im learning civil 3d, (and comparing it to my other older software) im needing to create a cut and fill report for a huge 1200+ housing and roads development which is on a steep hill site.

ive created a surface for the existing ground (EG) and also the surface for the proposed finish levels (FG)

now i can create a tin volume between EG and FG to get a rough idea on the cut and fill volume. However i need to get it more accurate, because its such a huge site even 50mm makes a 20,000m3 difference lol.

i have some questions:

first off i need to strip the toposil off the site, it varies from 300mm to 400mm in depth - i guessed at just lowering the EG surface by -350 on average, unless that is any other ways?

secondly, and most importantly, i need to account for the volume to calculate to the underside of the surface formation / construction build up of the FG

i.e. for a road it could be 600mm thick in hardcore/tarmac. Is there a way in civils 3d to specifiy certain areas of the site to have difference construction thickness?? for example, roads 600mm, gardens 200mm, buildings 300mm?

for example im looking for a volume, from the existing ground surface (-350mm in topsoil) to the underside of the construction depth of the proposed surface

hope that makes sense??