Without knowing anything about Dave's soil, I'd make the following comments:
- 3 holes 20 feet deep 3 feet in diameter is a LOT more than 1 hole 25 feet
deep 2 feet in diameter (about 5 times the volume..
- Assuming the three footings were spaced some distance apart, some of the
overturning moment of the tower is being taken up as compressive loads on
the pier, as opposed to bending/turning of the single pier in Dave's case.
Different tower, different loads, different footing design.
- Long and skinny vs short and squat, the choice is often determined by how
much room there is, what it costs to drill, etc. Consider that the
additional cost to drill 25% deeper (25 vs 20 ft) is probably negligible,
but the cost to get a bigger drill is probably substantial. The "setup
charge" for the auger is the dominant cost, not the depth of the hole.
- Consider that Dave's got a licensed specialist there to advise him, one
who presumably knows the local conditions, local construction capability and
relative costs, and will do a professional job serving his/her client in
coming up with the most cost effective solution to his problem.
Engineering (in the licensed professional sense, particularly) is more than
a cookbook exercise in running the calcs.
I have yet to have a client come to me and tell me that cost is no object
for a project. (Hope springs eternal, though!)
Jim, W6RMK
----- Original Message -----
From: "W1GOR" <W1GOR@maine.rr.com>
To: "Jerry Keller" <k3bz@arrl.net>; "Towertalk@Contesting.Com"
<towertalk@contesting.com>
Sent: Sunday, October 05, 2003 2:58 PM
Subject: RE: [TowerTalk] The tower base is poured BUT...
> Jerry,
>
> During the early 1990's, a 300 foot Rohn SSV tower was installed for the
> Long Island Rail Road. The foundations were 3 footings, 3 feet in
diameter,
> and 20 feet deep in 3000 PSF soil. The auger was trucked to the site from
> somewhere near Washington, DC. Why does Dave Giuliani's engineer require
a
> 25 foot deep hole..? You're right... Something seems incorrect..!
>
> 73, Larry - W1GOR
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Jerry Keller
> Sent: Sunday, October 05, 2003 13:21
> To: David Giuliani; towertalk@contesting.com
> Subject: Re: [TowerTalk] The tower base is poured BUT...
>
>
> OK, maybe my ignorance is showing, but does anyone else think it a bit
> preposterous for an engineer to recommend digging a 25 foot deep hole for
a
> tower base? If the soil content would allow augering a 25 foot deep hole
> only 2 feet in diameter, wouldn't it cave in long before it got that deep?
> Are there even 2 foot diameter truck-mounted augers available 25 feet
long?
> There's something about this idea that just seems wrong... but then I'm no
> engineer. Any thoughts? Jerry K3BZ
> ----- Original Message -----
> From: David Giuliani
> To: towertalk@contesting.com
> Sent: Sunday, October 05, 2003 12:23 PM
> Subject: RE: [TowerTalk] The tower base is poured BUT...
>
>
>
> The more I read about this, the more I'm liking my emerging plan to dig
a
> hole with a truck mounted auger rig -- no forms, no backfilling,
> relatively
> small diameter surface. We're looking at a 2' diameter hole, 25' deep.
> Relatively simple rebar for the lower 80%. Requires <3 cubic yards of
> concrete. See "deep base for MA-550" for this thread.
>
> David Giuliani, WA6PXX
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of K7LXC@aol.com
> Sent: Sunday, October 05, 2003 6:46 AM
> To: k1ttt@arrl.net; towertalk@contesting.com
> Subject: Re: [TowerTalk] The tower base is poured BUT...
>
>
> In a message dated 10/4/03 9:54:13 AM Pacific Daylight Time,
> k1ttt@arrl.net
> writes:
>
> > Doesn't anyone use forms any more???
>
> What for? I assume you mean below grade. The concrete is supposed to
> be
> poured into 'undisturbed' earth.
>
> An exception would be when the walls keep sloughing; then the forms
> would
> be necessary but you have to be real careful to backfill after you
remove
> the
> forms and tamp the backfilled dirt.
>
> Cheers,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for commercial and amateur
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any
> questions and ask for Sherman, W2FLA.
>
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>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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