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  1. #1
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    Default Civil 3D surface troubles - HALP!

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    The situation: I'm working on a project which is a 16 lot subdivision. I currently have my existing and proposed grades as surfaces, and I need to add the excavation for the proposed houses into the proposed surface so that we can run an accurate cut/fill analysis.

    What I've tried: breaklines, feature lines turned into breaklines, separate surfaces for each house to then be pasted into the proposed surface, adding points, wall breaklines

    What's worked well: None of it. It's possible that I'm simply going wrong with one or two small details in the process - my skill level is hardly proficient in Civil 3D surface modeling, yet is the most advanced in the office (the boss last did surfaces in Land Desktop).

    I'm now on day three of trying to get this thing to work, having been told repeatedly to try the same handful of things, which invariably haven't worked. I've had good luck finding information on CadTutor, so I'm now turning to these forums.

    Thank you.

  2. #2
    Super Moderator SLW210's Avatar
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    I moved your thread to the Civil 3D & LDD Forum.
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  3. #3
    Super Member CyberAngel's Avatar
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    Have you tried defining the edges of the excavation as a curb (or similar feature)? You can define the upper and lower elevations. I don't have Civil 3D here, so I can't test my theory.
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  4. #4
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    The problem with house lots is generally that at the edges you often need a vertical wall, as the batter can not proceed into the adjoining property.

    You need to check your grading and use a almost vertical batter, if the house slab taking AUS as an example has the garage with a step down versus the house area, in this case a 1mm offset will work giving you the vertical you need. Its gets interesting in the corner of the two levels.

    As mentioned you may need to create a boundary line that has this 1mm in it at the corners then batter each edge with a different slope. I played around with this problem a lot of years ago and there is no quick answer. You may need to add a "LINE" with the correct Z to the surface model to get the verticals working. As its house excavation you need to get as close as possible to the desired shape.

    I did a huge job in area size for a Chinese project 2kmx2km and just had to keep adding the new road feature shapes 1 at a time ad checking that the surface was correct shape, including curves that had to be approximated by straights. It had like 15 surfaces to get to the final shape.
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  5. #5
    Super Member CyberAngel's Avatar
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    The trouble with defining holes in Civil 3D, as I recall, is that it won't process vertical surfaces. That whole dividing by zero thing, I guess.

    Have you tried this? Start with the breakline for the upper edge of the hole. Offset that breakline inward by a tiny amount, such as .001. Change the elevation of that inner breakline to the bottom of the hole. Once you add that breakline to your surface, you have a set of almost-but-not-quite vertical faces to represent the sides of the hole. Your cut/fill totals will be wrong but only by a tiny amount. If you're a real stickler, you can calculate the difference and adjust your totals.

    For a split-level house, use two or more extra breaklines. Just make sure they don't overlap.
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  6. #6
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    regarding CyberAngel's comment:

    that's 100% true about the vertical

    I will suggest a possible solution that I've used in the past.
    If you use a generic linkwidthandslope and set the slope to 50000 or -50000, something just ridiculous, it gives you a near vertical "wall"
    you can also type in the word "vertical" in the slope/grade field but you will need a tiny horizontal piece at the end end to finish the surface.
    I hope i stated this in a sensible way...

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