Drive Sub base how deep ? , how many layers ? Do I have to go to go down to clay ?

[DavidEast]

Hi all ! could you advise me on the following please.

I'm looking at a parking space & drive , according to your site , its recomending 2 layers of 75mm each compacted seperately, for heavy duty traffic , mostly light vehicles but occasional heavy vehicle so thats why I am doing it at 150mm,

but what sub base aggrigate would be most economical and do the job.

1. will I have to go all the way down to clay ?
2. if I do I may need 200+mm of sub base would this be right to do?
3. or can i lay sub base 150+mm on soil ?
4. which aggregaretes should I use for each layer to keep it economical ?

C35 concrete going on top.
Thanks