Compressible board under/alongside groundbeam

[Static]

Would be simpler to just go traditional strip footings into the natural chalk and not mess about with beam/pads, should only really need to go about 200mm if that into the chalk to hit the non soft stuff that needs a pick axe to shift..

But if your hell bent on pads then best to pour more conc than build up in blockwork.. less effort..
My idea of a ground beam is a reinforced concrete beam spanning between the pads.. just gotta ask what you intend.. and what span they will be doing?

In the end if your in chalk then you dont need to worry about clay heave/shrinkage.. chalk doesnt heave or shrink.. it does wash away or turns into a slurry when vibrated..

 

[Deluks]

Each pad if 400 should only need a single course of foundation blocks, 2-4 blocks per pad, no big deal putting those in.

I intend to put a pad under each wall pillar, clear spans to be under 3m per section.
Rebar cage was specced after a quick chat with the bloke at the suppliers who reckoned 200mm square cage using 4 T16's, 8mm link every 200mm, beam to be 300 sq once poured. This leaves the beam sitting just below ground level and I can start building up from there. Or would you better to keep on pouring until the top of the beam is level with the top of the hole?

Still think pads are better for me as I can do each section at a time, which is important given the fact that this is taking place under and around my current concrete sectional garage. Which is chocka with 'stuff'

 

[theoldun]

Duke Sorry I did not come back to you yesterday, but get trouble with me mince pies every so often.
I reckon you have got it cracked mate.
About the only difference I would have said to yer, is I know you are trying to save work, but I would have filled pads from bottom to underside of beam with conny, reason, you have only one type of material and one type of construction.
I would have stuck a couple of starter bars down pads and tied into cage. I would have said T20s, but if your man said T16s, he is dealing with rod every day and will know more than me.
I would have said a 300mm cage in 400mm beam but now I suppose I am a round head where as I used to be a cavalier when I was younger.
With regard to voids, if ground is chalky as you say, and someone did take the big hammer to them trees, Sycamores are only moderate drinkers, (what a terrible expression, to be only a moderate drinker) made me tremble, where was I , yea, that chalk will soon soak up any additional water that comes down . Regards concrete finishing below ground or level with ground, your choice, what ever is easiest.
Will be thinking of you this week end with your head down and your a**e facing skywards.
old un.

 

[Deluks]

Another forum user, 'Wirecharlie' posted some info last year regarding his extension, beams onto piling.
Was 300mm conc beam, 200mm cage. 3 t16s in the bottom and 3 t12s in the top, 8mm link every 175mm. However his was also taking the floor slab along with cavity walls. I'm only doing single skin block plus roof.

Appreciate your and Statics advice, and now thinking about making the pads another 8 inches higher and binning the blocks.
I was going to use a run of hollows with starter bars running through into the pads.
Still seems like a "six of one, half dozen of the other" scenario though, and remember I'll have to self mix the concrete.

Also thinking about a run of 12mm bar through the bottom of the beams, so the tensile face would be 50mm cover>T16>100mm space>T12>100mm space>T16>50mm cover.

 

[Static]

Sounds good but you need to reduce the links to 175mm centres.. beyond that you have it in hand..
Doesnt really need the extra T12 in bottom