Builder's soil report contradicts Level 1 compaction report

Sorry for the long post. We recently bought a land in Berwick Waters estate and we are in the process of building a ~28 SQs single storey home with Carlisle homes(CH). Initially we were quoted 18K as site cost and now we reached the tender stage and the new site cost is 31K. The reason for this site cost as per the soil report done by CH is due to "Poorly compacted silty clay" soil/fill which reaches to a depth of around 2.4m and hence they need to upgrade the slab to H1 class slab(~6k) along with additional steel screw piles(~20k). Also the soil classification is P as per the soil report.

However the Level 1 compaction report from the developer clearly says that the fill was compacted to meet the requirements. Quoting the test result in compaction report - "The compaction results show that the fill was placed and compacted at a moisture ratio between 88.0% dry and 119.5% wet of optimum moisture content and at a density between 95.0% and 106.0% of AS1289 Standard Compaction".

Is it possible that the builder is over quoting if the developer has done compaction properly or can we not trust the Level 1 compaction report from the developer. I have forwarded the compaction report to the CH and awaiting their response. However the CH’s consultant mentioned during tender that their engineers will not review the report or rework the cost unless we sign the tender and pay another $2k. We already paid $2k to get to tender stage!!! It would be great if someone could share their thoughts on this.

I'm not sure which party is right but the exact same thing happened to us. Our compaction certificate from the developer is all good however our soil tests came back as loose to medium compacted clay. We also ended up screw piles and 31k for site costs.

It is possible that both are right because the compaction tests by the developer and the soil tests by the builder are only spot tests in a few places so its possible the compaction varies across the site. That said if the developers earthworks were done to the specification and supervised like they claim I would imagine you could expect it be similar across the site, but I'm no expert.

We were forewarned that our builders engineers don't care about the compaction report they go by the actual tests that they do. However I am aware of a big builder in our estate that does accept them and people have had their screw piles removed by handing over the compaction report. I'd be asking some more questions to find out if their engineers care about the compaction report.

If you do have loose fill I would feel more comfortable keeping the screw piles. The cost sucks but you get over it.

Thanks bank . Much appreciated. Agree with you on keeping the screw piles if there is a loose fill. Will ask the builder for more information.

Developers reports can't always be trusted.It is a problem in the industry and some steps are being made to fix it.
I would rely on the engineers testing and opinion over a developer.Dynamic cone penetration tests are common in the soil tesing
industry and go some way to confirming the compaction of the fill.
No one but the engineer/geotech signs off on your slab design and ultimately bear most of the responsibility for that design so I am more inclined to trust some who has the head on the chopping block.

Thank you insider

Hi Guys,

I am in a similar dilemma, I am building with Mimosa and they are nulling my fixed site costs because there is a clause in the contract. My developer (manor lakes, lollipop hill Estate) did not provide level 1 compaction report because according to them there is less than 150 mm fill.

So Mimosa is saying that I have to pay for all the bored piers which are throughout my slab and are yet to give me a figure.

What does your soil test report say?

Bored or backhoe piers/piles should be founded at minimum depth of 0.6m into the Natural Silty Clay. An allowable bearing capacity of 250kPa can be adopted in the founding material at this depth. If used due to existing/potential abnormal moisture conditions, piers/piles should be installed to a minimum depth of 2.5m, or directly onto confirmed continuous bedrock (whichever is shallower).

What does your soil report log sheet says more than 150mm of fill?

I am not sure as it is difficult to read soil test report. my builder is saying it is 400mm. Now i am not sure why estate guys would lie to me.

If you can post the page with the logs I will have a look at it.
You have too much faith in the estate guys.