Worse case soil model for grounding
Worse case soil model for grounding
(OP)
In terms of safty analysis, what is the worst case soil model(the soil model can be more than two layers) for substation grounding?
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Worse case soil model for grounding
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RE: Worse case soil model for grounding
2. Solid rock that is not porous to water.
3. Even solid rock that is porous to water presents a problem.
4. Clay that is nonporous to water.
5. What is known in Pennsylvania as pyrite shale, which when exposed to air and water turns into clay and expands. There is a section of the PA Turnpike between exits 3 and 5 north of Pittsburgh that have fences in the rock cuts because the pyrite shale landslides every time it rains.
6. 100% bentonite clay backfill. This will expand so much as to exclude water and turn into an insulator. You can get a prepared backfill from Erico that has a small amount of bentonite clay that produces moderate compaction.
RE: Worse case soil model for grounding
thread238-124763
Hi Rezaa -Welcome back to the forum.
Probably you meant soil model accuracy instead safety. If there is inaccuracy in the soil model, probably the natural way to balance this is overdesigning the ground grid to be in the safe side.
Soil for grounding purposes could be modeled as a single uniform layer, two, three or "n" layers. However, more than two soil seldom provide significant better results do to non homogeneous nature of the soil.
In any case, soil model is an approximation of actual soil condition and can be used to perform a safety grounding design.
Here are some quotes from the IEEE Std 80 that could be applicable to your question:
RE: Worse case soil model for grounding
RE: Worse case soil model for grounding
The soil layers that should be considered are the one under the crushed rock.
Double check if at the depth of the ground grid and ground rods are in the frozen leyer since 10 ft (~3 m) is normally below the frozen depth in most cases ouside permafrost regions.
Probably will be a good idea to check with a geotechnical consultant with knowledge and experience in this area to verify the worst case condition.
As general sample, check in the enclose figure will provide you ideas of soil measurement, model and seasonal variation of resistivity.
RE: Worse case soil model for grounding
RE: Worse case soil model for grounding
RE: Worse case soil model for grounding
RE: Worse case soil model for grounding
RE: Worse case soil model for grounding
See thread238-68202 for more discussion of frozen soil.
RE: Worse case soil model for grounding
from melted snow and follow with a thawed layer while the ground grid remains in frozen soil.