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Re: augered piles

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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
>
> Michael Hemstad wrote:
>
> . > I have a project in Texas with a large concrete slab
> . > supported on auger-cast piling, lots of them, going
> . > down about 25 feet to limestone.  Due to expansive
> . > clays, I have potential uplift.  I am resisting this,
> . > or trying to, using a high-strength (Dywidag or
> . > Williams) threadbar drilled and grouted into the
> . > underlying rock.  To install these, a plugged pipe
> . > (about 4 inch diameter) will be pushed down the middle
> . > of the pile before the grout sets.  Then, a few days
> . > later, the driller will drop a rock drill down the
> . > pipe and drill down into the rock.  The bar will be
> . > dropped in and grouted full length.
>
> . > My question is, should I take the opportunity to
> . > pretension this bar?  The potential uplift is a good
> . > deal more than the dead load, and probably greater
> . > than the tension capacity of the grout.  It means
> . > two-stage grouting of the bar, and the cost of the
> . > jacking, so it's not free, but not too expensive.  Any
> . > opinions?
>
> . > Thanks,
> . > Mike Hemstad
> . > TKDA
> . > St. Paul, Minnesota
>
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