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Re: augered piles

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Roger, I understand and have a broader view of it now.
I have mistakenly understood that, for the typical slab-on-ground residence,
influence
on foundations due to expansive soils occurred within the first 2 or 3 feet below
grade.

Steven A.
Los Angeles



Roger Turk wrote:

> Steven,
>
> I would NOT say that it is impossible to get moisture in the full 20' of
> expansive soil.
>
> Since soil moisture accumulates under a building, stone, rock, piece of
> plastic, piece of cardboard, etc. in even the driest of conditions, the
> moisture under a building can accumulate gradually and dry out so slowly that
> it can be characterized that moisture containing soil under a building
> *never* drys out, yes, the entire 20' layer of expansive soil can be
> subjected to increased moisture.
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
> Steven A. wrote:
>
> . > Roger,
>
> . > Assuming your 20' depth of expansive soil is bone dry, could you get
> . > moisture down that deep and fully
> . > distributed through the soil mass to realize its full (theoretical)
> . > expansiveness?
>
> . > Steven A.
> . > Los Angeles
>
> . > Roger Turk wrote:
>
> > Mike,
> >
> > You may be anchoring the piles to rock, but the expansive soils may blow out
> > your slab!
> >
> > IMO, the expansion index is meaningless for structural engineers.  The
> > information that *I* need is the confinement pressure that is necessary to
> > *prevent* expansive soils from expanding.  If the confinement pressure is
> > 5 psf, I am certain that I can handle that.  However, if the confinement
> > pressure is 5 TONS per square foot, there is nothing that I can reasonably
> do
> > to accommodate that.
> >
> > (If your expansive soils have a 1 percent expansion potential, but you have
> > 20 feet of expansive soils, the 1 percent results in a 2.4" expansion.  If
> > the confinement pressure is 1,000 psf, can the slab resist that kind of
> > force?)
> >
> > HTH
> >
> > A. Roger Turk, P.E.(Structural)
> > Tucson, Arizona
>
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