If you really have rock, why are you digging?
The big concrete bases above ground are impressive, but if not securely
attached to rock, they will easily turn over!
There's no need for all that rebar framing, except in a big hunk of
Why not just use some of the techniques shown to tie down your tower base to
If you don't think the base provides enough holes, weld it to a steel plate
and tie that down with as many rockbolts as you need.
I just used some 1" stainless expansion anchors from Fastenal to tie down
some large objects. They are well made and Fastenal can provide ratings.
They provide a psychologically reassuring grip at the bottom of the hole
that you may like, but I have no idea how they compare to grouting. For
sure, grouting depends upon adequate roughness of the pins, like the rebar
surface, and the sides of the hole.
The modern SDS drills are amazing. Harbor freight even has a cheap one that
will surely last long enough to finish your project. Your greatest hazard
is horizontal separations of the rock, so your hole has value to help you
asses the quality of the rock!
Since you have the hole started, how about setting some long anchors in the
pattern of your tower base holes with epoxy, welding them to a rebar cage
and then pouring concrete to level your hole at the original ground level?
It's sure worth getting the expected overturning moment from the tower
company and checking the anchor ratings against it, which is pretty easy.
It's hard to get comfortable with all this grout/epoxy technology, but done
right it's good. Remember all the concrete ceiling slabs held up in the Big
Dif in Boston? And the one that fell down because of improper epoxy use?
Here's a 3/4" drop in anchor. You can screw threaded rod of any length into
it after it's expanded by driving in a bolt to expand the lower part..
Adhesives for anchoring
Here's a manufacturer's catalog showing drop ins. They show relatively
shallow setting, so I doubt if the numbers are anywhere near the ultimate
capacity of the anchor. No doubt they would advise you about rock
Anchor performance with epoxy. Failure modes explained and example
Wow, this is fun stuff. I think I'll put up a tower this year.
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