You are sure right about engineers not always thinking about the people who
have to actually build what they design. In this case, there IS an engineer
in the hole and pushing the wheelbarrows, me, but no, I didn't design it.
Actually, there are two alternate foundations on my permit. One is a huge 9
'x9'x5' block of concrete and the other is the pad (9'x9'x1.5') and pier (5'
x5'x3.5'). I have a feeling most of these towers are installed out in the
boonies, by some commercial entity who has a crew that does this sort of
thing on a regular basis and doesn't care if they end up with a 9'x9'
concrete "slab" under their tower. That would be the simplest way to do it.
In my case I want to minimize the concrete "footprint" in my back yard so I
opted for the pad and pier. I just wish I hadn't spent the time and effort
trying to dig the thing so it wouldn't need forms and backfilling. That
would have been very doable if the pad were a little smaller, but a 2'
undercut was just too much.
At one point I was wondering why the hell the engineer didn't just design a
deeper 5'x5' hole, and forget about the inverted T pad idea. After actually
digging the hole I came to realize that if that were the design, we couldn't
have done it with the small backhoe that we had to drive through a carport
in order to get it into the back yard (and I'm sure there are other
reasons). Tradeoffs, tradeoffs. I remember one of the first things I
learned in engineering school. engineering is all about compromises.
Anyway, we now have a 9'x9'x4.75' hole in the ground (new pictures posted at
if anyone is interested).
Tomorrow, Sunday, I will go back in the hole and clean up the corners after
my Sunday AM sked with K5VRX (another engineer, who lurks on here but rarely
ever says anything). Monday we will haul off the last of the dirt that's
not being retained for backfill and Tuesday we are going up to the Sonoma
Valley to watch a parade, drink great wine and watch fireworks. Wednesday I
plan to build the rebar cage and get started on the forms if other business
One last note. after we finished today and I got back from driving Ernesto
back to his apartment, I was walking down my long driveway to retrieve the
RV, which I moved to get the dump trailer in. I was feeling real sore,
walking a bit crooked, and feeling a little sorry for myself, and then I
walked past Roy's back yard. Roy (another engineer) was out in his back
yard digging with a pickaxe and shovel. Roy retired from Bechtel 27+ years
ago. That's right, Roy is 92. I kid you not.
73 - JC, K0HPS
From: K7LXC@aol.com [mailto:K7LXC@aol.com]
Sent: Saturday, July 01, 2006 10:09 AM
To: firstname.lastname@example.org; email@example.com
Subject: Re: [TowerTalk] new AN-Wireless tower, floundaion question
In a message dated 6/30/2006 7:43:32 A.M. Pacific Daylight Time,
> As mentioned previously I am stick-building (like a giant erector set) a
AN-Wireless HD-80. I will be posting photos at:
if anyone cares to watch it go up and the antenna stack go on it. We just
started digging the foundation yesterday. It's a pad and pier foundation
(like an inverted tee) with a 9'x9'x1.5' pad and a 5'x5'x3.5' pier.
> Has anyone on here ever dug one of these by digging the 5'x5' hole first
then undercutting the bottom to create the pad? If so, I'd sure appreciate
hearing how you did the digging for the undercut. We got the 5'x5' hole no
problem but our experiments (so far) with the undercutting haven't been very
successful. We are in clay soil, fortunately with no rocks. If things
don't go better today we will probably dig out the entire 9'x9' hole, pour
the pad, form the pier and backfill around it.
IMHO the tower base designs that utilize some sort of
undercutting/belled out at the bottom are stupid and potentially dangerous.
In some designs the base is 6-9 feet deep and being that far down to hand
dig the undercutting is illegal under OSHA rules and dangerous in any case.
I know there's an engineering reason for it but it was designed by
an engineer in an air-conditioned office who never has to be out in the
field to install one. My suggestion would be to skip the undercutting and
compensate by making the hole a little bigger. It's easier and safer too!
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