# Re: Active, At-Rest, Passive Soil Pressure

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Active, At-Rest, Passive Soil Pressure
• From: "Reza Dashti Asl" <rezadashti(--nospam--at)hotmail.com>
• Date: Wed, 22 Aug 2001 15:47:21 -0700
I think the problem with the idea of "at rest" pressure comes from the meaning of the word "rest"(like how something "at rest" can exert more pressure than when it's "active"!) To explain the concept, let's look at the undisturbed soil. Every particle (and/or mass) of soil is under pressure from the particles on top of that. The reason that it's not going anywhere is that there is a lateral pressure, coming from other particles, that keeps it in place. Now if you put a wall of zero volume in the soil, the wall will experince the same pressure from the soil. Now you can give the wall a volume and excavate one side of the wall. There you have the "at rest" pressure being exerted to the wall. If the soil pressure is large enough (comparing to the wall stiffness)the wall will move a little and will experience less pressure. Then forces in the soil will re-distribute to form a wedge of soil with a shear plane at 45+phi/2 degrees to horizontal to balance everything (this is the so called "active pressure")
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If you need a complete explanation, try Chapter 11, "Foundation analysis and Design" by Bowles (BTW, thanks Stan, I'll be more careful from now on!)
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Reza Dashti P.Eng.

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```From: "a_more" <a_more(--nospam--at)penteres.it>
To: <seaint(--nospam--at)seaint.org>
Subject: Re: Active, At-Rest, Passive Soil Pressure
Date: Wed, 22 Aug 2001 23:05:28 +0200

i'm sorry folks..you and the at-rest pressure don't make
sense..sure..greater is better..and your butt is ok... but if no sheepsteps
(or how is called there) and no vib-constipation..then you are only wasting
concrete, and iron..no offense meant, as usual..
regards
andrea
(yet to see my taller wall to go down..it is 32'...not restrained)

----- Original Message -----
From: "John Schenne" <jschenne(--nospam--at)localnet.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, August 22, 2001 12:50 AM
Subject: Re: Active, At-Rest, Passive Soil Pressure

> Rodger:
>
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> I have used at rest pressures for design for 25 years with no failures and
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