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Re: Footing sliding resistance - Friction

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Making the footing bigger will help in 2 ways.
1) The soil weight on footing will increase thus increasing your gravity loads, thus your frictional resistance will increase. (This can also be achieved by taking your footings deeper to increase the soil weight)
2) There is soil passive earth pressure also available to resist sliding. Again a bigger footing (also a thicker footing) will help in this resistance. (For tall industrial structures with light claddings, wind load cases throw up foundation reactions with a lot of uplift & horizontal forces. In such instances the passive earth pressure helps more in resisting the sliding rather than friction)
Pankaj Gupta
----- Original Message -----
Sent: Tuesday, June 21, 2005 12:20 AM
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!!!!!

Haffner Consulting Engineering
Office & Fax:  541-478-3052

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