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Dead Rebar

Discussion in 'Surveying & Geomatics' started by John Thompson, Mar 18, 2017.

  1. John Thompson

    John Thompson 2-Year Member

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    Found this yesterday.
     
    Brad Ott and FL/GA PLS. like this.
  2. flyin solo

    flyin solo 3-Year Member

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    i wouldn't call that "dead." Dying, perhaps, but still sounds like a "dig here" to me.
     
  3. Steve Hankins

    Steve Hankins 7-Year Member

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    Maybe touch the top portion of the dead rebar with a magnet.
     
    Jim in AZ and Nate The Surveyor like this.
  4. Nate The Surveyor

    Nate The Surveyor 7-Year Member

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    It's got a null at the end. Go slow.
    Somebody may have pounded the magnetism out of it.
    N
     
  5. Sergeant Schultz

    Sergeant Schultz 7-Year Member

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    I've dug at many a null signal and found something, but usually only after pulling in a distance or two to narrow the search radius.
     
    Kris Morgan likes this.
  6. billvhill

    billvhill 3-Year Member

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    The scary thing about this is, it makes you wonder how many times you could have missed something. I worked on a job this week where I had this issue. I searched all morning and was almost convinced that nothing had been set. There was a railroad near by which had a curve about a half mile away. I ended up locating the tracks and calculating the pc and pt. I finally found something and was able to backtrack from there. When I started recovering corners, I almost had to be on top of them to pick them up. The monuments were capped 5/8" rebars about 18" long set in seventies.
     
    Nate The Surveyor likes this.
  7. Holy Cow

    Holy Cow 7-Year Member

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    I don't know about everyone else's case, but when the video is over for me two other potential videos appear to be selected. The one on the right is a banned scene from a Tarzan movie made in 1934. My, oh my !
     
    Dave Karoly likes this.
  8. Holy Cow

    Holy Cow 7-Year Member

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    This thread follows directly in line with the story I told here a couple of days ago about dead bars set by the DOT with about two inches of asphalt overlay over them.
     
  9. Shawn Billings

    Shawn Billings 5-Year Member

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    Always a good idea to do a little digging before you set a monument (unless you are the original surveyor, in which case it doesn't really matter). I don't want to someday find one of my capped rods to be 0.2' from an original rod that's buried a few inches below grade.
     
    Nate The Surveyor likes this.
  10. Mark Mayer

    Mark Mayer 7-Year Member

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    Many a time I have watched a supposedly experienced person use the Scheonny poorly. It's kind of a thing with me. Waving it around too fast, swinging it around such that the height above ground of the sensors is all over the place, not systematically covering an area. Every unit comes with a little instruction booklet which aught to be read, comprehended, and followed. There is a science to the use of the pin finder which few users seem to comprehend. It's almost like a guy should have to get a certificate of competency on the thing before being allowed to use it. (The guy in the video is using the unit reasonably well and, after all, he has found the buried "dead rebar" one way or another)

    The geologic history of Oregon has included numerous basaltic lava flows and basalt is a rock with a high iron content. As such a lot of times the pin finder rings for ordinary field rocks around here. That, together with the usual metallic garbage that accumulates around property corners, renders the Sheonstedt only search success rate somewhat lower than 100% even when used correctly.

    Most survey crew members seem to think of waving the pin finder around as the beginning and end of a pin search. I tell guys that before they even turn the thing on they should go through a checklist in their minds. Occupation lines? Bits of flagging or old lath? Evidence of digging by surveyors past? Location of previously found irons relative to road and curb lines? Look first, really look. This is the "art" part of the pin search. Then, and only then, go to buzzing. After you are done buzzing look again before abandoning the search.

    Then you really can't declare a point lost until it's been staked out and the position dug regardless of whether it buzzes or not. Sometimes bars don't ring.
     
