Earth mat design and soil resistivity measurement

[ct_sg]

Hi, I would like to ask if anyone can advise.
As I can’t wait for work to excavate to formation level, current RL111, my earth mat at RL101. How can I accurately test and obtain soil data from RL101 (approx. 9m below) and RL91?

I read wenner method provides apparent resistivity. If I need 10m, my prob spacing needs to be 10m apart giving me C1 and C2 probe at 30m apart. IEEE81 spells 300% to have tight margin of error.

I will be using CDEGS to compute the soil model. And when we reached RL101 level, all the soil above (RL111 to 101) will be removed and build basement. Therefore, i am not sure if by removing apparent resistivity value from current level to 9m below, and establish 9m value as "ground level, and anything lower will be deemed as 1m, 2m, 3m deeper layer to infiniti is feasible?

By the way, in the same requirement, there is a requirement of the earth mat shall be designed to limit the coupling between the lightning protection and the power system earthing mat to 110V when a discharge of 100kA from lightning strike occurs. How do i calculate/check this? Any recommended reading material from the internet you can recommend?

Thank you.

 

[jghrist]

I'm not familiar with the terminology RL111 and RL101. Your should use several probe spacings with the Wenner method, up to 4 times the maximum grid diameter. Put the measurements into CDEGS RSAP module to determine the soil model.

You would have to use the high frequency module of CDEGS for lightning analysis, which will be quite complex. I don't know what is meant by limiting coupling to 110V during a lightning strike, but I would expect lightning voltages to be much higher than this at all points on the system. The lightning and power system ground mats need to be bonded together.