Please add a column for the user to enter a surfacing material thickness for the top surface within the Bounded Volumes areas of a parent volume surface, and have that accounted for in the parent volume surface.
This way a person could compute and monitor site subgrade volumes using the Volumes Dashboard . There is an important need for a straightforward way in the design software to compute subgrade volumes.
There is a need for civil software used in civil site work, to continuously monitor subgrade volumes for site earthwork balance, while the designer is designing the contiguous top surface (FG).
*Kudos that the Bounded Volumes update dynamically when their boundaries are grip edited.
Ernst Engineering Fred Ernst, PE C3D 2013 SP2, C3D 2014 Hot Fix 1 W7x64; i7 8gb; Radeon HD 5700 www.ernstengineering.com
Why not use a differential surface (paste proposed grade onto new subgrade surface, then raise/lower; remains dynamic to original surface)? It's not the same as a corridor model, but it does work.
For an actual model of plaza pavement layers, I've been thinking about making a subassembly that targets the proposed grade surface, where I can specify several material layers, such as pavers, aggregate, and fill. Using offsets and dividing the links, such that the top links target the proposed grade surface every 2-5 feet, depending on a user input (tesselation), I'll have a corridor that's dynamic to my design surface, which is dynamic to my site grading, and one that shows materials in sections view. Can't do that with differential surfaces.