Soil resistivity under water table

[Power0020]

I am carrying out a grounding study for a distribution kiosk as the client requires 1 ohm combined Hv and LV resistance. The site is near to the sea but soil measurements show a deep layer of about 600 ohm.m which seems to the bed rock.

min. depth of water table is about 35 m deep however, the resistivity value suggest a coarse bedrock.

Another site had a 100 m deep rod resistance suggesting that the deep layer resistance is not exceeding 200 ohm.m.

I am not sure if I can adjust the soil measurement model with the deep rod resistance retrospectively. Is there any reference standard allowing using a deep rod resistance as an acceptable guide for deep soil resistivity other than Wenner measurements.

Any clue?

 

[cuky2000]

Deep ground well (electrode) is an effective method to achieve the desired ground resistance level of 1Ω with very little help of the high resistivity of the upper soil layer. (See the similar post) for references)

It is expected that the proximity to the sea there will be a salty water table with higher conductivity (low resistivity) that will divert more of the fault current to the lower status of the soil.

Due to the rock hard soil, driven rods are not an option. A deep drilled hole needs to be done with a driller/boring machine at a cost ($5K-$10K per electrode) Occasionally more than two well connected in parallel may be required for meeting a low resistance.