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Re: [TowerTalk] Pad and Pier Foundations

To: towertalk reflector <towertalk@contesting.com>
Subject: Re: [TowerTalk] Pad and Pier Foundations
From: "Alan NV8A (ex. AB2OS)" <nv8a@att.net>
Date: Sun, 10 Jul 2005 15:21:26 -0400
List-post: <mailto:towertalk@contesting.com>
The ability to dig an "undercut" hole no doubt depends on the soil. I 
gave a local concrete contractor the AN Wireless foundation plan, and he 
said there was no way to dig such a hole. He said the only way to do a 
pad and pier foundation around here would be to dig the hole the size of 
the pad, construct a form the size of the pier, then backfill.

(The photographs on the AN Wireless Web site show both undercut and 
backfilled mathods, IIRC.)

He initially proposed a two-stage pour, but when I told him that my 
understanding was that it was supposed to be a monolithic pour, he was 
quite happy to do it that way.

It had occurred to me that the higher concrete cost of a solid-block 
foundation might be more than offset by the saving of formwork and 
backfilling, but I thought that the smaller exposed concrete area of the 
pad and pier foundation would win on esthetic grounds.

73

Alan NV8A


On 07/05/05 01:09 pm ersmar@comcast.net tossed the following ingredients 
into the ever-growing pot of cybersoup:

>      Digging this kind of excavation is a royal PITA.  First, you dig the 
> hole the size of the bottom pad, e.g., 5X5 feet, to the final depth of the 
> hole.  You place rebar for the pad AND for the pier.  Then you pour only the 
> bottom pad concrete and let it set for a day.  The next day you form up the 
> pier and pour it.  
> 
>      After this entire block cures for another day or two, you can remove the 
> forms.  Now comes the fun part.
> 
>      You'll have to back fill the hole around the pier.  This means you must 
> place some earth into the hole around the sides of the pier, covering the pad 
> in the process.  THEN you must ensure that the replaced earth is as compacted 
> as undisturbed soil by pounding on it with, for example, a 4X4 or 2X4 piece 
> of wood.  Once that layer of soil (abt 6 inches or so) has been compacted, 
> then you add another layer of earth and repeat the pounding (compaction) 
> process until you reach grade.  One might have a tendency to slack off a bit 
> on compacting the upper levels of earth due to fatigue.  This won't give you 
> the mechanical performance from the earth that your tower will need.  
> 
>      I used the Trylon foundation design, that is, a monolithic concrete 
> pour, but with an undercut at the bottom of the hole.  I did this by having 
> the backhoe dig the basic hole (5.5 X 5.5 feet six feet deep) and then 
> shoring up the sides.  I then went INTO the hole (ever look up from the 
> bottom of a narrow hole in the earth?) and hand-dug the undercut.  The 
> backhoe bucket was small enough that it was in the hole with me, but I had 
> very little room to maneuver.  
> 
>      Thinking a bit about this compacting, if you decide to go the way of the 
> two-pour pad and pier design, you might want to really overdig the hole and 
> use a gasoline powered rented compactor to do the job with less human effort 
> (and fatigue.)  It'll sure beat using a two-b'-four!
_______________________________________________

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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