What do each of the Volume Options mean for the Mesh Property Feature Definition?
None - The mesh/terrain is totally ignored when the earthwork is computed. This is good for items like structures. There is no fill under a bridge.
Design - Mesh/Terrain(s) that are proposed design. The cut fill tool finds the bottom of all elements that have a Feature Definition that has volume option of Design and compares it to existing ground.
Existing - Finds all Mesh/Terrain(s) that are Existing and formulates a composite mesh sheet for earthworks. Typically, the existing ground is a Terrain(s).
Substrata - Volume option is for a geotechnical tm/mesh. The Cut/Fill tool will take this in account when toggled on. It separates cut meshes into 2 distinct meshes so a volume can be formulated for the "substrata" and normal cut so one can get distinct volumes for each.
Cut - Volume option is for the resultant Cut mesh created for the Cut FIll tool. Do not confuse this with template end conditions, these items are Design, as they were since the conception of ITL and the Roadway Designer.
Fill - Volume option is for the resultant fill mesh created for the Cut FIll tool. Do not confuse this with template end conditions, these items are Design, as they were since the conception of ITL and the Roadway Designer.
Unsuitable - Volume option is for items like Muck/Swamp/Existing Pavement that is needed to be removed. The Cut/Fill has a toggle to include this. This will in essence modify existing ground by taking the unsuitable material out. But the material is broken into 2 meshes-Remove Only & Remove and Replace. One cannot build a road on a void.
Custom is an extension of unsuitable but different. This allows you to model the likes of structural excavation in your template, so you can get a volume for backfill. but it allows you to get 2 volumes. One for the volume of existing ground that needs to be removed to fit this and a volume of this backfill does not need to remove existing. This is done to quantify the two items since their costs are different, the cut/fill tool has a toggle to take this in account.
Subgrade - Volume option is from the old InRoads realm. This was done back in the day for As-Built surveys. The logic is still there for TM to TM here but this item is not needed in the ORD realm but can be handy for old data.