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RE: Design for Liquifaction (or mitigation thereof)

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Gary,

I have had occasion to use them on several projects. I work with our geotechs and determine the liquefaction hazard, and if liquefaction is a hazard we determine if the structure can accommodate the movement. If the movement can not be tolerated, we then mitigate the liquefaction hazard by some sort of soil improvement scheme. The spacing interval and depth is determined by the geotechs on a calibrated geotechnical dirt dart board, alchemy, or other well defined guess;>)

Following are several web sites that explain the process very well:
Stone Col
http://www.vibroflotation.com/07.pdf
http://www.laynegeo.com/pdfs/vgi/StoneColumnsTechnicalSummary.pdf
http://www.stonecolumns.com/

This last one is particularly good:
http://www.ce.washington.edu/~liquefaction/html/how/soilimprovement.html

Specifications on the calibrated dart board are proprietary;>)

Regards,
Harold Sprague




From: "Gary Hodgson & Associates" <ghodgson(--nospam--at)vaxxine.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Design for Liquifaction (or mitigation thereof)
Date: Thu, 09 Dec 2004 07:44:55 -0500

Could Harold or somebody expand on "stone" columns?
I've never heard of them, but then this relatively
low wind and seismic country.
Gary

On 8 Dec 2004 at 9:39, Bill Allen, S.E. wrote:

