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RE: Sliding - Friction & passive resistance

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NAVFAC 7.02, Figure 15 on page 83, suggests a sliding factor of safety of 1.5 when passive pressure is not included with friction/cohesion and 2.0 when passive pressure is included.
 
My own approach is to use a conservative passive pressure combined with friction, based on wall deflection but not translation. I generally either use at-rest pressure or one-half ultimate passive pressure for my resisting soil pressure when combined with friction for sliding resistance. (This is based on EM 1110-2-2502, Corps of Engineers publication or ASCE's "Retaining and Flood Walls".)
 
Friction on side walls could be estimated by calculating the lateral soil force on the side walls and multiplying by the soil friction coefficient. But a question would be whether the pressures and friction coefficient on the side walls are affected by seismic effects?

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

-----Original Message-----
From: C Chan [mailto:seaint_list(--nospam--at)yahoo.com]
Sent: Thursday, November 14, 2002 10:10 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Sliding - Friction & passive resistance

Static frictional resistance occurs only when the wall is stationary. When the wall is stationary, there is no passive pressure being mobilized. After sliding starts, kinetic frictional resistance comes into play, which is always less than its static counterpart. I believe, the usual factor of 0.25 or 0.3 prescribed by the Geotech is the coefficient of static friction. So, is it rational to combine frictional resistance (i.e. W x static friction coefficient - assuming granular soil, not cohesive soil) and passive resistance together to resist seismic forces for a critical element like shear wall?

What do you think?

 RDAHLMANN(--nospam--at)aol.com wrote:

I have a question about sliding in long shear walls. In high seismic regions, sliding can govern footing sizes. Resistance is provided by the friction factor times the dead load weight (times appropriate factors) plus any passive pressure. This can also include return walls.

For long shear walls, it seems like there should be some sort of side friction factor also (similar to caisson skin friction). I have not seen this anywhere, but I would like some input about this possibility.

Thanks
Richard Dahlmann, P.E.
Phoenix