If you can't break up the shale and remove it then why not use it as the
anchor? Bore some holes in it, epoxy in some rebar and cast that in
concrete or epoxy in some anchor bolts and bolt in the guy anchor
extension.
I've seen one, and heard of another epoxy failure.
I saw where a tower was anchored into a huge slab of volcanic rock with
rebar, thick, maybe 1 - 1.5" thick, the epoxy crept over time, the
rebar, set in ~3 feet, popped out, and the tower came down. The rebar
had been set with a backward angle, so it was roughly 90 degrees to the
guys, with a cap welded on top to prevent the guy anchor from slipping
over the top, but the whole rod slipped out over time, bending it into a
nice curve over a couple of years.
The other instance was all over the news years ago:
https://en.wikipedia.org/wiki/Big_Dig_ceiling_collapse
Epoxy is nothing but tough plastic, and bends, moves, flexes, migrates,
and smears, just like plastic, but more in the long-term. It's very
tough any given moment, but over hours, days, weeks, it's more like a
hard wax. I play with JB Weld from time to time, and see it bend, flex,
peel, pull loose, tear, et cetera, usually with hand tools, but
sometimes just by hand. As strong at it is, it isn't, really. Get it
thin enough, even a few mm, and you can bend, tear, or break it with
your hands, and even put a dent in it over time, with a finger nail.
The clear epoxy resins are even worse, more like some sort of hobby glue.
Aside from occasional potting, where the material is static in an
enclosure, I've not found a use for epoxy, except in one mast/tower
instance.
~30' mast, with an 8"x8" base on a 12" wide concrete piling. I drilled
four 5/8" holes 8 inches into the piling, then blew them out, and washed
out with water, then solvent, partially filled the holes with JB Weld,
then I inserted four 1/2" threaded rods, with the threads filled with JB
Weld to avoid bubbles, into the holes, and removed any over-flow. I
then placed four washers over the rods, then nuts, NOT tightening them,
just very much finger-snug, knowing darned well the epoxy would fail if
I used a wrench.
Then, on top of these nuts, another washer, then a 1/4" thick steel
plate, another washer, and nut. These I tightened, as they were
tightening against the nuts and washers below, not straining the epoxy,
or concrete. The plate is to prevent the rods from breaking out of the
concrete if the mast is hit from the side, and splitting the piling, as
well as preventing any unusual pressure, if any, from the mast putting
strain on the epoxied rods, resulting in epoxy, or concrete failure.
The threaded rods extend upward a few more inches, so, more nuts, then
washers, THEN the mast base, more washers, and nuts.
Overall, a 36" deep 12" round cement piling, four 1/2" rods 8" into the
piling held with JB Weld, and a 1/4" thick steel plate to secure the
rods, all this just to hold up a roughly 30' mast made of chainlink
fence toprail to support a pair of inverted V's.
As rugged as it sounds, it can be likened to toenailing a 4x4 onto a
wooden deck, just a little more rugged for the conditions here, all the
stuff at the bottom just keeps the base from kicking out if something
bumps it. As there's no strain on the JB Weld, and overall the pressure
is downward into the rods, nuts, and large washers sitting right on top
of the concrete, it's working OK.
Honestly, I would not trust the epoxy beyond this, certainly, not for
anything that matters, or isn't secured in other ways. In this case, it
just keeps the four "pins" at the bottom of the mast assembly from
popping up out of the concrete.
Kurt
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