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Re: Retaining wall rotation

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I couldn't agree more with Brian K. Smith, I always use earth pressure at rest for permanent structures.  Active soil pressures are ok for temporary work.  If any seriuos restraint is present, many times you will find the wall "attracts" earth pressures that can exceed earth pressure at rest on the long term.  Most Foundation Analysis texts neglect the effect of long term soil creep.
 
John Schenne, PE
Schenne & Associates
----- Original Message -----
Sent: Thursday, May 24, 2001 12:44 PM
Subject: RE: Retaining wall rotation

I think the statement "wall rotation is inherent" should be clarified as "typically inherent" as it is dependent upon the design method.  Engineers typically design for active soil pressures; however, many times I design the wall for the Ko or at rest earth pressure, depending on the importance of the wall.  If the wall was designed for the active soil pressures, then the wall must rotate to produce these pressures.  In Foundation Analysis and Design, 4th Edition by J.E. Bowles, the following is given as to the required rotation;
 
    Cohesionless, dense        0.001 to 0.002H
    Cohesionless, loose        0.002 to 0.004H
    Cohesive, firm                0.01 to 0.02H
    Cohesive, soft                0.02 to 0.05H
 
Brian K. Smith, P.E.
Bossier City, Louisiana
-----Original Message-----
From: John P. Riley [mailto:jpriley485(--nospam--at)peoplepc.com]
Sent: Thursday, May 24, 2001 10:27 AM
To: Frank E. Stewart; seaint(--nospam--at)seaint.org
Subject: Retaining wall rotation

A homeowner made an insurance claim on his retaining walls, one each side of the front of his underground home.  Both walls have rotated since their construction in 1979, one has an outward lean of about 1/8" in 8" (just had my little torpedo level with me . . . not real accurate) and the other is about 1/4" in 8"; both are 12' high tapering to 0' in 12' (i.e.: they are 45 deg triangles).
 
I am about to prepare a report, saying among other things that retaining wall movement is inherent.  But I forget "how much" movement is to be expected.  Of course, I know its impossible to say for all cases, but I'm looking for an 'order of magnitude' number as a percent of height.   
__________________
John P. Riley, PE, SE
Riley Engineering
20 Oakwood Drive, Blue Grass, Iowa 52726
Tel & Fax:  319-381-3949
jpriley485(--nospam--at)peoplepc.com