Foundations. deep strip or piling ????

[Big Jimbo]

Evening all. I've got about 41 lin mt of footings to pull, or have piled. I'm told by a builder who has just built  4 masonary barn style properties about 500m from me in the same lane that "Its good ground"

He dug footings at a 1m deep for 2 storey masonary. Happy days you might say. However, i have trees. 2x poplar, 3x oak, 2 x silver birch, and conifers cut to about 5 m in height. Boo Hoo you now might say.  I'm going to need about 10 m at 3m deep, and the remaining to be 2.5 m deep. I have not had a soil test done yet (See below) but i should find clay with flints,  silt, sand, and gravel according to British Geological survey web site. Dont know yet but may have to make the trenches wider, ie; 700mm and stick in some clayboard re clay. I've got a decent size rear garden, about 100ft x 200ft, so unless what i pull out is total crap, i could prob spread most of the spoil, over the site without making much difference, or have it carted away. I think that i could do the deep founds for between 15 and 20 k allowing about 4k for muck away. I've been told by the engineer that i sould be able to get it piled, and do my own ringbeam for similar money. I've dug plenty of founds down to about 1200mm with my mini digger, but never any deeper. Any body on here dug deep founds ? Is it a pain in the butt ? 3m is bloody deep, i know, 2.5 aint exactly shallow. Am i mad to even consider it ? should i just get piles and do my 450mmx450mm reinforced ring beam ?

If i was to get my own soil test (plasticity) done. (lab locally) anybody have any idea at what depth i should take the sample from ? or do i need to do several tests at various depths ?

Thanks in advance gang.

[Oz07]

2.4 ish pictured. Don't stand in them as pictured though. Was preferable in this case as rest of house 1.5m so saving to be made. You've just got to crunch the numbers and make sure to allow for everything you can. Piling matt etc

[Temp]

Would a reinforced raft foundation be an option?

[Big Jimbo]

1 hour ago, Temp said:

Would a reinforced raft foundation be an option?

The deep foundations do look a pain. I'm not sure about a reinforced raft. I have a look on the interweb and see if one might be suitable.

[Bitpipe]

We dug 3.5m for basement and that felt deep.

 

The survey was 10m probes and 5m cores.

[Russell griffiths]

Our piles where cheaper than I expected approx £350 per pile 6-7m deep

my ringbeam cost £7000 to complete but that was with me doing all the labour, but mines in excess of 100LM if you only have 41LM then that’s fairly small and should be only a few days work to do. 

[Big Jimbo]

Thanks Russell. Yeah i quite fancy having a go at the ringbeam.

[Judy C]

Anything over 2m deep and you are into major risks to you or anyone you employ in the trenches, and you'll need to plan to avoid those risks.

 

I would take a structural engineer's advice on how deep to take a soil sample from and be guided by them in the best approach.  

 

I expect a raft would be off the table as you need to take out 50% of the foundation depth, and that in the end piles plus ringbeam will be a good option.

[Mr Punter]

If you are able to do an insulated reinforced raft, there is a saving on the slab and insulation.  With piles and ringbeam or deep trenchfill you will probably need to have a beam and block floor.

 

Make a load of calls for muckaway quotes.  There may be a landfill site needing capping or a farmer with a field depression he wants to raise.

[Jeremy Harris]

Our build was on fairly good ground.  For an insulated passive slab we only needed to excavate down 200mm over the whole area of the slab, +10% (I think) and lay compacted layers of stone down.  The insulation went directly on this, then the steel was tied in, along with the UFH pipes, and the slab poured and power floated smooth.  4 days work for a ~85m² slab:   http://www.mayfly.eu/2013/10/part-sixteen-fun-and-games-in-the-mud/