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Re[2]: Soil Bearing Pressure

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Roger,

I would suggest a slight modification: replace "equal to or less than" with
"greater than or equal to (>)".  A basic geotechnical concept is "soil has
memory".  Overburden consolidates, densifies and strengthens soils with time. 
But soils also have intrinsic strength independent of the overburden component. 
Almost always (except some Bay Mud sites, and other strange exceptions), your
basement level allowable bearing pressure should be greater than your at-grade
allowable bearing pressure for a given site.  As I always say, please consult
your project specific geotechnical engineer of record, in any case.

Tom Benson at Lowney Associates
1785 Locust Street, Suite 10
Pasadena, CA 91106-1614
(626) 396-1490
FAX: (626) 396-1491
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____________________Reply Separator____________________
Subject:    Re: Soil Bearing Pressure 
Author: <seaint(--nospam--at)seaint.org>
Date:       8/11/2000 12:48 PM

Old "Rule of Thumb":

The soil pressure that you can use has to be equal to or less than the weight 
of the soil removed.  After all, wasn't the soil at that level supporting 
the weight of the soil above it before you removed it?

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Paul Reilly wrote:

=-=-=-=-=-=-=-==-=-=-=-=-=-=-=----===-=-
> Ref Table 18-I-A, Allowable Soil Bearing Pressure, footnote 2...
"increase
> of 20% per each foot of embedment into natural grade greater than 1
foot".
> Is this provision for soil bearing applicable to sub-structures and
> basement footings


Overburden and skin friction were considered as candidates for the
increase, however, I was almost resolved to attribute the allowable bearing
increase to the probability of reduced deleterious materials in-situ.  Any
geotechs out there?
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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