Sure it does.  Silt has liquid limit, right?

Hmmmmmm

It has a liquid limit but no plastic limit, therefore no Plasticity index.  The liquid limit alone can have some usefulness, but is generally paired with the plastic limit for defining characteristics of clayey materials, not "non-plastic" materials.  For instance, there are correlations between liquid limit and consolidation, between liquid limit and liquefaction potential, etc.

You could simply assume a value of 16 percent, as that is considered the value below which realistic values cannot be obtained for the test equipment.

It does not look like a simpe question to me.

If a soil is clssified as no plastic, it means that it is not plastic at any water content. How can a liquid limit be defined without a plastic state.

A non plastic soil may behave like a liquid when liquified. However, that is due to the rise in pore pressure or excessive shear force applied to it. It has nothing to do with its water content.

I think the liquid limit only exists for a soil with three states of solid, plasticity and liquid at different water contents.

Here fishy fishy. Me thinks BigH is trying to stir things up!

This probably has as much to do with philosophical issues as engineering, if we give something a name, does that mean it does what it says it does.
I believe that if you are trying to interpret a value, you should be aware of how it is derived at and the limitations of the way it was measured. You should never rely on a value in isolation. When considering a liquid limit for a non-plstic soil, you need to try and appreciate and understand the effect of it being non-plastic on the measurement of the liquid limit.

Sure there's a liquid limit for (non-plastic) sand.  Go to the beach and build a sandcastle and you can drip the (liquid) sand out of your hand.  From another point of view, the liquid limit means that any non-zero stress will lead (theoretically) to an infinite strain.  Non-plastic sand should have a water content beyond which it will offer no resistance to stress.  Just like Ron said.  I'm not sure you could get any useful information out of a liquid limit done on non-plastic soil.

bigH,

the plastic limit of a specific soil may be above the liquid limit.   This is from a lab tech with 10 years of experience...

Rjeffery - so AASHTO T90 implies.  Now if the plastic limit represents that point at which a soil turns from a solid state to a plastic state and the liquid limit is where the soil changes from a plastic state to a liquid state (remember - remoulded sample), it seems that a soil can be a solid at a point where is should be liquid.  T90 says that if this happens, the soil is non-plastic.  I would surmise that it is a problem with an exactness of definitions - the soil doesn't have a plastic state.  

The debate goes on - philisophically, . . .  Any real "hard" facts out there guys?

Hummmm.  I will refer you to silty material with a heavy concentration of mica.  It generally has a plastic limit higher than its liquid limit.  but that was not your question.  ask the people in Kobe, Japan.  the sand that they build on is Non-plastic but with enough water and some vibration...

Rjeffery - granted, the Kobe problem is one of liquefaction - not of exceeding a liquid limit.  The liquefaction potential is relational to the fines content (e.g., <5%, 15%, >35%) and on the relative density at which the material is found - but is this a "liquid limit" as defined under our testing procedures?  I'd like to hear more about the mica concentration, etc.  Any references?  Couldn't this be an effect of the definition of the various states?  A similar problem occurs with particle size analysis where you try to match a sieve portion (say from #100 to #200 sieve size) to the results of a hydrometer test on the material.  Hmmmmm . . .

anicdotally, (i know i spelt it wrong[e?]) here in Northern VA, silty material has a minerology that sometimes contains asbestos and and its chemically similar cousins, like mica.  It seems that the shape of the mica/asbestos has a great deal to do with the plasticity, and its reaction to vibration.  when attempting to perform the LL i have has samples that tear in the cup when grooved with the flat ASTM tool (not the AASHTO, though) but will close in one blow and have a sheen of moisture in the surface.  The closure is due to a lack of adheasion to the cup.  but when rolled as prescribed in either methods the PL is reached well before the LL can be established (If at all)...

Rjeffery - have you tried using the fall cone for your liquid limits rather than the cup?

Big H,

No I have not.  Do you have a reference standard number I can research?

will look into getting a ref number - but it is used extensively outside US/Canada.

Rjeffery - Two standards that I know of:
  British Standard BS 1377-2-4.3
  Indian Standard IS 2720 (Part 5) - 1985

I got a four page bibliography from UMASS on the Fall Cone.  Lots of papers from Geotechnique back in 1980s.  I'm sorry I don't have the URL off-hand - you might be able to search. One paper:

Kumoto and Houlsby (2001) Theory and Practice of the Fall Cone Test, Geotechnique V51, No 8 pp 701-712

Some sites:

http://www.ecs.umass.edu/cee/faculty/LLFallCone.pdf
http://www.pubs.asce.org/WWWdisplay.cgi?0409176

First site it the UMASS bibliography. The second site points to a paper in the ASCE GTE Journal of June 2004 on use of cone for plastic limit.

