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RE: Soil Pressure

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The engineering basis for the inverted triangular seismic pressure is finite
element analysis of the soil structure subjected to certain accelerations.
I'm sure the geotechs in the audience can explain in more detail.  I don't
see how you can consider a uniform load with resultant lower down the wall
as "safer".  Also, I don't see how you come up with 20 pcf - looks much too
low compared to the criteria I've seen from geotechs.

P.S.  Let's be more precise in the terminology - the value in the first line
of your post is the resultant soil *force* per unit length along the wall,
not pressure.  

	-----Original Message-----
	From:	Alex C. Nacionales [SMTP:anacio(--nospam--at)]
	Sent:	Tuesday, January 26, 1999 10:24 PM
	To:	seaint(--nospam--at)
	Subject:	RE: Soil Pressure

	The correct pressure should be p=1/2x(35)x(8)^2=1120 plf.
	Maybe you just mistyped it.

	I have my own question.

	Regarding the seismic pressure, What is the engineering basis for
	the upside down triangle pressure distribution. A rectangular
	distribution would be safer applied at 1/2 the wall height. 
	Assumming soil weight is 150 pcf and g=.40 you get 20 pcf of siesmic
	load due to the earth. 

	Alex C. Nacionales