the reinforcing bars.
This was the approved method, designed by a structural engineer, no guesswork involved!
HOWEVER................ due to wet weather during construction, the earth bank started to collapse slightly and started filling the 'gap' between the rear of this wall and the bank (about 600mm gap), so we couldn't tank the rear of this wall as we had intended. (no access for excavator now) so we gave up on the idea. We finally fully backfilled hard against the blockwork and thought no more about it.
About 10 years later we started getting water through the rear wall due to hydrostatic pressure of surface water behind the wall. Only in a couple of spots but it was annoying to get puddles in the (otherwise dry) garage.
In the end I had to tank the interior in the same way you'd tank a basement, the materials cost nearly £1,000 (yes, one thousand pounds!) but it did stop the leaks. (the garage is 12 metres wide and 7 metres deep)
So what would have been a hundred quids worth of 'blackjack' turned out to be an expensive job.
So, in answer to your question, yes you can use the garage wall as the retaining wall, but the retaining wall has to be able to take the loading put on it. I would definately 'blackjack' the back of the wall before backfilling but by the sound of it, you may not have room to do this if you are building right up to the boundary??
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