Deciphering engineering plans to get an estimate of concrete required

Hi guys,

I'm up to the stage of contacting concrete/excavation companies to get a quote for my slab for a shed build.

Shed build thread for reference: https://www.renovateforum.com/f83/wh...-build-129772/

I got the following engineering report for the slab 12M x 12M slab:



I noted that the edge beams and internal beams need to be 300 wide by 800 deep min.

The note of "all footings shall be founded 100mm into the natural silty clay. Here is the soil test to clarify:




My question is: Am I correct in thinking that all the footings/beams need to be 900 deep ? (minus the hatched beam going down 1500). I also noticed that saw cuts were not mentioned in the engineering plans.

I calculated concrete at a total of 27.7m3 for the footings and 14.4m3 for the 100mm slab on top.

I assume it would go something like:

200mm cut to remove 'surface soil'
300mm x 700 deep footings after cut
fill/compact/box up etc
vapour barrier/mesh etc
pour

It's been quite difficult to even get a quote in Melbourne as everyone is flat out due to covid demand I guess. Figured I'd try to make it a little easier for concreters to give me a quote if I can give them a little more information other than all the plans/engineering/soil tests etc.

Cheers