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RE: Underground Structures

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Unfortunately this is a very complicated subject.  There will be a good
commentary that will be in the 2000 NEHRP that was developed by Maury Power
of Geomatrix and Chet Soydemer of Haley and Aldrich on  seismic induced soil
forces on retaining walls specifically, but are applicable to buried
structures in general.

The BSSC Technical Subcommittee 13 that I chair will be addressing buried
structures in the future, but first we need to understand the nature of
applied seismic induced soil forces.  That is what Maury and Chet are
working on first.  

Complicating the issue is the nature of vertical seismic ground shaking.  It
is applicable to all structures, but is more critical to structures
resisting large gravity loads with structural elements with short responses.
As little structural guidance that there is for buried structures, there is
less for vertical seismic ground shaking.

The nature of the seismic ground shaking induced soil forces is highly
dependant on fault proximity, fault type, soil type, soil stratification,
and response of the buried structure.

Harold Sprague

> -----Original Message-----
> From:	Vinod Sahni [SMTP:SAHNIVK(--nospam--at)]
> Sent:	Wednesday, August 02, 2000 4:08 PM
> To:	seaint(--nospam--at)
> Subject:	Underground Structures
> I am working on the conceptual design of underground structures
> (seismic zone 4 criteria).  The structures are buried some 150 feet below
> ground.  Because of inexperience with underground structures and the
> fact that it is conceptual in nature, I am analyzing for vertical loads
> only at
> this time.  I am wondering how I will tackle seismic design later.  I
> assume
> a geotechnical firm would provide seismic accelerations at the depths
> required.  Do I apply these accelerations like in a conventional 
> aboveground structure ignoring passive resistance of the soil
> (conservative). And,  I hope it is not some complex soil structure
> interaction analysis involved here.  Are there some good practical
> resources on the subject?  Any suggestions/recommendations would be
> greatly appreciated.  Thanks.

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