Talk:Shear strength (soil)

—Preceding unsigned comment added by 91.143.113.102 (talk) 10:08, 13 February 2009 (UTC)

Missing points
Two points seem missing in this article. Cohesion is not a function of negative pore pressure; it is caused by diagenetic forces between the solids in soil. Apparent cohesion is caused by negative pore pressure; that force dissipates as the negative pore pressure is satisfied and the soil shifts to the drained condition. Secondly, φ is the internal friction angle. It is not a resistive force. The resistive force from the friction angle is N*tan(φ); the resistance is proportional to the overburden pressure, N.

The term 'angle of internal friction' is prevalent in older literature, but is slightly misleading. The phi angle in soils is brought about by a more complex interaction of particles than the term 'friction' suggests, particularly in cohesive soils, but also in granular soils, where confining pressure, initial density, particle shape and angularity, orientation of particles, and physico-chemical effects such as cementation and bonding influence the phi angle, and ultimately the shear strength of a soil. A more 'correct' and generic term which should be used is 'angle of shearing resistance', as it encompasses all these effects not merely Coulomb friction. In the least, Friction should link to the main Wikipedia friction page: http://en.wikipedia.org/wiki/Friction I'd suggest shear strength be expanded or carefully linked to other pages that cover failure criteria; Linking to pages on Mohr-Coulomb Theory http://en.wikipedia.org/wiki/Mohr-Coulomb_theory, and for undrained shear strength, Tresca http://en.wikipedia.org/wiki/Henri_Tresca. Plasticity, http://en.wikipedia.org/wiki/Plasticity_%28physics%29, and Yield http://en.wikipedia.org/wiki/Yield_%28engineering%29 as general concepts for defining shear strength. But individual pages specific to shear strength of soils (for example) could be created, since there is much to expand on in this area. GeoEng 09:05, 11 March 2007 (UTC)

OK I decided I had nothing better to do, and had a go at editing this page (my first time editing on wikipedia, so dont shoot me). I have added non-existent links to Critical State Theory and Modified Cam Clay, in the hope someone (maybe me) will write entries on these. This article needs references I know. And links to similar articles. GeoEng 18:37, 11 March 2007 (UTC)


 * Thanks for your contributions; I'll try to help you out if I have time. Basar 19:53, 11 March 2007 (UTC)


 * Added some references and further info relating to cohesion and friction from those references. Really its just one actual reference at this stage (ref 2) by Prof. Schofield, and the others are cited in that document. May add some stuff from Prof. Burland if I get around to it, on 'post rupture' strength. This document needs some figures... i'll need to get around to those as well:) —The preceding unsigned comment was added by GeoEng (talk • contribs) 00:43, 18 March 2007 (UTC).


 * I am not sure I agree re. the cohesion concept presented in below--it may be true for non-cohesive sils, but for coehsive soils ex. "fat clays", inter-particle attraction forces would cause C to be non-zero at zero confining stresses. In otherwords, other than diagenetic forces, there is the plain old inter-particle attraction to consider--no?  Please let me know why I may be mistaken. Pathikoll 10:18, 20 July 2007 (UTC)

Move soils information
It seems to me that shear strength of soils should have its own article, perhaps shear strength (soil) or shear strength of soil. I'll move it if no one objects. Basar 19:53, 11 March 2007 (UTC)
 * Good idea. Still need to leave the basics at this site with a "Main article" link. I have a preference for Shear strength (soil), but, eh, no big yank one way or t'other. Zue Jay (talk)  20:05, 11 March 2007 (UTC)

Clarificaton
I would like to make a clarification re. the statement in the article that I have copied below:

"However, what is being plotted is not "true" cohesion, but is actually due to interlock of particles."

While this is no doubt possible for sands, for clays the cause is not so much intelock of particles, but rather inter-particle attractive forces. These are not quite the same and I would like to distinguish between the two if there is no objection. Pathikoll 18:09, 19 July 2007 (UTC)

Am removing this statement that I added at the bottom of critical state as it is valid not just to the CS, but to all other theories as well: "In recent years, critical state soil mechanics appears to have reached a dead end. For example, it has been unable to explain the emperical SHANSEP relationship. It may be that a theory which ignores soil structure is essentially limited in what it can explain."

