INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!

*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.

Jobs

Pseudostatic Analyses

Pseudostatic Analyses

(OP)
The recently published book "Soil Strength and Slope Stability" by Duncan and Wright discusses procedures for conducting pseudostatic analyses.  I often evaluate simplified seismic displacements of slopes/embankments and use pseudostatic analyses to estimate yield acceleration.

Duncan and Wright state a single stage pseudostatic analysis may be performed using the R strength envelope from a CU test together with effective stresses and steady state pore water pressure.  

The use of effective stresses and steady state pore water pressures with a total stress (R) shear strength envelope seems contrary to me and contrary to the dirth of literature on the subject.  I have always used total stresses and no pore water pressure when using a total stress (R) shear strength envelope.

Any thoughts on this?        

RE: Pseudostatic Analyses

The R envelope is not the same as the total stress envelope that you probably learned in soil mechanics classes.  It is actually intended to represent the variation in total stress shear strength that occurs with effective stresses (that's my understanding of it). Technically, it is not exactly accurate if the stress path or stress state in the field isn't appropriately modeled by the test used to produce the envelope, but a total stress envelope is even worse in my opinion.  

RE: Pseudostatic Analyses

To add to what GTeng said, the R-test is typically an ICU test which is fully consolidated prior to testing (pore water pressure equals 0 so this is an effective stress state).  So when plotting the results you plot the shear stress on the failure plane at time of failure (tau-ff) versus the effective normal stress on the failure plane at time of consolidation (sigma'-fc).  Like GTeng said, you essentially are assigning an undrained shear strength to a soil that exists at some effective stress in the field.  Limit equilibrium computer programs simply calculate the effective normal stress at the base of a slice and it is now easy to determine the undrained shear strength from the R-strength assignment.  (sidenote: remember this not a Mohr-Coulomb plot so the intercept and angle are not c and phi.)

RE: Pseudostatic Analyses

(OP)
Thanks for the replies.  Part of the confusion is the strength envelope is referred to by many as a "total stress" envelope, and that the effective consolidation stress is also a total stress (since u=0).  I also not that some agencies prefer not to use this envelope for some reason.   

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!


Resources


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