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Re: [TowerTalk] Compacted vs. Undisturbed Soil

To: Dick Flanagan <dick@k7vc.com>
Subject: Re: [TowerTalk] Compacted vs. Undisturbed Soil
From: David Gilbert <xdavid@cis-broadband.com>
Date: Mon, 27 Apr 2009 13:19:40 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I think that depends heavily on the type of soil involved, and how the 
soil is compacted.  When I backfilled under the slab of my house (behind 
the six foot high retaining wall) I removed all rocks, laid the soil 
down in 3 inch layers, wet each layer down, let each layer sit until it 
was just damp, and then compacted each layer with a heavy duty plate 
compactor.  It took literally months to finish, but the resulting adobe 
was so hard that when a 50 ton crane drove across it to install a large 
rock it didn't leave any tread impression at all ... only a dust print 
on the surface.  Even as hard as the natural undisturbed soil is here on 
this rocky hillside, that adobe I created under the slab is several 
times more resistant to flow.

Most contractors, however, just dump in the backfill dirt and tamp it 
every couple of feet with the backhoe bucket, and that is almost for 
sure not the equivalent of undisturbed soil.

The biggest issue, though, even if your friend goes to extraordinary 
means to compact the backfilled soil, is whether the building inspector 
will bless it.  Signing off on something that doesn't have engineering 
approval (and that cannot be independently verified later) puts the 
inspector in a pretty bad position.  It also gives the P.E. an easy out 
if any liability problems should arise later.  In a nutshell, your 
friend's contractor didn't follow the engineering drawing and, in my 
opinion, has hung your friend out to dry.

73,
Dave   AB7E



Dick Flanagan wrote:
> A friend of mine is installing his first tower.  It is a US Tower 
> HDX454.  (I thinks that's the right number.  I have an HDX572 and his 
> is the next one shorter than mine.)
>
> He had the tower specs checked by a local PE for the requisite wet 
> stamp needed for his building permit.  The PE calculated and 
> specified a tower footing of 5'x5'x7.5' in undisturbed soil.
>
> His contractor dug him a 10'x10'x8' hole and is going to put a 
> 5'x5'x8' plywood frame in the hole enclosing the rebar cage.  He is 
> then going to fill the frame with concrete and when it cures is going 
> to remove the frame and back-fill the hole with compacted soil.
>
> My friend is being told that properly compacted back-fill is the 
> equivalent of undisturbed soil.  Is that true??
>
> Dick
> --
> Dick Flanagan K7VC
> dick@k7vc.com
>
>
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