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SUMMARY:Unsaturated soil mechanics - Critical review of physical foundatio
 ns - Professor Sam Frydman\, Technion\, Israel Institute of Technology
DTSTART:20070815T133000Z
DTEND:20070815T150000Z
UID:TALK7838@talks.cam.ac.uk
CONTACT:Zelda Stuck
DESCRIPTION:Most constitutive models for unsaturated soils are based on id
 entification of soil water suction with the capillary component of the mat
 rix potential\, ignoring the contribution of adsorption. Identification of
  potential (energy per unit volume) with stress (or suction)\, is question
 ed\, since these quantities have different physical significance despite t
 heir common dimensions. It is suggested that the identification of suction
  as (ua-uw) results from neglecting the adsorption potential\, and adoptin
 g an unrealistic pore space model. Experimental studies of unsaturated soi
 ls commonly use axis translation\, wherein "suctions" are established by s
 imultaneously increasing air and water pressures to the desired (ua – uw
 ) value. This procedure ignores the fact that under normal field condition
 s\, the soil air pressure is atmospheric\, and the soil water cannot devel
 op tension greater than about one atmosphere without cavitating. Axis tran
 slation alters soil behavior by preventing cavitation\, thus casting doubt
  on the relevance of common laboratory results to actual field conditions.
  It is suggested that capillary potential accounts for only a small part o
 f matrix potential\, the major contribution resulting from water adsorptio
 n onto the soil particles\, particularly in soils having large specific su
 rface areas. Consideration of a double porosity model appears essential to
  the interpretation of unsaturated soil behavior. \n\n
LOCATION:Engineering Department - LR6
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