Cut and Fill Table different from Surface Volume

[m_kingdon]

Hi all,

A colleague is working on a cut and fill surface.  The surface is all fill.

The volumes added up from the elevations table do not equal the total volume of the volume surface.  This is because the elevation table is starting at 0.45m elevation.  The difference is 709m³ (table) vs 945m³ (surface properties)

I think I understand what Civil 3D is doing, but I can't really explain it to my colleague.  I assume the 0.45m is the minimum difference between the two surfaces and Civil 3D is generating a table from that elevation and below?

I assume we should trust the table and not the total surface volume?

[bstrandberg123]

No, do not trust the table, something is wrong here.  At your match between existing and proposed, the elevation of your volume surface should be 0.  Only way it would not is if you were not matching elevation exactly and filling up to the edge of your surface.

I would check the surface analysis and make sure your first region starts at 0 and goes to 0.70m.  I would also check you are not missing any on the topside (above 2.93)

[cwr-pae]

The surface volume is the more accurate. The table should be based on the volume surface and has errors introduced by rounding each elevation range. Also if the table is 'cut off' from reading the lowest elevation range of the surface it will be inaccurate from leaving that area out. You can manually set the minimum elevation in the surface properties, as well as the elevations of each range.

[tcorey]

You can tell the table is messed up by looking at the first row. You can't get 132cm of volume from an area that is 0sm.

[m_kingdon]

I haven't had a chance to fully investigate this issue.

To sum up my thoughts on this issue: it is just a case that Civil 3D wasn't really designed to produce cut and fill tables when a volume surface is generated by two surfaces than never intersect?  And in the scenario where you want to produce a "fill only" table you need to remember to set your own datum?

Or, could the issue be the result of some near-vertical faces on the design surface and that both surfaces are basic and don't contain many triangles?

Base surfaceTop surfaceComparing the two surfaces