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Re: Foundation on Expansive Clay

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Please hire a Geotechnical Engineer!
I have seen bldgs on pile foundations 15 to 29 feet down come out of the
ground. An exploratory boring and expansion test and sampling to find out
what type of clay you have is important. Local experience is also a must.
Chris Lillback P. E.

----- Original Message -----
From: "Bill Polhemus" <bill(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Wednesday, April 04, 2001 8:49 AM
Subject: RE: Foundation on Expansive Clay

> I think you should give serious consideration to putting these things on
> drilled piers.
> I'd make a pile cap, maybe 2 feet thick (which will negate any effect of
> expansive uplift on the supported equipment) on several drilled piers (may
> or may not be belled). I'd get the geotech to tell me the pullout
> along with the other data for drilled pier design, design the piers for
> gravity and lateral loading, then check for pull-out and adjust as
> necessary.
> You'll get a foundation that's a little more expensive, depending on where
> you live (in some areas drilled pier installation is so common it's
> cheaper to do than a bearing foundation), but you'll take care of
> expansive uplift with no problem.
> William L. Polhemus, Jr., P.E.
> Polhemus Engineering Company
> Katy, Texas
> Phone 281-492-2251
> Fax 281-492-8203
> -----Original Message-----
> From: Fountain Conner [mailto:fconner(--nospam--at)]
> Sent: Wednesday, April 04, 2001 6:05 AM
> To: seaint(--nospam--at)
> Subject: Foundation on Expansive Clay
> I need to put some lightly-loaded foundations on clay "with the potential
> for expansion".
> These foundations will carry a bark blowline in a paper mill.
> If all were normal these foundations would be 7 feet long x 8 feet wide x
> feet thick.  They each would have a vertical pipe 20 feet tall, carrying a
> horizontal blowline.  Maximum soil pressure (max load and wind) would be
> about 2000 psf.  Static maximum load is about 650 psf.  The geotechnical
> report allows at least 2500 psf, plus 25 percent for short-term live load
> (like wind).
> Plain vanilla...  Until I factor in the potentially expansive soil.
> My thinking is to turn down the outside edge of the footing an additional
> inches.  If this clay is expansive, it shouldn't be given to capillary
> action, and will provide a seal, preventing the soil beneath the
> from seeing the varying moisture content.
> What do you think?
> Item 2:
> I had intended to place each "mast" in a sleeve, plumb it and grout it
> into position -- cheap, but effective.  I *can* put a mast on a large,
> thick
> baseplate, and perch it on nuts below the base plate, with double nuts
> above.  If I do this, I can allow enough room below the lower nuts to
> adjust each mast plumb if there is some movement.  I'm hoping you guys can
> convince me that this step is overkill.
> Ideas?
> Thanx,
> Fountain E. Conner, P.E.
> Gulf Breeze, Fl. 32561
>    Phone 850-932-5547
>    Fax      850-934-1916