Grading (Platforms) (Civil 3D essentials)

Create Grading

Grading objects are mainly created by using Feature Lines. A feature line is a line type object which is more powerful than a polyline or a line.

A feature line can either be drawn or created from an existing object. To draw a feature line, in the ribbon, go to Home – Feature line and use the Create Feature Line command.

The following method for grading objects creates a feature line from an object.

1. Draw a rectangle which represents the future platform (using the polyline or rectangle command):

2. Convert the rectangle to a feature line by going to Home – Feature Line in the ribbon and selecting the Create Feature Lines from Objects command**.**

3. Specify the feature line's Style and select the Assign Elevation option:

4. Select the NGL surface to assign elevations from:

The image shows the created feature line:

1. Feature line elevations can be adjusted in the Elevation Editor. Select a feature line, right-click and choose Elevation Editor from the menu:

2. Adjust the elevations and slopes as per design needs:

3. In the ribbon, go to Home – Grading and select Grading Creation Tools:

4. Grading objects can be grouped into grading groups. Civil 3D allows for final surface creation and volume calculation per grading group, each object can have its own grading group. To create a new grading group, click on the first icon on the left side in the Grading Creation Tools toolbar:

5. Specify a platform Name. Untick the Automatic surface creation and Volume base surface options because they might cause software instability due to doing more operations at the same time. Once the design is finished, the surface can be created, and volumes can be calculated:

6. Select the Grade to Surface rule and click on the Create Grading icon:

7. Select a feature line and follow the prompts in the command line:

The image shows the created grading object (platform):

1. To view the platform in a 3D view, select the entire platform, right-click and select Object Viewer from the menu:

2. Set the visual style to Shaded and change the view to a 3D view.

3. You can see the cut and fill, but the platform has a void inside. To fill the inside part of the platform, go back to the model space and click on the Create Infill command in the Grading Creation Tools toolbar:

4. Once the cursor is in the void area the feature line is highlighted. Click inside the void area to create the infill. An infill can be created in any closed feature line. Once the infill is created, a small grey diamond marker is placed in the infill area:

Diamond markers are part of every grading and used for grading modifications. This will be explained in another chapter.

1. Select the entire grading and go to object viewer (use the same settings as before) to see the infill:

Edit Grading

1. To modify grading, select either the grading itself or select the grey diamond marker, right-click and select Grading Editor from the menu:

2. Change the values in the Grading Editor as required:

Note: Diamond markers are automatically placed on the C3D-No Plot Objects layer. Freeze this layer before creating a final plot to ensure that the markers won't print:

Sites

Sites help to manage the interactivity between the feature lines and grading objects. If the feature lines or grading objects are in the same site then they are interactive, thus if they intersect, Civil 3D will calculate their intersecting planes and levels. For example, if two feature lines are crossing each other in the same site they have the same levels at the intersecting points (second feature line will override the levels of the first feature line at the intersecting point).

1. To create a new site, go to the Prospector, right-click on Sites and select New from the menu:

2. Specify the site name:

3. Created Sites in the Prospector:

4. To move a feature line to a new site, select the feature line, right-click and select Move to Site from the menu. The same method can be applied to grading objects:

Sites need to be used in the cases where two overlapping grading objects should be created. The image below shows two platforms on top of each other:

Each platform has its own site to ensure there is no interactivity between them:

Platform2 targets the combined surface NGL plus Platform1.

Clean Up Grading

When two overlapping platforms are modelled, the final output is not presentable due to the crossing slope pattern lines (note that the final surface looks correct in the image below):

To clean up the overlapping slope patterns, the new platform must be created on top of Platform1. In fact, Platform1 is only used for the target surface (combined with NGL) for Platform2.

1. Go to the View panel in the ribbon, Views and then select a suitable Isometric view:

2. Go to the Prospector and create a new site, Platform1 Final:

3. In the Home tab of the ribbon, use the Feature Line − Create Feature Line command:

4. Specify Platform1 Final for the site and the Style (select any style, the example below uses a blue feature line to distinguish between different platforms):

5. Draw a feature line around Platform1 from the points where Platform2 cut/fill crosses the Platform1 feature line:

6. Switch back to the Top view:

7. A new grading group must be created for Platform1 final. Go to the Home tab in the ribbon and use the Grading – Grading Creation Tools command:

