For those of you that do subdivision work...How do you go about calculating earthwork volumes?
I'm not talking about the actual steps taken within Land Desktop to perform the calculation...more so the method used to arrive at your final quantities.
I have seen people simply calculate the overall volume and that's it (maybe with some manual calculation using area in roadway to subtract/add cut or fill at sub-grade or use a total area disturbed to calculate topsoil to be stripped) and then compare to a contractors quantity to see if they're in the "ballpark" and then use the contractors quantities for an engineers cost estimate.
Around here, we tend to be a little more particular. We have gone so far as to lower existing surfaces a certain amount to simulate a surface stripped of topsoil...or lower a proposed surface a certain amount to sub-grade and use parcels to calculate earthwork volumes within streets. We may choose to use a number of parcels in roadways and on lots to calculate volumes in different scenarios...i.e. Ex. Surface (adjusted for topsoil) -vs- Prop. Surface (adjusted to sub-grade) with 10% compacted fill in roadways, Ex. Surface (adjusted for topsoil) -vs- Prop. Surface with 10% compacted fill in areas from the roadway to the rear of building pads, Ex. Surface (no adjustment) -vs- Prop. Surface with no compaction in rear yards. It is not uncommon for us to take trench dirt into account as well. As you can probably imagine, this method can get a little "intense" sometimes (not to mention what happens if our quantity differs from the contractors).
Where we have run into trouble recently is when we model a surface to sub-grade (in roadways) for purposes of preliminary design...and then when the project is all but submitted for approval, we go back and perform final earthwork volume calculations and try to compare "apples to apples" and need to start all over again with the final proposed surface.
I am just curious to know what types of methods/processes others have used to calculate earthwork volumes for an entire site or a building phase within a site.
Also...if any of you have similar experiences with Civil 3D, what is the workflow like when trying to accomplish these tasks?