[TowerTalk] ROHN tower anchor question

[Jim Rhodes]

At 08:29 AM 07/30/2000, Pete Smith wrote:

>At 09:09 AM 7/30/00 -0400, Jim Idelson wrote:
> >
> >While I cannot give any further numerical insight into how the soil
>contributes
> >to the effectiveness of the anchor, I do recall one practical piece of
> >information that my PE gave me when we designed my installation. He made it
> >clear that undisturbed soil retains significantly more strength than soil
>that
> >has been excavated and replaced during the construction process. For this
> >reason, he strongly recommended hand-digging base and anchor holes,
>instead of
> >using a backhoe or other excavation machine. He felt that the end result
>would
> >be significantly stronger if the holes were dug to exact spec by hand.
>
>I'm confused.  There's no way you can pour a concrete anchor without
>disturbing the dirt above it, because you have to fill after pouring.  Was
>he talking about the soil around the anchor, including (I guess) the
>portion that is in the pull axis but outside the hole itself?  Similarly,
>as far as the base block is concermed, was his objection to the backhoe the
>idea that one or more sides of the hole would be somewhat cut out?

Exactly, The soil the anchor would have to be pulled through by the cable 
is what matters.


>It's hard for me to picture that Trylon and other manufacturers of
>self-supporting towers with multi-yard bases really expect the installer to
>dig the hole by hand.  Maybe their specs already have soil disturbance
>accounted for(?).

A totally different application. The tower base of a freestanding tower 
needs to resist overturning forces. And to a lesser extent torsional 
forces. It has to sit firmly on the bottom and the sides become less 
important. Its mass is its most important feature.


>73, Pete Smith N4ZR
>
>The World Contest Station Database
>is back up and running at
>http://www.qsl.net/n4zr
>
>
>
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Jim Rhodes K0XU
rhodes@willinet.net


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