Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Constrained Modulus Estimate for Hard Clay

Constrained Modulus Estimate for Hard Clay

Constrained Modulus Estimate for Hard Clay

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

RE: Constrained Modulus Estimate for Hard Clay

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?


ípapß gordo ainÆt no madre flaca!

RE: Constrained Modulus Estimate for Hard Clay

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

RE: Constrained Modulus Estimate for Hard Clay

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.

RE: Constrained Modulus Estimate for Hard Clay

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:


Look at the bottom of page 7.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close