Am adding the last line back at the end of the introduction: "It may be that a theory which ignores soil structure is essentially limited in what it can explain." —Preceding unsigned comment added by Pathikoll (talk • contribs) 18:51, 25 October 2007 (UTC)

Am removing this text as I am not sure why it is here, the topic is about soil shear and not advanced soil mechanics: "Advanced soil mechanics is often taught in specialist masters degree programs, and the prerequisite to practice as a geotechnical engineer often requires such training, particularly with the use of modern numerical techniques such as finite element analysis and with the adoption of critical state soil models."

Measurement
Could expand on measurement e.g. by vane, Torvane. —DIV (128.250.204.118 09:15, 10 October 2007 (UTC))

Critical State Vs. Steady State
There seems to be a lack of understanding of the difference between the critical state and the steady state. I am personally in contact with both Andrew Schofield and Steve Poulos, the two representatives of these respective states.

Thus the Critical State occurs at the quasi-static strain rate. It does not allow for differences in shear strength based on different strain rates. Also at the critical state, there is no particl alignment, all grains presumed to have broken to form spherical shaped grains.

The steady state can occur at any different strain rate, but has a slightly different value depending on the strain rate at which it is measured. Thus the steady state shear strength at the quasi-static strain rate would seem to correspond to the critical state shear strength. But it does not as the steady state does not assume that grains are crushed to form spherical particls. Rather it states that the grains align in the direction of shear, forming a special structure called the steady state structure. —Preceding unsigned comment added by Pathikoll (talk • contribs) 15:35, 25 November 2007 (UTC)

Maintanance
Am moving all notes to references, and linking them in-line using Harvard Citation already in place —Preceding unsigned comment added by Pathikoll (talk • contribs) 15:55, 1 November 2007 (UTC) Adding back a link to a review of Andrew Schofield's new book. This review was requested and approved by Andrew and as such does not qualify as spam (under which criterion it had been removed.)  —Preceding unsigned comment added by Pathikoll (talk • contribs) 12:42, 6 April 2008 (UTC)

Formatting
Equations should conform to accepted formatting convention, such as. —DIV (128.250.80.15 (talk) 02:30, 25 July 2008 (UTC))

Writing about own research
This is the policy to write about own research NOR sanpaz (talk) 15:27, 27 May 2010 (UTC)

Dutche cone test
Dear friends, Dutche cone test result is presented as depth vs qc in kg/square cm. How to get the safe bearing strength of soil based on qc in kg/square cm?

Correction to this statement
Fol. stmnt. imprecise:

This idea was extended to laboratory data in the empirical SHANSEP (stress history and normalized soil engineering properties) method.(Ladd & Foott 1974).

Shd b: This idea was systematized with the empirical SHANSEP (stress history and normalized soil engineering properties) method.(Ladd & Foott 1974).

Will chg in 2 wks if no obj. Jankar68 (talk) 16:53, 22 November 2010 (UTC)

Steady-state and critical-state: Not a matter of "semantics"
Can someone clarify in steady-state section? Much confusion on part of many "learned" profs. Jankar68 (talk) 15:21, 11 March 2011 (UTC)

Good idea! I too have come across people who think they know a lot about soil shear but are clueless about the steady-state and gaze at one blankly when the term is mentioned and think you are from the moon! (LOL!)

How's this--replace this line:

Steady states are associated with dynamical systems theory and indeed, a model describing soil shear as a dynamical system has been proposed by Joseph (Joseph 2009).

with:

The difference between the steady-state and the critical-state is not merely one of semantics as is sometimes thought, and it is wrong to use the two terms interchangably. The additional requirements of the strict definition of the steady-state over and above the critical-state viz. a constant deformation velocity and void ratio, places the steady-state condition within the framework of dynamical systems theory. Joseph used this strict definition of the steady-state to describe soil shear as a dynamical system (Joseph 2009).

