Backyard ob pier slab specs?

[2stroke]

Backyard ob pier slab specs?
Heya guys I'am looking at doing a backyard pier for ap work. I later plan to build an ob around this when funds permit. I have gone over a large lot of styles and design specs, what has me stupped as the ground block and what works best. I have herd of people using a full m^3 sized block but to me this seems stupid due to soil change, settling and the fact its going to sink unless your living on rock. So what specs are you guys using for your backyard ob pier slab base, for something thats going to have a eq6 with a 10 newt and your ap gear? BTW i'am talking about just the pier base/slab not a ob slab, I plan to isolate the ob foundations a good 1 meter away from the pier base/slab.
http://www.iceinspace.com.au/vbiis/images/misc/progress.gif

[sheeny]

My pier footing is 350 x 350 x about 750 deep (it was going to be 1000 deep but I hit rock). It is isolated from the obs slab which I walk on so the scope doesn't move whe I do.

The deeper the footing goes the better (within reason)... increased ground pressure makes the footing more stable.

Al.

[2stroke]

Cheers Al.

Thanks for sharing your specs wish i had rock but its a clay bed down there for me. Have you noticed any sinking or movement with your specs?

[Marke]

I went 700x700x 1m mostly clay , it aint going to move and imho the more mass the less noticeable any movement or settling but thats why you use
an adjustable to plate.

[2stroke]

Cheers mark, thats half a cubic meter of concreate thats working great on clay cheers. 1 full cubic would be great to hear from though i think its to much overkill and sinking would be an issue with that volume. Was more worried about the slab sinking feet not mm hahaha and thats my main reason for asking.

[sheeny]

No I haven't noticed any movement. Gotos are spot on and tracking is likewise. Haven't actually checked alignment, but if the gotos and tracking are fine why bother?

It won't matter how much concrete you use, if you are over clay, it will move as the clay dries out or gets wet with the weather. Not much you can do about it... it just means you'll occasionally have to give your alignment a little tweak.

Al.