maintenance of P-Class soil

hardy · Feb 27, 2007 3:48 pm

Hi all,
We are currently building my new home in South east of Melbourne and soil of my block is classfied as "P". Although developer claiming that block has been comapcted upto 95% of M class soil and block should be treated as M-Class or H-Class. but builder doesn't accept their claim and classified as "P" class. I understand builder concern because they have to give 7 years gurantee for the house. My question is if you build double story house on a "P-Class" soil block, does it need any special attention/maintenance in a long run. Once house is finsihed and handover to us, Do we have to do something around the house so that movement of slab will be minimal during weather condition change and keep the house intact. We will appreciate if anyone know how to keep "P-class" soil maintained and give us advice. Thanks is advance..

Regards,
Hardy

Vlad76 · Feb 27, 2007 3:56 pm

The block I am about to build on has been identified as P class as well, and the independant engineers have recommended screw in piers to be used to reinforce the slab.

This adds the cost to the project, but we're being told that once compete, there should be no issues going forward.

Casa · Feb 27, 2007 7:02 pm

Vlad,

I'm interested in hearing more about screw in piers. Are these piers that are screwed into the slab? Or is it steel reinforcement that links the pier to the slab? Anything special at the base end?

Cheers,
Casa

ausdesign · Feb 27, 2007 9:31 pm

Hardy, a P class site, as it seems to be the case with yours, is normally classified as such when there has been deep fill placed on the site. The classification is nominated by the Geotechnical firm providing the soil test. It is not provided by the builder.
The foundations will be designed by a structural engineer to ensure that there is the correct 'support' for your home.
Because you have a class P site does not necessarily mean that you will have any more problems than a more 'stable' site. You may possibly find that you have less movement than you would find with a class E or H site, as any soil expansion & contraction relates to the amount & type of clay in the soil.
The CSIRO Division of Building have iformation on home owners foundation maintenance which may be worth reading through.

epiphany · Feb 27, 2007 9:51 pm

We were in a similar situation. Our developer insisted the soil test would come back as H. We had one done as part of our contract (we were the first purchasers to do so)...lo & behold, it came back as a P.

Given the cost of our land, we were quite disappointed...but weren't expecting the reaction by the developer. They were furious & sales of the subdivision were put on hold until they got things sorted with the company who had been contracted to do the subdivision.

It turned out, the contractor hadn't filed the necessary compaction reports with the council...so when the soil test people went to find a compaction report, it wasn't there. In absence of such a report, they had to classify the site as a P.

Once the mistake was sorted, another independant soil test was conducted (this time right across the subdivision, not just on our property) & the site was reclassified as an H.

You might just want to check that all the necessary paperwork has been done - especially if the developer & the soil test people are saying different things. Good luck!

Vlad76 · Feb 28, 2007 9:06 am

Casa

Vlad,

I'm interested in hearing more about screw in piers. Are these piers that are screwed into the slab? Or is it steel reinforcement that links the pier to the slab? Anything special at the base end?

Cheers,
Casa

The piers go into the slab and are supposed to reinforce it - that's my understanding of it.
They don't have to be screw ins in theory, but apparently what often happens is once a hole is drilled, the soil simply fills it immediately. In such a scenario screw ins are the only way to go.

elchagie · May 30, 2009 12:21 am

my soil test cane P -class which is bad ,my drafty told me the engineer maybe will design piers in every 3.5m in foundation depth of each them about 2.5 m wich will cost to much money ,any one could advice me what I should do? what are the cost for this piers ?do I should keep going or I forget about my project and sell my land ? need urgent advice please .

I feel like I'm lost .

mjl · May 30, 2009 1:31 am

We had our block come back a "P" and I was actually onsite with the Geo-tech when he conducted his tests. With our land we had some rather large trees removed from the site and this causes your soil test to result an instant "P".

There was a time when we were going to sell up and take a $2000 loss with the preliminary contract and accept defeat. BUT!!!! I can assure anybody going through this that if you love your land stick to your guns.

With the knowledge and resources available to engineers you should try not to get anxious as we did. (hard to do but it is possible)

Finally to screw piers... we have actually had them installed with our slab design and they simply screw into the earth below the slab at around 3 meters deep and they pour the concrete over the top. They are designed to help with the Australian conditions with extreme dry spells and then crazy wet weather.

The only issue with a "P" class site is the fact that all builders will charge you more to build your home, but if your block is priceless like ours... what's another few dollars...

Best of luck...

kek · May 30, 2009 11:18 am

hardy

Hi all,
Although developer claiming that block has been comapcted upto 95% of M class soil and block should be treated as M-Class or H-Class. but builder doesn't accept their claim and classified as "P" class.

Did the developer not provide a compaction report? I don't blame the builder for not accepting a verbal statement, but if there's a controlled fill certificate, that could help to lower the cost.

We got a copy from our developer and sent it to our builder, and while we still needed an H-class slab, the need to pier the entire slab was removed, which reduced our site costs significantly.