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RE: Soil Pressure

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Soil Pressure
• From: "Alex C. Nacionales" <anacio(--nospam--at)skyinet.net>
• Date: Wed, 27 Jan 1999 14:23:52 +0800

```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

Alex C. Nacionales

> -----Original Message-----
> From: EphHirsch(--nospam--at)aol.com [mailto:EphHirsch(--nospam--at)aol.com]
> Sent: Wednesday, January 27, 1999 9:44 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Soil Pressure
>
>
> Sorry, last post contained nothing (I hit the wrong key before
> anything was
> typed).  Based on the data your geotech gave you, the equivalent
> pressure at
> the base of the wall (assuming 8 ft. ht. as you stated) due to 35 pcf
> equivalent fluid pressure is 8 x 35 = 280 psf with a triangular
> distribution
> diminishing to zero at the top and therefore an overall
> horizontal total force
> = 1/2 x 280 x 8  = 1,140 plf (i.e. pounds per horizontal linear
> foot of wall).
> How did you arrive at 75 psf for an answer??  How this force is
> resisted and
> what the reaction/shear /moment distribution is of course a function of
> whether or not the wall is a cantilered one from its base or
> restrained its
> top by the floor framing system.  Strictly speaking of course
> this would also
> affect the soil pressure distribution itself, but the geotech
> presumably just
> assumed triangular distribution in either case, based on how the
> data appears
> to be stated.
>
> Now, in addition to the above there will be added horizontal
> pressure of 15H
> (psf), where H is height of surcharge, NOT wall, with a total
> horizontal force
> of 8 x 15H (plf).  Since you didn't give the surcharge height,
> the numerical
> values are not obtainable.
>
> The inverted triangular earthquake equivalent fluid pressure of
> 20 pcf will
> not increase the horizontal pressure at the base of the wall, but
> will impose
> an additional total horizontal force of 1/2 x 8^2 @ 20 pcf = 640
> plf applied @
> 2/3 the wall height.
>