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Joe-Bouza
Posts: 4,755
Registered: ‎12-15-2008
Message 21 of 43 (337 Views)

Re: Grading Contours not true to slope values

02-17-2013 12:41 PM in reply to: area51visitor

Most typical sections would be constructed perpendicular to the base line. If 2:1 is exceeded in that direction, the onus is on the designer to corect the typical section to provided for the inevitable skewed slope exceeding maximum.

 

 

Thank you

Joseph D. Bouza, P.E. (one of 'THOSE' People) Civil 3D 2012 & 2013
HP Z210 Workstation
Intel Xeon CPU E31240 @ 3.30 Hz
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Note: Its all Resistentialism, so keep calm and carry on

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wfberry
Posts: 1,749
Registered: ‎09-05-2006
Message 22 of 43 (333 Views)

Re: Grading Contours not true to slope values

02-17-2013 01:48 PM in reply to: SDcivil

I am on the CADvisers side in this.  A 2:1 slope on a typical highway project is measured perpendicular to the direction of the roadway.  Send a knowledgeable surveyor to set slope stakes and he sets them based on perpendicular distance from his hinge point on the edge of the slope.

 

Bill

 

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area51visitor
Posts: 116
Registered: ‎03-05-2011
Message 23 of 43 (332 Views)

Re: Grading Contours not true to slope values

02-17-2013 02:42 PM in reply to: CADvisers

The OP won't post his drawing with the example, but I suspect CADverse is correct, he isn't building his 2:1 slope correclty, but adamantly believes that he is. I'm done looking at this until he responds with his file.  Still, there probably is room for improvement with contour construction, but I can't see how such a miniscule deviation would matter in the case of land development. Most state and local regulations I believe allow some deviation in construction.  If something needs to be that precise I recommend the OP to create the points himself and send those to survey; good luck constructing it that accurately.  I've never had an asbuilt completed that didn't show at least a tenth or two in deviation.

- Brian
"Very funny, Scotty. Now beam down my clothes."
Valued Mentor
fcernst
Posts: 1,086
Registered: ‎01-07-2011
Message 24 of 43 (301 Views)

Re: Grading Contours not true to slope values

02-17-2013 06:33 PM in reply to: SDcivil

Right it's simply a Convention matter... Like Ms. Mercier said long ago, Gradings (and Corridors) construct their Daylight projections perpendicular from the Feature and the contour output is a function of that Convention.

 

So, it's not "wrong" per se. It's correct for its Convention.

Fred Ernst, PE
C3D 2015
Ernst Engineering
www.ernstengineering.com
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BrianHailey
Posts: 2,749
Registered: ‎04-27-2005
Message 25 of 43 (281 Views)

Re: Grading Contours not true to slope values

02-17-2013 10:05 PM in reply to: SDcivil

Another thing to think about, why is the requirement 2:1? Well, it's because 2 is a nice easy number to remember. Why not 1.94:1? Why not 2.37:1? Did someone actually go out and calculate that in this particular situation, the optimal slope for this design, based on good engineering judgement, life and safety considerations, cost of the project, ease of constructability, is exactly 2:1?

 

Absolutely not!

 

Instead it probably went something like this, "I've used 2:1 in the past in areas like this and it seems to work pretty well, we should probably use 2:1 again in this area."

 

So, ask yourself this, why is slightly steeper then 2:1 in this area a bad thing and the answer is most likely, "because the city/state/county/<insert other reviewing agency> said we can't go steeper than 2:1".

 

I had the same type of thing come up when I was doing design for some utilties. The design criteria said that the sanitary sewer and the waterline had to be a minimum 10' apart. In my design, for about 2', they were only 9.5' apart.

 

Who came up with this magic number of 10'? Again, it's a nice easy number to remember and is close to (error on the side of caution) what the actual minimum distance between the two utilities actually should be.

 

And, yes, I ended up redesigning the utilities.

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Joe-Bouza
Posts: 4,755
Registered: ‎12-15-2008
Message 26 of 43 (258 Views)

Re: Grading Contours not true to slope values

02-18-2013 06:31 AM in reply to: BrianHailey

Better yet add some coordinates to those contours to get extra close :smileywink:

 

 

"All Contours are lies"; all it take is one look to see - flip a face for example

Thank you

Joseph D. Bouza, P.E. (one of 'THOSE' People) Civil 3D 2012 & 2013
HP Z210 Workstation
Intel Xeon CPU E31240 @ 3.30 Hz
12 GB Ram


Note: Its all Resistentialism, so keep calm and carry on

64 Bit Win7 OS
Valued Mentor
fcernst
Posts: 1,086
Registered: ‎01-07-2011
Message 27 of 43 (257 Views)

Re: Grading Contours not true to slope values

02-18-2013 06:31 AM in reply to: BrianHailey

2:1 max slope is definitely per Code (IBC, IRC, HUD) that US jurisdictions follow. 

 

  • Must check steepest slope for max criterion compliance: The steepest path on a slope is perpendicular to contours.

In that regard, I acknowledge the OP's original concern of the use of C3D projection grading tools by his staff, if they do not understand the projection grading convention. 

 

 

 

 

Fred Ernst, PE
C3D 2015
Ernst Engineering
www.ernstengineering.com
*Expert Elite*
BrianHailey
Posts: 2,749
Registered: ‎04-27-2005
Message 28 of 43 (248 Views)

Re: Grading Contours not true to slope values

02-18-2013 07:20 AM in reply to: fcernst

fcernst wrote:

2:1 max slope is definitely per Code (IBC, IRC, HUD) that US jurisdictions follow. 


Ok, so, what's my slope? 2:1. I label it 2:1, not 2.0:1 or 2.00:1 so, if I have a slope of 1.6:1, that rounds to 2:1, right? :smileywink:

Valued Mentor
fcernst
Posts: 1,086
Registered: ‎01-07-2011
Message 29 of 43 (240 Views)

Re: Grading Contours not true to slope values

02-18-2013 08:38 AM in reply to: BrianHailey

Regarding that,  I would not want to give the other side's attorney any opportunity to demonstrate the design is below 

code in deposition.

Fred Ernst, PE
C3D 2015
Ernst Engineering
www.ernstengineering.com
*Expert Elite*
Joe-Bouza
Posts: 4,755
Registered: ‎12-15-2008
Message 30 of 43 (221 Views)

Re: Grading Contours not true to slope values

02-18-2013 06:31 PM in reply to: fcernst

Wow ! So now we need a projection grading that finds the first contour then turns to be perpendicular to it?

 

Add more coordinates!

 

The 2010 maintenance code fro ADA forces a maximum 2% cross slope ... Actually 1:48 which theoretically is 2.08%, but reviewers are stuck on 2%. So now when I grade an ADA accessible route that will obviously have a longitudinal slope less than 5% - 2% of that will invariable lead that some point being a tad over 2%. What's the answer? 1.9%

 

sometimes you need to adjust for code values. If ambient conditions are going to create a daylight slope to exceed 2:1 then my suggestion is to use a value slightly flatter to insure maximum is not exceeded.

Thank you

Joseph D. Bouza, P.E. (one of 'THOSE' People) Civil 3D 2012 & 2013
HP Z210 Workstation
Intel Xeon CPU E31240 @ 3.30 Hz
12 GB Ram


Note: Its all Resistentialism, so keep calm and carry on

64 Bit Win7 OS

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