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Depth finder for ground imaging

Discussion in 'Electronic Design' started by Noone, May 13, 2006.

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  1. Noone

    Noone Guest

    I need to dig a trench in some very rock soil which may
    include Volkswagen sized boulders. I can pick any
    course I want, but need to make sure that sub surface
    features are manageable.

    My idea was would couple a portable depth finder to
    a water filled cylinder placed on the ground and look
    at the LCD images. A VW size rock should produce
    a large echo.

    Anyone have any experience with this or can recommend
    something that they might have used to solve a similar problem.


  2. Jim Thompson

    Jim Thompson Guest

    Hire it done, with a "hard-dig" clause in your favor... you should
    hear the noise when you blow a hydraulic hose on a Michigan end loader

    ...Jim Thompson
  3. Pooh Bear

    Pooh Bear Guest

  4. Ken Smith

    Ken Smith Guest

    What's the soil like that isn't the BFRs[1]? The depth finder will see a
    very large contrast at the water to soil transition. This is likely to
    make the idea unworkable.

    [1] BFR is the industry term for a large rock.

    GPR won't work in wet clay soils.

    Seismic is too much of a blunt instrument for this sort of problem.

    If the BFRs are rare enough and the soil is otherwise uniform enough, a
    simple resistivity system may work for you. You would just avoid any
    place with a differing resistivity.

    You may be able to find the rocks magnetically also.
  5. bruce varley

    bruce varley Guest

    Many years ago I tried to detect caves using this technique. It didn't work,
    soil is a pretty poor medium for conducting sound at any frequency.
  6. Michael

    Michael Guest

    Ken Smith wrote:
    In my industry, "BFR" means a very-large-value resistor. :)
  7. Noone

    Noone Guest

    Soil is glacial drift gravel with lots of baseball sized rocks and smaller.
    BFR's are Canadian Shield granite boulders. Path is 75 feet from the
    edge of a lake, so with the gravel, I would expect a high water table
    which should help. And I can flood an area before starting to ensure
    adequate saturation for signal propagation.
  8. Ken Smith

    Ken Smith Guest

    I suspect you are just going to have to start digging and find your way
    past the rocks. Glacial till is a highly variable material. You will
    have a hard time telling, lets say, a pocket of sand from a BFR.

    Assuming this echo sounder works at a highish frequency, a mixture of
    sand, rocks and water will just eat any signal that gets into it. Most of
    the energy will reflect back at first bit of rock it hits.

    Remote sensing technologies tend not to have enough resolution for this
    sort of job. I'd try GPR before I gave up because it may work.
  9. Ken Smith

    Ken Smith Guest

    Anyone who lives in earthquake country knows this isn't true. The energy
    in an earthquake is sound.

    Also, there is an entire seismic industry based on the fact that soil is a
    good conductor of sound.
  10. Rich Grise

    Rich Grise Guest

    I've always used "BMF", which is actually an adjective and can be
    applied to any large unwieldy object: BMF rock, BMF cap, BMF
    hammer, etc. ;-)

  11. Rich Grise

    Rich Grise Guest

    Do you have enough water to actually wash the gravel away from the BMR's,
    and just haul them away? (and check the tailings for gold nuggets and
    gemstones. ;-) )

    Good Luck!
  12. Rich Grise

    Rich Grise Guest

    So stick a bunch of microphones in the ground, and wait for an earthquake. ;-)

  13. Guest

    The primary conduction is probably through rock, not the soil on top of
    it. Also earthquakes and even seismic sounders are pretty "loud" to
    being with.

    To solve the original problem, how about drilling a core every few feet
    along the path? Commonly used when siting buildings to figure out what
    they are going to be built on/if they'd have to blast bedrock to finish
    the excavation.
  14. Rich Grise

    Rich Grise Guest

    Get a piece of tube, maybe 6' long, and connect high-pressure water to
    one end of it, and use the other to shove through the loose gravel until
    you hit something big.

    Good Luck!
  15. Ken Smith

    Ken Smith Guest

    They're called "geophones" when they are stuck into the dirt.

    This exact experiment has been done a lot of times. They have also stuck
    them into the ground and just listened to the random noise of wind hitting
    the trees etc. With enough CPU power, you can make something out of the
  16. Ken Smith

    Ken Smith Guest

    You missed the entire "refraction" market. They are looking at the near
    surface stuff and the signal source is a person with a big hammer.
    Seismic sounders are mostly in the oil industry. They cost way too much
    for the guy bidding on making a road to afford.
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