Soil Resistivity Testing Scoping 1

[ThePunisher]

Hi all, we are working on a scope for the soil resistivity testing for an undisturbed/ungraded area where our new plant would be located. The proposed testing would be a 4 point Wenner Method. We have the proposed plot plan and site grading plan. The plant and substation areas are also indicated in the proposed plan. An initial Geotech report was made (without soil resitivity) based on selected bore hole nos. and locations (both process plant and substation locations). The area is tropic and have both rainy/summer seasons and the area is still not developed.

I would like to seek guidance as to where and how many test locations should we specify? Is there a recommended spacing criteria?

Will it be ideal to perform the tests on area which is still undisturbed, undeveloped and ungraded presently? OR just do the testing after it is site graded? We were intending to get initial results that we can use in our grounding calculations?

I have read the IEEE 81 but I find difficulty in getting answers and I am hoping to get your suggestions and guidance as the contractor may come back and ask us the test locations, how many points and what are the spacings required.

 

[ThePunisher]

I apologize for the duplicate. My original post went missing in my desktop and I was under the impression that it did not go through.

 

[lume7006]

Hello,

I think that:

1) You may do some resistivity measurements in the area which is undisturbed and they may help you to get a rough idea of the kind of soil you have. Preliminary analysis to determine possible layers deep of each one, and so on.
In this way you may get an idea of native soil composition that could be used for the next step.

2) If the ground is to be graded (I understand it as to make some cuts on it, like stairs) the values of resistivity will surely change because, what used to be deeper now, it will be closer to the surface, but you have from the step 1 some information.

3) There is also the possibility that soil be "filled" with some materials after some studies are done by the construction area, depending on the type of material used, there may also be a change on the resistivity values.

4) IEEE recommends to perform the resistivity measurements when the soil is dry, in this way you will get the most critical case to size your grounding grid.
It may be difficult to find that seasson but, otherwise you may get some nice results which will not be true in a dry seasson.

5) Related to the number of locations to be measured, this depends on the size of the area and feasibility to perform them.
If you have the chance to take some large traverses in which you can start from a very close separation (less than one meter) and continue until a very large one you will get a deeper vision of the kind of soil, deep of each layer, and so on.
Of course you need to take a look at the measurement equipment characteristics, leads, and so on.

I hope to have helped you!

 

[ThePunisher]

Very informative, thank you. I actually decided to perform the soil resistivity during the summer season and when the site is already graded in order to obtain the realistic soil resistivity measurements.