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TBC Conditional Corridor Instruction

  • 1.  TBC Conditional Corridor Instruction

    Posted 10-26-2020 15:15

    Is it possible to create a conditional instruction for cut/fill slopes where the verge varies in width? 


    Fill Slope

    Verge Varies In Width - (1.0m to 2.5m)

    Side Slope Varies (1:2 & 1:3) Interfaces with Existing Ground




    Verge Constant In Width - (0.7m)

    Side Slope Varies (1:2 & 1:3) Interfaces with Existing Ground


    Are there any good training videos on this subject?


  • 2.  Re: TBC Conditional Corridor Instruction

    Posted 10-26-2020 21:44

    Figured it out


  • 3.  Re: TBC Conditional Corridor Instruction

    Posted 10-31-2020 21:17

    Looking at the model and we can do a call this afternoon when you get on line - I would be happy to show you a couple of things that can help you here, but your conditions in the model shown could have been done using Slope by Depth Tables. The areas where your triangulation is wrong are areas where the conditions failed to come up with a solution


    1) I see that the MC00 PENLINK surface displayed is built using Corridor Instructions - in general that looks good - there are a few places where evidently you run out of existing ground for the sideslopes or your conditions are not handling the full situation to create the sideslopes to tie to which leaves a gap that then gets triangulated in the surface representation of the corridor model - so we need to look at your conditions and what they are doing - I saw your post on that last night and will be getting to that today to get you an answer


    The Conditions depend on what / how the designer wants the conditions to work - you said in the email that the Verges can vary as can the sideslope - but how do they vary / why do they vary is the question I need to know before advising. Normally the conditions are there on sideslopes to vary the sidelope for one of two or three reasons


    1) The sideslope varies based on the material it is cutting through e.g, a steep slope in Rock and a shallower slope in soil

    2) The sideslope varies based on depth of cut - this is also dependent on the material - if over a shallow depth it can stand a steeper slope but on a deeper Cut / Fill it needs a shallower slope, or in some cases they use a steeper slope in deeper cuts / fills because they dont have the Right of Way width to handle the shallower slope and they dont want to put in a retaining wall etc.

    3) The Right of way controls the slope - ie we want a 3m verge and a 3:1 slope but if that goes outside the Right of way, steepen the slope to a max of 2:1 and if that still does not come inside the ROW then narrow the ditch from 3m to a min width of 1m or similar (the order of this is important - do you first narrow the ditch and then steepen the slope or do you steepen the slope and then narrow the ditch - and then lastly what happens if that doesn't solve the issue?


    If the sideslopes are varying by depth of Cut or Fill then you dont need to use Conditions at all - you can do that with the Slope By Depth Table Method that incorporates conditional variations based on different depth of cut / fill scenarios. In the Slope by Depth Table option you can also embed Tables for the Width / Depth values as needed - so your first two conditions for cut and fill could have been handled by a single Sidelope Instruction using a Cut and Fill slope where the first element defines the width element and the second element defines the sideslope in the Depth by Slope Table. The only challenge with this is that the depth by slope table instruction stops as soon as any defined element intersects the target surface - so that can be in the first or second element.


    Knowing the order of the "Varies" and the reason for the "Varies" helps me to construct the conditional steps and these will need sometimes nested conditions. Take example 3 above. If the Order of change is as follows


    3m Verge and 3:1 Slope

    3m Verge and 2:1 Slope

    1.2m Verge and 2:1 Slope


    Then I would build the conditions one way.


    If however it was

    3m Verge and 3:1 Slope

    1.2m Verge and 3:1 Slope

    1.2m Verge and 2:1 Slope


    Then I would build the conditions differently


    The first thing to create is a "Test Shot" for the Condition that can be used to see if the Test Passes or fails. So for example if the test is to see whether the Tie Point lies inside or outside the ROW line, then I need to add the ROW line into the model as a reference line. I would take a 2D ROW and drape it on OG to make it 3D and then add it as a refrerence line in the corridor. Then for the test shot I would build the test condition something like the following


    1) The verge / ditch is in two parts, the part that has to be there no matter what (the first 1.2m) and then the part that varies the up to 1.8m piece. So I would create a node outside the conditions 1.2m out from its source to create the ditch / verge that has to be there.

    2) Now I would do the Test Shot for Condition 1 - that would be two points, not assigned to any material layer that create the test condition. Node 1 would be 1.8m out at the slope needed. The second node would be a sideslope at the slope needed. This creates Test Point 1.

    3) Then I would create the Test Shot for Test Condition 2 - that being the 1.8m verge / ditch and the 2:1 slope - this creates Test Point 2

    4) The third condition should be the catch all (ie if 1 and 2 fail, then 3 does the last set of instructions to fill in the gaps left by condition 1 and 2. If that fails then I assume there is another condition that says you need a Retaining Wall somewhere and that would be another condition.

    3) Now you create the Condition Instructions for Condition 1 - and the test that you are doing is to find out whether Test Shot 1 is inside or outside the ROW line. You will use the Nodes Horizontal Distance From Node condition, and you want to set it up so that if inside it passes and if outside it fails. So when you define the Greater than / Less Than values you enter the appropriate values. The Node to Node Distance Check will typically be if ROW - Test Shot offset from CL (ROW - CL) - (Test Shot to CL) is a Positive Value then it passes, and if the opposite it fails. Then you want to enter your values as > 0 and less than 10000 (this checks the positive range - and if negative it will fail.

    4) Now if it passes you draw the connect between the end of the 1.2m Verge, the first and second points of the test shots and you are done.

    5) If it fails, then you have to determine what happens - when it fails the second test is needed - and that is if Test Shot 2 is inside ROW or not (Repeat the above0 so you will use an Else IF statement for that and test in the same way. If it is a Pass then

    6) You will draw the connections from the edge of the verge to the first and second points of the Test Shot 2. This will however create a step from a 3:1 slope to a 2:1 slope over the interval between the two calculated sections. Engineers will likely go back into this after it has been computed this way, and transition that slope change over a defined distance. If it is chopping and changing a lot, they will also modify the existing to stop that from happening - (now you are into redesign because the engineer did not give you what they actually wanted though ....)

    7) When this option 2 fails, now you do a third condition - the catch all that hopefully works for all other scenarios. Because this involves the ditch narrowing, then I would compute this as follows


    1) From the ROW I would do a slope slope instruction towards the centerline that takes the 2:1 sidelsope from the ROW point down to the interesection with a slope of 0% from the edge of verge towards the ROW. this will compute the outer edge of the verge for you.

    2) Then use a Connect instruction to connect the verge edge to the computed toe of sideslope to create your variable ditch width.


    If you have the second scenario above then it would be handled in a similar way but as follows


    1) Create your test shots for Condition 1 exactly as before

    2) Condition 2 will use a sideslope only at 3:1 from the 1.2m verge edge because this will do something like condition 3 in the last example - when 1) fails you will use the ROW to compute the slope slope back to the verge edge until the offset goes to 0 at which point condition 3 kicks in

    3) Condition 3 will just do a 2:1 slope from the edge of the verge


    I will record a video to show you how this works in practice.

  • 4.  Re: TBC Conditional Corridor Instruction

    Posted 11-02-2020 22:26

    Thanks, Alan, always helpful