@lurker I'm only talking vertical for shooting over the out pipe.?ÿ For horizontal we did shoot the center of the lid.
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I was wondering about that. I thought 0.05 was a bit large to miss rims by, if they had good control.
To emphasize my point?ÿ ........ 0.05' is a lot if you are shooting the same point on the structure. But considering the topography of the typical lid and its frame, it's not so much.?ÿ ?ÿThen you should be doing your measure downs to the point that you rim tied. Which, if you tie the center of the lid?ÿ - which I think is very commonly done - isn't possible to do. Then there is the matter of correcting for slope and getting the rod on the actual invert. All these things are potential sources of error that do quickly add up to well in excess of a tenth, IMHO.?ÿ
Has anyone tried lowering a scanner in to a structure to obtain data that way??ÿ I have one of these tripods, but have tried lowering our scanner in yet.?ÿ ?ÿ
@lurker entering a manhole for any reason is never a wise thing to do for than a few reasons, the first being that your insurance company would be extremely unhappy about it, another being, at least in my area of practice, most are a minimum of 4' deep and, by definition, a confined space entry.?ÿ OSHA would have a field day if they caught us doing that.?ÿ The reason I mention it is because shortly before I started with one of the companies I have worked for, a crew chief climbed down into a 10' storm manhole and collapsed at the bottom, the IM went down to help him and they both died as a result of methane gas being present.?ÿ My crews are not allowed to enter manholes for any reason, they are also not allowed to walk foundation walls. we do most new building and home construction with basements.?ÿ I refuse to locate a foundation that is not backfilled.
We have one.
Woohoo baby does it ever flex and shift when the scanner is panning.
Boss won't let us invert the sx10 to get covered in cobwebs roaches and the other well know substance found in SAniSewers.
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We elevate it as little as needed.
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Otherwise use the pipe Mic and do it with teams for traffic and even developed a cheat sheet that has the added measurements needed to convert when deflecting the arm into deep and or smaller diameter drops in a vault.
We had a sanisew manhole that required a 35' rod to measure.
I asked the GIS tech I supervised who trained him how to get the rim elevation with that big of a triangle.....
Tyler.?ÿ Tyler left before i got there.....
Tyler was a computer programmer turned GIS. Tech.
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@john-putnam The fun part is when the bend in the pipe is NOT made at the manhole.?ÿ There is a large (42 inch) sanitary sewer line near me that has manholes and then a joint downstream there is a precast bend.?ÿ Don't ask me why it was done that way, it just was.
Andy
Yes. It worked great. It was rather too time consuming for everyday use. Might possibly be worthwhile if as-building a subdivision's worth of new construction in one go. In the circumstance it served to confirm the measure down I got using a Bosch "Disto".
You don't need to lower the scanner all the way into the manhole. In fact, you want to keep it high enough that it will pick up the rim as well as the bottom in the same scan.?ÿ
The Disto method (ie/using a handheld EDM in "indirect mode") works great for as-builts of new construction. "Indirect mode" means applying an internal clinometer reading to correct for slope. It doesn't work for in service pipes because of the flow..... and the stuff that is in the flow. Neither does scanning for the same reason.?ÿ ?ÿ?ÿ
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@jitterboogie Manholes can be entered in compliance with OSHA and confined space regulations. Why does everyone assume I'm talking about entering them in an unsafe manner?
This may sound picky but when it comes to dead flat grades (0.5% or flatter) I prefer somebody to get down in the manhole with the grade rod & a 4?? carpenters level for the inverts coming in so long as the flow & fumes allow. Men up top hold the rod level & shoot with the automatic level. The invert out can typically always be rodded with just a vertical rod as the manholes around here are eccentric with the lids & steps over the inverts out.
I say the easiest and best way to get invert elevations is the two-prisms-on-the-rod method.
You can hold the rod at any angle and get horizontal and vertical location at the same time.
I wasn't lambasting you. I agree completely and have been OSHA trained beyond where most people even want to know.
I was just agreeing with the dont send anyone down into a manhole unless absolutely necessary. And with land surveying I can't see why you ever would descend into one.?ÿ
I say the easiest and best way to get invert elevations is the two-prisms-on-the-rod method.
You can hold the rod at any angle and get horizontal and vertical location at the same time.
Do you have a spreadsheet that helps with that XYZ math?
Plus, I would still think in reality we are talking +-0.1-0.2??.
I am picturing an old nasty sanitary sewer with rough conditions at the inverts as well as a 25?? fiberglass extension rod sort of curving as it leans while taking prism shots at two different section heights. ?ÿThis is all in my head, though, I admit I have never actually tried this.
I usually do measure downs very first thing on the job, before control is set even. ?ÿOne, it gets the nasty out of the way early. And B, it often identifies that one more structure downstream or upstream that I might have missed otherwise.
Why does everyone assume
Because this is a land surveyor??s message board. ?ÿIt is what we do.
