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Resistivity measurements

Resistivity measurements

Resistivity measurements

(OP)
Hello everybody,

Is there any recommendation to do resistivity measurements of the soil in a land with several "levels".
I mean, the land to measure is formed by several stairs, and the question is:
do the measurements have to be done by each stair or all stairs at the same time?

If somebody could provide some clues or a good reference, I would thank you!

Happy new year for everybody!

RE: Resistivity measurements

You typically use a ground rod, which should extend below the top soil, into the sub soil.

These measurments are not extreamley accurate, as the soil conductivity depends on the soil mosture.

RE: Resistivity measurements

How big are the "stairs"?  How were the stairs formed?  Cutting into a hillside?  Filling in with non-native soil? Combination of cuts and fills?

Will the ground grid extend over more than one stair?

You would like to develop a soil model that reflects the actual layers or volumes of different resistivity soil, but unless you are going to use this detailed soil model in your analysis, it may not be worth the effort.  Do you have software such as CDEGS that allows modelling separate soil volumes?

I would at least make measurements at short probe spacings on each stair to get the upper soil resistivity on each stair.  If the stairs are large, I'd make short distance measurements several places on each stair.

Unless you are going to try to model the soil with resistivity variations horizontally as well as vertically, long probe distance measurements could be made without respect to the stair locations.  
 

RE: Resistivity measurements

(OP)
Hello jghirst

I thank your answer.
We have a main substation and this one has a grounding grid, however, the rest of the facility has also some ground rods as well as some perimetrical grounding grids (only some grounded conductor surrounding every building) and all those "perimetrical networks" are link together with the main grounduing grid of the substation.
Because of that, the grounding grid extends through all the "stairs of the land" (sorry, but I do not know the word in english language, in spanish this kind of stair is called "talud"!).
In fact we do have CDEGS and you have given a very good idea, in order to represent the soil and try to get a better representation and evaluation of the grounding grid.

If you could provide some other references, books or something similar, it would be good!

 

RE: Resistivity measurements

If you have existing ground grids and building perimeter ground wires, it will be difficult to get accurate resistivity readings of the type needed for a complicated soil model.  The existing wires will provide paths for the test currents other than through the soil.  

You will probably have to test the resistivity of the soil away from the existing wires, with your probes 90 degrees from the existing grids to avoid large errors.  Considering this, you should probably make resistivity measurements in several locations and use an average to develop a single multi-layer soil model to be used for the entire site.

SES has very good technical support for CDEGS.  They may provide some suggestions and have some technical papers that will be of use.  Give them a call.
 

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