Dshields51 (talk) 14:38, 14 March 2011 (UTC)


 * OK; wrong->incorrect, two terms -> two terms/concepts, interchangably->interchangeably, void-ratio->stead-state structure
 * Change in 30 d (14 April) if no obj. by others Jankar68 (talk) 20:41, 18 March 2011 (UTC)

Most engineers do not understand either critical state or steady state. If we argue about the distinction instead of focusing on the similarity, we are confusing instead of helping soil mechanics beginners understand. I agree that steady state could be mentioned in this article, but it should be introduced as a refinement or special case of critical state. If the importance of the distinction between Steady state and Critical State is not settled (i.e., there are some researchers in the last 2 years who believe critical state is adequate in most cases (e.g., me), and others (e.g., you) who believe steady state is so much better) then, Wikipedia should not enter the fray. The case should be made in peer reviewed literature not Wikipedia. Joseph (2009) made the case, and that is great, but that recent publication does not prove broad acceptance. Original research should not be the topic of Wikipedia. Blkutter (talk) 07:11, 19 March 2011 (UTC)


 * The statement of Blkutter is correct--the steady state is the is the refinement of the critical state which is the stepping stone to it.  This is the precise reason the dynamical systems theory can be applied to the steady state (but not to the critical state) and this is the why that the distinguishment proposed by Jankar is useful and of importance. Efischer80 (talk) 16:58, 23 March 2011 (UTC)


 * Thanks Efischer, Can we change the article so it says that steady state theory is a "refinement" or "extension" instead of and "alternate" theory? Blkutter (talk) 16:24, 24 March 2011 (UTC)

Efisher--plz wait to 14 April for addl. feedback (if any) Jankar68 (talk) 19:30, 24 March 2011 (UTC)

Change made as per above Efischer80 (talk) 22:44, 16 April 2011 (UTC)
 * Efischer -- thanks for making this change. Blkutter (talk) 07:27, 19 April 2011 (UTC)

One more question - the section on steady state theory in one place suggests that deformation velocities must be constant at steady state. In another place it suggests that strain rates must be constant. I think the latter is correct and suggest that "velocity" should be changed to "strain rate" throughout. I don't think you can require velocities and strain rates both to be constant at the steady state. Do you agree? Blkutter (talk) 07:27, 19 April 2011 (UTC)


 * Blkutter makes the good point--it is (locally) constant deformation velocity that is important. For small strain (Euler), this ist roughly same--for large strain, it is Lagrangian that is constant (I think).  So not the strain rate, but the rate of deformation should throughout be used. Please do inform us thereon. Efischer80 (talk) 16:38, 17 May 2011 (UTC)

Also, I suggest removing the statement that their are common misconceptions for two reasons. First, I think pointing out misconceptions suggests that there are two competing points of view and that the matter is not settled; I think pointing out the misconception makes it sound more controversial than it really is. Second, there is no good source given to back up that statement that there are common misconceptions. Blkutter (talk) 07:27, 19 April 2011 (UTC)


 * Blkutter I here mus disagree as have I also into these two objections run by others. Efischer80 (talk) 16:38, 17 May 2011 (UTC)
 * Efischer80 can you clarify or reword this point? I cannot follow.Blkutter (talk) 04:52, 31 May 2011 (UTC)
 * Blkutter these are the common misunderstandings into which in my discussions with others, I run. I do not follow why not to eliminate the confusions or what is the mistake in the clarifications?  Efischer80 (talk) 15:32, 3 June 2011 (UTC)

Critical state given free ride?
50+ yrs, yet accountability lacking for CS. Very poor matches of models to shear data, issues with over-consolidated soils, strain-softening issues, incorrectly shows zero shear under pure hydrostatic stress, models extremely complex, unwieldy, practically unusable, physical basis yet unknown...etc. Can someone plz. add accountability para to CS section? Jankar68 (talk) 15:12, 26 March 2011 (UTC)


 * You are correct but the finding of secondary or even the primary source to bak up is not possible from present publications. This is the elephant of a big size invisible but present in the critical state room! Efischer80 (talk) 22:47, 16 April 2011 (UTC)


 * From my point of view, I have seen many books and papers that compare critical state model predictions to data and very few that show that steady state theory is much better than critical state.  I percieve "steady state theory" as one refinement in a  wide variety of "critical state" models.  Some of these models are modified to include rate effects, particle size effects, cyclic loading, fabric evolution, sensitivity, etc. When you say critical state perhaps you are thinking of a narrower group of critical state models such as "Cam Clay". I just want to figure out why we cannot agree. Blkutter (talk) 04:49, 31 May 2011 (UTC)


 * Blkutter I am not aware of elasto-plastic/critical state models that are good as said by you. Please point out to me one such.  On the other part, the part of the steady-state there is only one model and that is, producing the fits that are very good. As best I know the objections of Jankar68 are valid. Efischer80 (talk) 15:37, 3 June 2011 (UTC)


