Retaining Wall Sanity Check

7 Oct 2015
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United Kingdom

I would appreciate some observations on my design for a back garden retaining wall.

I plan to dig out a wedge of a sloped area to fit a garden office in. The retaining wall will be u-shaped - 6.5m long and 1.38 down to the new flat ground (the returns will be 3.5m long and taper from 1.38m high to zero).

If I put the bottom of the footing below the frost layer - say at 850mm, this makes the top of wall to footing 1.83m.

With a 215mm wide hollow block inner skin (filled cavities) and a 102.5mm brick outer skin I get, using the Masterseries design program, a footing of 1288 mm wide x 400 mm deep (the wall sits almost central on the footing).

For the reinforcement
Inside the blocks: vertical 10mm rebar at 400 c/c
Footing bottom face: 10mm 100 x 100mm mesh

The only thing I've yet to factor in is the soil type, I'm just using the program's defaults until I learn about soil properties. The soil is clay (I'm about to go and dig a test trench to find out what type) and the wall will be backfilled with appropriate material - need to look that bit up. To groud from the top of the wall slopes away 5 deg.

I'm worried I'm in danger of over-engineering this and any alternative design suggestions are most welcome.
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I have just cut out a piece of clay to level out a barn floor, It was a miserable 12" at the back and nothing at the front. The cut edges immediately dribbled water at me and a damp puddle appeared in the centre of the barn. The ground rises a lot (6'?) in about 40 yards behind the barn. Sort of like a warning that you can have fissures in clay that are full of water which has accumalated over geological time or could be fed from active underground streams. I wonder if you should have bleed holes near the base of the wall to let this water to dribble out.
Thanks Frank,

Yes, I am definitely going to have bleed holes along the base of the wall. I've dug a trial trench and there's no sign of any water, but then the house a few metres away may be protecting it from water ingress.



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