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Re: [TowerTalk] tower installation HG52SS / options

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] tower installation HG52SS / options
From: jimlux <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Sun, 14 Feb 2010 11:36:56 -0800
List-post: <">>
Michael Goins wrote:
> I based it upon my original decision to locate the tower where it is.
> Once we found rock and did the initial hole (such as it is), I decided
> it was not practical to continue to chip away rock to replace it with
> concrete. The factory dimensions are obviously engineered, and we all
> know they are likely slightly over-engineered from a litigious society
> legal aspect. They are also engineered for "average soil" - whatever
> that is supposed to be - 

I'm not a soils guy, but I'm pretty sure there is an actual definition 
for what "average soil" is from a foundation design standpoint. 
Probably something to do with density and resistance to movement (I 
vaguely recall something like 2500 or 3000 pounds/square foot bearing 

Obviously, sand isn't "average soil", but neither is rock.  In an 
engineered application, the engineer would take the actual soil 
properties (either by testing or by local knowledge..) and scale 
appropriately. If your soil were, say 1250 psf bearing capacity, and 
"average" was defined as 2500 psf, your foundation would need twice the 
area to resist the same forces.  If your soil were 5000 psf, then half 
would do (assuming all the other design requirements are met.. pushing 
soil out of the way is only part of it)

There's also the density part of it. If the foundation design depends on 
  the weight of the soil on top of something, then if the density is low 
(you live in Pumice Flats) you'd need more depth.

It might seem that is is pretty common sense if you've ever pounded in a 
fence post or tent stake or built sand castles at the beach, but where 
the engineering comes in is reducing the common sense to actual numbers, 
so you know how to adjust, rather than just taking the "add a few yards 
of concrete and make it wicked strong" approach.  At some point the few 
hundred bucks for the Engineer is cheaper than the few hundred bucks for 
the concrete and rebar.

In your situation, you've got lots of land, presumably nothing really 
bad happens if you estimate wrong, so either way works.

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