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RE: Enlarging a footing

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Bill:

"Pucker factor"...nice classic post!! Thanks for the amusement for the
day!

FWIW, you are correct.  Bearing capacities that geotech give are not due
to soil "failing" (as in possible collapse, etc) but rather due to what is
considered an "excessive" amount of settlement.  This will then really
depend on the type of foundation system and how the loads are distributed.
>From that, the geotech usually makes an assesment of what would be an
acceptable settlement and from there the corresponding bearing pressure.

Regards,

Scott
Ypsilanti, MI


On Mon, 8 Sep 2003, Bill Allen wrote:

> Gerard-
>
>
>
> No soils report? To me, that's the easiest (and probably the cheapest)
> solution. You could go to a Geotech and tell him you only need specific
> information, like a letter saying you can use 2,000 PSF (or whatever) on
> an existing, already settled, foundation. Sure, he might have to poke
> his finger in the soil and run a couple of tests to reduce his "pucker
> factor", but he probably doesn't have to run a full blown report. IIRC,
> soil doesn't actually "fail", but it may consolidate excessively
> producing undesirable settlement. You would probably be coming up with
> the best solution of all (not disturbing the existing foundation) with
> this approach. Of course, I'm not a Geotech (nor do I play one on TV),
> so you need to consult with one to get more definitive information. I
> just know that if this were my job and the owner balked at getting a
> soils report, I would remind him (in writing) that I am not responsible
> for geotechnical performance nor does my insurance cover failures
> related to geotechnical issues. At that point, they usually spring for a
> report.
>
>
>
> With regards to the various structural solutions, I think either is a
> judgment call. If you widen the footing, make sure your new
> reinforcement is developed into the existing well enough. I'm not sure
> if there will be room to do this.
>
>
>
> Regards,
>
>
>
> T. William (Bill) Allen, S.E. (CA #2607)
>
> V/F (949) 248-8588
>
> San Juan Capistrano, CA
>
> http://members.cox.net/ballense/
>
>
>
> -----Original Message-----
> From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com]
> Sent: Monday, September 08, 2003 10:43 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Enlarging a footing
>
>
>
> Robert's step by step account for the load re-distribution is what I was
> thinking as well. Once the existing footing deflects beyond it's current
> deformation, the new footings start to help out and do the work.
>
>
>
> The footing in question is about 40 feet long and the width increase is
> necessary because there is no soils report and I have to assume 1000 psf
> soil pressure by code. It is very likely the soil's capacity is more
> than twice this amount based on back calculating the loads and original
> footing sizes.
>
>
>
> This footing is being enlarged because it is under a shearwall and I am
> strengthening the wall system for a larger seismic demand. This is also
> a voluntary action by the owner, his goal is to take care of the easily
> correctable deficiencies with a minimal disruption to daily operations
> within the building.
>
>
>
> Yes, I was adding new full depth concrete on either side. I think that
> compressed air sandblasting and/or bush hammering would be suitable as
> Jim suggested. I'm not sure if this classifies as "a lot" - I think this
> about 1 or 2 days work (for 1-2 persons) for this amount of footing -
> but I could be wrong.
>
>
>
> Thanks for the responses so far, keep them coming if you have more to
> add.
>
>
>
> -gerard
>
>


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