  11. Tyler Parsons

    Tyler Parsons 7-Year Member

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    I have one of the indicating Schoenstedts GA-72. Most in-place monuments show indication to the right side. When I buy new rebar, I test each with the pin finder to see if they have a strong mag field. If not, I touch a very strong magnet to one end and usually give them a hammar tap at the same time. I paint the end that gives a right indication red and that gets set for the top.

    I usually throw my 60d coontrol spikes in a bin with the same magnet for a while. It makes them much easier to find weeks or years later.

    Also, waving the strong magnet over the area you are searching can sometimes induce enough magnetism to make the monument visible to the pinfinder. Doesn't go too deep though.
     
  12. Mark Mayer

    Mark Mayer 7-Year Member

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    TMI. Those are personalized based on your Youtube viewing habits. My, oh my indeed.
     
  13. Shawn Billings

    Shawn Billings 5-Year Member

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    I don't know how often this happens by percentages, but it's a lot. I turn on the locator and start sweeping. I'm looking where I'm sweeping and I see the stake, or evidence of the stake, before I pick up a signal, because at the same time I'm sweeping with the locator, I'm also sweeping very intently with my eyes ("really looking"). The stake itself, some bit of color from old ribbon, a piece of an old wood stake, a depression from previous excavation, etc.
     
    Andy J and RADAR like this.
  14. Mark Mayer

    Mark Mayer 7-Year Member

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    For me that comes under the heading of staking the point out and digging, regardless of pin finder response, before declaring the corner lost.
     
  15. Shawn Billings

    Shawn Billings 5-Year Member

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    If the guy in the video slowed down a bit over the dead rod, he probably would have noticed that the locator buzzes a little when off the rebar and goes almost silent when over the rebar. It still gives a tonal notice that there is a "disturbance in the force", just not the squeal one would normally expect.
     
  16. Shawn Billings

    Shawn Billings 5-Year Member

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    @John Thompson,
    this is a great thread by the way and probably would be a good PDH/CEU topic (something people would actually benefit from). It's amazing to me how many surveyors are unaware that locator signals are not always determined by size and depth alone. The direction of the magnetic field plays a crucial role. When we were developing the Javad locator, we tested on all sorts of objects and depths. Our locator provides a numeric signal strength indicator. The same material may give widely differing values. A 1/2" rebar, for example, may give a numeric value of 10 and another give a value of 300 (which would be closer to average).

    As Mark says, whatever your locator is, you need to know how to read it and use it. You also need to understand its limitations and have a method for making sure you didn't miss something (i.e. digging).
     
  17. Mark Mayer

    Mark Mayer 7-Year Member

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    I respectfully suggest that, doing it that way, your attention must be divided. Take just 5-10 seconds (a couple of breaths) to look around before turning on the pin finder and I think you will find your hit rate increases. Or at least the time spent making a successful recovery will be reduced.
     
    Shawn Billings likes this.
  18. Nate The Surveyor

    Nate The Surveyor 7-Year Member

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    I just want to nominate this thread for "Thread of the month".

    And, I'd like to suggest we do a "thread of the year", based on the best thread of the month.

    To qualify for "Thread of the month", it should be surveying oriented, and substancially move our profession foreward.

    And, I'll throw in a prize, for the thread of the year.

    I've got a few items in mind, for prizes. If this catches on, and our moderators approve.
    So, a yr from now, is .... Lets call it the last day of march. Ok?

    Nate
     
  19. Holy Cow

    Holy Cow 7-Year Member

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    The prize of the year is available to all. It's the Tarzan and Jane clip as they go for a dip.
     
  20. billvhill

    billvhill 3-Year Member

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    It's usually in the winter when the ground is frozen a foot or two deep, when one seems to be a little more reluctant to dig for every sound they pick up. With experience one can tell sounds that are promising but in winter I usually try to narrow the search before digging. It's kind of like digging in a grass or well landscaped yard, you want to be pretty sure something is there before you start to dig.
     

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