The other consideration about undercutting for the pad is whether the
concrete will fully form to the shape of the pad. I certainly wouldn't want to
be in the hole forcing concrete into the undercut areas as it's being
poured...
Even if you could do that, you still wouldn't be sure it filled out the top
corners.
The principle, I believe, is that once the dirt has been backfilled and
properly compacted as Gene describes, there is as close to undisturbed
earth sitting right on top of the pad..
73, kelly
ve4xt
> From: ersmar@comcast.net
> Date: 2006/06/30 Fri AM 08:55:47 CDT
> To: "JC Smith" <jc-smith@comcast.net>, <towertalk@contesting.com>
> Subject: Re: [TowerTalk] new AN-Wireless tower, floundaion question
>
> JC:
>
> It's nearly impossible to undercut safely the full size of the pad for
> this
type of foundation. When I was working in the electric utility industry as an
engineer, we used these foundations all the time for our substation
structures. The crews dug out the full size hole for the pad (in your case,
that would be a hole 9 feet by 9 feet by five feet deep.) They set the rebars
for both the pad and pier, the poured the concrete for the pad. Next day
they set the forms for the pier on top of the pad and poured the pier. ANd I
believe there is a material that is applied to the concrete to allow this
second pour to adhere to the first. Anyone help here?
>
> The next step is the trickiest: backfilling the excavation after
> removing
the pier's form material. In your case you ought to back fill a foot deep
around the pier, then spend a bit of time with a tamper banging the soil in
compaction. You can rent a motorized tamper for this. Then add another
foot and tamp it, etc until the entire excavation is filled and the earth put
back in near-undisturbed state.
>
> My Trylon tower's foundation is similar in construction except that the
undercut is a slanted cut only a foot wider than the main hole. I was able
to use a spade, with proper shoring of course, to loosen the earth and
haul it out with a backhoe. But yours is a bit too wide to safely support the
overlying earth.
>
> I know - a PITA, but it has to be done that way so you don't injure
anyone should the hole collapse.
>
> Good luck, and remember - On towers as in driving a car, there are
no such things as accidents.
>
> 73 de
> Gene Smar AD3F
>
>
> -------------- Original message ----------------------
> From: "JC Smith" <jc-smith@comcast.net>
> > Hello All,
> >
> > As mentioned previously I am stick-building (like a giant erector set) a
new
> > AN-Wireless HD-80. I will be posting photos at:
> > http://s14.photobucket.com/albums/a317/k0hps/Tower%20Project/
> > 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 and
> > 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.
> >
> > Suggestions appreciated.
> >
> > 73 - JC, K0HPS
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
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> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> _______________________________________________
>
>
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