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RE: Seismic loads on retaining walls

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Mononobe-Okabe equations are based on the wall being able to translate a
little bit at the base. For restrained walls, I use AASHTO 's procedure for
estimating seismic soil pressure on anchored walls (AASHTO Standard
Specifications for Highway Bridges 16th ed, Section 5.7.4.) They use the
Mononobe-Okabe procedure but use a seismic factor of 1.5A where A is an
acceleration coefficient. This compares to 0.5A which they recommend for
unrestrained abutment walls in section 6.4.3 of Division IA of the same
document. 

There is another method for nonyielding walls by Wood which is summarized in
Steven Kramer's "Geotechnical Earthquake Engineering." It predicts a total
horizontal dynamic thrust (added to the static soil load) equal to the
following:

Delta Peq = Gamma * H^2 * ah * Fp /g. In this equation, gamma is the unit
weight of the soil, H is the height of the wall, ah/g is the seismic factor,
and Fp is a coefficient that varies with the geometry and Poisson's ratio of
the soil, but a value of 1.0 is in the general range. The resultant is
located roughly .6H above the base.

These are the only two guides I have come across. I have heard a real range
of opinion from other engineers on how to handle seismic soil loading. The
above can give you some pretty big numbers for a tall wall. I know some
people who ignore seismic soil loads altogether, but I am not one of them.



-----Original Message-----
From: Will H [mailto:haynewp(--nospam--at)hotmail.com]
Sent: Friday, October 18, 2002 4:08 PM
To: seaint(--nospam--at)seaint.org
Subject: Seismic loads on retaining walls




I have a restrained (at top and base) retaining wall about 14' high. I 
noticed that Retain Pro uses the Monokobe-Okabe equations for cantilever 
walls but this is not an option for restrained walls. Does anyone know why 
this would not be applicable to restrained walls? The two foundations books 
I have seen don't even have a reference for seismic loads on retaining 
walls. I also need to calculate the top restraint reaction required. Any 
information?

thanks, Will






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