My Rohn catalog says 2'6" deep for the base and 4' for the guy
anchors. I'm guessing you were trying to drive the screws by hand, a
machine that pushes and turns them in may make a big difference.
Otherwise, a small or mid-sized backhoe or mini-excavator probably will
dig deep enough unless the rock is granite. Check your local rental yard.
If not, then engage a PE for a spread footing design. Enough mass of
concrete can work at very shallow depths.
Your trench idea seems way too little IMO.
Grant KZ1W
On 8/30/2014 3:27 PM, Linux Mercedes wrote:
So I have been trying to put up a 50' 25G tower for a little while
now. I bought some 6'x8" screw anchors thinking they'd go into the
clay soil pretty easily, and they do...for about two feet. Then they
hit rock; I am pretty sure it's bedrock or something similar from
talking to my neighbors. Obviously that's hardly enough earth for a
screw anchor to hold on to.
What are my options here? Looking at Rohn's drawings, I am entirely
sure that going down 4' for a concrete base is out of the question. I
am currently thinking I'll bust a hole about 8" around down maybe 3',
dig an angled trench for the bar of the screw anchor, and set it in
the hole with a bag or two of concrete. Hand digging that hole doesn't
sound fun, though.
For what it's worth, I'm in central Missouri.
Thanks!
--Nathan
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