Subbase construction

[Matt10]

Hi guys,

Wonder if you can offer some advice?

I'm planning to build a retaining wall approx 70cm in height & fill in behind it in order to create a terrace/patio. The area is approx 40m2 so to fill it up will require loads of material! Access is rubbish!

My question is can I part fill the void with soil removed from another area of the garden thoroughly compacted in layers & then topped of with a good layer of stone?

I did see contractors compacting clay with a site roller to form the initial base for the ramp road upto a flyover once so wondered if I
could do it.

Thanks in advance, Matt

[Pablo]

I'm going to say yes cautiously it is possible to do but you must use the right soil and compactor. You cannot use any topsoil in the fill it must be subsoil and it can't be to wet or to dry. You will also need a soil specific compactor a wacker plate won't do. The compactor is where you'll have a problem they're hard to hire and weigh more than a couple of men could lift. They're like a small twin drum roller but the drums are knobbly to push the soil into itself. The only other way of doing it is to put in a 100mm layer of soil then dress it with a dusting of stone so a plate can travel over it without sticking. If you do this you need to use a heavy plate of at least 100kg. If the soil is to damp then it'll turn to soup when compacted.



Edited By Pablo on 1310286460

[lutonlagerlout]

its not advisable but as pablo says in the real world it gets done
I have tiered gardens where the spoil from the retaining wall gets used to level the garden behind the wall
this happens in 3 or 4 tiers and saves a fortune in waste costs
the soil will settle within 5-6 months
most important thing to remember are weep holes
cheers LLL

[Matt10]

Thanks guys.

I'm unable to get a rammax roller compactor into the garden so it would need to be the heavy plate. I understand the need for a dressing of stone over each layer of subsoil to keep the plate moving.

I've dug a test hole in the potential backfill material & no clay appears to be present (at 900mm deep anyway). There seems to be a continuation of the topsoil layer, obviously far more compact & does change in colour slightly.( the site is on the side of a hill if that makes any difference). Is this soil unsuitable for backfill?

If each layer is compacted maximum refusal is there still chance of
settlement or no??

I appreciate you guys couldn't no for sure!!

Matt