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RE: subgrade modulus

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A good source of information is Chapter 4 in ASCE 41-06.  There are
some practical ways to quantify presumptive subgrade spring stiffnesses
for different foundation types.  Getting a geotechnical engineer's value
is always the best though.
Harold is right in that the effective subgrade stiffness of the soil
is dependent on the shape and stiffness of the foundation element
relative to the soil stiffness.  Embedment is another factor that has an

Harold Sprague <spraguehope(--nospam--at)> wrote:
I am not really sure.  I am not a geotechnical engineer, but it has to do with the slab on grade being essentially unreinforced concrete bearing on a prepared subgrade and a small area of applied load as opposed to a large foundation being a reinforced concrete rigid element bearing directly on soil.  It also has to do with the transient loading of a slab on grade vs. more long term effects on a raft foundation. 
I just know enough NOT to use the subgrade modulus given in the geotech report for slab on grade when I design a mat foundation. 
Harold Sprague

From: Truitt(--nospam--at)
To: seaint(--nospam--at)
Subject: RE: subgrade modulus
Date: Thu, 27 Mar 2008 08:10:08 -0700

Can you tell me why its markedly different?
Truitt Vance

From: Harold Sprague [mailto:spraguehope(--nospam--at)]
Sent: Wednesday, March 26, 2008 9:33 AM
To: seaint(--nospam--at)
Subject: RE: subgrade modulus
This is a geotech question, but you need to let them know the application.  A subgrade modulus for a raft foundation is markedly different than a subgrade modulus for a slab on grade. 

Harold Sprague

> Date: Tue, 25 Mar 2008 14:38:38 -0700
> From: ankiswani(--nospam--at)
> Subject: subgrade modulus
> To: seaint(--nospam--at)
> can any body tell me how to calculate the subgrade
> modulus from the soil test report
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