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.

Students Click Here

This query is reallocated from stru

This query is reallocated from stru

This query is reallocated from stru

This query is reallocated from structural discussion group.

Dear All!
I am considering to soil improvement by using prefabricated vertical drain (PVD) method. The methods to calculate the final consolidation settlement, consolidation rate, PVD spacing ... are introduced quite clearly in most of geotechnical & foundation engineering textbook. But I could not find any lines or instruction regarding to how to calculate the shear strength of soil after a certain settlement is reached (let says 90% of final consolidation settlement reached) or pore water pressure is dissipated.

I understand that we have to make some field test & lab test to determine that parameter exactly, but how about the theory method?

Does anybody show me the way to calculate that parameter? Which book or which site contains necessary information? Also, by your experience with practical approach, how many times will the soil shear strength increase from the initial value? In my case the initial value of shear strength is 4 ton/m2 approximately, Will it increase to 8 or 10 ... ton/m2?

Thank in advance! All opinion will be highly appreciated!
From BigH

There was a technical note written back in 1975 I believe by N. Som regarding how to determine the increase in the undrained shear strength after consolidation.  I have the paper, send your e-mail address to bohica@indiatimes.com  and I will forward it to you - maybe, after a little procrastination (couple of days).  I, too, am currently involved in similar exercise (Dr. Som is a consultant for the contractors on this one).  I have very week soils and 9m high retaining walls to go on (RE Walls).  Some data I found interesting from a soils boring programme here in the Calcutta area - undrained shear strength after long term (say plus 15 years) under 5m high embankment doubled the natural undrained shear strength where there was no embankment (and far enough removed, but adjacent, to not have been affected by the embankment.  


RE: This query is reallocated from stru

In all practical purposes the increase in shear strength due to consolidation can be calculated by 0.2 of increase in effective vertical stress (in your case either the full embankment height for one go construction or the height of embankment corresponding to a particular stage construction)

RE: This query is reallocated from stru

Thank 1967pradyot!
Could you explain your idea more detail? Any background experiences & calculations to support for the factor of 0.2?

RE: This query is reallocated from stru

The relation which I have mentioned is a conservative estimate. Of course, remember this is valid for only normally consolidated clay. Actually this is based on the relation that the undrained shear strength of normally consolidated clay increase almost linearly with depth. You can refer any book (say, Foundation Analysis and Design by Bowles)to get the relationship as proposed by Skempton & Henkel. Their equation relates undrained shear strength, effective overburden (or vertical) pressure and plasticity index.
Hope, this will be helpful to you.


RE: This query is reallocated from stru

npthao121 - the relationship that Praydot is talking about is the slope of the line of undrained shear strength with depth.  As the overburden pressure is more, the clay is "stronger".  Plot your undrained shear strengths vs depth and you can see your own "site" curve.  Of course, the 0.2 that was given is a "typical" value - Terzaghi, Peck and Mesri suggest 0.23.  I discussed this in a thread a while back - about how to estimate settlements in clay from SPT samples - the thread escapes me at present.  You could do a word search.  

RE: This query is reallocated from stru

I did the search for you - it is thread 256-40097.

RE: This query is reallocated from stru

Thank a lot BigH & pradyot

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! Already a Member? Login


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