Concrete garage base

[jstrong]

I have an existing L-shaped shed base approx. 3-4 inches thick.

I want to square it up and thicken it in readiness for building a timber double garage.

My thinking is to create a rectangle first by infilling the 'L' to create a 3 inch rectangular slab.

I would then lay a dpm over the rectangle and add a further 3 inches to the whole slab giving a min of 6 inches in total.

Does this sound ok?

Any thoughts or advice appreciated.

I am also thinking of adding a pit so any thoughts on how to do that would also be appreciated.

 

[theprinceofdarkness]

The L shaped bit has been compressing the soil for years, it is important that the new rectangle is sitting on fully compacted soil +hardcore.
Normally garage bases are laid with a 8" deep times 12" wide edge to the foundation with thinner concrete in the centre. This is to stop the soil moving outwards. Your set up sounds a bit marginal, I reckon it will crack, but should be useable.
Frank