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# SURVEY INFORMATION - Rookie Question

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(@jzamora1073)
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Hello All,

I am new to surveying, I am actually working on a site connection design for a house in new york city.

Since I am a mechanical engineer I have no real experience with site surveys, can someone please give me some advice on the following:

1. What is RIM elevation and CL on a site survey? (File Attached)

2. How can I find the invert elevation of a sewer line from a site survey at any point in the survey (The land survey marked some INV elevations on two manholes).

Any advice would really be appreciated by this forum, Thanks a lot.

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Member
(@va-ls-2867)
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CL is the centerline of pavement elevation

The invert is calculated by finding the difference between the upstream and downstream invert elevations divided by the distance between the inverts to determine the slope. Then multiply the slope by the distance from MH to the point you want to determine and you will have a delta elevation to add or subtract from the starting manhole depending on if you are going upstream or downstream.

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(@norman-oklahoma)
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To restate what Jason wrote - "CL" indicates the elevation of the roadway surface at the centerline of the road.

Note that pipes run straight and at constant grade between manholes. At least in theory. Very rarely do they curve. Any changes in grade or changes in direction occur at the manholes. And 300' is about the maximum distance allowed between manholes. "INV" is short for "invert", which is the elevation of the flowline (inside bottom) of the pipe. The slope of the pipe is the rise/run (elevation change/length of pipe), and you can calculate the elevation of any particular point along the pipe between manholes by applying the slope to the distance from the nearest manhole.

The "RIM" annotation merely indicates the elevation of the rim of the manhole lid, which is fixed in place.  They typically make a convenient and secure elevation reference.

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(@am95405)
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Using this opportunity to learn, is the 286.6' the horizontal distance or the slope distance? That is, side A or side B in the attached picture?​

​

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(@peter-ehlert)
Joined: 10 years ago

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@am95405

you need to hit the used book stores, look for highschool level geometry text books.

Member
(@am95405)
Joined: 2 years ago

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@peter-ehlert: What's up with all this negative commenting? Why can't you just answer the question?

I understand the difference between horizontal and slope distance. But I know in surveying, sometimes one is used, other times the other, and in this case, I wanted to know which one. The answer could have been A or B, that simple.

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(@mark-mayer)
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@am95405

The 286.6' dimension shown on the OPs map would typically be assumed a horizontal distance. Notably, with an elevation difference of only 0.67' in that distance, the slope distance rounds to 286.60'. SO ... the difference between slope and horizontal difference is practically nothing in this example.

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(@am95405)
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@mark-mayer

Thank you for the clarification that the documented value is B, the HD. And the observation of the small difference between SD and HD in this case.

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(@field-dog)
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Posted by: @jzamora1073

1. What is RIM elevation and CL on a site survey?

RIM is the rim of a manhole. We normally indicate north rim because manholes aren't perfectly level. Quite often surveyors use a chisel and make an 'x'-cut in the rim to indicate exactly where the described elevation was shot. CL, if I remember correctly, is normally the physical centerline of a road vs. the centerline of a right-of-way.

Posted by: @jzamora1073

2. How can I find the invert elevation of a sewer line from a site survey at any point in the survey (The land survey marked some INV elevations on two manholes).

INV is the elevation at the bottom of a pipe where it enters a structure (sewer manhole or storm water manhole).

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(@bstrand)
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I shoot the middle of the manhole lid for rim elevations since the bottom of manhole CL shot is usually directly under that.  But yeah something along the lines of what others have said.  The pavement CL shot is probably the crown so that's just not a very good label, imo.  It's better to avoid labeling the crown the centerline in case someone takes that to mean the surveyor shot the middle of the right-of-way.

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(@mike-davis)
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@bstrand

No problem, plus I just right clicked on his avatar and he is in Queens, New York which is highly unionized ... so he's liable to get a visit from some guy named Guido who'll convince him that his knee caps are more important than trying to engineer something out of his realm of comprehension.

FWIW - Don't Feed the trolls !

Member
(@jzamora1073)
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@mike-davis

Hi mike Davis, I am unsure what you are referring to with your comment. I am an actual engineer just starting in this profession. I work for a consulting engineering firm (non-union) and I was Just had doing some research for my own knowledge.

Thank you,

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