Best way to design ditches

Hi, 

I have a problem with designing ditches which have own vertical alignments. When I create vertical alignment of ditch in point nr 2, the alignment is shorter then the axis of ditch - so when I project the slope for ex. 2% it will have on the ditch less then 2%.

When I create vertical alignment of ditch in point 3 and then displays profile with vertical alignment elevation of axis is different in cross section then in profile (difference is about +-1 cm) becasue the cross section is made in stationing of the axis of road, while the profile has own stationing which is a bit longer.

So what is the best way to desing a vertical alignment of a ditch?? How to do it in InRoads without little misteakes?? Is there a special tool to create vertical alignment of ditches?

  • I do not know of a special tool for roadway ditches to help control the vertical geometry.  I do often use the method you describe above i.e. a vertical geometry in the Mainline geometry.  The grade of the ditch will as you see not be an exact match on curves.  The difference is typically not much but if you have a sharp corner it can be noticeable.

    If you need to improve the accuracy of your ditch one solutions would be to create a ditch horizontal geometry in closer proximity to the actual location.  This would require some trial and error and extra work, but can improve the grade accuracy.

    Mike Longstreet
    Vermont Agency of Transportation
    Civil Engineering Technical Support
    VTCAD Help

  • I'm not an InRoads user so I can't offer any suggestions using InRoads tools. However I will suggest a technique that might get you close to the desired result.

    The idea is to create planar surface along the ditch alignment that can be used as a target for the road slope that projects to the ditch. You layout an alignment for the ditch that is a close approximation of where the road slope will intersect the ditch bottom. Create a profile for that alignment at the required slope and apply a template that is flat on either side and wide enough to ensure the road slope will find a target. Create a surface from the template to use as a target for the road slope and you should end up with a ditch that is very close to the design profile.

    Neil Wilson (aka Neilw)

    Power Civil v8i 08.11.07.245

    AutoCAD Civil 3D 2018

  • Hello,

    I am not sure whether it is worth its effort. Actually I am sure it is not. I usually follow your workflow and do not take care of the difference on curves. Typically I have vertical alignments for each side ditches designed in the mainline horizontal alignement. Of course there are some situations when you are close enough to the allowed grade limits to take care of this problem. However in most cases the difference is negligible. This is not Inroads or other software issue it refers to roads designing at all.

    Adam

    Best,

    Adam


    OpenRoads Designer 2023   |  OpenRail Designer 2023

                 

  • Since InRoads allows multiple vertical alignments on a horizontal alignments, I have found that using a ditch vertical alignment with a separate horizontal alignment for the ditch centerline makes it easy to controll the ditch elevations since the station for the verical is the cenerline station.

    I have also allowed the ditch to float - no horizontal alignment - based simply off side slopes and grade elevation.


    Charles (Chuck) Rheault
    CADD Manager

    MDOT State Highway Administration

    • MicroStation user since IGDS, InRoads user since TDP.
    • AutoCAD, Land Desktop and Civil 3D, off and on since 1996
  • I agree with caddcop , ditch vertical alignments are easier to control as a vertical alignment under the centerline horizontal alignment.  Also this makes it easier to display and annotate in your centerline profiles.  Anymore, I create all my ditch profiles under the centerline alignment.  I control the ditch horizontal alignment by either points controls or a horizontal alignment only.