Civil 3D surfaces do not support vertical faces.
The steps in stripes.dwg were vertical. I offset the bottom of each vertical face 0.01 toward the center of the trench so there was no vertical face or overhang. I saved the drawing as stripes offset.dwg.
I suspect that stripes and stripes offset are corrupt. Selection all ([CTRL] [A]) shows 389 lines, 2 Xrefs 10 3D polylines and 1 polyline. A window selection shows only 132 lines.
I selected 1 lines, [Right click] ... Select Similar and Wblock the lines to stripes offset wblock.dwg.
Working with this clean drawing I selected all 132 lines and created feature lines on Site FG. There was a warning and only 131 feature lines were created. (I have no idea what the phantom parcel is.)
I selected all of the feature lines and added as breaklines to surface FG. I ignored the minor error at each end.
I temporarily turned off the display of triangles for FG. Then added lines across the top of the trench, shown in red.
I converted these lines to feature lines on Site EG. and added the resulting feature lines to a new Surface EG.
Compute the volume by creating a TIN Volume Surface based on FG and EG.
Drawings are attached (2020).
Good Luck.
Christopher Stevens
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