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Re: Earth pressures on retaining walls

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Dear William:

I believe they CE reference is correct and have used the at rest pressures
for designs on many projects.  In additon to the factors you mentioned long
term creep of the soil, can in my opinion, raise pressures to somewhere
between active and at rest.

John Schenne, PE
Schenne & Associates

----- Original Message -----
From: Sherman, William <ShermanWC(--nospam--at)cdm.com>
To: SeaInt Listserver (E-mail) <seaint(--nospam--at)seaint.org>
Sent: Tuesday, January 18, 2000 3:50 PM
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
>
>
>