 * I can see that the specialization of the steady state is different as it puts soil shear in a whole new realm--that of dynamical systems and so it justifiably different than other specializations. But, IF you are going to critique the critical state approach, then you MUST also qualify the steady state approach.  Though Joseph's hypothesis is intuitive he has not demonstrated its physical basis!!!  Also, it is not a true constitutive model--can't generalize to all stress paths!!!  Further it has not been independently verified!!!Tcat64 (talk)


 * and physical basis of critical state is??? of gravity??? At least Joseph hypoth. is intuitive.Jankar68 (talk)


 * I stand corrected--he appears to have provided the physical basis after all at: http://dx.doi.org/10.1061/(ASCE)GM.1943-5622.0000209 (preprint at: http://www.soilmechanics.us/GMENG-311_R2.pdf). Also a very bleak picture of the critical state at: http://soilmechanics.wordpress.com Tcat64 (talk) 20:03, 3 February 2012 (UTC)


 * will add ref. in 30d unless hear otherwise Jankar68 (talk) 13:00, 10 February 2012 (UTC)
 * I don't understand what exactly you are planning to add. It is nonsense to say that critical state has been given a free ride.  There are a multitude of references pointing out errors associated with various critical state models and proposed improvements. Go to any of the major journals Geotechnique, ASCE JGGE, Soils and Foundations, Computers and Geotechnics, Numerical methods in Geomechanics. The paper by Joseph is interesting, but it is not generalized to a complete constitutive model.  At least the critical state folks have produced complete constitutive equations that can be implemented in a FE model and compared against any available element test or centrifuge model test data. Blkutter (talk) 21:10, 12 February 2012 (UTC)


 * Can u plz. point me to a comprehensive critique of CSSM in jnls u mention. Have u read review link Tcat64 posted:  http://soilmechanics.wordpress.com  Generalizing J's model is just question of "time and materials"--no conceptual challenge. Jankar68 (talk) 13:02, 13 February 2012 (UTC)

phys. basis of dyn. sys. model
Propose mod. to the Steady State entry as follows: 1) "Steady state theory" -> "Steady state/dynamical systems theory"

2) >>In fact, Joseph (Joseph 2009) used this strict definition of the steady state to describe soil shear as a dynamical system. to:

Dynamical systems are ubiquitous in nature (the Great Red Spot on Jupiter is one example) and mathematicians have extensively studied such systems. Joseph (2009) used the strict definition of the steady state to describe soil shear as a dynamical system. Joseph (2012) showed that the underlying basis of the soil shear dynamical system is simple friction. These findings describe a new paradigm for soil shear that is at once both simple and powerful.

[note: point 2 is based on email received]

3) Add a link to the critique of critical state soil mech.

Unless hear otherwise, will target March 10 (30d since my orig. proposal) Jankar68 (talk) 15:47, 17 February 2012 (UTC)

Normalisation of stress-strain curve
This was an important discover--earliest known proposed by Henkel and then Perry in 1957. Suggest adding the following: "Perry and Henkel were one of the earliest who proposed that soil shear data could be usefully normalized by the initial confining stress."

Will add in 30 d unless I hear otherwise. This basic finding was later fine tuned to become SHANSEP. Jankar68 (talk)

Done. Jankar68 (talk) 11:56, 22 October 2012 (UTC)

Dynamical Systems--Self Study Course
There is by Dr. Joseph offered a online course (self-study, and seemingly free) on the dynamical systems based soil mechanics (dssm) approach. The link: http://www.soilmechanics.us/dssm/ Since it is free to use and seems useful, I propose to add it to the external link. Let me by 30 days know accordingly if ok. Efischer80 (talk) 00:32, 25 November 2013 (UTC)

It looks good (and is free!) Go ahead! Tglowes88 (talk) 18:55, 26 November 2013 (UTC)

Ok. I will the following add in 10 days(dssm section): "A detailed exposition of dynamical systems based soil mechanics is available at Joseph (2013)" Efischer80 (talk) 11:11, 16 December 2013 (UTC)

Dilatant
I am not a scientist so I had to look up the meaning of dilatant. However, the article dilatant and the OED definition are not obviously related so I am asking for someone to clarify (add a synonym or brief definition) dilatant or use another more widely known term. Thanks. Jim Derby (talk) 15:38, 17 March 2015 (UTC)