I did exactly this with a base for my Rohn HDBX48 tower. The plywood will
slowly decompose and as it does, soil will filter in to take its place. For all
practical purposes, it all remains "undisturbed." What the tower engineers do
not want is for the base to be sunk into fill dirt -- that won't be stable and
you will likely have stability problems (the base may wobble with time such
that your tower is no longer vertical).
With sandy soil and high water table, you risk having the hole walls collapse
into the hole, which changes lots of stuff you don't want changed and violates
the "undisturbed soil" requirement.
Kim N5OP
________________________________
From: Mike Reublin NF4L <nf4l@comcast.net>
To: towertalk reflector <towertalk@contesting.com>
Sent: Wednesday, April 30, 2014 7:20 PM
Subject: [TowerTalk] Crank-up base
I'm negotiating to get the base for my HG70-HD dug and poured. I have a high
water table, soil tends toward sandy, and an engineer said he would be happier
if the hole were 10' deep rather than the 7.5' called for in the manual.
The concrete guys I'm talking to want to line the hole with plywood to prevent
collapse. One guy who does a lot of big sign installations says he does it
regularly, and there would be no stability issues.
I've read several times the pour needs to be into undisturbed soil, no
backfill, altho that's not in the manual.
What are the facts?
73, Mike NF4L
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