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RE: Increases in Foundation Bearing Pressure For Wind and Seismic Loading

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Tom,

As a designer of soil supported structures, I depend upon the
recommendations of geotechnical consultants define the appropriate soil
parameters applicable to the nature and magnitude of loads I anticipate will
be applied to the soil for a specific project at a specific site.

The way I have read your posts, you would like to shift some the
responsiblity for making this decision to the structural consultant. The
decision to permit a 1/3 increase in the allowable bearing pressure for a
given combination of loads HAS to be the geotechnical consultants decision.
Just as the structural consultant is paid to apply their technical expertise
to analyze and transmit the forces developed in a structure safely and
economically to the ground, the geotchnical constultant is being paid to
provide their technical expertise in establishing the design soil parameters
which will facilitate this endeavor.

Isn't the determination of the soils ability to properly support the
structure for presribed conditions of loading part of the scope of services
for which you are contracted? If, in the geotech. consultants opinion, a 1/3
increase of allowable bearing pressure unacceptably increases the probablity
of soil failure so as to reduce the factor of safety deemed appropriate for
a particular soil condition in response to a load state then the increase
should not be recommended. Personally, I have never read a soils report
which prohibited an increase.

I'm not trying to be provocative here. I realize that there is more
uncertainty in determining soil behavior that there is in the
superstructure. More uncertainty, more risk. But I strongly feel that to
re-assign the determination of a temporarily increased maximum permissible
bearing pressure would be asking the structural consultant to make a
decision outside their area of expertise. For myself, this would be
irresponsible and an ethical violation.

Climbing off the soapbox,

Brent R. Koch, P.E.
KOCH ENGINEERING, INC.
Livermore, CA
mailto:kochengr(--nospam--at)pacbell.net