AutoCAD Civil 3D

[#1]

I’m wondering if there is some good advice on the board regarding how one might model an existing drainage channel.

Here’s the scenario – field crews are going to collect data for a 500 ft long concrete (trapezoidal) drainage channel. The bottom width varies from 7 ft to 19 ft wide with vertical walls varying from 4 ft to 7’ high. The channel will be filled and capped.

I considered using one of the channel subassemblies with Civil 3d and establish targets along the existing channel top and bottom of walls. However, I don’t see that the stock subassemblies are intended for this and don’t really lend themselves to perform this. I suppose the other option is to use linkwidthandslope subassemblies and use multiple targets for inside bottoms, inside tops and outside tops of walls.

Any thoughts?  

[#2]

Not sure what you are asking here - aren't the field crews just going to survey what's there (assuming it's not still got water in it)??

[#3]

Typically the existing channel is just added to the existing terrain model as breaklines based on the suvey. If there is some specific need to model the structure itself that could involve a bit of custom work depending on the complexity.

[#4]

Yes, survey crews will "as-built" the channel. This work is part of a remediation project so that several feet of material in the ditch will be removed, the ditch fillled and capped.

As you might expect, determination of material quantities is part of the scope of work. Also, the capping will be an 8inch thick concrete slab. The cap I can model as a "road" and establish low points for surface drainage. We will likely need x-sections as the variable height walls will require scalping so that remaining wall heights are no higher than 8 inch above the cap. I'm going to consider very basic linkwidthandslope subassemblies to target the existing wall features but was curious to know if there is a better way. 

Thanks for your reply.    

[#5]

I don't know if I have a better way. But I've always found trying to use assemblies to model existing be more trouble than it's worth. What I'd start out with is a few different surfaces defined by the existing survey and the proposed levels. So one for the bottom of excavation in the channel, one for the bottom of the cap and one for the top. They you can get the volumes between surfaces.

Modeling the cap as a road does sound like it might be a good idea. You can use the bottom surface to get the fill between the bottom of the cap and the final grade in the channel.

Allen

[#6]

Thanks for the feedback, Allen.

[#7]

I think that I understand what is supposed to happen - you're going to have survey at the top and sides of the channel down to the existing material at the bottom.  The problem is defining the section down to the actual bottom of the channel.  Do you have any profile data for it? 

[#8]

Yes, SBoon, that's much the issue although I guess my initial description wasn't all that precise. I don't have a datum for the channel.

[#9]

If you don't have the elevation of the original channel bottom then I don't see how you can calculate a volume of the material to be excavated.  All I can suggest is that you get someone to dig a few test holes, and use that data to interpolate a profile.  There are subassemblies that can be used but right now you don't have enough data.

[#10]

If field crews are collecting the data why wouldn't you use the survey database to have figures automatically drawn from description keys?