Allowable step and touch potentials for a grass surface

[cuky2000]

Below is a picture with substations with crushed rock and green grass. For the same clearing time and same SC current level, the allowable step and touch potentials will depend of the wet resistivity of the surfacing material.
For instance, crushed rock δ=3000 Ω.m. However, wet grass and organic soil the resistivity will be less than the crushed rock.
If anybody know the green grass resistivity and the design rational for the grounding/earthing grid, please let us know.

 

[HamburgerHelper]

I guess someone has to periodically mow the grass in the substation? I suppose ,too, deal with a grass fire if something faults?

 

[bacon4life]

Well, I have used wet grass to test 10 kV electric fences, perhaps we could use that to back calculate the bulk resistivity of grass? A 15 cm piece of grass is usually enough to drop the jolt from to

More seriously, was this the original design or a later evolution? If no one is championing touch/step potentials, other factors seem to degrade the yard rock over time including:
1. Desire to lower herbicide usage.
2. Airborne dirt and organic material contamination.
3. Trenching or excavation without careful segregation of dirt vs. yard rock.
4. Soil fines working their way up through the yard rock.
5. Desire for more environmentally friendly appearance.
6. Storm water management rules may treat grass more favorably than yard rock.

 

[jghrist]

I would assume no surfacing material in the calculation of allowable step- and touch-voltage. C_s=0 in IEEE-80 Eq. 29 & 32.