AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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rwhitlock1
Posts: 26
Registered: ‎12-05-2007
Message 1 of 10 (470 Views)

Model Existing Drainage Channel

470 Views, 9 Replies
09-28-2012 11:13 AM

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?  

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neilyj
Posts: 3,926
Registered: ‎08-01-2008
Message 2 of 10 (461 Views)

Re: Model Existing Drainage Channel

09-28-2012 11:42 AM in reply to: rwhitlock1

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)??

neilyj
(No connection with Autodesk other than using the products in the real world)


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Neilw
Posts: 2,320
Registered: ‎09-04-2006
Message 3 of 10 (458 Views)

Re: Model Existing Drainage Channel

09-28-2012 11:50 AM in reply to: rwhitlock1

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.

Neil Wilson (a.k.a. neilw)
Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1
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Active Contributor
rwhitlock1
Posts: 26
Registered: ‎12-05-2007
Message 4 of 10 (454 Views)

Re: Model Existing Drainage Channel

09-28-2012 11:57 AM in reply to: neilyj

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.    

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AllenJessup
Posts: 6,100
Registered: ‎05-21-2003
Message 5 of 10 (438 Views)

Re: Model Existing Drainage Channel

09-28-2012 12:44 PM in reply to: rwhitlock1

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

Active Contributor
rwhitlock1
Posts: 26
Registered: ‎12-05-2007
Message 6 of 10 (425 Views)

Re: Model Existing Drainage Channel

09-28-2012 01:28 PM in reply to: AllenJessup

Thanks for the feedback, Allen.

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sboon
Posts: 2,204
Registered: ‎11-08-2005
Message 7 of 10 (399 Views)

Re: Model Existing Drainage Channel

09-28-2012 07:53 PM in reply to: rwhitlock1

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? 

Active Contributor
rwhitlock1
Posts: 26
Registered: ‎12-05-2007
Message 8 of 10 (368 Views)

Re: Model Existing Drainage Channel

09-30-2012 12:41 PM in reply to: rwhitlock1
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.
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sboon
Posts: 2,204
Registered: ‎11-08-2005
Message 9 of 10 (350 Views)

Re: Model Existing Drainage Channel

09-30-2012 08:08 PM in reply to: rwhitlock1

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.

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jmayo
Posts: 3,002
Registered: ‎11-13-2006
Message 10 of 10 (322 Views)

Re: Model Existing Drainage Channel

10-01-2012 06:53 AM in reply to: rwhitlock1

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

 

John Mayo, PE
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