Corridor Design Theory

[kiarianc]

I'm learning Civil 3D alignments/profiles/assemblies and corridor creation, but I'm still in the dark about how would someone go about creating an alignment and a profile from scratch. I have started work, and am trying to figure out a Civil 3D model, drawn over a year ago, by someone who no longer works at my company.

If you had an empty drawing, with a topo survey showing an existing road, and you had a certain area where you are creating a new corridor using Civil 3D you would first plot out a 2D polyline to get an alignment? Correct?
So now you have your alignment, you can create an assembly. OK, I'm understanding all of this. What I am lost on, is how do you generate your profile? The profile is a 3D line which follows the alignment, but has elevations which give the corridor it's longitudinal fall (the assembly giving the corridor the lateral fall?).

I suppose the one thing I really want to know is how do you generate a profile for a corridor? How do you know to get the right elevation at the right point? I have a 2D Setting Out drawing with a back of footway level. Could I use that to generate a corridor from the edge of kerb? Or does the profile always have to be central to the corridor?

Feel free to explain this to me in simple terms. I'm just over two months into learning Civil 3D, so I may be missing an obvious point. If there are any resources that can help then please let me know.

Thanks

Kiarian

[jroot · Accepted solution]

There are a lot of questions in the post 🙂

As you asked, let's start out simple.  You have your horizontal alignment and existing surface.  Next step would be to create a profile (and Profile View) using those two objects.  This will show the existing grade along your alignment.  Then you will want to use "Profile Creation Tools" to draw your proposed grade over the alignment.  So if your alignment is on the center of your design feature (a road), you would build your Assembly to be the crown of the road.  Or if your alignment is the edge of a walkway, you would build your Assembly out from that (perhaps 6' over at 2% to the other edge).  

Now you would have all your ingredients to build a Corridor, following the prompts to select each one.

[jeff_rivers · Accepted solution]

You're on the right track, and I have a couple of questions for you.  

You said you have the topo survey, but you didn't say if your drawing includes the Civil 3D Surface that was created from that topo.  

If it has a surface, great, skip this next bit.  If it doesn't, you'll need to create one, then after you create your Existing Ground Surface, you create an existing ground profile, based on your alignment.  

The tutorials are very good at explaining how to do these things, so I won't go into how to create a surface and a profile.  Assuming your surveyors picked up elevation points along the crown of the road, Civil 3D will happily generate the existing crown profile for you.

Just know that after you create the existing ground profile, it doesn't actually show up anywhere until you next create a Profile View.  The Profile View can be anywhere in your modelspace that you want.  Once you've created the EG Profile and the Profile View, you can then use the profile layout tools to create your Proposed Profile in that profile view.  

Generally that's the order of operations: Get survey, create EG surface, create alignment, create EG profile, create profile view, create proposed profile, then create your assemblies and your corridor. 

And yes, the profile controls the corridor's longitudinal fall, while the specific lane subassemblies control the lateral fall.  

And you can create your profile using the 2D elevations you have for the footway (sidewalk) points.  You don't have to use the road centerline or the road crown to make your corridor, but using one or the other makes your corridor more straightforward.  

[kiarianc]

@ jeff_rivers - Thanks for explaining the design profile setup. That's the main thing that was causing confusion. I assumed that it was possible to create a design profile from above, looking down so to speak, onto an existing surface. So I use the profile creation tools and literally plot on the design profile, 2D style, onto a generated section which uses the existing surface and existing profile Civil 3D information. Got it!
I'll look into it further. I was tinkering about with corridor's the other day and trying to create a two-lane road, with a central crown falling either side assembly, but using the edge of road as the reference, as that was the only level I had annotated on the drawing.

Thanks again.
Kiarian

[kiarianc]

Thanks jroot. Didn't realise two people had responded. Appreciated.