Constrained Modulus Estimate for Hard Clay

[Dirt Dept.]

I'm looking to estimate the constrained modulus (ksf) for use in the Janbu method for a hard dry clay that we were unable to extract brass cylinders for in the field during investigation. The clay was so hard that we could not drive the cylinders into the clay. Knowing that typical values for a stiff to hard clay at the upper end is around 60-70 ksf is there any literature or advice for estimating or quantifying the modulus of a very hard clay?

Thank you.

Blair Rushing, PE
Nelson Engineering
Jackson, Wyoming

 

[fattdad]

what's the end game? To calculate elastic settlement under some areal load? Do you know that it's unsaturated? Clearly it's preconsolidated. Did you do the SPT? For N-values in the 20's, I'd guess more like 200 tsf for soil modulus. I'm also wondering why you are seeking constrained modulus.

So, care to provide the backstory?

f-d

ípapß gordo ainÆt no madre flaca!

 

[Dirt Dept.]

End game is to calculate the estimated settlement beneath spread footings. We do know that it is and will remain unsaturated. The site is pretty remote so we only have information from test pits. Pocket penetrometer readings greater than 4.0 TSF. And sorry I didn't state correctly. I'm looking to estimate the virgin modulus number to utilize in the Janbu method.

Thank you.

Blair Rushing, PE
Nelson Engineering
Jackson, Wyoming

 

[BigH]

Pretty hard material. Doubt you would have any settlement to speak of subject to no disturbance during construction (and I know how that can happen) . . . this assumes, though, you have "normal" type footings with normal loadings - not like trying to support 1000 T on a 3ftx3ft footing! The following, which I would take as "fair use" is given in Hunt's book on Geotechnical Investigations and may be of help.

 

[Okiryu]

Agree with BigH. As additional reference, it should be more information available for Young modulus rather than constrained modulus, so you can refer to this paper from Paul Mayne to see the relation between these two parameters:

http://www.marchetti-dmt.it/pdffiles/mayne_dorms_2005.pdf

Look at the bottom of page 7.