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Active Contributor
Posts: 32
Registered: ‎11-15-2006
Message 11 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 11:58 AM in reply to: Balex
Unfortunately the problem is exactly what Balex brought up. When using the grading tools with a feature line that varies in elevation (and with mulitple horizontal angle points) the surface generated by the grading does not produce slopes that meet the criteria set. For example: If you do a simple grading to a distance and set the slope to 3:1 you end up with slopes that are greater than that. The difference is great enough to cause over a 7 ft bust at the toe of a 110 ft high slope at 3:1. In simple terms-the grading tools don't work(again) this time with a hidden error that only now has been discovered(since most of us never suspected that it wouldn't produce the correct slope). I would suggest that any one who has used the grading tools for the development of slopes go back to every job and hand calc the toes and tops of slopes to verify that don't have a serious problem, like a slope that now projects past your project property line. I have attached a simple example dwg that illustrates the problem. The slope shown should be 33.33 % not 34.+%.
*wfb
Message 12 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 01:21 PM in reply to: Balex
I think the grading tool produces the proper slope normal to the grading
object's X-Y plane. Unfortunately due to a sloping grading object it will
not produce the minimum slope that you want. It will take a little "trial &
error" to get the proper slope.

Bill

wrote in message news:5435420@discussion.autodesk.com...
Unfortunately the problem is exactly what Balex brought up. When using the
grading tools with a feature line that varies in elevation (and with
mulitple horizontal angle points) the surface generated by the grading does
not produce slopes that meet the criteria set. For example: If you do a
simple grading to a distance and set the slope to 3:1 you end up with slopes
that are greater than that. The difference is great enough to cause over a
7 ft bust at the toe of a 110 ft high slope
at 3:1. In simple terms-the grading tools don't work(again) this time with
a hidden error that only now has been discovered(since most of us never
suspected that it wouldn't produce the correct slope). I would suggest that
any one who has used the grading tools for the development of slopes go back
to every job and hand calc the toes and tops of slopes to verify that don't
have a serious problem, like a slope that now projects past your project
property line. I have attached a simp
le example dwg that illustrates the problem. The slope shown should be
33.33 % not 34.+%.
Active Contributor
Posts: 32
Registered: ‎11-15-2006
Message 13 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 02:19 PM in reply to: Balex
I beg to differ. The proper and only calculation of any slope is the ratio of the vertical distance to the horizontal distance regardless of what plane it is in. Any "trail & error" required is due to a program that was not written to meet the exacting standards that we all must meet, as I am sure you must also. It's one thing for the problems(most in the past after sp3) of crashing and losing work but to have it calculate the wrong information is border line if not out right negligence. Are we now required to check each and every function for each and every update to verify that the numbers and information given to us is correct and then to "work around" and use "trial and error" to adjust those that we are lucky enough to find out are wrong? Bill, you have given those of us using C3d and looking for answers to our issues a lot of great information. My frustration is not with you and is more directed at Autodesk for them not finding this error out on their own.
Member
Posts: 5
Registered: ‎07-18-2006
Message 14 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 02:32 PM in reply to: Balex
You guys are confusing me. Are the grading tools not suposed to produce the slope that you specify from a 3D feature line? What is all this "correct slope from the XYplane" business?? There is no use for a tool that does that. We are trying to do grading. Shouldn't we expect the correct result from an automated tool like this one? This sounds huge (unless i'm missing something).
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Civil3DReminders.com
Posts: 2,430
Registered: ‎10-13-2005
Message 15 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 03:22 PM in reply to: Balex
Accepted engineering design is for the slope to be measured perpendicular to a baseline, hence why Civil 3D and Land Desktop calculate it this way, and probably every other civil engineering software out there.

Take a road for instance your typical cross section will show a 3:1 slope, this is measured perpendicular to the centerline. If you wanted the distance between contours to be 3:1 then the 3:1 slope on your section would have to be an odd value (ie 3.27:1) depending on the slope of your road for each and every cross section.

Look at any of your corridors with a set slope and measure the contours and you will see that this is the case, not because it is wrong but because this is how it is done due to standard engineering practice.

When the project get staked out the surveyors will create a line to go off of, usually parallel to the centerline, and set slope stakes. The Contractor will set temporary stakes perpendicular to the baseline to get his 3:1 slope. I don't think any of us want to see slope stakes be adjusted to produce 3' between contours for a 3:1 slope, because it would cost a lot of money to accomplish.
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Registered: ‎10-13-2005
Message 16 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 03:41 PM in reply to: Balex
Its not an error it is the correct way to do grading. If you want a set distance between contours then do it one of the ways I have already posted about.

Just because you didn't understand what you where doing, don't take it out on Autodesk and the program. This method was used in Land Desktop and I'm sure its the same "issue" in all other computer programs. Even the paper and pencil method of creating contours from a road centerline had this "issue".
Civil Reminders
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Active Contributor
Posts: 32
Registered: ‎11-15-2006
Message 17 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 04:29 PM in reply to: Balex
How often do your field crews come back in the office and show you a slope toe or top that is off many feet due to the method you espouse? Have you ever worked on a hillside project? Obviously not. It is simple geometry (but time consuming) to correctly calc contours off of a 3d baseline using circles and lines. This method was used back in the pencil and paper day. Calculating the contours from a line perpendicular to a base line shows a lack of basic geometry skills. LDT calculated the slope wrong and so does C3d.
Member
Posts: 5
Registered: ‎07-18-2006
Message 18 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 04:55 PM in reply to: Balex
Standard engineering practice around here is: if i say "3:1 slope" on my grading plan, it needs to be 3:1 measured perpendicular to the contours (that's what a 3:1 slope is), and I note it as such with an arrow and rate drawn along the fall line.
If the surveyors use a base line as a basis for their slope stakes, they need to calc a rate at that station from the top to the toe based on my true 2:1 slope.
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Message 19 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 04:57 PM in reply to: Balex
I have worked for a large contractor in the Santa Clarita, California area on projects with hillsides. Every project the surveyor set a line, usually parallel to the centerline of the road. The grade checker would set temporary stakes from the hub the surveyor set up the hill at the ratio on the stakes. Usually 2:1 or 3:1, rarely an odd amount such as 2.34:1. I have attached the sample drawing with the slope labeled showing the 3:1 slope.

So I think you need to decide are your contours incorrect or are your typical sections incorrect? Based on your response all of your typical sections for roadways need to be redone because they don't reflect what you want built. It is impossible to have the contours be exactly 3' apart on a 3:1 slope shown in section view on a sloping baseline.
Civil Reminders
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Registered: ‎10-13-2005
Message 20 of 31 (121 Views)

Re: Create slope perp to contours

12-26-2006 07:30 PM in reply to: Balex
I agree totally and just as the surveyor has to adjust so does the designer when grading from a baseline with sloping elevation and make the same calculations the surveyor has to make or choose a different method to get the intended result.

A wish probably needs to be added to the other area of this group for it to calculate a slope based on the steepest slope possible. Although I'm not entirely sure that for a curved line with sloping grades that a clean solution is possible. Some contours would be greater than the intended distance apart.
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