FG datum for earthwork

[jmayo-EE]

I have a commercial site with a bunch of blds, parking areas and access aisles. We have a composite FG surface and I need to create a datum srf for the pavement depth and the underground stormwater storage below the pavement.

How would you go about this? I have tried to paste FG into an empty surface, lower it to pavement depth, apply boundaries as required. The surface looks good but it won't paste into the FG. I'm figuring this is because there is no common tie between the srf's. As I attempt to get this tie in created I was wondering if you folks had some other thoughts on this process besides a full blown corridor (pilot project in the works).

[Lisa_Pohlmeyer]

Just as a starting point, I would have copied the FG instead of pasting it into a new surface. Then made my edits.

[jmayo-EE]

I am trying to do this in a separate file with dref's so editng would only work if I pasted all new surfaces in for lowered depths no? Is this along the line you are thinking Lisa?

[neilyj666 · Accepted solution]

I'd create boundaries around all the different areas e.g, pavements, paths, planting etc and offset (to an new layer) inside each enclosed shape by a nominal amount (0.025m in metric/1 inch), give these polylines an elevation of the level drop required i.e. for a 0.6m construction thickness, the elevation is 0.6m.

Create a surface from all these offset polylines and then create a volume surface with the offset polyline surface as base and the FG as comparison.

Past the volume surface into a normal surface and you have it done

[MikeEvansUK]

I'm not sure why it won't past together?

I normally create boundaries (hide/outer) for each, create a new surface. Add these first as break lines then paste in top down. So long as the boundaries match they'll fill in in the gaps.

[Civil3DReminders_com]

I usually end up with the surfaces not pasting when the boundary names are the same between the surfaces. Or at least that's what I justify why I make jibberish surface boundary names. I also wrote a program that does what you are attempting to automate the process. The UI sucked, the economy crashed, and I haven't picked it up since. I might pick it up again and see if I can get it working better.

[jmayo-EE]

Just crashed and a a min to respond. 1st THANKS!!

I found that one surface was not pasting due to hidden boundary that was not not working. Still have issues with another surface not pasting and don't have much time to investigate. I have not had issues doing earthworks with boundaries on surfaces but if I remove the hidden boundaries the paste works for one paste but not another...

Mike, I am using this method now to get done. I have done this before but it does make for a heavy file with all of the elv points.

Chris, I will look into this. I have not been naming the boundaries and C3D could be using he same name in multiple surfaces.

[jmayo-EE]

Sorry Mike confused the posts. I typically do as you. Boundaries and pasting surfaces. Typically works great. Now I am doing the feature line solution to get done. This makes for heavy files.

[fcernst]

Vote here for Neil's suggestion. Then you have a dynamic subgrade surface to compare to EG for earthwork, that reacts to any grading changes to FG.

[neilyj666]

Not sure how having contiguous boundaries will work if the construction depth varies as this will cause the triangulation to fail due to vertical edges at different elevations?

[jmayo-EE]

Thnx Fred.

Neil, I'm having a tough time visualizing this. If the breaklines are all at elev's of -.5, -.67, -.1 foot and I paste them into a volume surface I would have a datum hanging out close to elev 0 +/- my depths. If I create a new surface and paste that volume into it don't I have elv's from real datum to the volume datum?

[jmayo-EE]

I do have offsets to remove the vertical edges.

[neilyj666]

---

@jmayo wrote:

Thnx Fred.

Neil, I'm having a tough time visualizing this. If the breaklines are all at elev's of -.5, -.67, -.1 foot and I paste them into a volume surface I would have a datum hanging out close to elev 0 +/- my depths. If I create a new surface and paste that volume into it don't I have elv's from real datum to the volume datum?

The breaklines shouId NOT have -ve elevations they MUST be +ve or the technique will add to the FG surface rather than subtract.

You need to create the volume surface with the construction thickness breaklines as BASE and the FG as COMPARISON. You then paste the volume surface into a new regular surface where it behaves as a normal surface that you can cut sections through etc. I think Eric Chappel's blog had this technique well documented but I have failed to find it although there is an AU class from 2012 and 2013 (search for dynamic differential TINS) if you can find anything on ths AU site nowadays...!

[fcernst]

The idea is to get a dynamic material depth subtraction from your FG. You use the C3D volume surface capability to achieve this.

So the 0.5's, and 0.67's and 1.0's are all positive values to create the "subtraction surface". Then create a volume surface comparing FG to this subtraction surface consisting of  ( 0.5's, and 0.67's and 1.0's) as Base.... Base is then subtracted from FG.

Then paste this volume surface into an new empty normal surface and call it "subgrade". You have now "normalized" the volume surface used to create subgrade, and it itself can be used for volume comparisons. Then do a dynamic volume surface between EG and subgrade with EG as Base. Subgrade will react dynamically to changes in FG.

The first part is weird to visualize because typically our volume comparison surfaces are closer together than hundreds (or thousands here in CO) of feet apart in elevation difference....

[jmayo-EE]

Thanks again. I will look into this after I get done what I am doing now...

Kudos to all because it was all good advice. I'll give Neil the prize.

[neilyj666]

🙂

[Civil3DReminders_com]

I found the post that I finished the command in http://blog.civil3dreminders.com/2009/06/surface-subgrade-surface-finished.html and a video of it in action: http://screencast.com/t/yp7a4RV9e5w

[jmayo-EE]

Looks pretty cool. Thx. I'll test next wk

[jmayo-EE]

Neil & Fred thanks for this. Great stuff. THe handout Fred supplied says to convert everything to 3dpoly or Fline. It does not seem that this is a required step. Please correct me if I am wrong.

I do have one lingering question. It seems that this method works great for a constant depth below FG. Can this method account for an undergound basin that needs to hold a constant Z under the pavement depth?

[troma]

I have used this method for stripping topsoil from Original Ground, and for building a proposed subgrade surface.

But I'm not sure if I follow your question.  You may need to build this basin as a separate surface and paste it onto your subgrade surface as the last step.  Otherwise it will be difficult to maintain a constant z (presumably your FG does not maintain a constant z in this area).