Disturbed Soil Properties and Geotechnical Design

[VAD]

Has anyone read the subject book by Andrew Schofield which points out the error made by Terzaghi on the concept of cohesion. In the foreword of the book by Mark Randolph, Terzaghi is identified amongst others as a Villain. Not sure if this was to be taken literally or in the context that he may have misled us through his ideas. The literature is perhaps full of such Villains.

However, interesting stuff for those who have been groomed in Critical State Soil Mechanics. Clear enough for the practicing engineer but not clear for those who are now a student unless the Profs decide to discuss the topic.

Like everything else every one sounds good. Again the problem I have is that in my opinion there needs to be a better job to convince us and students on how to comprehend this info in light of overwhelming info on the use of cohesion. Certainly there are sufficient practical issues that can be used in layman terms.

In some ways I feel that what is happenning so far is - here is my take on the subject, I am the expert, and you believe. All whell and good until we hit the real world and find that many have different ideas, we rread books and article that speak the other language, then confusion reigns.

All of us have ideas on many of these topics, some of which never surface because we think others would feel that they are foolish or crazy and therefore leave them in the subconsious.

What are your opinions?.

Book is published by Thomas Telford 2005. Much of the content, I think, comes from his Reappraisal of Terzaghi's Soil Mechanics Invited Lecture, ISSMGE, Istanbul Turkey.

 

[Mccoy]

I do not know this author's ideas, but I would welcome anything which turns out to be better, in the real world, then the preceding current state of the art.
Does Schofield presents case histories, calculations, and more showing the benefits of missing cohesion?
If yes, and if he has been convincing enough, then he should wait for some big names willing enough to try out his ideas and disseminate them. Long and hard work.
Harr's probabilistic theory for stress propagation sounds much better then boussinessq, but probably I'm one of the few ones in the world who ever used it.
Jambu's method to calculate settlements is so much sensible and in a way easier then Terzaghi's but in professional practice I bet the latter is still predominant.
VAD, do you know about any links in the web summarizing Shofield's theory? After all we know phi and c is just a convenient representation, convenient but not necessarily the best one. But

 

[VAD]

Mccoy- Try this link and do some searching around. Schoefield's Critical State Soil mechanics can be downloaded. You may find some interesting articles as well by searching the site

http://www.eng.cam.ac.uk/

This link is in the book

http://www2.eng.cam.ac.uk/-ans.

htm. I did not try that.

Good Luck

 

[Mccoy]

VAD,
after seeing University of Cambridge I recall that in this forum we've already spoken (a little) about Schofield's theory.... If my memory is not totally off the beam.
I'll have a look at the book.

 

[VAD]

Mccoy:

Yes, I think so.

I am not sure if you or other members have seen this site, perhaps so. Anyhow there is enough to fill one's cup and some more. Some of Schofield other articles re the subject are on this site.

http://www.geotechlinks.com/

SlideRuleERa: You may want to review this site and add to your web page.

 

[eric1037]

It is interesting to note that William Housel of the University of Michigan (1924-1971) (a contemporary of Terzaghi) had serious problems with Terzahi's concepts of cohesion and consolidation.

Professor Housel was marginalized by the soils community. I would find it ironic if he is proven correct in the long run.

If you are interested in Housel's ideas, try to google "Housel Soil Mechanics". I have most of his publications, most of which are, unfortunately, out of print.

 

[BigH]

Don't have the book - but have seen a few of his articles dealing with the issue - I think there are two of them. I have downloaded the Critical States book - I had a photocopy of it from University days. Malcolm Bolton's book should also be looked into about the theoretical soil mechanics.
I must admit that not "much" of the critical state concepts have entered into my working career - I toyed with them but the other engineers I dealt with didn't seem to know anything about them - I think that there is the disparity among "just" practicing engineers on normal/typical problems and those who work on or are party to, for the lack of a better word, "big ticket items" that requires super-expertise. McCoy is correct in that it is totally doubtful that anyone other than a small handful have ever used stress states set forth by Harr's particulate vs elastic continuum.
Good point VAD - but can we pick a problem where we can study the points of Terzaghi vs the points of Schofield? Perhaps this would be a good exercise for some of us to look into - and how such can affect/help or not one's own practice. Terzaghi - even if found somewhat out of sync has surely been successfully applied 99% of the time.

 

[VAD]

Big H - You are thinking the same way I have been once again recently having read Schofield's recent literature. I have books on critical state Soil Mechanics as well and did a graduate course on same some 30 years ago. Course was given by one of the Profs who did his Ph.D at Cambridge.

Was interseting at that time especially being able to predict stress-strain curves from simple soil parameters. Another Prof figured at the time that there was little practical value for this concept in the real world.

However, I have started thinking about this again and am in the process of examining the cohesion aspect from some very rudimentary thinking which uses no laboratory testing but going back to "playing with mud" as a kid and some of the observations made through the times based on ones experience.

Some interesting thoughts are coming to the fore, probably full of holes but so what. If it has taken so many years for someone to come out and challenge the concept so why not put some ideas together whether crazy or not, after all this whaole subject of soil mechanics has its roots in observation and experience.

So my subject is to look at the concept of cohesion. If you were to look at pile design closely you would realize that the toatl stress approach leaves much to be desired especiall with the use of adhesion factors. We have all use it and we have all designed and things haave stood up but is it because of our design concept or is it that we have been fortunate that we have employed a factor of safety.

While this is a sensible approach it always leaves me thinking if we really understand the subject. My own opinion. Or we are fortunate because of a method of practice. I suppose I like to push the envelope for satisfaction of understanding. I am not very taken up with finding capacities etc as one can sometimes do that at the back of a cigarette pack. Understanding then numbers is my preference.

When I get some of my thoughts down in a more organized fashion I will pass on for comments. What we need is some real practical cases or reasoning that can be readily appreciated by all for or against the use of cohesion.

Regards

 

[SlideRuleEra]

Good link, VAD - I'll take a look.

http://www.SlideRuleEra.net

 

[vulcanhammer]

Schofield's Critical State Soil Mechanics can be downloaded from

http://www.vulcanhammer.net/download/general_soil_mechanics.php

Also on an unrelated matter: I managed to put some of the FHWA's documents (drilled shafts, driven piles, etc.) on a badly needed pdf diet and reduce their download size. So perhaps it will make these more accessible. I have attempted to update the driven pile book with the new one from FHWA but they are charging for it every way they can so this will have to wait.