[TowerTalk] Pad and Pier Foundations

[ersmar@comcast.net]

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 at 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 at 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.
> > >
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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.
> 
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