Removal of concrete and sub base

cat-lady_2

Hello.  Grateful for comments on my project.
I've just had a lot of concrete taken out from my garden.
I now have a fairly thick layer of clayey sub-base left and not sure how much of that to excavate and remove.
It's a bit hard to figure out how thick the soil layer is on the adjacent lawn.
Am I right to think that I should try to dig a test hole, say, maybe a foot away to see how thick the topsoil layer is and then excavate to that depth?
Many thanks.

twopenny

Is it possible for some photos Catlady? Its hard to understand what you are up against.

Also what is your soil normally like?

It sounds as thought the 'clayey sub-base' is sub-soil which is what you get below the good top soil but then it sounds as though it's above the top soil.

Not really knowing but from what you've said I'd dig away a corner of the clay sub base and see what's underneath.

cat-lady_2

Hi, thanks for your comment, it looks something like this.  You are correct, the subbase is somewhat similar to subsoil found under the lawns.  It is not very obvious from the trench how deep the adjacent soil layer is because there was some mixing of the material.

twopenny

Looking at that diagram I would start by digging a small area of the subsoil adjacent to  the turf/soil.

See how deep it goes and how it breaks up. Perhaps you can add compost to the material in the sub base to give it a good consistancy and something for turf to get a hold of - or find out what it is made of and how far down you need to go.

If it's like sub soil thats easy enough to turn into a growing medium for grass.

That will give you more idea of what you are dealing with and the depth you need to prepare the area to.

cat-lady_2

It's a lot of very sticky clay with large stones,  it won't mix with compost.   It needs to be excavated and replaced with soil.
I did a test hole in the turf, and under the turf the soil layer is a good foot thick.  So it looks like I need to remove at least 9-10 inches of that horrid clay and stone mixture. 
I am surprised that concrete removal discussions do not mention removal of hardcore and aggregate found under the concrete.