Cross Sections and Volume Tables

In this post I want to spend a little time with cross sections and computing material and earthworks volumes from the cross sections. I have been using AutoCAD Civil 3D for quite a while now and I have to admit that what I am going to show you next is something that I have not used before, and frankly never thought to ask, "What does that do?" Let's assume that we have created our corridor model, you know existing ground surface, alignment, profile from surface, proposed profile, and assembly. In the process of creating the corridor we also created our Top and Datum surface from the corridor model. In turn we used the boundaries feature in the Corridor Properties dialog box and added boundaries to each of the surfaces at our daylight line.

Then we start to look at our corridor sections and we see something that just doesn't look right. For some reason out datum surface has jumped from the bottom of the subgrade at the edge of the travel way to the top of the back of curb and back down to the extended subgrade. As seen in this image, the datum surface is jumping all over the place.

We know that this is not correct. So, how do we fix it? It just so happens that there is a very simple fix to this issue. All we have to do is open up the Corridor Properties and click on the Surfaces Tab. In the table showing our surface definitions we see that there is a column called Overhang. This column is the correction for the jump in the surface shown above. This is what I had been missing!

By clicking in the Overhang column for each surface, we can tell Civil 3D how to "correct" the jumps in our datum surface. By setting the Overhang for the Datum surface to Bottom Links, the software forces the surface along the bottom links of the assembly, something we probably thought was happening automatically. After setting the Overhang corrections, we simply rebuild the Corridor Model and the surfaces are updated. We can use the View/Edit Corridors Function to verify that the surface has been updated. This image shows the corrected Datum surface.

Here we can see that the Datum surface more closely resembles how a contractor would construct our roadway with a 1 foot extension of the sub-base under our curb and gutter.Now lets talk about material and earthworks volumes based on our cross sections. We are going to assume that at this point that we have created our cross sections from the alignment associated with our corridor model and that we have created multiple cross section views on a D-size sheet. At this point we realize that we forgot to add the volume tables to our cross sections. Can we fix this rather easily? You bet we can.

First of all we have to go to the Sections pull-down menu and select Compute Materials. Make sure that you select the Alignment for which you have cut cross sections and the Sample Line Group for that particular alignment. This will bring up the Compute Materials dialog box. In the Compute materials dialog box there is a drop-down for Quantity Takeoff Criteria. It depends on the final output that I am looking for as to which criteria I select. In this instance we are going to select Material List.

At this point I will edit the Material List Criteria to make sure that have the materials listed that I am interested in, such as Pave1, Pave2, Base and Sub-base. After setting the materials that I want I click on OK to close the Compute Materials dialog. Next I go back to the Sections menu and select Compute Materials again.

I want to click on the Import another criteria. This will allow me to add additional criteria to the current materials list. Here I want to select Earthworks so that we can calculate the cut/fill volumes at each section.

Here I can set the cut/fill factors for the soil if I know what they are. Once I have added the Earthworks Criteria I click on OK to close the Edit Materials dialog box. Now I need to add the Volume Tables at each cross section. To add the tables, I am going to click on a grid line for one of the cross sections, then right-click and select Section View Group Properties.

Click on the ellipsis button in the Change Volume Table column. This will bring up the Change Volume Tables dialog box. In this dialog box I want to select Total Volume from the Type drop-down. I want to select the Table style to use, in this case I am using the Basic Style. Click the Add button to add the table definition. Then I want to make sure that I select the corresponding Material List from the pull-down in the table definition. Then I can set the location of the table using the section view and table anchors.

Then click on OK and you should have your volume tables attached to each of the cross sections. One caveat here is that when you add the Volume Tables to existing cross sections, you will probably have to go back and edit the spacing of your sections. So, you may have a little more work to do, but it is automated by editing the Section View Group and the Array on your Group Plot Style. Remember that you can create the Volume tables as you create the Cross Section Views, but you have to compute the materials before creating the views. Here is an image of a completed section with a volume table.