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RE: Foundation on Expansive Clay

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1. Probably not much. Typically you've got to cut out and fill an
appreciable depth depending on the "activity" of the expansive soils. But
this might well be a viable option depending on what the geotech says.

2. That's really up to the geotech. Obviously you don't want to make so much
as an "educated guess" at this, since the liability just isn't worth it.

IMHO, I would seriously consider the drilled pier option.

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)pcola.gulf.net]
Sent: Wednesday, April 04, 2001 12:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Foundation on Expansive Clay


Unfortunately, it appears that these expansive clays extend to China.

1.  What would a couple feet of undercut and backfill gain me?

2.  How likely am I to get differential movement in excess of 1/2" in a
yard foundation 7ft x 8ft?

Fountain

----------
> From: Bill Polhemus <bill(--nospam--at)polhemus.cc>
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Foundation on Expansive Clay
> Date: Wednesday, April 04, 2001 11:02 AM
>
> Oops, I didn't catch that (I'm used to an active zone of 10 ft or so here
in
> Southeast Texas).
>
> You're right, John. If it's only a 6 inch active zone, excavating it out
is
> the best alternative. In fact, I'd recommend doing that up to about 5 or
6
> feet or so. After that, it's worth looking at a cost comparison.
>
> William L. Polhemus, Jr., P.E.
> Polhemus Engineering Company
> Katy, Texas
> Phone 281-492-2251
> Fax 281-492-8203
>
>
> -----Original Message-----
> From: John P. Riley [mailto:jpriley485(--nospam--at)peoplepc.com]
> Sent: Wednesday, April 04, 2001 9:55 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Foundation on Expansive Clay
>
>
> "My thinking is to turn down the outside edge of the footing an
additional 6
> inches.  If this clay is expansive, it shouldn't be given to capillary
> action, and will provide a seal, preventing the soil beneath the
foundation
> from seeing the varying moisture content."
>
> Is the expansive clay layer only 6" thick?  If this "turn-down" method is
> effective in protecting the soil within the 6" zone, what about the soil
> beneath IT?
>
> My first inclination is to overexcavate and backfill.
> __________________
> John P. Riley, PE, SE
> Riley Engineering
> 20 Oakwood Drive, Blue Grass, Iowa 52726
> Tel & Fax:  319-381-3949
> jpriley485(--nospam--at)peoplepc.com