In a few words - every installation is different and just because it worked
at one guy's house one time doesn't mean it will work at yours. I think the
biggest variable is the soil you put them in.
My GUT said there should be as much buried as there is exposed, but you can
overcome that shortcoming with concrete and steel. Even still, my GUT says
the hole should be at least as deep as the anchor is high above the ground.
Another caveat, one way to make SURE they fail is to dig out the dirt with
the backhoe's butt in the direction of your tower base and scraping the soil
towards the tower base. By doing this you're foolishly putting the softest,
loosest soil ("back-fill") right where you need the hardest, densest soil
("undisturbed"). Always put the backhoe on the OTHER side of the guy anchor
hole from the tower base.
Elevated guys are not to be taken lightly! With ground-level guy points,
you can always put in a 3 or 4 foot high fence running from a ground-level
guy anchor towards the tower as far as necessary to keep anyone or anything
from running into the guy by accident. This is a common treatment out in
vacant fields where the commercial towers get put up - that or the
higher-security "put a fence around the whole guy anchor" approach.
I had 12-foot long 6-inch so-called "thick-wall" oil well casings sticking 5
feet in the ground and 7 feet out of the ground. The holes were augured,
not dug with a backhoe. The holes were 8-10 feet deep, with several 5'
sticks of rebar in the bottom. The towers were smallish - 80 feet tall Rohn
25 towers. No problems.
But that's purely anecdotal, and YMMV, of course.
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