Metallic pipes are known to show low resistances compared to their surroundings(Vickery & Hobbs 2002). Does this imply we can effectively use ERT method to detect metallic pipes in the subsurface.
Dear Emanual,
The basic theory about conductive pipe detection based on conductivity is right but there are some factors due to which usage of ert for burried pipe detection becomes tricky
1. polarization of the metallic pipes which blocks the charge carriers at its external boundaries. The conductive pipe will not allow much current to penetrate below so that other layers can be detected clearly.
2. You will be needing specific inversion program to tackle that sharp conductive layer which might become tricky
3. Know the subsurface lithology if it comprises of weathered rocks or intrusions with rich conductive mineral content then detection will be tricky.
If you want to detect subsurface pipes then you should go for GPR survey but if resistivity is the only option then i recommend you to go for induced polarization (IP) survey as the charge build up around the pipes will support to localise them. If IP is not possible and you have to perform ERT then i would suggest you to start the acquisition from an area that is without burried pipes and gradually enter into area where you have subsurface pipes by doing this you can have the idea of any new anomaly introduced (by knowing the response of pipe)
Umair Bin Nisar , I am trying to use ERT technique and thank you so much for this wonderful response, the points are well noted.
On the specific inversion tool, would you recommend any efficient program?, I currently own ZondRes2D and Res2DInv.
Also, do you have articles or books that deal with this scenario very well, that you may share with me?,
I really appreciate your input.
Regards.
I think you can use effectively the ERT method to detect metallic, but the Induced polarization(IP) gets more effective results. you can Also, using GPR techniques if your target is located Near-surface.
Thank you Ahmed Abd El Gawad and Ahmed J. Al-Heety for spending time to contribute.
A joint interpretation of ERT and gradient magnetic techniques will be a good choice.
Provided that the acquired data is well interpreted, electrical method will be effective. However, GPR can also be used if the depth of burial of the metal is not significantly high.
ERT and GRP are a good combinations towards detecting a buried object considering the depth abd comparing their results.
Depending on the depth of the pipe and the properties of the surrounding soil, the ground-penetrating radar method can be a great tool for the detection, localisation and mapping of utilities, such as metal pipes. I assume that the pipe is located in the shallow subsurface (since it presumably has been buried in a utility trench), the you should be able to detect clear reflection hyperbolae when crossing with a GPR profile across the pipe. These hyperbolae are very useful to determine the average velocity of the GPR pulse in the medium above the pipe, and thus to derive a quite accurate depth. Different GPR antennae transmitting pulses with different mean frequency can be used, depending on the diameter and depth of the pipe. The higher the frequency used, the greater the spatial imaging resolution, but the lower the penetrating depth. Unless you are dealing with highly conducting (top) soils, GPR should work fine. In case of ferromagnetic pipes, magnetometry should work nicely. Electromagnetic induction measurements are as well efficient means for the detection of metallic structures/objects. Can you provide more information on the expected depth of the pipe and the surrounding soil?
ERT is good but factors like depth of buried pipe, size of pipe which determines the inter-electrode spacing, is the pipe void or does it contain fluid, hence, type of fluid and the properties of the overburden soil.
It depends baisically on the resistivity contrast between the buried pipe and its surrounding...... The specific characterestics of the pipe itself determine if ERT is useful or no..... The combination of different geophysical methods with their good interpretations provides the optimum detection way.....
hello dear ebong you can use forward modeling with different diameters of pipe and depths
Pipe mapping need to focus depth and size of pipeline and material of the pipe such as iron, or coated or mixed material and fluid type.
1. ERT is a suitable method to study the cross section of the pipe crossing
2. Magneto Telluric method 2D and 3D scan used for leakage of fluid and material of pipe in shallow and deeper level.
3. In under water survey we recommended 2D ERT floating electrodes
https://www.springerprofessional.de/en/mitigation-dredging-in-seabed-geotechnical-engineering-study-usi/18350182
ERT is efficiently effective in mapping buried metallic pipes provided there is quantifiable contrast between the metallic pipe and the Earth's environment in which it is buried.
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