Two areas of comment:
1) You live on what is essentially a solid rock, albeit somewhat
porous... why can't you
drill into it and epoxy rods into the caliche to hold the tower
base? Or pressure-grout?
Similar techniques are used in New England with bedrock.
It will require some engineering work, and cost you a few
hundred to get it documented,
but it's surely doable.
2) The idea of holding up a rohn 25 by partly relying on guys, and
partly on the base isn't
quite right. When a tower is guyed, the overturning forces get
translated into compression
forces, which push the base down. The main role of the foundation
is to keep the tower from
I think your best solution will be to find an engineer who has worked
with caliche, in
erecting light poles or similar structures. He'll know what's
available to machine drill
clean holes for the foundation rods, to tie into the stratum. You
may actually have to
pour a small concrete cap, just to make up the distance from the
caliche to grade level.
But it would be the underlying stratum itself which provides the
resistance to the overturning
moment of the loaded tower.
Jim Jarvis, President
The Morse Group, LLC
Achieving Results in a Changing World
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