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RE: Active, At-Rest, Passive Soil Pressure

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I typically assume k=0.50 for the at-rest lateral pressure coefficient for
granular soils, unless otherwise provided by the geotech engineer. Thus, for
a granular soil with a saturated unit weight of 125 pcf and with hydrostatic

0.5(125-62.4) + 62.4 = 93.7 pcf

For clays, I've been told that the lateral soil pressure coefficient can be
as high as k=1.0 for at-rest conditions. I typically ask the geotechnical
engineer to provide at-rest earth pressures, as well as active and passive
earth pressures.   

-----Original Message-----
From: Jeff Smith [mailto:smthengr(--nospam--at)]
Sent: Wednesday, August 22, 2001 5:51 PM
To: seaint(--nospam--at)
Subject: RE: Active, At-Rest, Passive Soil Pressure

|~|However, at-rest pressure is now codified in the 2000 IBC, which
|~|does a much
|~|better job with basement walls and retaining walls than the UBC did.  IBC
|~|Table 1610.1 gives prescriptive active pressure values for USCS
|~|soil types
|~|and indicates to use 60 pcf for granular soils on walls
|~|restrained by rigid
|~|floors [at-rest pressure] and 100 pcf for silt-clay on restrained walls.
|~|Further it indicates wood joist floors are not considered rigid.

What would be the highest pcf force on a restrained retaining wall with no
drainage to relieve hydro static pressure, assuming no surcharge forces and
level backfill?


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