Some silts have a liquid limit, but you can't roll the threads even near the dia. to get a plastic limit (following ASTM 4318). Goes straight from liquid to plastic.

Some auger cutting samples I got once had a liquid limit, but the plastic limit we couldn't roll. Turned out that the drillers hit rock and didn't note it, and that was the ground calcareous rock. (Legitimate soil?)

Got some stuff from CMEC that almost defied soil mechnaics once.

Given the above discussions - I have a granular subbase (GSB) material.  It is actually crushed stone.  The specfications say that the GSB must have a Liquid Limit and Plastic Index of less than 25 and 6 respectively.  The limits at 0.425mm is a range of 10 to 25% passing.  The material is classified as non-plastic but the lab did do a liquid limit test and got a value of 27.  Question:  Does the material pass the specifications (in strict compliance)?  The GSB is non-plastic - does it fail due to the "liquid limit" being greater than 25?  and, is this a case that there really is no liquid limit to a non-plastic material?  This is a real life situation.

Big H,

As the guy out in the field, presented with the data, I would not accept the material as it does not meet the 25% LL Max.  As an advisor to the engineer, I would recommend that, at a minimum the lab run the test again or review the labs procedures...  they should not be outside of the SDev of similar labs.

My experience of looking at the liquid limit and plasticity index of sub-base materials is it's there to provide an indication of how the material will behave (similar materials act in similar ways), and is the material likely to be frost susceptible. Experience has shown that where a sub-base has fines that are plastic, the material is more likely to be frost susceptible, even to the point of 'suggesting' that if the fines are plastic, its not worth spending the money on a frost heave test.
Going back to the point about the result of the LL being 27, and the limit being 25, I think this depends on whether you want to approve the material or not. If your experience suggests that this material is suitable, and there is evidence that this source has been succesfully used in the past, I don't think it should be a problem - subject to all other tests complying. There is an increasing interest in the 'degree of certainty' of measurement, what are the statistical confidence limits on the result? - not easy to determine but even taking a rough +/- 5% certainty on the result you get a rough range of 25.6 to 28.4. If there is statisitcal data available you should get a much better 'feel' for the range of the result. Also its worth looking at the repeatability and reproduciblity of the testing lab - again if its available. I am not sure of the QA system in India, but in the UK under the UKAS system, you have to be able to provide evidence of repeatability, reproduciblity and tracability of testing and equipment. Its not called in to question often, but on 'big' jobs where the cost implication can be massive it can be a very powerful tool to allow the identification of erroneous results.
If it was me, I would not worry about a single result, but would want to see the spread of results on a selection of samples, or at least the 'typical' range of results on the material over a suitable period of time. Similar to the way in which the new EN standards look at the typical property as opposed to singular values.
If on the other hand you don't think the material will be suitable - you can always argue that its failed so its no good, but somehow I get the feel you value your engineering judgment above conflicting arguements.
I would also like to make the point (I think I've posted this before) that from my own experience of doing the test, it is VERY difficult to get repeatable liquid limits on samples which are non-plastic - hence my suggestion of getting a spread of values and making an engineering decision, a single reading on this type of material would not, in my opinion, be sufficient to pass/fail the material source.

Big H,
I was just looking at your real life situation.  What did they end up doing?  Based on your specs data of <25LL and <6PI, the required material would be fine grained.  Since crushed stone hardly meets fine grained criteria, I'd say the GSB material should be rejected.  What's the GSB supporting, anyway?  Regards.

Just saw this thread. BigH-you haven't said what the %passing for #200 sieve is. If it is less than 50% passing, you have coarse grained soils and the LL and PI specs would not apply. As Iandig suggested run multiple tests and look at the range.

If the lab can run a sand equivalent test, have them try it and that will help us get better feel of these soils.

A Member of
www.civilvillage.com

    Aw - there's the rub.  The material is a crushed stone GSB with less than 8% passing #200.  Surely, it is not a fine grained soil so it must be classified as G or S if you go that way on crushed aggregates.  The point is the nature of the fines - are they plastic or not?  Most highway specs have a clause that say that the GSB must be non-plastic or, as in our case, having a PI<6 and LL<25 (meaning the fines portion, e.g., <0.425mm). This is so the fines that are there don't cause "harm" to the subbase (read that expansion).  
    Our PI was less than 2 or non-plastic. The "determined" liquid limit was really slightly less than 25% so it was passed. The point to my original post was a what if?  Having 24% in the tests, we were close.  We didn't get 26% - here, it would have been rejected by nearly all; for me, I would have passed it as the "liquid limit" (in this context) has no meaning without plasticity, in my view.
    Thanks for your interest -