Browse Forums Building A New House Re: Pier depth for cut and fill site 3Dec 30, 2018 8:52 am Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Pier depth for cut and fill site 5Dec 30, 2018 10:40 am Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Pier depth for cut and fill site 7Jan 02, 2019 4:24 pm You have clay which turns into a mud when it gets wet. Piers means point loading so your slab is more or less semi-suspended as there won't be much of the compaction achieved on a clay material anyway. I would be considering alternative approach, if I were you, ie excavate and get rid of the clay soil up to approximately 700-800 mm level under your footings, put a well compactable clean fill such as a road base or crushed concrete or sandstone and compact it to high levels with compaction certificates being provided. This will create a reliable building platform for your footings and turn your H1 site into almost an A-class site. You will be able to save a lot of money on: 1) the cost of your footings as this approach will work fine with lighter footings; 2) thinner slab with less expensive reinforcement, e.g. 100 mm slab with SL82 reo, shallower edge beams. 3) you won't be requiring piering at all. But you would have to pay for more excavation, soil removal, clean fill and compaction. Also, if you consider 3D concrete re-inforcement fibers such like HelixSteel, you will be able to save many thousands on your steel and steel-fixing labour costs. So the costs have to be evaluated. But point loading on uncompacted reactive clay soil... Don't know if it is ever a good idea. Discuss with your engineer and see if it is viable option. When it gets to piers (if you really want to stick to them), each pier depth won't be determined by engineer or your soil testing guys but by the level of hard soil (shale) to which you can drill, so some piers may be 1400 mm or less, others 1800 mm or more. You only have to pay extra for the cost of additional concrete. Re: Pier depth for cut and fill site 8Jan 02, 2019 4:41 pm Ah, just noticed it is actually a waffle pod. Well, waffle pods are not recommended for highly reactive clay sites at all, you won't be able to achieve a good drainage on such sites (I personally wouldn't be recommending them even for moderately reactive clay sites too). Especially, when there is cut and fill too. In my opinion, this design is just asking for trouble. Re: Pier depth for cut and fill site 9Jan 02, 2019 6:25 pm Drainage can be achieved, you just need it sorted from day 1 until you take possession. Lots of yard drains, spoon drains etc and you should be apples. The builder and engineer will sort that out for you. Re: Pier depth for cut and fill site 10Jan 03, 2019 1:46 am sweetswisssteel Drainage can be achieved, you just need it sorted from day 1 until you take possession. Lots of yard drains, spoon drains etc and you should be apples. The builder and engineer will sort that out for you. I wouldn't risk as builders generally have no idea of what good drainage on clay means. Especially I would never go for waffles in cut and fill scenarios on reactive clay soils. Cornell Engineers strongly believe that waffle pads are "red light" for H1/H2s. https://www.cornellengineers.com.au/bew ... fle-slabs/ But considering that average Australian house has life expectancy of 25 years, this will probably work, anyway. Just my 2 cents. I should have followed up on this thread. So, the pier foundation wasn't large enough on the side it was leaning towards, and the NBN cable went through the pier, just… 8 10705 Just be careful with building stability during construction, that is when the structure may be weakened, refer to your engineering drawings for stability methodology. 1 6170 |