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Re: augered piles

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Mike , what would happen, let's say, you pour an 8"
thick slab, rebar mat of 5/8", 3000 lbs psi concrete,
and let the home "float", hand in hand with a
comprehensive landscape design ie positive site
drainage. Just a thought, Jim Jensen, an unlicensed
builder in Arizona
--- Roger Turk <73527.1356(--nospam--at)compuserve.com> 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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