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Discussions with the hardheaded
I was participating in a thread on a survey related FB group where the original poster was talking about a drilled in threaded anchor bolt that he uses in concrete to achieve 0.005 repeatable measurement values over a period of 10 years. In later comments he notes that StarNet was used to adjust and tighten his control.
My point of contention was that achieving 0.005′ values when points are set in sidewalks and light stand concrete bases is not realistically possible to achieve that repeatability over a period of time for several reasons, the first being using adjusted values for the control, followed by subsurface soils, freeze, thaw, soil moisture content, with even more variables involved.
He refuses to understand the fact that, no matter how secure his point is anchored in the concrete, the concrete will move, however so slightly it may, and his point anchored in it, will move with it.
This person seems to be quite experienced and thinks that I am bashing him by pointing out the flaws in what he is saying.
What do you all think? What do you all teach your field crews about setting control?
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This discussion was modified 6 months, 3 weeks ago by
chris-bouffard.
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This discussion was modified 6 months, 3 weeks ago by
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11 Replies
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Totally agree with your assessment of the situation. The ground moves, freezes, thaws, settles, and heaves. Everything that is on top of it is moving as well. That includes trees and power poles.
We did a precise elevation monitoring project for 10+ years, and every year we ran through all of our benchmarks. It was very interesting to say the least.
As long as everything is relative, you will be ok.
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I had a similar project, although I was only involved in for about 6 years. We had to monitor settlement over a closed and capped land fill that a section of interstate highway was recently built over. Monitoring the settlement plates went on for a period of 15 years.
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It depends, we have a control point established twenty years ago in the driveway of the office. It’s stayed very stable at least compared to the local HARN and CORS points.
If you want very stable points, do it like DOT and drive rods until you get to the point of refusal, pour concrete in a ball out shaped configuration and pack it down.
There are some standards from the NGS to set those points and we’ve done a couple using a contractor and a backhoe. The last point we did was for an airport and that point has stayed very stable. Of course plate tectonics and all is shifting everything.
You might show him the DOT requirements or the NGS ones. Maybe it will open his eyes. Honestly hold a seminar about it with some local surveyors, get a few CPUs.
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Reminds me of a pharma plant I was working on…they wanted grid in certain areas on the poured floor for penetrations for multi-floor equipment. I asked how tight he needed it…”perfect”. After my withering stare and excessive eye rolling he allowed for 0.005′. I explained that I could do that for $200k. We came up with a more reasonable expectation…never had a complaint so it must have worked.
The guy you are arguing with doesn’t have anything that is spec’d to measure 0.005′, much less obtain those results after applying PPM. Yeah, my gun is within 0.005′ of a foot every time I get to the baseline, but I do it when it is overcast and about 50 and in the fall, so the conditions are almost always identical. (And every instrument I ever had exceeded the specs by an order of magnitude.)
But, we are surveyors. We deal in what we can sign our name to…and having done more Starnet networks than I can remember, I can assure you he didn’t run a traverse with error ellipses at 0.005′, unless he lied to the software. (Can you lie to software? P&R question, I guess.)
This is assuming he isn’t in a climate controlled room using metrology equipment…
-All thoughts my own, except my typos and when I am wrong.-
This reply was modified 6 months, 3 weeks ago by dmyhill.
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This reply was modified 6 months, 3 weeks ago by
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Oh, and “Discussions with the hardheaded” was the other name Wendell was considering for this website.
-All thoughts my own, except my typos and when I am wrong. -
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It’s not easy to offer constructive criticism on a public forum. Maybe his reaction had more to do with the way you engaged him than hardheadedness. Then again, most folks allow their ideas and beliefs to become woven into their identity, which makes critiques a personal affront.
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I have seen drive rod monuments jacked 15′ into the air from frost heaving. But they were not set to NGS 3D specifications with the sand, grease sleeve, etc.
I have set many NGS spec monuments for project control, but haven’t had the opportunity to go back to see if they jacked.
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It was not in the way that I engaged him, it was his persistence that his way of setting points in concrete somehow stay put while the concrete moves.
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He is working outdoors in the normal seasonal fluctuations and temps. He is insistent that the concrete will not move because hip point is, essentially a molly bolt anchored is a drifting slab.
Nothing is perfectly stable under varying conditions.
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The discussion hinged on setting points in typical concrete, the photo presented appeared to be a typical sidewalk. The methods that you describe for high order control are about as good as they get but, in this case, he is essentially setting a modified type of molly bolt in a hole drilled into the sidewalk.
His contention is that his points won’t move and while they may not move within the slab of sidewalk, the sidewalk slab will move for a variety of reasons. He doesn’t understand the idea that when the concrete moves, it takes his point with it.
Another thing that he does not understand is that by adjusting the control network, his points, at least mathematically, move from the measured values and that 0.005′ goes right out the window.
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