[TowerTalk] Pad and Pier Foundations

[Don Moman]

 An alternative base system often used up here (Edmonton, Alberta) is to
screw in some piles, weld up some base feet and put up the tower.  No
waiting for cement to dry.  And the hydraulic  auger unit can weigh a lot
less than a loaded cement  truck, which is another obvious advantage.  Yes
it depends on how far down the bedrock is.  But in the larger sizes, we are
talking some serious pilings with holding power for significant structures
into the hundreds of feet.  I'll be doing a few much smaller systems this
summer using this system, using a homebrew hydraulic drive - gear reduction
and a low rpm hydraulic motor mounted on a front end loader.  It also make
short work of driving in similar anchors for guyed towers.  Haven't used any
cement around here for many years, and don't plan to again.

73 Don
VE6JY


----- Original Message -----
From: "Alan NV8A (ex. AB2OS)" <nv8a at att.net>
To: "towertalk reflector" <towertalk at contesting.com>
Cc: <ersmar at comcast.net>
Sent: Sunday, July 10, 2005 19:21
Subject: Re: [TowerTalk] Pad and Pier Foundations


> 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 at 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!
> _______________________________________________
>
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Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
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>
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