> Harold -
>
> Thanks for your response. BTW, I for one appreciate your contribution
> to the list. All of your posts have a high content to noise ratio but
> still manage to include entertainment (i.e. as in sand pounding).
>
> I agree that a mat or grade beam solution does not inhibit the effects
> of liquefaction and I'm not sure if the owner (County of Riverside)
> will be willing to accept a project that might change elevation 3"-8"
> after an event.
>
> I'm only obliquely familiar with stone columns. From a structural
> standpoint, they work like piles, right? IOW, the foundation spans
> between the stone columns during a seismic event, right? Aren't they
> at least 3 feet in diameter? If so, then it seems to me that a grade
> beam grillage would not make as much sense (grade beams would have to
> be about four feet wide, right?) as a mat where the mat would act as a
> two way slab sitting on a grid of stone columns, right?
>
> FWIW, the geotech did list stone columns in his report. In option 5,
> he listed drilled piers, geopiers, stone columns or piles founded at a
> depth of 40 feet as an option. It was more than likely me who
> discounted the cost effectiveness of stone columns for a project like
> this. If CIDH piles 24" in diameter w/ 3 foot wide grade beams or
> precast drilled piles 18" in diameter w/ 30" wide grade beams were
> used, do you believe that stone columns are still more cost effective
> on a project of this size? One of the problems I have with grade beams
> with or without piles is the slab. Is it designed as a structural slab
> spanning without soil support between grade beams due to either design
> live load (down) with piles or some level of hydrostatic pressure (up)
> without piles.
>
> Thanks,
>
> T. William (Bill) Allen, S.E. (CA #2607)
> ALLEN DESIGNS
> Consulting Structural Engineers
> http://www.AllenDesigns.com
> V (949) 248-8588	 .	 F (949) 209-2509
> -----Original Message-----
> From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
> Sent: Wednesday, December 08, 2004 8:50 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Design for Liquifaction (or mitigation thereof)
>
> None of the options mitigates liquefaction itself, and then you have
> to predict (crystal ball technique) the soil movement.  Some of the
> techniques will minimize liquefaction, but they do not mitigate it.
>
> What about stone columns?  They are cheap and mitigate the problem.
> If the geotech does not know about these, get a new geotech.  There
> are many structures around the world that use stone columns to
> mitigate liquefaction.
>
>   For your soil conditions they may not be appropriate, but I would at
>   least
>
> consider them.
>
> Regards,
> Harold Sprague
>
>
>
>
> >From: "Bill Allen, S.E." <T.W.Allen(--nospam--at)cox.net>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: <seaint(--nospam--at)seaint.org>
> >Subject: Design for Liquifaction (or mitigation thereof)
> >Date: Tue, 7 Dec 2004 15:44:13 -0800
> >
> >Dear Colleagues;
> >
> >
> >
> >I'm looking at a new project where liquefaction is an issue.
> >According to the soils report, total induced settlements, should
> >liquefaction occur, are estimated to be approximately 3 to 8 inches.
> >
> >
> >
> >The geotechnical engineer has suggested that I consider the following
> >five options:
> >
> >
> >
> >1.	Densified potentially liquefiable sand/silt layers at 10 to 40
> >feet depth by use of vibro-compaction, vibro-replacement, compaction
> >grouting, or deep dynamic compaction. 2.	Deep dynamic compaction of
> >the upper 40 feet of soil by use of falling weights. 3.	Foundations
> >that use grade-beam footings to tie floor slabs and isolated columns
> >to continuous footings (conventional or post tensioned). Flexible
> >connections for utility tie-in required. 4.	Structural flat-plate
> >mats, either conventionally reinforced or tied with post-tensioned
> >tendons. 5.	Deep foundations (drilled piers, geopiers, stone columns
> >or piles) founded at a depth of 40 feet.
> >
> >
> >
> >The geotechnical engineer has no experience with option 1. He thinks
> >option 2 will be unacceptable because the project site is in a
> >populated area and dropping 2.5T weight from 40 feet might be
> >objectionable. We both believe option 5 would be cost prohibitive for
> >this project.
> >
> >
> >
> >For some background, the structure is a one story medical office
> >building in UBC/CBC country. The site is 15.6 km from a Type A fault.
> >Groundwater was encountered at a depth of 9 to 15 feet. The soil is
> >classified as 5 feet of sandy silt over 10 feet of silty sand over 5
> >feet of sand.
> >
> >
> >
> >A foundation I recently designed for a similar structure can be found
> >here:
> >
> >
> >
> >http://www.allendesigns.com/projects/20325/20325S11.pdf
> >
> >
> >
> >The geotechnical conditions were different in that this foundation
> >was moderately expansive and was designed using UBC section 1815.
> >However, you can see the types of loads from the foundation design.
> >The exterior walls are bearing walls and there is a center girder
> >line with columns and pad footings. The proposed structure will be
> >framed similarly.
> >
> >
> >
> >If it helps, the roof framing plan can be found here:
> >
> >
> >
> >http://www.allendesigns.com/projects/20325/20325S21.pdf
> >
> >
> >
> >In talking with the geotechnical engineer, I told him that I would
> >have to charge the client extra $$ if I designed using either option
> >4 or 5. I only included conventionally reinforced UBC 1815 type
> >footings in my Basic Scope of Work. He said he thought that a grade
> >beam foundation would be acceptable and he referenced a subgrade
> >modulus in his report of 200 pci and an allowable soil bearing
> >pressure of 2,000 PSF.
> >
> >
> >
> >One of the problems I'm having is that, for a uniform pressure of
> >2000 PSF, based on k = 200 pci, I'm only getting a deflection of 0.07
> >inches. I guess I was expecting something like 50 pci or an allowable
> >soil bearing pressure of 500 PSF during a seismic event. Fortunately,
> >I only have to consider dead load since this is a one story building.
> >FYI, the proposed building is approximately 141 feet x 225 feet.
> >
> >
> >
> >Now my question(s):
> >
> >
> >
> >1.	If I choose a grade beam system similar to the job I recently
> >completed, what should I use for methodology/criteria in designing
> >the grade beams? 2.	Any other observations/recommendations?
> >
> >
> >
> >TIA,
> >
> >
> >
> >
> >T. William (Bill) Allen, S.E. (CA #2607)
> >
> >
> >ALLEN DESIGNS
> >
> >
> >Consulting Structural Engineers
> >
> >
> >  <http://www.allendesigns.com/> http://www.AllenDesigns.com
> >
> >
> >V (949) 248-8588
> >
> >.
> >
> >F (949) 209-2509
> >
> >
> >
> >
> >
>
> _________________________________________________________________ Is
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