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RE: Earth pressures on retaining walls

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Have you considered having the wall constructed so that it is out of
vertical plumb leaning toward the source of active pressure? Any
unanticipated long-term deflection will then bring the wall closer to being
vertically plumb.

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Tuesday, January 18, 2000 12:50 PM
To: SeaInt Listserver (E-mail)
Subject: Earth pressures on retaining walls


I'm curious if anyone has any data or applicable experience regarding long
term deflections of cantilever concrete retaining walls.  I have a deep wall
which we are concerned about limiting long term deflections but can accept
reasonable deflections during initial construction.  (We can adjust for
initial deflections but have an interface in final construction which
requires a more limited tolerance.)  The following questions have come up: 

1. If a retaining wall is designed for active lateral earth pressure, will
all of the deflection required to develop active pressure occur immediately
during backfilling or does it take time after backfilling to fully deflect
and develop active pressures?  It is understood that a concrete wall will
continue to deflect some due to creep of concrete but is there any ongoing
movement due to soil pressures?

2. According to U.S. Army Corps of Engineers (COE) engineering manual EM
1110-2-2502 (1989) for Retaining and Flood Walls: "Designers have often
assumed active earth pressure on the driving side because movements required
to develop active pressures are small.  However, several reasons exist to
design walls for at-rest pressures.... Even for foundations capable of
yielding, certain experiments with granular backfill (Matsuo, Kenmochi, and
Yagi 1978) indicate that, following initial yield and development of active
pressures, horizontal pressures may in time return to at-rest values.
Another reference (Casagrande 1973) states that the gradual buildup of the
backfill in compacted lifts produces greater than-active pressures as do
long-term effects from vibrations, water level fluctuations, and temperature
changes."   The manual then concludes that walls should be designed assuming
at-rest earth pressures on the driving side - this is rather conservative
relative to common assumptions for retaining wall design.  Has anyone seen
these references or seen other data which supports the concept that lateral
earth pressures in granular fill may gradually return to at-rest values over
time? 

3. My own general impression is that retaining walls tend to deflect more
with time, which could be due to any of the above noted reasons.  If a wall
is founded on rock or on drilled piers, will the cantilevered stem wall
deflect more with time?  Will total deflection exceed that calculated solely
based on concrete creep for long-term effects?  

Thanks in advance for any info you can provide.

William C. Sherman
Camp Dresser & McKee, Inc.
Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com