Hi Gene,
As you know, I'm planning on this type of tower. I've been looking at the
foundation options and I really don't want a 9' x 9' (or even an 8' x 8')
concrete pad under the tower (the Solid Block option) but I don't like the
idea of forming and compacting either. Seems to me that if you do two pours
you will have a cold joint between the pad and the pier. Moisture would
eventually get in there and rust the rebar (which is where most of your
strength is... or all of your strength with a cold joint) and at some point
you would have a weakened foundation. I suppose it would take a long time,
and there are rebar coatings to mitigate this, but it seems to me a
monolithic pour would be better. It would seem that a variation of the
Drill and Bell that Rick posted might be an answer. You could still dig the
5' x 5' hole with a backhoe and then dig the "square bell" pad section by
hand or with the aid of some yet-to-be-determined mechanical device. You'd
still have to build the rebar cage inside the hole and to the same
specification but at least you'd have some clearance to work with when tying
the rebar. I really can't see lying on my back in the hole while working
under the ledge of the undercut tying rebar. It would be hard enough with a
sloped, bell X-section. It would take more concrete, but so what, and not
as much as with the Solid Block.
If one is going to go with two pours then I heartily agree with you that
digging out enough that you can fit a mechanical tamper is the way to go. I
recently did my own underground utility conversion (beneath a new driveway
we subsequently installed) and the compactor we rented was worth its weight
in gold. We used the type that looked like hand truck with a gas engine on
it (or a square lawn mower with no wheels) and backfilled about 6" at a
time, watering the fill as we went. We purchased fill (sort of a crushed
rock mixture) rather than try to use the clay we dug out of the trench. I
think the width of the footprint of the tamper was about 18", but of course
you'd have to dig out enough to be able to turn the corners. I believe
there are other types of compacters as well. They look sort of like a
jackhammer with a big foot where the bit should be. They wouldn't be any
fun to use on a long trench (ours was well over 100 yards) but on a 6' x 6'
rectangle they might not be that bad.
As was suggested by others on here, I plan to post photographs of the entire
process in my Photo Bucket as it happens, so anyone interested will get to
see the whole thing. Someone suggested a video. I think a time-lapse video
would be really neat, but I'm not sure I'll be able to pull that off.
Missed you on Sunday BTW.
73 - JC, k0hps@amsat.org
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of ersmar@comcast.net
Sent: Tuesday, July 05, 2005 10:10 AM
To: Kelly Johnson; towertalk@contesting.com
Subject: Re: [TowerTalk] Pad and Pier Foundations
Kelly:
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!
GL es 73 de
Gene Smar AD3F
> This wasn't exactly what I was looking for. The Super Titan towers
> and the AN Wireless Towers show foundation plans where the bottom of
> the hole (the foundation) is wider than the rest of the hole (the
> pier). The foundation at the bottom is significantly wider (like
> 18"). How do people dig these types of holes?
>
> On 7/5/05, Rick Scott <rickn7hj@gmail.com> wrote:
> > http://www.windturbine.net/files/Misc%20Data/anchor%20system.doc
> >
> > 1.4.4.1
> >
> > Figure 1.4 shows the diagram.
> >
> >
> > Scotty N7HJ
> >
> > On 7/5/05, Kelly Johnson <n6kj.kelly@gmail.com> wrote:
> > > Can someone explain to me how a Pad & Pier Tower Foundation hole is
> > > dug? I had never seen a Pad & Pier Foundation Spec until this weekend
> > > and after seeing it I couldn't help but wonder how you would dig such
> > > a hole.
> > > _______________________________________________
> > >
> > > 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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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