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SURVEY INFORMATION - Rookie Question

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jzamora1073
(@jzamora1073)
FNG Member

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.

This topic was modified 3 years ago 2 times by jzamora1073
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Topic starter Posted : August 16, 2019 3:54 pm
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VA LS 2867
(@va-ls-2867)
200+ posts Member

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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Posted : August 16, 2019 7:32 pm
Brad Ott liked
Norman Oklahoma
(@norman-oklahoma)
5,000+ posts Member

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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Posted : August 16, 2019 8:00 pm
Ethan liked

Field Dog
(@field-dog)
1,000+ posts Member
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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Posted : August 17, 2019 6:44 am
BStrand
(@bstrand)
1,000+ posts Member

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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Posted : August 17, 2019 8:23 am
Ken Salzmann
(@ken-salzmann)
500+ posts Member

Good advice above.  Here is some more:

MH rims can be raised or moved during paving projects, so depending on the age of the project, your survey may or may not be what is there today.

If you compute the invert along the pipe  for a specific location, do it from both manholes, once downstream, again upstream.  If you get the same elevation, you have a check.

If the elevation is critical, check the inverts and top elevations again. Or better yet, have the surveyor come back to verify things.  Once construction starts and you discover a mistake, and Murphey's Law says the mistake is never in the right direction, that extra expense to check things is now minimal.

Redundancy keeps you out of trouble. 

Ken

 

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Posted : August 17, 2019 8:52 am

Mark Mayer
(@mark-mayer)
1,000+ posts Member
Posted by: @bstrand

I shoot the middle of the manhole lid for rim elevations since the bottom of manhole CL shot is usually directly under that. 

That is the case with coned manholes, which may be common in your area. They are relatively uncommon in mine.  Usually around here the manhole cap is the donut type and the lid is offset from the center of the barrel. One edge of the rim will come close to the center of the barrel, and that is the part of the rim  I shoot.   

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Posted : August 17, 2019 10:12 am
holy cow
(@holy-cow)
10,000+ posts Member

What concerns me a tad is the information for the two rim elevations provided.  The one on the right appears to be a few inches higher than the driving service of the road.  That is not ideal.  The one on the left is more than a foot below the road surface.  That is terrible when access is critical.  You would need to tear up the road to get to the lid, then attempt to loosen the lid to get it out of your way.

Interpolating between the end invert elevations, as described by others, should be very close to the actual elevation of the flow line.

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Posted : August 17, 2019 12:05 pm
A Harris
(@a-harris)
5,000+ posts Member

I always shoot the manhole rim above the inlet and outlets and give an invert as measured from those locations when the manhole was not practically level.

Label the manhole as "MH #1" and to the side or on a separate sheet show manhole diagram of the location of the inlet and outlets and an "X" to depict the location of the MH elevation and then list the invert distance and show elevations.

Locally, most original manholes were practically level, even the ones that fall in a road. They have begun to set them according to present pavement elevation and slope. Never want to run over one around here, might need to realign your front end afterwards.

The ones that fall in a road are subject to be raised and lowered according to change.

They do not like for roads to be dug up for any reason and to do so means mucho red tape before or mucho fines afterwards for the destruction of property.

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Posted : August 17, 2019 1:06 pm

Mike Davis
(@mike-davis)
100+ posts Member

I hate be the bearer of bad news but the aforementioned mechanical engineer is practicing outside of his area expertise (and can be fined & reprimanded) and you have just aided & abetted him in his crime, which is a common issue if you look at most states boards of registration Disciplinary & Enforcement Actions

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Posted : August 18, 2019 1:00 pm
hpalmer
(@hpalmer)
200+ posts Supporter

@mike-davis

The ME did exactly what he should do when he sees acronyms he is not familiar with, he asked questions.  He is not practicing outside of his expertise.  I disagree.

 

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Posted : August 18, 2019 1:07 pm
holy cow
(@holy-cow)
10,000+ posts Member

May be a case of being an ME and an LS but the ME part pays the bills.  Some of us are multitalented.

Asking questions is a very positive thing.  NOT asking questions is something a foolish egomaniac does.  I saw nothing here requiring a surveyor's license.  Could simply turn loose a plumber and a backhoe operator and make things fit.

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Posted : August 18, 2019 2:10 pm

Mike Davis
(@mike-davis)
100+ posts Member

@hpalmer

Au contraire, please direct your attention to his attached pdf file, he's asking how to calculate the INV ELEVATION AT ANY POINT IN THE SEWER LINE ... the lack of knowledge to perform a simple rise over run equation is prima facie evidence that he's practicing outside of his area of competence. He needs to contact a Civil Engineer or Land Surveyor, depending what state he resides in. If you have any doubts about about my concerns, call up your state board and run the above scenario by them and see what they say about the blatant violation of the rules & regulations let alone the morality of the situation.

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Posted : August 18, 2019 2:10 pm
Norman Oklahoma
(@norman-oklahoma)
5,000+ posts Member

@mike-davis

I answered on the assumption that he was working on his own property. That would not be illegal.

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Posted : August 18, 2019 2:17 pm
dmyhill liked
holy cow
(@holy-cow)
10,000+ posts Member

Believe this is a case of being unfamiliar with the specific terms.  Engineers are fully trained in understanding slope calculations.  ALL ENGINEERS.  Electrical, chemical, etc.  INV is not commonly used elsewhere to mean what it does relative to sewer lines.  One does not need a land surveyor's license to work around a sewer line.

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Posted : August 18, 2019 2:17 pm

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