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Thread: Is GPR a well-worn subject?

  1. #1
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    Default Is GPR a well-worn subject?

    Hey Guys.... maybe this has been discussed to death. sorry if it has.

    We have a lot of GPR (Ground Penetrating Radar) locating in our area. Seems to be a bit of a polarization between GPR and EM camps.

    Personally I am 100% EM but that is just my training and working in Telcom locating, is all I need. Yet, I run into the GPR guys on sites and they are able to find non-conductive structures and lines. Also, they can sweep a street crossing and find several utilities in short period of time. Lets say for instance there is new water main planning to cross a street. Seen GPR guy cross 20 meters of street and find/mark 5 utilities in half an hour. Didn't have to hook up to each one.

    Can't account for their accuracy or ... no idea. And did he know what he was finding? Or just that he found things? Not sure what GPR tells.

    On other hand, if line running along roadway/boulevard/sidewalk, I know we can knock off many kilometers of telcom line with a single hookup and walking a normal pace. Can't see that happening with GPR.

    Also spoke to a buddy whose a staff locator for civil contractor. Uses both GPR and EM but favours EM. We are in a very rainy area.... (south-west British Columbia, Canada). He claims GPR is no good when ground soaked. Also, another crew frustrated when it snows cause can't roll GPR very well on bumpy snow surface. Would imagine same for mud or bushes. Yet we EM locate over mud and bushes all the time.

    Do you guys come across a lot of GPR use in your areas?

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    Default Re: Is GPR a well-worn subject?

    They are both just tools and sometimes you need one or the other or both. GPR basically shows upside down V's on the screen when it passes over an object you then mark the spot and record the depth you might know what it is by the size but not a positive ID like an EM hook up. Sometimes the gpr shows disturbed soil (prior trench digging) and that is what gets marked. One thing on GPR is the very center of that big unit is the area that it uses not the whole antenna you see. I have both and use what I need at the time.

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    Default Re: Is GPR a well-worn subject?

    Thanks Cuda.... so once you find something, you still need to determine what it is by other evidences... like tracing back to manhole, as-builts, valves, clean-outs, etc at the surface?

    I've heard criticism ... or maybe concern is the better word, that GPR can, as you've said, give readings on stuff that isn't actually a utility. What about like rocks, or buried old junk... like abandoned pipes,etc? Just have to get used to picking that stuff out and reasoning around?

    We have parts of the city that are 150 years old and have so much crap buried, excavations are always an adventure. Some require archeological surveys before starting.

    Guess like anything, it is something you learn with experience.

    I guess I just hear a lot of the arguments between camps... yet not really a competition for anything.

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