Thread: Settling of fill under new garage slab: necessary?

Hire a vibrating compacting plate and do the job properly.
Put down a 150mm layer, compact, repeat, repeat, etc, etc.

about 8 years ago we filled an area, mostly clay fill, to a depth of about 1.2m, over 5 or 6 years it settled down about 150mm, mind you, we did not use a compactor at all, though I did spread it with a bob cat, does that give you an idea.

If you're going to prepare a platform 1200 high and big enough for a double garage you'll be looking at a lot of fill. Filling to that depth and with that amount of fill you'll need at least a bobcat to spread the fill and a vibrating pedestrian roller to compact. You'll also need to scalp all the topsoil off the site beforehand.

Mick

Thanks a lot for your input. I have a much better idea of what's required now. Cheers, Brett

It would probably crack with normal reo with no internal beams if you drive a car on it.

I filled an area to about 900mm for my 6M X 14M shed. It has sunk about 50 - 70 mm in a couple of places - Unfortunately a family of Red Belly Black Snakes have now moved into the gap

woodcutta

Originally Posted by woodcutta

I filled an area to about 900mm for my 6M X 14M shed. It has sunk about 50 - 70 mm in a couple of places -

filled areas have a bad habit of doing that, even if you roller compact as you go.

Unfortunately a family of Red Belly Black Snakes have now moved into the gap

woodcutta

look on the bright side..... ummmm, can't think of one at the moment, but 'always look on the bright side of lie, da dum, da dum dum dum dum'

What you could do is put your fill in and compact as well as possible, then get a machine in to drill some holes into solid ground beneath the fill area, then fill with concrete to act as piers to hold up your slab.

[quote=
look on the bright side..... ummmm, can't think of one at the moment, but 'always look on the bright side of lie, da dum, da dum dum dum dum'[/quote]


Maybe they sleep in the winter??

woodcutta

One part of our house sits on an infill slab. It has brick piers every metre with extra reo over the piers (as specified by the engineer). It is back filled with sand, which does not compress - however it only needs to act as formwork for the slab pour because the piers will take the weight. The piers are founded in solid ground with a 600x600x600 footing under each. The perimeter of the slab sits on continuous brickwork which is laid on a strip footing. There is a slip joint between the slab and the brickwork.

4 foot is a decent depth to fill, Brett. Not something I'd take too lightly. The idea of dumping fill in there and compacting it doesn't work for me. It will settle over time and cause problems.

In fact, I don't think I'd tackle it myself because it sounds like it needs:

* Something to retain the fill, i.e, retaining walls
* Piers into solid ground
* Crusher dust or sand (non-compacting fill)
* Then the slab (that sits on the piers.

But most of all, you need a soil test and an engineer. I'd be very surprised if the council will let you do anything other than have an engineer look at it if you want to raise it four feet. Silent's post outlines the way it needs to be done.

Thanks for all the advice. I knew what to expect when I called the garage people who put me on to the concreter. He said it wouldn't be a drama - he'd put piles down to hard ground and lay the slab on top. No big deal (it would cost a bit more of course, but that was to be expected). He did make the good suggestion that I step the garage down, ie only half the fill-height, so the buildings flowed more with the block. Sound idea. Thanks again everyone. It's amazing how quickly you can go from knowing absolutely nothing to having a bit of an idea.

cheers, Brett