If you rely on the weight of the base to settle itself, two things will
happen. The first is that it will settle progressively over a LONG period
and may actually bob up and down depending on water content of the stuff
under the base. Second, and most dangerous, is that it will settle
unevenly, making your new Rohn the Leaning Tower of Whizzer! Without a
proper footing, I would bet money on both happening.
I suggest that you talk to local contractors and ask them what they have
done for other jobs in the area under similar soil conditions. The usual
method for buildings is to drain the area (if possible and permissible),
then put in several deep cores by drilling holes and filling with
concrete. Then a crushed rock pad is put down and the concrete foundation
put in over that, tied to the cores. Expensive!
I take it that the idea is to put up a vertical in the swampy area? I
think the concrete base idea is going to be either too expensive, too
difficult, or too risky if done on the cheap.
Why not consider a more flexible, lightweight structure made from
irrigation tubing or EMT? A tripod-like affair mounted on a pad made from
pressure-treated 4x4's or railroad ties could be anchored in the swamp and
guyed. The pad could be anchored to trees or long stakes driven into the
ground (rebar? galvanized pipe?)
73, Ward N0AX
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