The only way to "as-built" a pipe run is to make measurements as it is built. Making observations at the top of the pipe, and subtracting the thickness and diameter will give you the invert, alignment, and actual proof of how the pipe was constructed.
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Oh no!
All that tells you is the "as-laid" situation. Trench was then backfilled and construction traffic probably ran over it.
In any case, as others have said - read to 0.01' but state quoted values only accurate to 0.05'
where I live curb is frequentyly laid at 0.5%, street's strip-paved with side ditches at 0.3% and larger 48" & 54" RCP sewer outfalls are laid on ridiculously flat slopes so that you can run them for miles and miles along a stream or creek's watershed before a lift station is needed - just has to be done that way but it works. Even a recent smaller outfall of 24" was laid at 0.15% at times in order to maintain adequate vertical separation where needed or be deep enough to run that sewer to an area further up the reach and lower than what's in between potentially. Throughout my limited career I've always heard other engineers (typically at firms that performed the engineering & project's surveying) want to refer to these plans as record documents rather than as-built plans. Essentially it's a record of what that particular survey crew shot that particular day. They some times better understand that no two surveyors are gonna agree exactly on everything and I have seen it too where some streets' utilities or subgrade were not properly bedded or compacted which later on led to settlement. Some may get upset at this and say it's lack of diligence or improper procedures in surveying but it's the truth if the field crew happens to shoot something good on one particular day only to come back years later and note the same vertical isn't holding true anymore due to changing site conditions and circumstances. Some times it was best to put a record document note stating such and noting the day that the surveying was performed.
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as the project engineer before, I have seen 4 different 3man crews all from the same firm's survey department go out to "as-built" shoot the inverts on dual 72" RCP in large precast storm manholes close to 8' interior diameter that were close to 23' deep (large industrial project close to 80 acres). On certain instances, the field book's level notes by the different party chiefs agreed within 0.02' on the same inverts and at other times as much 0.18' out. This required one man down at the invert holding a 4' or 6' masonry level in the invert of the pipe where the other end had a piece of flat bar stock screwed to the tip so that the grade rod could be supported by it at the same elevation. Man up top at the grate or MH rim would do his best to level up the grade rod while the part chief was booking rod readings. I had doubts to the contractor that did the work as they bid it much cheaper than any of the local outfits and laid it much faster. But hey - the GC got exactly who they wanted at the price they wanted. Being that I wasn't comfortable with the results nor the work of said contractor I left the record documents up to the firm owner to decide on. But the project got it's map recorded and the CO awarded and it's functioned just fine for several years now
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While some might say this is sloppy surveying with that sort of variation, I'd gladly ask how close do you often agree with another surveyor's wide open & easy boundary survey - given changing sites and some times just flat out lack of agreement? Much less the task of shooting inverts over 20' deep with it requiring 3 people at times and being confident in your results? Do you have it in the budget to shoot said inverts multiple times on projects such as these? Most don't I'd wager.
While I agree on any inverts on an as-built being actually accurate to 0.01'?ÿ You can use a hidden point routine in SurvCE or record the data and use a spreadsheet. I think this is much better than sloping poles and other +/- methods.?ÿ
The place I work put together a 15' rod from old carbon fiber pieces that we put the 12I on and simply stick the rod all the way down to the invert.?ÿ Works pretty slick.?ÿ Deeper stuff seems uncommon fortunately but for that they're got a pipe mic...
It always amazes me how they calculate the slope of a pipe run between manholes with only two pieces of data, disregarding the 200 to 300 feet in between. Theoretically that may be fine for a design.
The only way to "as-built" a pipe run is to make measurements as it is built. Making observations at the top of the pipe, and subtracting the thickness and diameter will give you the invert, alignment, and actual proof of how the pipe was constructed.
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That's what I did on a sewerline project I did about 2 years ago.?ÿ Had to meet 1/2% for about 200' so I was out there shooting TOP almost every stick.
With the rod tilted, and sometimes guessing what you're resting on, broken pipe, covered with crap, etc, it's tough to pretend to get that kind of accuracy.?ÿ
I've seen guys spending time, trying to compensate for tilt, and record numbers that show flow running opposite from reality, and you can clearly see that one pipe is lower than the other, but their notes say otherwise.?ÿ Oh, well
Most manholes (I think) are designed with a "drop" or inlet invert some 1 to 2 tenths higher (or more, I've seen consistent 0.5' drops in network designs) than the outlet. So for the tight stuff you have to shoot both inlet and outlet inverts.?ÿ I've done the "compensate for tilt" method a few times using a smart level (which can read in degrees so it makes that calc even easier for us).?ÿ I'll record to a .01 but wouldn't guarantee that - like @frozennorth and @jim-frame allude.?ÿ I'd put money on a consistent .03-.05' accuracy, though
While I agree on any inverts on an as-built being actually accurate to 0.01'?ÿ You can use a hidden point routine in SurvCE or record the data and use a spreadsheet. I think this is much better than sloping poles and other +/- methods.?ÿ
In Excel your data is represented by Columns and Rows, H is the column the coordinates are in so H3,H4,H5 are represent the first coordinate. Sorry I did not have the rows and columns on when i printed the pdf.
