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RE: Seismic load on retaining wall

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While the M-O method gives a top-heavy triangular distribution, the
semi-rigid case using the 1.5 factor at the top, also results in a trapezoid
using 0.5 for the base pressure.

Thor A. Tandy P.Eng, MIStructE, Struct.Eng
Victoria, BC
Canada
vicpeng(--nospam--at)telus.net


-----Original Message-----
From: arshad vali [mailto:arshadvali(--nospam--at)yahoo.com]
Sent: Thursday, March 20, 2008 7:34 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Seismic load on retaining wall


Hello Arturo,

You are correct about "the Mononobe-Okabe method
cannot be used."

I was reading the current AASHOT Code and in Section
A11.1.1.3 it states that

"The Mononobe-Okabe analysis assumes that the abutment
is free to latreally yield a sufficient amount to
mobolize peak soil strengths in the soil backfill. For
granular soils, peak strengths can be assumed to be
mobolized if deflections at the top of  the wall are
about 0.5 percent of the abutment height. For
abutments restrained against lateral movement by
tiebacks or batter piles, lateral pressures induced by
inertia forces in the backfill will be greater than
those by a Mononobe-Okabe analysis. Simplified elastic
solutions presented by Wood (1973) for rigid
nonyielding walls also indicate that pressures are
greater than those given by Mononobe-Okabe. The use of
a factor of 1.5 in conjuction with peak ground
accelerations is suggested for design where doubt
exists that an abutment can yield sufficiently to
mobolize soil strenghts."

Hope this helps. If you need the actual sketch and
more information let me know.

Arshad Vali, SE
Los Angeles, CA.
--- Arturo Martinez <amartine(--nospam--at)udep.edu.pe> wrote:


---------------------------------

Is there any method used to estimate the seismic load
on a retaining wallthat is restrained for lateral
movement? This wall is buried and isrestrained by a
concrete slab on top and a mat foundation at the
bottom. Iassume that under this condition, active
pressures cannot develop, hence theMononobe-Okabe
method cannot be used. Am I right?. This wall is also
belowphreatic surface.
I will appreciate your input.

Arturo
Piura,Peru


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