Browse Forums Building A New House 1 Jun 05, 2015 12:06 pm Hi There, We are building on top of a demolished house site. The original house subsided due to uncompacted fill and poor drainage. The soil samples show uncompacted fill to 1mt depth. ( No idea why this would of been done it is a 10 acre flat block ) Class H1 - D, P. (lucky us) To compound this we need to raise the FFL 500mm as we are in a newly appointed 1:100 year flood plain. The engineering is massive, being reinforced raft footings continuously trenched 200mm into natural ground. The footing has been designed for uncontrolled fill. We need to bring in 500 Ton of fill. The builder has some fill but not enough from a development 25 kw away. They have included the fill in the price, but we will need to wait until they can get it all. Or we can pay extra for quarry rubble. We have a quarry 5km away that can supply: Quarry rubble @ $20 +GST a Ton Under foundation sand @ $12 +GST a Ton. The explanation of the under foundation sand, sounds like crusher fines. They say they sell it for specifically for that purpose. This would work out to be $6600. There is also limestone rubble available from another nearby quarry. A local builder had mentioned that this was good as a base. I thought it would still be quite reactive though? So my question is: What is the best fill to use on this site? If the builder was to say it will take 6+ months to get the fill, we will most likely pay the extra as we are in our rental property losing rental income, so it balances out. I would prefer to negotiate with the builder to use the under foundation sand instead of the fill as I suspect the fill will most likely be a high clay composition, as is most of Adelaide. Thanks for your time, Regards, Clayton. Our Build Here: viewtopic.php?f=31&t=74037&p=1255246#p1255246 Re: What is the best fill to use under slab? 2Jun 05, 2015 1:30 pm For raising the slab I would be going for good quality quarry rubble with controlled compaction. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: What is the best fill to use under slab? 3Jun 07, 2015 9:51 am Cheers for the reply, I agree the rubble is the best option, but a further 10k option. I gather the theory is the whole of the slab is supported on the trenched piers or continuous trenching. Which criss cross the whole slab and are founded deep down past the unstable fill. These will be some serious trenches being: 500mm for the raised FFL imported fill, 400 – 1000mm for the existing fill (bore logs, 0-400mm fill, 400-1000mm possible fill) then 200mm into the natural soil. = 1000 -1700 depending on depth of existing fill. So at that depth for the continuous trenched piers is it fair to say the only drama would be, if imported fill is super dry highly reactive soil that after the build becomes wet and creates heave? Other than that is the fill such a drama as the piers will be well founded deep down on existing more moisture stable soil? In any case I will ring the engineer and get some clarification. Thanks again for the input. Our Build Here: viewtopic.php?f=31&t=74037&p=1255246#p1255246 Re: What is the best fill to use under slab? 4Jun 26, 2015 4:04 pm No highly reactive fill not rubble or any loose material that will collapse during excavation and therefore lead to a change of footing type ie screw piles clean fill without concrete etc Clayey sand or weathered rock would be ideal but It might be expensive If you're in a flood zone, not only are you dealing with the importation of fill and laying it down in 150 lifts to achieve compaction, you're going to have to consider… 4 5533 Thanks for the insights, that makes perfect sense, and yeah, I will be leaning on the experience of the excavator operator entirely. 6 16147 |