Adding a surface to an existing section view in Civil 3D can be a useful tool for visualizing the relationship between the surface and the section. Here's a step-by-step guide on how to do it:

1. Open the drawing that contains the section view you want to add the surface to.

2. In the Prospector tab, expand the 'Surfaces' category and locate the surface you want to add to the section view.

3. Right-click on the surface name and select 'Add to Section View'.

4. In the 'Add to Section View' window, select the section view you want to add the surface to from the drop-down menu.

5. Click 'OK' to confirm the addition of the surface to the section view.

Once you have added the surface to the section view, you can now visualize the relationship between the surface and the section in a more comprehensive way. This can be especially useful for analyzing the impact of the surface on the section or for evaluating the design in 3D.

Adding a surface to an existing section view in Civil 3D is a simple and effective way to enhance your design and analysis process. Try it out in your next project and see the difference it makes!