Configuring Grading Limits in AutoCAD Civil 3D

Frequently, I am asked, “How would you grade a site?” There is no set answer to this question because it depends on the site. A common place to start would be to establish your grading limits.

You may already have a closed polyline representing your limits of disturbance which is where you will be matching existing. Convert the polyline to a feature line:

1. From the Home tab > Create Design panel, click Create Feature Line from Objects and select the grading limits polygon.

   

2. In the Create Feature Lines dialog, you can name the feature line and apply a style to it as shown below. If the polyline is disposable, you may check the box next to Erase Existing Entities.

   

3. With the Assign Elevations checkbox filed, click OK and the Assign Elevations dialog opens. Select From Surface and use the dropdown to select the existing surface. Do check the box next to Insert Intermediate Grade Break Points. This will add elevation points to the feature line where the grade breaks occur which happens to be where surface triangle lines intersect with the feature line. Click OK.

   

   At this point, we can create a new finished grade surface and add this feature line. This in effect will level out the site.

4. Select the feature line and on the contextual ribbon > Modify panel, click Add to Surface as Breakline.

   

5. In the Select Surface dialog, click the Add button to create a new surface.

   

6. In the Create Surface dialog, enter a name for the surface, select an appropriate style, and click OK.

   

7. In the Add Breaklines dialog, you can enter Grading Limits under Description, ensure Type is set to Standard, and under Supplementing Factors, with Distance checked, enter 25’ in the field below. Any gaps between elevation points and vertices greater than 25’ will get a supplementary elevation point along the segment. Click OK to finish.

   
   At this point, if we truly wanted to level the site out, we could add grading to grade up to an elevation.

8. Select the Grading Limits feature line and on the Launch Pad panel of the contextual ribbon, select Create Grading. The Grading Creation Tools toolbar opens.

   
   To grade to an elevation, you will want to use some criteria that is configured to do so. If there isn’t one available, you can create one by doing the following:

9. On the Grading Creation Tools toolbar, click the drop-down as pictured below and select Create New. The Grading Criteria dialog will open.

   

10. In the Grading Criteria dialog, click over to the Criteria tab. Change the Target to Elevation, and configure a cut slope and fill slope value. You can click the Information tab to give these new criteria settings a name, then click OK to close.

    

11. On the Grading Creation Tools toolbar, click the Create Grading button as shown below.

    

12. You may be prompted for a site and a grading group name. Grading Groups and Feature Lines must exist in the same site to work together. More than one grading in the same group can be used to create a surface if needed.

    

13. After the dialogs for selecting the site and naming the group have been satisfied and dismissed, you will be given a pickbox for you to select the Limits of Grading feature line.
14. After selecting, you may see the Grading – Weed Feature Line dialog. Click Continue Grading without Feature Line Weeding.

    

15. When prompted to select a side, click inside the closed feature line.
16. Respond to the prompt Apply to Entire Length with Yes.
17. Next you will be prompted for the absolute elevation to grade to. Enter that value at the prompt and press Enter.
18. Next you will be prompted for the cut slope, the default value being what you initially configured to the criteria. You can press Enter to accept that default value.
19. Next press Enter to accept the default value for the fill slope.
    You will see a slope projection appear representing your slope grading. This slope projection consists of a feature line running almost parallel to the original feature line that is on the elevation and placed at the slope configured to the criteria. This feature line will maintain a dynamic relationship with the Grading Limits feature line.

    

20. Click the grading projection feature line and using the contextual ribbon, click Add to Surface as Breakline on the Modify panel.
21. In the Select Surface dialog, choose the finished grade surface and click OK. Click OK to accept the defaults in the Add Breaklines dialog.

You now have a leveled surface to work with.

If you need to change any of the criteria properties of the grading, you may select the grading’s diamond glyph and on the contextual ribbon, select Grading Editor. This will open the Panorama and present you with an interface for you to change the target elevation or the slopes being used to define this projection.

At this point in your grading, you may create a cut and fill analysis with this surface and the existing surface to see where you are. You can add slope or elevation labels to give you feedback. Any other gradings, feature lines, or even points will cause the surface, labels, and volumes to update.

– Cyndy Davenport