Thread: Soil test validity

So why would the geological structure of the soil have changed ???

echidna is right, not much would have changed. unless there has been major earthworks done on the site, 10 years is a mere blink in the geological landscape.

Clueless, can I ask who did the test?

My brother works for a company and he might be able to look up records?? I wouldn't have a clue what they do to tell you the truth though!

PM me if you want to as I may forget to follow this thread...

Originally Posted by clueless1

Hi all,

I've just signed a contract to purchace a block of land and received a soil test report done over 10 years ago (class, wait for it...P!!). My feeling is that one would need a current soil test for building. The thing is I really like this block of land even though it might cost a bit more to build on. Is it too much to ask for another soil test to be done?

TIA

Just thought I'd let you know that we are having a new house (305 m2) built now that we have had to pay extra for footings due to the soil class. Ours is 'H', a little less unstable than yours. It is costing us an extra $3500. Hope that gives you an idea of what yours might cost.
-mrsxtro.

Thanks guys. Probably nothing to worry about unless it's near a landslip area.

Personally, if it's a new estate I'd check with the council about two things: whether it's old landfill and whether any major drains/sewers have been laid nearby in recent years.

If landfill, there'd be no question - I'd have it retested purely for peace of mind. I'd also give it serious thought if sewers have been laid; even new ones can disrupt the local water table & alter stability. If the house is damaged by subsidence 'cos of drainage problems, you could sue and win... but IMHO it's better to not go there in the first place.

Originally Posted by clueless1

Hi all,

I've just signed a contract to purchace a block of land and received a soil test report done over 10 years ago (class, wait for it...P!!). My feeling is that one would need a current soil test for building. The thing is I really like this block of land even though it might cost a bit more to build on. Is it too much to ask for another soil test to be done?

TIA

"P" classifications are generally given to sites that have been filled using uncontrolled fill ie; fill that wasn't compacted in layers and tested as it was placed. It can also be used for sites that have several different subsoil types, eg; one end of the site is rock, the other end is clay or for sites that are heavily sloping.. All it means is that the engineer designing the footings has to make allowances for the specific issue(s) discovered.

As to whether it's worth getting it redone, it would depend on how trustworthy the original testing was. I have seen so-called soil tests that consisted of the "tester" arriving on site and simply driving a DCP (dynamic cone penetrometer) into the middle of the block. There should be at least 2 bore holes logged and, depending on what was found, possibly more. If there is a defined building pad, that should be tested for compaction if it has been filled. It sounds like a lot of work and it's a pain, but the alternative is to have the footing/slab designed for a worst-case, which will be considerably dearer still.

Yep I concure with exador on this as its best to be safe than sorry. I have to get soil tests done here for our deck even though the house has stood for 50 plus years. We live on black soil which extremely reactive. We had been in the house for 6 weeks and I had removed doors to shave bits off them to get them to close. Some houses Here in Ipswich have had to be under pinned due to the soil movement and the slabs giving way. A little bit extra for piece of mind in years to come can go a long way.

If you have a copy of the report clueless it will list the number of drill holes and the depth of each with the soil type (or rock).
There will be a recommended footing depth given to attain (100 kPa) foundation bearing pressure.
The extra cost on a class P site will vary depending on the flooring type.
A weatherboard home on stumps could have deep stumps spaced as far apart as possible with deep bearers & joists spanning big distances.
A brick veneer will need pylons down to bearing pressure spaced along the brick footings with the concrete strip footing poured on top spanning the pylons.
The last brick veneer home we designed on a P site had 4.5 meter deep pylons at 2.4 met centres around the perimeter, deep stumps internally with C purlins for joists spanning 4.2 meters.
Total extra on the footing cost - $17700

Take care & check it out thoroughly before signing.