8. Click on the first icon on the left-hand side in the Grading Creation Tools toolbar:

9. Specify site Platform1 Final:

10. Create a new grading group with the icon highlighed in the image below:

11. Specify a Name:

12. For the target surface use the combined surface of NGL and Platform2. To create this combined surface create a new surface and name it NGL plus Platform2:

13. Go to the Prospector – Surfaces – NGL plus Platform2 – Definition right-click on Edit and select the Paste Surface command:

14. Select the NGL surface and click OK (the order in which you paste surfaces is very important because the surface which is pasted last overrides the other surfaces at the areas where they overlap):

15. Use this command again and select the Platform2 surface:

16. Use this surface as a target surface, go to the Grading Creation Tools toolbar and click on the second icon from the left-hand site:

17. Select the surface:

18. Before creating gradings switch off the Platform1 grading, otherwise the result will overlap with Platform1. Create a new layer, name it C3D-Grading-Dummy and freeze it:

19. Select the Platform1 grading including its infill and move it to this layer. The image below shows the result:

20. Use the Create Grading command and follow the command line prompts:

Final cleaned up platform in plan and 3D view:

Tips for Working with Grading Objects

1. Split your design into multiple sites to remove interactivity between objects. When grading objects become more complicated, Civil 3D needs to calculate more interactions between objects and this can cause the drawing to become unstable.

2. Do not create a single grading along the entire length of a long feature line, rather create it in parts (sections) especially if the feature line has a complex shape or if it contains a lot of vertices.

3. Avoid creating grading objects crossing other gradings and feature lines.

4. Try not to model everything using gradings, use a combination of gradings, feature lines, corridors and 3D polylines (breaklines) to model an object or a final surface.

5. If the resulting surface created from gradings does not look correct, it might be easier to create a new surface and use objects from a grading as breaklines.

6. Avoid vertical walls (C3D surfaces cannot contain vertical edges), use 1 mm offset/slope.

7. Create drawing backups regularly, because the undo command (only when working with gradings) or a Civil 3D crash can corrupt the grading objects or the entire drawing.

Quantities

Grading Volume Tools

For quantities calculation, a final surface from the platform must be created and a reference surface must be defined.

1. This can be done in the Grading Group Properties window. Go to the Grading Creation Tools toolbar and click on the Grading Group Properties icon (third icon from the right-hand side):

2. Tick Automatic Surface Creation, specify Tessellation spacing (spaces between platform surface triangles), tick Volume Base Surface and select a surface which will be used as a base surface for volume calculations:

Created platform surface:

1. To see the resulting quantities, go to the Grading Volume Tools command in the Grading Creation Tools toolbar:

Quantities:

1. The Grading Volume Tools window allows users to raise or lower the platform to optimise the cut and fill. Use the second icon from the right-hand side to balance cut and fill quantities:

2. Specify the required volume:

The balanced quantities are shown:

Keep in mind that balancing quantities might not work properly for very complex platforms. Rather do the preliminary sizing on a very simple platform and then design the final platform.

Volumes Dashboard

Another option for calculating volume is by using the Volume Dashboard. Firstly, create a platform surface as explained in the previous example.

1. Go to the Grading Creation Tools toolbar and click on the Grading Group Properties icon (third icon from the right-hand side):

2. Tick Automatic Surface Creation and specify the Tessellation spacing (spaces between platform surface triangles):

3. Select the created surface and click on Volume Dashboard in the contextual ribbon:

4. Create a new volume surface:

5. Specify the volume surface's Name, Base Surface and Comparison Surface:

Result:

1. A volume surface can be analysed like a normal TIN surface. You can display cut and fill in the drawing by performing a surface elevation analysis (see the Surface Elevation Analysis chapter), specify two ranges and use different colours for cut and fill:

Cut and fill displayed on the volume surface:

Final Surface

The final surface combines the NGL and platform surfaces.

1. Create a new surface by going to Home − Surfaces in the ribbon and selecting the Create Surface command:

2. As a type use TIN surface, specify the Name and Style:

3. Go to the Toolspace − Prospector –Surfaces – NGL+Platform (name of the surface created in the previous step) – Definition, right-click on the Edits and select Paste Surface from the menu:

4. Select NGL surface and click OK. Note that the order of the pasted surfaces is very imported because the latest surface overrides the previous one in the areas where they overlap:

5. Use the paste surface command again and select the Platform surface:

Final surface: