Does anyone know much about compaction reports?

Our block has a fair bit of fill and a bit of a slope too - soil test came back with a P classification. Before buying the block we spoke to the neighbours (whose blocks have a similar amount of fill) and we got a good idea of how much they'd had to spend on site works and slab. We were actually able to negotiate for the developer to do the site cut for us as part of the purchase price of the land which'll save $$. The builder doesn't normally allow it, but in this case they were happy because they know his work. The plan was to get the preliminary contract, do the site cut, do a secondary soil test to check that everything was good and nothing much had changed from the original soil test, and then get the contract finalised.

But in the prelim the site works/slab upgrade turned out to be a bunch more $$ than we were expecting - about double that of either of our neighbours (one of whom has been using the same builder). We were told that the soil report was a bit surprising and that perhaps the tester was just a bit over-zealous. They said that if a compaction report was available and the fill was nice and stable, then that could drop the slap upgrade cost by a couple $K. When the developer was approached about a compaction report apparently he said there was no point in getting one done before the site cut because that'd change everything.

We've now been told that a secondary soil test is probably unnecessary and that slab costs won't change. I don't understand why the story has changed but I suspect that the people making the decisions haven't invested any time in looking at our situation. I'd like to find out a bit more about what a compaction report might show up and whether anyone thinks there is a possibility that, once the site cut is done, a soil test would lead engineers to rethink the preliminary plans, and maybe even reduce costs. Any ideas???

We just don't want to have to pay for unnecessary slab costs.

the builder charge us under $300 for the soil compaction report. This would be way cheaper than an over estimated site cost of thousands. In our case it did bring down our site cost significantly from over $27k to about $7k

Sorry I can't help you with any information, but I want to wish you all the best in getting this resolve in your favour. Umm where is TDL?? He might be able to explain to you about engineering stuff.

Thanks Fruitty & Polo for your responses! Wow - $27K to $7K - that's amazing! Well done

Our site cut is scheduled for this Saturday, weather permitting, and a secondary soil test is booked for early in the week. We'll see what that shows up, and then go from there, I guess. Got my fingers crossed

The different stories you are hearing may relate to the type of compaction report in question. A retrospective report done post fill/compaction wont be accepted by many builders, they want one done during the fill/compaction process at various stages. I'm sorry I forget the name of these 2 versions of the report.

Basically we had the same thing happen, we had a post compaction report saying the fill was more stable than the original ground, but alas too bad so sad for us, the builder wouldn't accept it as it wasn't done during the fill/compaction process. Had we had the right sort we would have saved $8K.

In the grand scheme of things I don't mind, our house wont be sliding down the hill any time soon!

Thanks heaps Aqua! That does clear things up a bit for me. What a pity you weren't able to knock that $8k off the costs. But like you said, at least you can be confident that your house is solid!

Because the developer is the one who would have done the original compaction, and because he seems to take such pride in his work and do a really good job, and because the neighbours didn't have to pay as much as we've been quoted, I can't help wondering if what we're getting is going to be a bit of an overkill. Which would be fine if we weren't on such a tight budget. Oh well, we'll make it work if we have to.