Substation Rock Wheel Traction

[RSChinn]

Our substation rock is sized 3/4 to 1-1/2 (years ago it was larger) and some of the heavier utility trucks have a tendency to sink their wheels into the rock making traction difficult. Our normal depth is between 4 and 5 inched. Any ideas or suggestions?

 

[7anoter4]

In my opinion, you have to prepare the truck route –a wide path of 10 feet will be fine-up to the farthest place to be reach-and restore the rock layer in the required location.

 

[PHovnanian]

Not a civil engineer, but I would suggest mixing in smaller aggregate with the rock you have. That will in the spaces between rocks and keep them from shifting under load.

 

[RSChinn]

To Zanoter4- preparing a truck route and then restoring it is time consuming and restoring the rock after usage tends to mix dirt with the rock when re-using it. This problem is quite common is many of our substations. Thanks for the suggestion anyway.
To PHovnanian- using smaller rock will make the void spaces smaller and the resistivity will go down. If anything, making it larger, but with sharper spall edges might, might work. therefore...

New Question: What are typical rock spalls that others are using that stabilize while driving over them with a heavy truck such as a boom truck? Larger sizes than 1-1/2? Rock spall specification (if such a thing exists)? Who determines rock spall size and its resistivity?

 

[cranky108]

Our Civil engineer belives this is a rock specification issue, which he should be an expert with after having his Prius stuck in the deep rock.

We have since been using a different rock mix.

On another sub, we just used aspault, for grounding issues, and hence no geting stuck.

 

[bacon4life]

We use fractured rock rather than crushed rock. I am not sure exactly why the difference is between the two, but the fractured rock seems to lock together better and therefore is much more drivable. Here is what we order:

1 ¼ Inch minus, 100% fractured, uniformly Railroad Ballast

At one of our substations the crew used a vibratory roller/compactor on the whole yard after spreading yard rock. The roller seemed to lock the rocks in place quite well.

 

[RSChinn]

To cranky108- great idea with the asphalt. IEEE80 even states that asphalt is 10,000 ohm-meters at its worst (wet). One thing we need to make sure of is the drainage of rain water. Thanks for the answer.

To bacon4life- We will certainly look into what "fractured rock" is vs spalls. How do you determine a value for resistivity for this stuff? Thanks.

 

[bacon4life]

I think one of neighboring utilities some testing on it a decade ago, but I don't have any of the details.