[TowerTalk] new AN-Wireless tower, floundaion question

ve4xt at mts.net ve4xt at mts.net
Fri Jun 30 11:45:38 EDT 2006

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 

Even if you could do that, you still wouldn't be sure it filled out the top 

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

> From: ersmar at comcast.net
> Date: 2006/06/30 Fri AM 08:55:47 CDT
> To: "JC Smith" <jc-smith at comcast.net>,  <towertalk at 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 at comcast.net>
> > Hello All,
> > 
> > As mentioned previously I am stick-building (like a giant erector set) a 
> > 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 
> > started digging the foundation yesterday.  It's a pad and pier 
> > (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 
> > hearing how you did the digging for the undercut.  We got the 5'x5' hole 
> > 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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