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Re:RE: RE: Factor of safety for cantilever Pile Retaining Wa

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I agree.  That is the issue.  Not all geotechnical reports state that a factor
of safety is used, when one often is.

Tom Benson at Lowney Associates
251 East Imperial Highway, Suite 470
Fullerton, CA 92835-1063
(714) 441-3090
FAX: (714) 441-3091
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Geotechnical & Environmental Engineering Services
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____________________Reply Separator____________________
Subject:    RE: RE: Factor of safety for cantilever Pile Retaining Walls
Author: seaint(--nospam--at)seaint.org
Date:       3/1/2001 9:25 PM

Just commenting that what Geotechs are writing and Structurals are reading
may be two different things here in California.

George Richards of Borm Associates

-----Original Message-----
From: TBenson(--nospam--at)lowney.com [mailto:TBenson(--nospam--at)lowney.com]
Sent: Thursday, March 01, 2001 4:48 PM
To: seaint(--nospam--at)seaint.org; 'seaint(--nospam--at)seaint.org'
Subject: Re:RE: Factor of safety for cantilever Pile Retaining Walls


George,

Not an assumption, just an observation regarding "most" (OK  if you prefer
"the
majority of") California geotechnical reports I have reviewed.  I have
reviewed
a few  ; ) .  If they are not using a factor of safety, then many are using
very
conservative soil strength assumptions (once again, for California only). 

Is this George Richards of Borm Associates?  I agree "Not all Geotech's ..."

Tom Benson (P.E., G.E.) at Lowney Associates
251 East Imperial Highway, Suite 470
Fullerton, CA 92835-1063
(714) 441-3090
FAX: (714) 441-3091
---------------------------------------------------------------------------
Geotechnical & Environmental Engineering Services
---------------------------------------------------------------------------


____________________Reply Separator____________________
Subject:    RE: Factor of safety for cantilever Pile Retaining Walls
Author: seaint(--nospam--at)seaint.org
Date:       3/1/2001 7:33 PM

I think most Geotech's do not know that we will add a second 1.5 factor of
safety to their numbers.  I look at the friction angle and then ask.  By the
way, not all Geotech's give you the numbers with a FofS in them. so don't
assume.

George Richards, P. E.

-----Original Message-----
From: TBenson(--nospam--at)lowney.com [mailto:TBenson(--nospam--at)lowney.com]
Sent: Thursday, March 01, 2001 2:43 PM
To: seaint(--nospam--at)seaint.org
Subject: Re:Factor of safety for cantilever Pile Retaining Walls


I see this all the time, and generally agree.  Most Geotechnical Engineers
in
California are factoring down the "ultimate" passive pressure (Rankine
calculation) down to an "allowable" passive pressure, typically by a factor
of
safety of 1.5.  This, of course, is in addition to the factor of safety you
probably apply as the Structural Engineer for sliding and overturning
analyses. 
Seems redundant, but that is the current standard of practice for
Geotechnical
Engineers in at least Southern California and most of the Bay Area.  The
first
factor of safety could be justified by potential earth material strength
variations.  But, I bet if you reviewed 100 geotechnical reports from
California,  the recommended passive pressures would not fall outside of 250
to
350, or maybe rarely 450 pounds-per-square-foot, per foot of embedment,
doubled
for isolated soldier piles.  Personally, I have never had a Structural
Engineer
or any other wise client question these numbers (mine or any other GE's),
possible because often there is little cost impact associated with the
passive
pressure magnitude.  Perhaps this is due to just habit and familiarity.

Tom Benson at Lowney Associates
251 East Imperial Highway, Suite 470
Fullerton, CA 92835-1063
(714) 441-3090
FAX: (714) 441-3091
---------------------------------------------------------------------------
Geotechnical & Environmental Engineering Services
---------------------------------------------------------------------------


____________________Reply Separator____________________
Subject:    Factor of safety for cantilever Pile Retaining Walls
Author: seaint(--nospam--at)seaint.org
Date:       3/1/2001 5:40 PM

The geotechnical engineer includes a factor of safety of about 1.5 for the 
allowable passive lateral earth pressure used for designing embedment 
restraint of cantilever piles.  based on information from the geotechnical 
engineers I work with, an additional factor of safety on top of that value
is
not required, and typically not added by engineers in the design of 
cantilever pile systems. 
paul franceschi, S.E.