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Create slope perp to contours

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Message 1 of 31
Balex
1475 Views, 30 Replies

Create slope perp to contours

How can I create a slope that gives a true slope perpendicular to the contour lines? e.g. specifying a 3:1 slope from a sloped baseline will give a 3:1slope perpendicular to the baseline alignment but the actual slope will be steeper than 3:1 as measured by the contours.
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Message 2 of 31

You could always calculate it out, basic geometry, just a pain if you have lots of slope changes. You could even do it with three lines graphicaly.

I can't think of a reason you wouldn't measure the slope from a baseline though; since it seems to be standard engineering practice to do so. But I am sure someone will give examples of the exceptions. Message was edited by: ChristopherF
Civil Reminders
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http://www.CivilReminders.com/
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Message 3 of 31
Balex
in reply to: Balex

Thanks Chris for your reply.

I've always done it graphically using older ACAD versions. I thought I had seen a newer version that produced a true slope perp to contours.

I need perp to contours for landfill design where maximum slopes are typically regulated at 3H:1V or 4H:1V. For long slopes produced from a berm baseline with significant slope along the baseline, I don't want to be steeper (violate regs) nor too flat (requiring more construction materials and losing waste airspace).

Upon further thought, I guess I'll just calc out what the slopes are required for ACAD input for different baseline slopes and create a reference table that will generate required slope perp to contours.
Message 4 of 31
Anonymous
in reply to: Balex

Balex:

You have certainly made some valid points. In some cases your assessment of
incorrect slopes should be checked out.

Bill
Message 5 of 31

Why not do it the other way around? Choose a contour as a baseline location and grade up and down from it. Come back and create your berm baseline from the surface (elevations from surface). Add the created feature lines to a new surface and delete the unneeded featurelines. This assumes that the berm baseline is flexible in its location and slope.
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http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
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Message 6 of 31
Anonymous
in reply to: Balex

Hi,

Can your clarify what you mean by "Contours".

A contour is defined such that it is horizontal and the maximum slope is
ALWAYS perpendicular to the contour.

You must be talking about something other than contours.

--

Laurie Comerford
CADApps
www.cadapps.com.au
www.civil3Dtools.com

wrote in message news:5434904@discussion.autodesk.com...
Why not do it the other way around? Choose a contour as a baseline location
and grade up and down from it. Come back and create your berm baseline from
the surface (elevations from surface). Add the created feature lines to a
new surface and delete the unneeded featurelines. This assumes that the berm
baseline is flexible in its location and slope.
Message 7 of 31
Anonymous
in reply to: Balex

Laurie:

I believe that Christopher has a legitimate answer.

Bill

"Laurie Comerford" wrote in message
news:5434946@discussion.autodesk.com...
Hi,

Can your clarify what you mean by "Contours".
Message 8 of 31
Anonymous
in reply to: Balex

Laurie is correct. The problem must lie in the configuration of the grading.

"Laurie Comerford" wrote in message
news:5434946@discussion.autodesk.com...
Hi,

Can your clarify what you mean by "Contours".

A contour is defined such that it is horizontal and the maximum slope is
ALWAYS perpendicular to the contour.

You must be talking about something other than contours.

--

Laurie Comerford
CADApps
www.cadapps.com.au
www.civil3Dtools.com

wrote in message news:5434904@discussion.autodesk.com...
Why not do it the other way around? Choose a contour as a baseline location
and grade up and down from it. Come back and create your berm baseline from
the surface (elevations from surface). Add the created feature lines to a
new surface and delete the unneeded featurelines. This assumes that the berm
baseline is flexible in its location and slope.
Message 9 of 31

Yes, the maximum slope is always perpendicular to the contour, but a 3:1 slope created from a sloping baseline does not give a result of 3 units of measure between the contours. The value between contours is less than 3, therefore producing a steeper slope measured from contour to contour rather from the baseline.

The posters question was to get 3 units of measure between the contours. The two ways I can think of to get his desired result is to calculate the slope required off the baseline to get 3 units of measure between contours or grade from a baseline with no slope, ie a contour. So, I think you would have perfered I stated a baseline with no slope, which is the same as a contour.

I think the original poster needs to determine what the regulatory agencies definition of maximum slope is. If they accept a 3:1 slope off a sloping baseline or if they actually measure the distance between contours to determine compliance with the maximum slope. I searched the California regulations and they did not provide a definition how a slope is measured.
Civil Reminders
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni
Message 10 of 31
Anonymous
in reply to: Balex

I guess I didn't discern from his original post what he was trying to do. I
understood that for whatever reason, he was not getting contours with 3 foot
horizontal spacing from his grading. From your comments I now see what he
was trying to do and I concur that drawing a 3D sloped line will not give
the 3 ft horizontal spacing for the contours. It comes down to the principal
of fundmantal orthographic projection, or in our 3D automated world, a
strategy to make the tools do what we want.

wrote in message news:5435118@discussion.autodesk.com...
Yes, the maximum slope is always perpendicular to the contour, but a 3:1
slope created from a sloping baseline does not give a result of 3 units of
measure between the contours. The value between contours is less than 3,
therefore producing a steeper slope measured from contour to contour rather
from the baseline.

The posters question was to get 3 units of measure between the contours. The
two ways I can think of to get his desired result is to calculate the slope
required off the baseline to get 3 units of measure between contours or
grade from a baseline with no slope, ie a contour. So, I think you would
have perfered I stated a baseline with no slope, which is the same as a
contour.

I think the original poster needs to determine what the regulatory agencies
definition of maximum slope is. If they accept a 3:1 slope off a sloping
baseline or if they actually measure the distance between contours to
determine compliance with the maximum slope. I searched the California
regulations and they did not provide a definition how a slope is measured.
Message 11 of 31
Anonymous
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.+%.
Message 12 of 31
Anonymous
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.+%.
Message 13 of 31
Anonymous
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.
Message 14 of 31
Anonymous
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).
Message 15 of 31

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.
Civil Reminders
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni
Message 16 of 31

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
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni
Message 17 of 31
Anonymous
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.
Message 18 of 31
Anonymous
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.
Message 19 of 31

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
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni
Message 20 of 31

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.
Civil Reminders
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni

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