Filling retaining wall

jenifa, Apr 19, 7:01am
Going through planning stages of getting a retaining wall built for my rental to widen the driveway for a car to park. It slopes gently from 0.5m then to the current drive so will be 0.5m high and about 4m wide x 20m long. Will it be fine to just fill with metal and the car can park on that? If so what type do you recommend. PHOTOS: https://builderscrack.co.nz/trades/landscapers/manukau/jobs/86259

tintop, Apr 19, 8:02am
Back fill with crushed aggregate is a good move.

Check out prices for aggregate that is described as GAP 40, or SAP 40. ( General All Passing, Scoria All Passing) the '40' refers to the maxmimum aggregate size.

After excavating, place a layer of ';mudstop' fabric directly on the ground and then place the aggregate.
Place in 100mm layers and compact with a vibrating plate compactor.

Do not rake out excessively, the 'fines' will drop out and the 'bones' will be on top. This can partially be rectified by dressing out the surface with a fine aggregate mix - (10mm builders mix is good. BM10 ) with plenty of water before the final compaction runs.

Final compacted thickness should be not less than 125mm.

jenifa, Apr 19, 7:23pm
thanks. Would you recommend digging a trench for drain coil etc? Or given the slight slope away from the drive will it be oK?

tintop, Apr 19, 10:06pm
It may not be needed - what sort of retaining wall are you going to build ?

jenifa, Apr 20, 2:04am
Cool. It will be timber.

tintop, Apr 20, 2:09am
If there are gaps between the timbers, and I have not seen a timber wall yet that did not, don't worry about drainage - any water will just weep through the gaps.

jenifa, Apr 21, 9:59am
Thanks heaps!

pauldw, Apr 21, 11:38am
True but if this wall is supporting a car park it should need a Council consent and they will probably insist on a drainage system.

tintop, Jan 27, 6:14pm
Its up to the OP of course, but given the low height of the wall (500mm), and its apparent distance from the side boundary - personally I would not bother.

The purpose of any drainage behind a retaining wall is to ensure that there is no hydrostatic pressure - it would only be a matter of labelling a row of holes at the base of the wall as 'weep holes' :)