take the edge off CIVIL 3D

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At every training session we’ve done for local councils where road reconstruction is the brunt of the work being done, we get told that green field work is irrelevant and there is really only one question they want to know about:

“what is the easiest and most reliable way to widen a road at its existing grade?”

It starts our reasonably simple but can become complex when the road is suddenly part of an intersection which also has to be partially reconstructed while making sure the crossfalls stay within the max/min tolerances (roundabout reconstruction for eg).

The answer to all this (and a lot more) is REFERENCE PLANES

[More:]

widening a road at grade..

What we’re talking about here (initially) is extending the existing crossfall of a road, whatever it is, to a specified offset or alignment. This is itself is not so difficult - Civil 3D has a specific subassembly and ARD can do it with some simple Variation Commands.
The challenge comes in when extra parameters are added:

• Add a little overlay to one or both strings.
• Check that it is within the max/min slope ranges.
• Don’t use the exact CL and EB/INV for the level calcs - instead offset a reference point to ensure the correct grade is calculated.
• Make some changes to the horizontal geometry of the widening string to see the effect..

This all becomes a bit complex so the alternative approach is to make a surface of exactly what the widening plane should be, extend it way out and work off that.
When the widening horizontal geom changes, the profiles of the reference planes will update instantly so the design can be adjusted.

Is this a new idea?

No, not at all.

This idea has been out for many years. I don’t think there is an official name for it but ‘reference planes’ seems to describe the system nicely.

This is the first post in a sequence. We’re only describing the concept here - the specifics will come later, building up to complex intersections being reconstructed with multiple reference planes representing the many considerations to get the job done.