Grading problems

[Anonymous]

I have problem to cut a volume from EG.

I want to cut out a volume between EG and a feature line under the surface.
And I want the slopes to be 90 degrees.
How do I do that?
And how do I calculate the volume from the cut area?

Please help me!!

[autoMick]

When you say 90 degrees, do you mean vertical? Is your feature 'line' just a line, or is an enclosed shape at a particular elevation? You basically need to create 3 surfaces, EG, FG and a volume surface (which compares EG against FG). If you want the volume within a vertical sided space, the easiest is to find the 'bounded' volume (right click the volume surface in the prospector and select a boundary).

[Anonymous]

Yes, I mean vertical. The feature line is a closed line, who I lay on a specific elevation below EG.

I am kind of newbie in Civil 3D, so hope you can wright a list who I can follow.

[autoMick]

OK no problem. I hope I don't leave out anything.

1. I assume you have your EG surface. If not, you need to create a TIN surface and then add your data points, contours, breaklines or whatever to make it represent reality.
2. Create another TIN surface (by right clicking surfaces in the prospector tab - call it FG), then drill down in the prospector tree and right click breaklines under definition. Click add, then select your feature line representing the cut. If the elevations of your feature line are correct, you should now have two surfaces, one somewhat lower than the other. You can edit the feature line elevations if needed.
3. Create yet another surface, but this time the type should not be a "TIN Surface", but a "TIN volume Surface". When you do this, you get options for setting the base and comparison surfaces (which are the EG and FG surfaces created earlier)
4. Draw a polyline to represent the plan area for the 'bounded volume'. This can be the same as your feature line that you used for FG if desired.
5. Now right click the volume surface in the prospector tab, select the polyline you've just drawn and voila, you should be presented with the volume between the EG and FG surfaces, but only vertically within the boundary you selected. You can look in the volumes dashboard as well. Look at any tutorial on volumes and you'll find it's reasonably understandable.

If you have any other questions, you should post your drawing so that it will be easier to explain.

Cheers

- Mick

[jmayo-EE]

Bear in mind that tin 's do not like vertical faces. Due to this we typically approximate vertical edges.

Another method is to take your feature line, create a stepped offset .05 or .1 units outside and assign elevations from the eg srf to the new fline. Place both of these in an FG srf and you now have two surfaces to compute volumes with.

[autoMick]

I was figuring that you don't even need to put in the vertical (or near vertical) edges, since you can achieve the same thing way easier with a bounded volume. 

Cheers

- Mick

[sboon]

Actually you don't even need to create a boundary.  A surface to surface comparison will calculate at all x,y locations where both surfaces exist, and it will automatically form an edge anywhere one surface or the other is missing.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[autoMick]

So true Steve, but I think it is good practice to specify the boundary just so the user is fully aware of what is being reported.

Cheers

- Mick

[mathewkol]

I think it's neither good nor bad practise. If it were me I would not bother with the vertical boundary since it's really as unnecessary step. But if it gives people the warm fuzzies to have that boundary go for it 🙂

Or if it's important to see that line in a section or profile.

[jmayo-EE]

I agree with you Matt. Sometimes you need a boundary (disconnected areas) most often you don't. Don't create it unless you need it.

I was just trying to provide some insight into the app for the OP. I also gave an alternative method not a preferred method. Bounded volumes are the correct tool IMO for this job but I'm betting the OP will get more work. 😉

[autoMick]

Regarding specifying a boundary - I was really considering the needs of the learner. Also, being unsure of the geometry of the lower surface I still thought it was a good idea. Anyway, I agree, no use adding redundant geometry if you understand what's going on.

What happened to the OP anyway?