EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: SPRX on March 10, 2016, 01:10:06 pm
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Has anyone ever tried or used Ground-penetrating radar to detect solid (like concrete) items underneath the soil ground?
I need to do an inspection on the installation of Footing Piers of the slab underneath my house from sides without digging the ground, and revealed that Ground-penetrating radar would do the job. I need to inspect about 1-2m depth in the soil.
I did a quick search, and it seems there are lots of high-end, Ground-penetrating equipment are available and are freaking expensive.
Has anyone build this sort of jig to do this sort of job, or any better idea?
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Seen one being used in an archaeological excavation in the 00's.
It could distinguish between different densities surprisingly well but the geometrical resolution is +- 10cm at best. We could easily distinguish between soil and adobe walls buried underground. Stone walls and cavities were a piece of cake.
We were able to obtain results similar to this
(http://i.imgur.com/SLzPwaL.jpg)
Actually I think the geology team had both radars and resistivity machines. They were a 20 strong mining exploration team working with our excavation only for a short while.
Here is another excavation using the same technique.
http://www.kerkenes.metu.edu.tr/kerk1/05remote/geophyss/resistivity/res02/index.html (http://www.kerkenes.metu.edu.tr/kerk1/05remote/geophyss/resistivity/res02/index.html)
As you can see antique walls up to 12 meters below surface are clearly outlined.
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The Wikipedia article includes a table of penetration depth vs object size at different frequencies:
https://en.wikipedia.org/wiki/Ground-penetrating_radar
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Hi,
There is a lot of information on this company's website.
http://www.sensoft.ca/ (http://www.sensoft.ca/)
GPR is fairly sophisticated, and probably made in small quantities. That is why it is expensive.
Regards,
Jay_Diddy_B
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The maximum depth that the GPR can "see" is highly dependent on the permittivity of the soil as well as operating frequency. The soil permittivity largely varies based on soil water content , Clay/sand ratio and mineralogy. 2m is fairy deep and I would say is only possible (IF possible at all) in relatively dry soil. Forget about what is advertised by the companies (they probably test their stuff in 0% water content and 100% sandy soil). GPR is a great tool if you know where to use it and what to expect from it. Also GPR output is usually inform of parabola reflections (not a map like it was posted by HAL-42b ) to get to the map that you see there the output needs to be processed heavily and also spatially arranged by a total station. Moral of this comment if you haven't used it before you cannot do it yourself you usually need to hire a surveyor to do it.
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http://hackaday.io/project/4440 (http://hackaday.io/project/4440)
You will probably also have to spend some time in the RF forum here if you decide to design your own.
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Look at any episode of the BBC "Time Team" program. They used these high-tech subsurface measuring systems before deciding where to dig. There were a lot of inconclusive results due to a range of reasons and it really requires an expert to be able to make an interpretation of the results.
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Hi,
I'm a geophysicist and use GPR daily for a broad range of applications. A couple of points:
In my experience, 2m depth is readily achievable provided the clay content of the soil is not too high. Water saturation has relatively little impact these days provided its conductivity is less than about 2000 mS/cm. When GPR systems originally came out, they typically used average front ends and 8 bit ADC's with correspondingly poor dynamic range. Nowadays almost all systems use orders of magnitude more sensitive receiver analog amplifiers and around 30 ENOB sampling which provides dramatically improved results. Indeed we use radar routinely underwater in dams and reservoirs to inspect liners.
For a 2m depth range, a 450MHz broadband antenna would be appropriate. I suspect, like others have said, that it would be very difficult to construct your own electronics with appropriate front end and sampling and write your own software to be able to produce cross sections suitable for interpretation. To give you a feel for cost, our lower end systems were on the order of $35K while our larger high speed 3D ones cost us around $500K.
This being said, I would think you could hire one of any number of underground utility locators to come and do a quick survey for you. Our local ones here in TAS provide this service for around $150/hr.
Interpretation of GPR is relatively complex. The image shown previously is a time slice from a 3D GPR volume. This would have been collected by doing as series of closely spaced orthogonal lines on a grid on the ground surface, with data subsequently interpolated into a 3d volume and then sliced at a given time to provide a plan map of the GPR response at the corresponding depth.
Unless your footing piers extend out laterally beyond the footprint of your slab, you will most likely be unable to use GPR to see them. The reinforcing mesh in the slab will almost certainly prevent you from seeing through the slab to the pier footings beneath.
If you happen to be in southern Tasmania, let me know - I'd be more than happy to give you a hand on a weekend some time.
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Great, Thank you guys, and really appreciate the replies.
Hi Htassell, Thank you very much for the description provided, and I am based in Brisbane, QLD.
The survey service around $150/hr seems very reasonable, and could you please let me know if anyone you know around Brisbane who provide the service.