Volumes Can Be a Delicate Balancing Act

What a catchy title 😉

OK, many people have asked about balancing proposed surfaces in Civil 3D. So far, I’ve found how to do this, but I’ve had mixed results actually doing it. In other words, it crashes. A lot. I’m hoping this is fixed in the upcoming service pack.

So let’s look at what I’ve got – I have a 6 lot subdivision with an existing surface in it. I’ve imported some 2D polylines in that represent building pad locations. I’ve converted those polylines to feature lines, assigned elevations from my surface, and elevated the feature lines to the building pad elevation. I’ve also graded these building pads to the outside. One issue that I ran into when doing this is the face that create grading infill doesn’t seem to work correctly. I’ve worked around this (somewhat) by grading to the inside at a very small relative elevation and very steep slope. 0.05′ at a 1:1 slope filled in the inside of my grading quite nicely. This gives me a complete surface to balance. So here comes the fun – you can see where we’re starting:

Before we start, let’s do a quick check of the volumes here. To do this, go to Surfaces>Utilities>Volumes. Select your base surface (EG here) and your comparison surface, and it will do a quick check of the volumes for you:

OK, to get started, let’s go to our Grading menu. Next, select Grading Utilities, and then Grading Volume Tools.

This will bring up the following window/toolbar:

The first thing we need to do is select the grading group that we’re trying to balance. Note that this will only work if you already have a grading group defined and graded.

Now, we have two different ways that we can balance our volumes – we can input a value and raise/lower the surface manually, or we can automatically balance the surface. Here’s a screen shot showing how to raise/lower the surface manually:

The other way is to automatically balance the surface. This will bring up indow that asks for the required volume – set it to 0 and it should balance the volumes:

Please remember that grading, whereas more stable than 2006, is still buggy. I have issues with it every day. This may work for you, it may not. As with almost everything in Civil 3D, please save your drawing before performing any functions that require intense calculations (and boy, does this one require intense calculation).

Have fun!

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