Decoding Utility Markings Spray-Painted on City Streets

Re:Decoding Utility Markings Spray-Painted on City Streets by irrational on Tuesday November 06, 2018 @12:56AM (#18388738)

I was putting in a gate once and had them come out to mark the utilities. There was a gas line running through the area, but it was marked at 3 feet off from where I was digging the post holes. When we pulled the auger out of the ground I noticed the gas pipe right on the very edge of the hole. I'm still not sure how the auger didn't cut through it. I'm also not sure how they managed to be so far off the mark.

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Re:Decoding Utility Markings Spray-Painted on City Streets by jaclaz on Tuesday November 06, 2018 @10:44AM (#18391982)

Anecdata, but I worked several years in infrastructure projects (and in the course of that cut numberless pipes, cables - both electricity and communications - and what not), the basic issue in my experience was the sloppyness with which the drawings of the utilities layouts were made or the use of "unreliable" references.

A typical one, is the indication (on the drawing) that a cable is 30 cm from the border of the sidewalk, but in the - say - 30 years since that cable was laid down the sidewalk has been enlarged by 40 cm AND a new cable has been laid down at 30 cm from the new sidewalk AND this other new cable has not been added to the drawing (or it has been added to another drawing by mistake).

So you go there, actually find "a" cable 30 cm from the sidewalk, believe in good faith that it is the one on the drawing, and next minute you cut the one now under the sidewalk.

It is only a few years that GPS positioning is used for cable and pipes layout (which should give better "absolute positioning") but the issues about mis-labeling and mis-reporting (given also the number of different companies, particularly telecommunications ones that may lay new cables) have not changed much AFAIK.

We once had a set of bored piles (Ø 1000 mm) for the foundation of a sustaining wall miss a high pressure large diameter (Ø600 mm) methane pipeline by millimeters (the drilling rig bit the steel pipe covering, making the actual metal of the pipe shiny).

The explanation was that the people making the drawing and maintaining the pipeline took as reference the milestones of the road (that were replaced because a curve was added some kms before and shifted by 100 m) and gave our project the green flag because we were almost 100 m away from the pipeline.

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Re:Decoding Utility Markings Spray-Painted on City Streets by CapitalistCartr on Tuesday November 06, 2018 @12:14PM (#18392874)

We were putting in an electrical line for the City, had the utilities marked out, all good. Apprentice cut through an 1-1/4" (32mm) gas main with the ditch witch. Suddenly saw sand puffing up; had the presence of mind to cut the engine before running. It wasn't our fault, though, because the gas utility marked it 5' (1.5m) off. It happens.

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Re:Decoding Utility Markings Spray-Painted on City Streets by Jaruzel on Tuesday November 06, 2018 @02:55AM (#18389163)

UK anecdote here, but I remember reading that the paper maps that this stuff is recorded on, can be many decades old and were originally hand-drawn so not very accurate. In the UK at least, quite often roadworks cut through pipes and cables accidentally even though they should know where everything is.

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Re:Decoding Utility Markings Spray-Painted on City Streets by benzofuran on Tuesday November 06, 2018 @09:04AM (#18391017)

That's fairly poor locating there - either they were using a paper map or using a radiodetection line locator and the operator wasn't very good or the line/tracer wire was electrically continuous with another nearby structure and it was throwing off the signal.

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