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Re: Sliding factor of safety for retaining walls
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- Subject: Re: Sliding factor of safety for retaining walls
- From: Thomas Chiu <Tomchiu(--nospam--at)worldnet.att.net>
- Date: Wed, 03 Sep 1997 20:32:06 -0700
Bill: I would use method 2 based on reasoning that your resisting forces are the combined passive pressure and the footing's frictional forces. Sometime I even neglect the passive pressure at the footing toe because of backfill condition. For example, if you have a line of 3 frames in the building resisting say 100 kips. wouldn't your F.S. = sum of the capacities of the 3 frames / 100kips. I don't think you can subtract 1 frames from 100 kips and use the other 2 frames to calculate the F.S. Tom Chiu, SE Thomas Engineering Bill Sherman wrote: > > How do you calculate the sliding factor of safety for a retaining wall? For > example, if you have an active sliding force due to soil of 2000 lb, a passive > resisting soil force of 400 lb, and a frictional resistance of 2400 lb: > > Method 1: > > Net lateral force = active force - passive force > = 2000 - 400 = 1600 lb. > > Factor of Safety (FS) = base friction / net lateral soil force > = 2400 / 1600 = 1.50 > > Method 2: > > Total resisting force = base friction + passive soil force > = 2400 + 400 = 2800 lb. > > FS = total resisting force / active sliding force > = 2800 / 2000 = 1.40 > > Which number is correct? I've seen designs and guidelines done both ways. > (Note: when passive soil resistance is neglected, the question goes away.) > I've typically used Method 2 on the basis that the intent is to have a total > resisting force greater than the force causing the tendency to slide. > However, this would mean that a wall with equal soil height on both sides > under at rest pressures doesn't meet stability criteria without adequate > frictional resistance! Thus I am starting to lean in the direction of Method > 1. (Note: this question also occurs when calculating safety factors for > overturning - should a passive soil force be included in the numerator or > denominator? The answer affects calculated factors of safety and resulting > deigns.) > >
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- Sliding factor of safety for retaining walls
- From: Bill Sherman
- Sliding factor of safety for retaining walls
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