If I have a site that I want to grade using two different configurations whats the propoer hierarchy of everything? I am confused as to sites-grading groups-surfaces and how they mesh.
Concept A - Site with FFE of 471
Concept B - Site with FFE of 465
Due to the way C3D utilizes topologies I recommend you prepare each model in separate files. Every featureline must reside in a site and a featureline can only belong to one site, so you'll have to create 2 sets of data. To try to do it all in one drawing would be impractical.
I should mention that you'll want to store the existing terrain surface model in a separate drawing and use data shortcuts to share it between the design drawings.
If I can ask a question - What would happen if I just used two different "finished" surfaces and used volumes based on a comparison between each and the existing surface?
That is typically the way to compute volumes. Did you have some other approach in mind?
You can do it that way, but the surfaces do not have to be in the same file. I would create concepts A and B in separate files, each with it's own finished surface. Then I'd create a 3rd file and use shortcuts to all 3 surfaces for comparing the volumes.
If on 2013 or 2014 use the Volumes Dashboard on Analyze Tab of Ribbon and Create a new volume surface using your EG as Base surface and proposed as comparison surface. Volumes Dashboard is also available as a subscription extension add on to 2012.
Note: you may also want to offset the Floor surfaces downward to account for actual excavation limits.
Merely comparing EG to FFE won't include total excavation ie: subgrade excavation etc.
I agree 100% with separate files. It makes things nicer and cleaner moving forward. Less Fline/grading management.
All surfaces can be D'refed into an analysis file for comparison.
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