Dipping Manholes
Dipping Manholes
(OP)
Do your surveyors dip the center of Manholes, or do they dip all inverts?
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RE: Dipping Manholes
RE: Dipping Manholes
RE: Dipping Manholes
RE: Dipping Manholes
Anyway, back to the original question, in my opinion, since they've popped the manhole lid off, why not get all the inverts while they're there? Why take chances to assume the drop across the manhole? The drop could be anywhere from 0.1' to 2.0'
RE: Dipping Manholes
We work with deep manholes all the time, (>8' depth) and when manholes get this deep, this error is magnified, and it does become significant (10' deep manholes will be approx. 0.2' off).
It's hard to get real accurate measurements without actually crawling down to the inverts, but guys that crawl into sanitary manholes this deep have special codes and requirements they need to meet, and most surveyors are not certified to do this. So, we usually just shoot the middle of the invert and assume a 0.1' rise/drop to both inverts (obviously, only after a visual inspection). While this also has some error associated with this methodology (usually in the hundredths), I've seen much bigger errors when surveyors take vertical measurements when their level rod is not plumb.
I will say, the most accurate way to get these inverts is to use the attachment that CEE98 mentioned. Great idea! That's why I come here, to learn something new, and hopefully offer some positive feedback. Thanks.
RE: Dipping Manholes