Help verifying/understanding my site investigation report

insider · Jan 28, 2019 1:39 pm

Justme15 I would prefer a conventional raft slab siting on bored piers that are at least 3m deep.Conventional raft slabs have edge beams and internal beams dug into the ground and have sand formed slab panels.Waffles sit on the surface and have poly formed slab panels amongst other differences.
Clayton sth in general has moderate to low reactivity soil profiles and some deep sand profiles.There are some localised swamp deposits that have highly reactive clays which are usually dark grey to black you might be on one of them.
One possible reason for your current slab to be cracking is that it doesn't have piers and the nearby large trees are drying the soil under your slab and causing slab settlement.The trees may have been small and not planted when you current slab was built.
If your new slab is on piers then this should mitigate the influence of the trees as long as they are deep enough.

kirashogun · Jan 28, 2019 5:11 pm

What sort of foundation is your current house on?

sweetswisssteel · Jan 28, 2019 7:01 pm

Great thread, and as always opinions are like a@#$holes, everybody's got one.
I think the general consensus is let the engineer do his job.
Cheers

insider · Jan 28, 2019 7:38 pm

This is an interesting statement form the report considering it is in Clayton Sth

"The slab as recommended above, is designed to act as a whole unit so that it can tolerate the differential soil movements that may occur in the basaltic clay "

Justme15 Can you confirm the geology that is stated in the report.

justme15 · Jan 29, 2019 6:19 pm

kirashogun - according to what I've got it's a waffle slab.

insider - Thank you for your input. I will keep that in my back pocket. It will be a good baseline on what the engineer designs.
In my 2007 report, it states the following: Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Share

sweetswisssteel - Very true. Such is the nature of a public forum. But I needed some assistance in understanding the latest report. And like you rightly pointed out, there is a consensus here which is helpful. With all the horror stories, it's made me doubt both the engineers and builders alike - rightly and wrongly so. But it would seem that if anything, it would be the builders that would be questionable.

sweetswisssteel · Jan 29, 2019 6:32 pm

It's great to question everything, just don't fall down the "analysis paralysis" trap. I have been there, done that.
At some point you either walk away and find a new builder, engineer etc or you learn to have faith and get yourself a good independent building inspector (recommend for stage inspections).
Take care and good luck with it all.

justme15 · Jan 29, 2019 6:55 pm

Thanks for that. Great reminder re: analysis paralysis. And thanks for the good building inspector suggestion. Any recommendations?

sweetswisssteel · Jan 29, 2019 7:00 pm

I am in Qld and have found Darbecca very good.
If they are available in your area, I would go with them.
Take care.

justme15 · Jan 29, 2019 7:42 pm

Cool. I’ll look them up. Thank you.

StructuralBIMGuy · Jan 30, 2019 8:29 am

justme15

Thanks for that. Great reminder re: analysis paralysis. And thanks for the good building inspector suggestion. Any recommendations?

In WA when you pay for the Site report you get the footing Details/Data from the Engineer
Building Inspectors have nothing to do with Certifying Structurals unless they are qualified Engineers.
"Analysis Paralysis" results from conflicting, unqualified opinions, always ask for supporting data and proofs. my2c

sweetswisssteel · Jan 30, 2019 9:05 am

StructuralBIMGuy

justme15

Thanks for that. Great reminder re: analysis paralysis. And thanks for the good building inspector suggestion. Any recommendations?

In WA when you pay for the Site report you get the footing Details/Data from the Engineer
Building Inspectors have nothing to do with Certifying Structurals unless they are qualified Engineers.
"Analysis Paralysis" results from conflicting, unqualified opinions, always ask for supporting data and proofs. my2c

Same here in Qld, the engineer inspects the slab layout, piers etc pre pour. But the building inspector has found issues at every stage and backed up each defect with photos and ref to building code.
Some defects my inspector found included boney slab edge / cold joints and framing issues. 44 pages worth from base/frame inspection alone. The builder fixed them all with signed off engineering as required.
I cannot fault Darbecca and happily recommend them to inspect every stage of the build.

justme15 · Jan 30, 2019 12:34 pm

Just for those who might find it interesting, I learned this today.

Recommendations made in a soil report doesn't necessarily translate over to the real build.
In my case, while the 2007 soil recommendation is for a stiffened raft slab (amongst other things), what was built is a waffle slab.

Now as indicated by some, that doesn't necessarily mean it is wrong. It all depends on how 'good' that waffle slab is. I'm just trying to get details of the waffle slab installed currently. If any are still interested, I can post the details here. It would certainly help me too as I would struggle to make sense of the entire thing ahahah.

alexp79 · Jan 30, 2019 5:01 pm

justme15

Just for those who might find it interesting, I learned this today.

Recommendations made in a soil report doesn't necessarily translate over to the real build.
In my case, while the 2007 soil recommendation is for a stiffened raft slab (amongst other things), what was built is a waffle slab.

Now as indicated by some, that doesn't necessarily mean it is wrong. It all depends on how 'good' that waffle slab is. I'm just trying to get details of the waffle slab installed currently. If any are still interested, I can post the details here. It would certainly help me too as I would struggle to make sense of the entire thing ahahah.

Waffle pods on reactive soils is something that needs to be prevented.

https://www.cornellengineers.com.au/bew ... fle-slabs/

insider · Jan 30, 2019 5:09 pm

justme15

Just for those who might find it interesting, I learned this today.

Recommendations made in a soil report doesn't necessarily translate over to the real build.
In my case, while the 2007 soil recommendation is for a stiffened raft slab (amongst other things), what was built is a waffle slab.

Now as indicated by some, that doesn't necessarily mean it is wrong. It all depends on how 'good' that waffle slab is. I'm just trying to get details of the waffle slab installed currently. If any are still interested, I can post the details here. It would certainly help me too as I would struggle to make sense of the entire thing ahahah.

If you are using a soil report form 2007 then you will definitely need a new as the Australian standards have changed since then.
An engineer can use engineering principles to design a slab so don't get to worried regarding the previous soil test.
As structuralbimguy said your engineer will design the appropriate footings, just as long as you end up have deep piers to combat the trees at the rear we should be fine.