Soil Tests & Slab Types

Our soil test (carried out by our building company) has come back as an MD classification. They only use waffle pod slabs, and have said we need screw piles all through the slab.

I've since heard that for an M class soil if you use a raft slab screw piles aren't necessary. Therefore a hell of a lot cheaper than the $30+k that our site costs have come in at.

We are really, really set on this house design and want to stay with our current builder, but if we need to have this waffle pod/screw pile slab we just can't afford it...we were'nt expecting thsi cost blowout!

Can you get a different slab type...or do these large building companies only offer one and thats your choice or you don't go with them? Anyone know of any major building companies that do NOT use waffle pod slabs????

Given the M-D soil classification I'm guessing that you're from a dryer climate like WA for instance.

You do not have standard M-class soil with shallow moisture changes/movement, you have M-D class soil which means you will have moderate soil movement at greater depths - sounds to me like you do not have good solid clay or even rock at a sufficiently shallow depth to support the footings of the house so the screw piles are needed to provide additional support.

Slabs aren't like something you'd buy in a store I'm afraid - if your soil is reactive and there isn't a solid subsurface soil structure or rock to support the house then burying the slab footings into the ground (which is what a raft slab involves) isn't going to help much because the soil below still won't be able to support the house.

Regardless of which slab type is used I suspect those screw piles will still be needed if the soil classification is correct.

Thanks for your help, we're from the Mornington Peninsula, Vic. Apparently sandy soil. Here's hoping our 2nd soil test says different then! :S
Appreciate your reply.

That's a bit wierd then, unless the water table is unusually high where you are - sandy soil in and of itself should not be that much of an issue because the movement should be minimal so perahps the stability of the sub-surface soil is an issue so they want to disturb it as little as possible.

mmm we are only learning about soil and slabs, but uneducated on the topic find it odd. we have friends next door and 2 doors down same block size, almost the same drop etc etc...both didnt need this kind of slab or have nearly this kind of cost. I know it varies per block but wow...thats a massive difference?..
eagerly awaiting this 2nd soil test now..