laying down astro questions

[Aaran]

Going to ask here so if anyone can help let me know.

our new track is being built and we are going to lay down astroturf. its mainly in regards to the base prep we need for laying astro down.

is it just a case of cutting off the grass layer then laying it on a flat soil surface?
or will we be better off laying down a rubble base and flattening it soild?
or is it just possiable to cut the grass down then flatten the land and lay the astro ontop? will the latter cause any growth issues with things growing through the astro?

we want to run all sizes of cars from 1/10th up to 1/5th on it (so for the smaller 1/10th we want and need a very smooth surface). we have a digger on site permantaly and a massiave 30ton roller (the wheels are bigger than me on this thing!)

jsut unsure where to start as we used to put astro down on our last track but it was forever sinking and rutting up when it forms to the surface of the base