Surface Volumes 301

A post in the discussion group today got my attention.  Calculating end area volumes based on your EG versus your Corridor Datum is easy and it’s explained in various publications including the Civil 3D tutorials, the Learning Civil 3D manual, among others.  There are often far more complicated calculations that need to be done, however.  Read on…

This is a longish post, so hopefully I can keep your attention.  Here’s the situation from the discussion group.  4 volumes are needed.

Backfill above EG – blue hatch
Backfill below EG – purple hatch
Type C – blue solid
Base removal – green solid


There are several techniques going on here.  One is the corridor itself.  The road, sidewalk, and wall are obvious.  The Red and Yellow lines may not be so obvious, but they are part of the corridor.  Another thing is the blue line.  This is a new surface used to calculate removal of base material.

  1. Create a new surface
  2. Paste the EG into it (not the two surfaces are idential)
  3. Attach an outer boundary to limit this new surface to only the road
  4. Lower the surface the required amount (now we have the bottom of the road structure to be removed)

Now, creating the red and yellow lines in the corridor is easy and I’m not going to explain that, but getting all the surfaces created is the fun part.  The red and yellow lines are Generic Links.  The cool thing about these links is that you can name the Links whatever you want.  Why would you want this?  Because it will make surface creation VERY easy.

The red line is actually two generic links; Link Width And Slope and Link Slope To Surface.  Here is what the properties look like for both.

image   image

Note the Link Codes are “RED”.  When you create a corridor surface you will see this code and it’s the only thing you need to add to the corridor surface…bam you’re done!

The Point Code for the Slope To Surface has been changed from P2 to Daylight.  All generic links have P2 as the code and it would have been impossible to use the Automatic boundary feature had I not changed this.

The yellow line is essentially the same except the Link Codes are named “Yellow”.

You need to create the Datum surface for the road as well.  For the wall I used the Link Slope To Surface.  I left the Link Codes as-is (Top,Datum), but I changes the Point Code to “Wall” so the surface boundary is quick and easy.

We now have 4 surfaces: Datum, Base Removal, Red, Yellow.  Ensure you sample all of these in all of your sections and you’re ready to calculate volumes.  You can use the Earthworks criteria that comes with the Civil 3D DWT’s or you can do it this way.


Civil 3D will calculate the quantity of material that exists Below the Red line and Above the yellow line.

Note that I have 2 different hatches for backfill.  Given the shape of the surfaces calculating it in a single operation can’t be done (I don’t think).  I needed to calculate below EG and above EG in separate operations.

Another more complicated scenario is this section:


Let’s say you want to calculate the volume within the grey cloud, bounded by the 4 differently coloured surfaces.  For argument’s sake let’s say the red line above is Rock, yellow is Yellow, blue is EG, and white is Datum.  Below is how you would set up the material.


Confused yet?  You might be, but given a little practise you’ll get it and then you can perform these complicated volume calcs in your sleep.

The poster in the discussion group asked for muck and rock surfaces to be calculated as well.  All you need are to create the surfaces and set up the sample line materials appropriately with the above’s and below’s in the correct place and voila.

Matt K

p.s.  If you’re interested in having a look at the drawing, click here.

p.p.s.  I don’t actually have the surfaces made for the complicated example above.  You’re not going to find that in the file.


  1. Dane Martin says:

    Great post! I just started on some volumes today that are very similar. Great timing. I liked the idea of how you got the surface for pavement removal and the generic links with point code names for surface & boundary creation.


  2. Neil says:

    It looks like you have the workflow figured out Mark. One thing that puzzles me is how you got those generic subgrade links to be tied to the assembly. They don’t seem to be connected in any way. How does that work?

    Once adjustment that might need to be made to the workflow: the subgrade subassemblies likely would need to follow the existing ground profile rather than being tied to the Roadway. How would you handle that?

    Great thinking though.

  3. Steve Boon says:

    You might have a problem with the four surfaces calculation Matt.

    The area to be included in the ‘Test’ material would be
    – Above the blue line (EG) AND
    – Below the Datum line (White) AND
    – Below the Yellow line (Corridor) AND
    – Above the Red line (Rock)

    The resulting area would be a triangle on the left side of your polygon, but would not include anything beyond the right end of the blue line.

    • Matt Kolberg says:

      Hmmm, well, I didn’t actually try it with this particular data set. Sorry if I confused anyone.
      It’s simply fixed by making one more material and specify the right half.

  4. Matt Kolberg says:

    I thought it would work. I tried it. Steve, this does work, but the surfaces need to overlap ever so lightly. For example, where you see the blue intersect the red, the blue needs to extend even 1cm past the red and it will work. In this example, same needs to happen with the white line. It needs to extend past the yellow a tad.