Recently we ve conducted a group of time domain Induced polarization test in awaste landfill site in an island with very low resistivity(0.2-3 ohm.m, maybe due to sea water intrusion, and the contaminate lechate).
In many tests, when we only conduct electrical resistivity tomography, the result is good. Each point has been tested to times with opposite charging direction and the error is quite low (less than 1%). However, when we do the ERT and TDIP together by employing non polarized electrodes to measure the voltage, we found the chargeability measured is quite strange. It could be close to or even larger than 100%(or 1000mV/V), and also can be negative. The waveform of current is large and stable. But the waveform of voltage is quite strange. (Please find my attached photos, 1. is the waveform of voltage 2. is the waveform of current 3. is the IP test result profile, 4. is the resistivity measured when ERT IP are conducted together 5. is the resistivity when we only do ERT)
Our device compensate self potential (SP) automatically. The test array is established with 60 electrodes, 5m spacing. Wenner array, 2second power supply, 1 second stop.
We've checked the self potential of all the non polarized electrodes, tried different power supply time (4s, 8s, 12s), different battery voltage, different electrode spacing (1m to 5m), also tried what we can do to reduce the contact resistance of non polarized electrode. But the result is still bad.
The site is an incineration ash landfill in an island surrounded by sea water, the buried material includes incineration ash, demolition waste, and some metal pieces.
May I know if you have any similar experience or any suggestions about how to solve this problem?
If you are interested in this problem, please feel free to contact me if you need any additional information.
Thank!
This problem is caused mainly by cable and instrument. It's usually very diffculty to measure IP respone by an ERT instrument. You may get differeny result if you use an IP instrument. In order to measure a reliable IP response, not only the measuring electrode and the power supply electrode need to be separated, but also the measurement electrode and the power supply electrode need to be connected separately with different cables.
I have done a lot of IP projects in recent years. Since the SSIP instrument I used was separated from the measuring electrode and the power supply electrode, and different cables were used to connect the measurement electrode and the power supply electrode, we successfully obtained the induced electrical response in all projects, and the maximum exploration depth exceeded 1000 meters.Please find one of our result in page 41-43 in the attached files.
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