Back in December, I had the honor of spending a week in Manchester with some awesome Autodesk and non-Autodesk folks. We of course spent a lot of time talking about Civil 3D and out of that came one of the most ingenious ideas I've heard in quite some time. Creg Dieziger of Morrison-Maierle came up with a really nifty way of including material depths when doing your volume calculations. It goes something like this:
- Create polylines that enclose each type of material that you have. In the example below, I have light duty pavement in yellow, heavy duty pavement in green, and building basement in red.
- Offset each closed shape inward just a little bit (I used 0.01).
- Set the elevation of each polyline equal to the depth of that material. For example, heavy duty pavement that has a depth of 1 foot will be a polyline at elevation = 1.00. Sound weird? Stay with me, this is like the part where Mr. Miyagi wants Daniel to wax the car.
- Create a surface for each type of material that you have using the polyline as both the breakline and the boundary. I used a supplementing factor of 10 and a mid-ordinate distance of 0.1 when I did this.
- Paste all of the individual material surfaces into one common surface. I named mine "Material Depths".Step 2 is necessary because of the abrupt elevation change where two materials meet. Without the offset, they will just blend together at the edges.
- Create a TIN volume surface (I called mine FG-Materials) using your "Material Depths" surface as the base surface and your Finished Ground surface as the comparison surface. The elevations of the resulting surface will be material depth subtracted from FG - Get it!?
- Next, create a new surface (I called mine "Adjusted FG") and paste the TIN Volume Surface into it. Again, weird...this is the part where Daniel has to paint the fence.
- Now you can perform a volume comparison between Adjusted FG and EG and you'll get a result that automatically subtracts out the material depths! (this is the part where Daniel sees how it all works.) The reason for step 7 is that you cannot do a volume comparison with a volume surface - it has to be a "regular" surface.
If you have to read through this more than once, don't feel bad. I had to read through it about 10 times to make sure it made sense to me. But...once you get it, it works! And the beauty of it is that once you create the "Material Depths" surface, you're done...you don't have to create it or adjust it again unless there's a specific design change that warrants it. You are free to play with the FG elevations to achieve the slope, drainage, and/or volume targets you're trying to achieve. Just remember to set everything to "Rebuild Automatic".
Try it out and comment on how it worked for you.