Building on Landfill

We are about to have a house built on land fill.

The site slopes and there is approx 300mm of fill at the front and 1 metre at the rear. The builder is proposing to cut in to a depth of 750mm and transfer up to 250mm to the front.

Delfin, the developer, has stated they will provide a engineer's compaction report, although this hasn't been sighted yet.

Should we be concerned?

Our house (that we have just moved into - woo hoo) is on an old dam and therefore 80% of the house is on landfill.

Our original compaction report stated that we needed 'x' amount of piers due to the fill ... but then 8 months later when they did a second compaction report, they found that the land had settled (or something similar to that, can't remember the exact word) better than they expected so we only needed 'x-10' piers. Still needed quite a lot because of the fill but due to the piers, plus building on a waffle slab, we weren't concerned (although hubby to be was annoyed that we are the only block in all of the estate on a dam!!).

I guess it's not a best case scenario to be on fill, but I wouldn't think that it is too much to be concerned about.

I could be proven wrong I guess when our house falls into the dam in 10 years time )

Thanks Amber. Our concerns are what is liekly to happen in 10 years time.

Is there anything we should be asking the developer and builder to do to ensure that the fill is not likely to shift or cause foundations don't fall apart?

I understand where you are coming from and we had the same concerns initially. But as it was explained to me, nothing really can be guaranteed and we have to put our trust in the engineer's that come up with the best ways so that our homes don't fall into the dirt!!

We spoke to the guy that was doing our slab and when we expressed concern, he said that in 30 years he has not yet had a house that has had anything go wrong with the slab so we just put our trust in him and that there were enough piers.

I also got my dad (a builder) to check the reports and see if he was happy with it and said that there were more than enough piers.

I guess the only thing you really can do to ease your mind is to get an independent engineer's report and see if they come up with the same thing for how to control the fill.

Good luck ... keep us posted!

My parents built on landfill 30 yrs ago - no problems for first 5 yrs - then some air pockets in the fill collapsed and the rear of the house started falling away! These pockets were deep - maybe 15m down - but quite large. Eventually the house was stabilised but it took $100k+.

Hopefully compaction techniques have improved since then.

Thanks Stonecutter.

Drove past the site last night. The developer is still spreading fill and is intending to release the tiltes this month (June). They're also saying they'll get the site compacted before the release.

Is this a reasonable proposition???

I must admit I'm getting a little scared!

Is a solution getting the site cut back to the original level before we start building?

les,

If it concerns you, you could ask for the slab to be built on foooting that go down to the level below the uncompacted soil (ie the original level)

Will cost a few $$$ but will put your mind at ease!!

Matt

Are we talking cut and fill here or landfill??? Stonecutter seems to be describing landfill and other seem to be referring to cut and fill.

My understanding of the difference is:

Landfill - a large hole (many metres deep) is filled with something (maybe rubbish topped with soil, hardcore topped with soil or all soil)

Cut and fill - usually not exceeding 1m cut and 1m fill. The soil that is cut is used for the fill.

With Cut and Fill, pillars are put through the fill layer to just below the original layer to give extra stability.

With landfill, this is not really possible and some other techniques (unknown to me) have to be used.

Cut and fill, I have no problem with. Landfill I won't touch.

3xb

Yep - I was describing landfill - it was an old quarry that they later filled in with soil, garbage, more soil etc.

Thanks to everyone for their feedback.

Just to be clear on what's happening on our block:
It was orginally farmland with a slight grade. The developer has been spreading what I have been told is land fill across the site and it now has a gradient of slighlty less than 1:32. The front of the site has 300mm of fill and the rear 1 metre of fill.
The fill is pretty clean although these appears to be some small rock mixed with it.

It's only a couple of hundred dollars for a soil test if that's going to put your mind at ease. The soil test will tell you the quality of what you're going to build on. You're going to need one for the house, although the developer may provide you with on.

If it ends up being crap soil, it will cost extra for the pillars and stuff.

It was a soil test that saved us from about 40k worth of site costs.
We had signed a contract for a block of land that had 800mm of uncompacted fill on it, some of which was "builder's rubble". Luckily we had stipulated a soil test in our contract so we lost nothing when we pulled out of the land sale.

I would definatly suggest getting the soil test done before you sign any building contract,as david s said, you will need one anyway.

hi les ive just bought a block of land on one of the delfin estates. im intending to build later this yr. my block has fill on it too.and my soil test has been done the slab will be a p slab which i hear on here isnt good. i have a house and land package so i dont think i will incurr extra costs i hope. im wondering wether ur building in the same area, i know delfin has different estates over melbourne.

Clath
We're in Caroline Springs - Cypress Views. Is that anywhere near you?

I have a class 'P' soil and I don't think it is something to fear.

I have just knocked down an old house on our block which was built in 1930s so the fill is quite old. The old house stood there for a long time, so it has to be put into perspective.

Our new house being double storey, would be heavier of course, but the engineering report explained that putting the piers under the slab should take care of the problem.

hi les im building in the south east ...lakeside pakenham. porter davis lifestyle house and land package. when u spoke about your landfill prob on here thought it may have been my way as some of the blocks in my street have fill. and titles are due june like urs. have my tender appointment tomorrow. cross fingers they dont slug me with more sites costs but being a house and land package i dont think they will. good luck with urs hey.