How deep is deep enough?

[Dusty2017]

Hi

I've bought the book and read the website and forum pretty extensively, amazing resource thank you!

I've just started to excavate the front of my house for a block paved driveway.

Plan is 150mm hardcore 40mm bed 50mm blocks.

I've excavated approx 250mm all around below final pavement level. My question is when can I determine if I have hit robust enough ground to lay the hardcore?

I've read I should excavate soft spots further what defines a soft spot? Is there any test I can do to determine if the ground I have reached is deemed hard or soft?

Sorry if this is answered in the forum already I have been searching.

Thanks
Matt

[seanandruby]

You should know when you hit firm sub soil.
soft spot is what it says on the tin...soft. If your In any doubt you can always use a membrane. Make sure all organic material is excavated.

[lutonlagerlout]

sub grade usually loses the dark humus rich colour of topsoil,so it could be white ==>chalk or orange ===> or it might even be sand
LLL

[Tony McC]

If you leave heel marks in it, then it's too soft. This assume you are wearing work boots or similar and not your stilettos!

[Dusty2017]

Thanks for the responses.

Think part of my problem is I dug it all out and then the heavens opened for 2 days straight.

It's all dry now and I leave no indentation when walking on it with a pair of work boots.

I've hit chalk in places so I guess it's far enough.

Planning on using a membrane but first filling in the craters with type 1 and compacting before laying the membrane is that wise? Then 150mm type 1 on top to bring me to the right level for the bedding coarse.

[seanandruby]

Sounds good to me dusty. Place the mot in 75 ml layers compacting each layer to refusal.