Retaining wall backfill

[deuce22]

Hi.

 

I'm looking for some advice on the best way to backfill behind a separate retaining wall and 2 retaining walls which will be a part of the house. The separate wall is 1.7m away from the property and starts at 1m high, up to 3m high, over a 10m span. It is constructed from ICF and has an 200mm fill.

I have wrapped 100mm perforated pipe in a geotextile sock, covered it with around 300mm of 40mm clean stone and then backfilled it with the earth I removed. I'm not concerned about water penetration on this wall, just hydrostatic pressure. I'm not 100% sure if this is adequate, however a local groundworker said this is sufficient to drain the excess water.

 

On the 2 retaining house walls, I will use waterproof readymix concrete and a peel and stick waterproof DPM. The span of the one wall is 13m, so the last thing I want is pressure to build up behind and cause problems. Due to the ground behind being around 4.5m high, it had to be chamfered back and is around 500mm back at the bottom and 4m at the top. This would cost to much to completely fill with clean stone, so I've had to think of another way.

My plan is to sandwich lengths of 10x2 timbers between 2 OSB sheets and stick this to the back of the wall. I can then fill this void with clean stone and fill behind it with the earth that I removed. I will drill a series of holes to the outside sheet and then cover with geotextile fabric.

 

Would this be a better option than to just fill the bottom 1m with clean stone and then put the earth on top.

 

Thanks.

Edited September 5, 2020 by deuce22

[Adam2]

A 4.5m wall I'd get an SE to advise due to consequences of failure.

 

Personally I'd not put organic materials in a structurally important location under ground. How well does your backfill soil drain? Fill around a perforated drain I thought would be pea shingle 10/20mm yours sounds quite large at 40mm but maybe that is better?