×
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!
  • 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

Jobs

Horizontal Consolidation
6

Horizontal Consolidation

Horizontal Consolidation

(OP)
Is there any standard test to determine the coefficient of horizontal consolidation? I am assuming Cv = Ch. Is this reasonable.

Thank you.

RE: Horizontal Consolidation

Only if the permeability is homogeneous (unlikely).  Horizontal permeability is often 4 to 10 times greater than vertical permeability when dealing with settlement sensitive soils (i.e., sedimentary soils).

f-d

¡papá gordo ain't no madre flaca!

RE: Horizontal Consolidation

fattdad makes the correct point - in most fine grained soils due to deposition, the horizontal permeability will always be higher.  If you want to do horizontal consolidation - get a block sample and cut it to fit in the consolidation ring at 90deg.  In this case you will find that the time for t95 will drastically reduce.  Years ago, Lee put out a book on state of art in geotechnical (have a copy but in storage) and they had a huge chapter on 1-D and 3D consolidation.

RE: Horizontal Consolidation

I'm confused.  What does Ch mean?

You can test a 90-degree sample, and you will probably find that it is substantially higher than Cv of a normal sample, but how do you use that?  For typical consolidation analyses, we pretend that perfect drainage (zero excess PWP boundary condition) is provided by more pervious layers above and/or below the soft clay.  What is the analogous boundary condition for horizontal consolidation?

Or, is the OP referring to vertical consolidation with radial drainage to sand drains or wick drains?

RE: Horizontal Consolidation

(OP)
Thanks for the responses.

dgillette, Ch - coefficient of consolidation for horizontal drainage

fattad, I agree with your point

BigH, I don't think 90-degree turned sample really measures Ch. If you think about the forces acting on this sample:
Sigma(h) - vertically (i.e. on the horizontal face)
k0.Sigma(h) - radially (i.e. on the vertical face) instead of Sigma(v).

 

RE: Horizontal Consolidation

It is really a horizontal permeability test that you should be doing at various pressures perpendicular to the horizontal, isn't it? That is what you are really looking for (and ci does correspond to ki - though applied stress does have an effect (see Conduto's book on Geotechnical Engineering Principles and Practice, eq'n 12.1).
http://www.maa.com.tw/common/publications/2000/2000-059.pdf
http://geosystems.ce.gatech.edu/Faculty/Mayne/papers/PiezoDissipation.pdf (see first page - first half)
http://www.infomine.com/publications/docs/Miller1989.pdf
 

RE: Horizontal Consolidation

You won't find a standard test for a laboratory determination of Ch. In the field you can determine Ch values from dissipation tests with a CPTU.
Now if you need a value for Ch it means than you have to design a vertical drain grid. Ch can vary from 1.5 to more than 10 times Cv. Usually between 5 to 10. The more the soil is layered ( with sandy layers for example, the bigger the coefficient ). You must keep in mind that you start from a Cv value which itself is questionnable !
from my point of view, I "guesstimate" the coefficient from the geological description of the borehole logs and the confidence I have in the Cv value given to me.
The most important aspect you should keep in mind is the economics behind it. Vertical drains are cheap : check both designs with Ch = 5 Cv and Ch = 10 Cv and you will see that the extra money is generally not work the risk unless you are not in a hurry ( but who isn't nowadays !  

RE: Horizontal Consolidation

For lab test, you can refer to the method proposed in BS1377-6:1990. See the chapter "Procedure for consolidation test with drainage radially",I think it is more reliable.

For in-situ test,CPTU with dissipation test is a good and convenient way to do that.The interpretation approach could refer to http://www.trb.org/publications/nchrp/nchrp_syn_368.pdf

RE: Horizontal Consolidation

This brings up something that has  caused me to question many a settlement-time prediction by engineers I have run into.

I can recall only a few jobs where the time-settlement prediction followed what the lab tests would compute out to.

Most times, the jobs settled much more rapidly than predicted.

A few jobs had a "test surcharge" to give a notion as to what to expect.  Past experience in nearby sites also helped.

RE: Horizontal Consolidation

oldestguy

With Asaoka's method, you will have an accurate prediction of the consolidation times after a few weeks of surcharge.

RE: Horizontal Consolidation

You can use a Rowe cell (something like the oedometer but allows control over radial drainage)...if you can find one...

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