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RE: Footing sliding resistance - Friction

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I would agree that friction is independent of surface area but is based
solely on total downward force.  Thus a wider footing would only help in
adding weight.  I would include the weight of any soil directly above
the footprint of the concrete footing. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Christopher Haffner [mailto:chaffner(--nospam--at)gorge.net] 
> Sent: Monday, June 20, 2005 12:51 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Footing sliding resistance - Friction
> 
> I'm having a Monday morning brain freeze and thought this was 
> a no-brainer but can't find a definitive answer.  
> 
> I am being told by the Geologist on a sloping (2H:1V) 
> residential lot that the coefficient of friction is .45 (no 
> units).  He is also indicating that a wider footing will add 
> some needed resistance to sliding.  
> 
> I don't think this is correct in that the coefficient should 
> only depend on the amount of gravity (vertical) load and not 
> on the area of the bearing area.  Therefore, making my 
> footings wider won't really help my sliding problem other 
> than to add a little more weight.  Am I thinking clearly here?
> 
> 
> Another question.......I will have some granular fill (varies 
> from 1' to 6'
> thick) below a basement floor slab.  I think this helps my 
> sliding resistance by adding weight to the system as it 
> interfaces with the soil below.  Since I am having the slope 
> benched I would like to use this resistance (weight x coef of 
> frict).  Opinions????????  
> 
> Thanks for your input!!!!!
> 
> Chris
>  
> Haffner Consulting Engineering
> www.haffnerconsulting.com
> Office & Fax:  541-478-3052 
> 
> 
> 
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