In all inspections I had,
I never saw anything close to the earthquake related failure of retaining
walls. The Proceedings of NEHRP conference on Northridge earthquake
does not appear to include any discussions of such failures.
There is an article about landslides
(II-146), but still no retaining wall failures.
An your are right, in our search for
"bodies" that do not appear to exist we start to resemble Lenny Briscoe et
al. Will there be a happy end, with the bad guys punished?
V. Steve Gordin, SE
----- Original Message -----
Sent: Monday, November 10, 2008
Subject: Retaining Wall Design Practice
The inclusion of seismic is actually driving the
design on our subterranean projects now. My question, "where is the
justification for this"; or as Frank Lew used to say, where are the
Is anyone aware of a bunch of basement wall failures
or retaining wall failures due to seismic? How about any failures?
I would really like to be able to point to something to explain the added cost
to the client besides, "it's the code now".
Paul Feather PE, SE
Well, I'm the last person to be considered an authority
on anything related to soil design values, but I would like to point out
that now that we're required to consider earthquake forces in our design of
retaining walls (at least in my area of California), I think in terms of 1/3
increase in earth pressure is more or less offset by 1/3 increase in
allowable timber stresses. Where does that leave us if we've already
taken a 40% reduction in loads??
Ralph Hueston Kratz,
Richmond CA USA
In a message dated 11/10/08 2:12:01 PM,
I typically use method #1.
Fisher SE PE
From: Phil Doody
Monday, November 10, 2008 4:01 PM
Soldier Beam Retaining Wall Design Practice
Is there a consensus on the design
of wood lagging for soldier beam retaining walls? Several design methods
appear to be in use and each gives very different answers.
Basically, there appears
to be at least three ways of designing wood lagging that I have
#1 Determine the uniformly applied load on the
lagging due to the soil pressure at a given depth. Select the lagging based
on the required section modulus, S = (Moment)/(Allowable bending
#2 Same process as above but instead apply only 60% of
the theoretical uniform load. The justification for the 0 .6 reduction
factor is that soil movement causes the lagging to flex outward, and induces
a redistribution of soil pressure away from the center of the lagging thus
reducing the bending moment. This method is described in the Caltrans
Trenching and Shoring Manual.
#3 The third method of sizing lagging is based on FHWA
recommendations contained in Federal highway Administration Report Number
FHWA-RD-75-130. A table in this report provides the minimum thickness
lagging for various soil conditions, soldier pile spacings and excavation
depths. This method cannot be used if there are surcharges behind the
The most conservative method is the first method and the
one which I am most accustomed. However, I would like to know if
others use methods #1 and #2 and if anyone has observed lagging failures
using these methods?
Thanks for your input, Phil Doody
AOL Search: Your one
stop for directions, recipes and all other Holiday needs. Search Now.