Dynamic Subgrade Modulus

[theCorkster]

I'm working on a project in which the structural engineer is requesting values for "dynamic subgrade modulus" for input to his computer model. This will apparently be used for modeling the dynamic response of the soil foundation. I'm not familiar with this parameter, and this is the first time this has been requested. Any help with references and/or experience with this is apppreciated!

 

[RWF7437]

http://scitation.aip.org/getabs/ser...00129000004000434000001&idtype=cvips&gifs=yes

 

[sdz]

The cross-hole test is a common method used for determining shear wave velocities and, hence, to characterize the shear modulus. This gives a low strain shear modulus.

See "Design of Structures and Foundations for Vibrating Machines," by Suresh Arya, Michael O'neill and George Pincus.

 

[coneboy]

In the past we have conducted shear wave velocity testing in order to determine a modulus of subgrade reaction. This modulus is quite often required for machine foundation designs.

Get a local CPTU contractor to perform a SCPTU test.
Using a shear wave source at the ground surface, a single SCPTU test will give you all the necessary data for determining the modulus of supgrade reaction.

We have always avoid doing cross hole seismic testing due to the costs. On other projects I have compared downhole and crosshole seismic data. Both types of testing usually produce the same results.

If you have ground that is not "cone-able" then you could install casing and conduct Vs testing in a cased hole. Maybe a local geophysics company could do testing from the ground surface?

Coneboy

 

[msucog]

there's other surface performed geophysical methods avaialable to measure the shear wave velocity which i have compared to downhole and refraction data with good results. see ReMi (refraction microtremor).

by the way, is the shear modulus often referred to as the dynamic subgrade modulus? i have thought these were two seperate "things". maybe i've misunderstood/confused something.

 

[theCorkster]

Thanks for the responses - however, I believe that I'm looking for something different.

RWF7437: The reference is directed toward flexible pavement design and evaluation. The paper refers to "dynamic stiffness modulus (DSM)", which represents the average dynamic modulus of elasticity of subgrade materials.

I believe that this value is the same as the subgrade resilient modulus, Mr, which is also applicable to flexible pavements.

sdz: I do not believe that it is the dynamic shear modulus (G) that the engineer has asked for as I've given them a value for that.

coneboy: I've already provided a modulus of subgrade reaction for the design - their request is apparently about a "dynamic subgrade modulus".

msucog: Your question is mine, although I've only seen the dynamic shear modulus refered to as the dynamic shear modulus!

Still looking to clarify ......

 

[sdz]

What's SCPTU?

 

[mudman54]

CPTU is a piezocone test; why don't you ask the structural engineers what computer program they're using and maybe we can figure out what the parameter is.

 

[BigH]

sdz - seismic cone