Non Plastic silt soil
Non Plastic silt soil
(OP)
Is it possible that a soil sample that can be drawn to 3mm thread when drawn delicately be classed as non plastic. I think all silt soil samples need to be drawn delicately but if they can be drawn to 3mm from a ball then they cannot be classed as non plastic.
Our lab classed it as NP with a soil described as clayey fine sandy SILT. I sent it for re testing and they came back with same result. Please tell me what to do.
my description for that soil would be fine sandy SILT. It contains little clay but not enough to class as clayey SILT.
Our lab classed it as NP with a soil described as clayey fine sandy SILT. I sent it for re testing and they came back with same result. Please tell me what to do.
my description for that soil would be fine sandy SILT. It contains little clay but not enough to class as clayey SILT.





RE: Non Plastic silt soil
f-d
¡papá gordo ain't no madre flaca!
RE: Non Plastic silt soil
In basic terms, the soil is rolled using two fingers, at a constant pressure, to reduce the thread from 6 to 3mm, between 8 and 12 times on a scrach free glass plate. If you can't form the thread using this method, the soil is non-plastic, even if other handling techniques can form a 3mm thread with the soil. The test is very operator sensitive, and I have seen numerous occasions where the technician uses the palm of the hand to form the thread and even rolling the soil between two palms. Any variation in the testing technique can and will return lower moistures than you can achieve using the two fingers as per the BS(i.e. soils which should be "non-plastic" return values for the palstic limit.
You have to be very careful when undertaking the test to ensure the data accuratley reflects to soil.
RE: Non Plastic silt soil
My argument was just what you said if there is clay no matter what percentage it cannot be classed NP
Now our lab has performed particle size analysis on the sample. The sample has 55% fine sand, 35% silt and 10% clay. So the sample is clayey very silty fine SAND. Now the lab has come back saying that it is sand hence the sample is NP but my argument still is that it has got 10% clay and hence cannot be NP, probably low plastic.
RE: Non Plastic silt soil
RE: Non Plastic silt soil
which classification system you using?
i read "clayey fine sandy silt" to mean a "sandy silt with a trace of clay" and not a "clayey silt". i'm not expert on the classifications and haven't plotted your situation on the classification charts but that's the way i see it from this side of my computer.
i quite often see sandy silts that have some percentage (sometimes rather high amounts) on the clay fraction of the gradation be NP...it just happens to very fine soils but NP. i also see very similar soils have low PI's. heck, sometimes even mica influences the gradation since it hangs up on the coarse fraction artificially classifying it as a SM instead of an ML...or it ends up with 48% passing #200 (and 40%+ mica) and the mse designer talks about "all the sand" on the site when it's definitely a silt.
sometimes even the seemingly most elementary subject can be complex to decipher...maybe it's just me.
RE: Non Plastic silt soil
Which is right? For engineering, I'd agree with the ASTM - behavior is more important for engineering projects. For soil moisture charactistics pertaining to capillarity and plant growth, USDA may be better. Mixing the two (e.g., Burmiester) never made sense to me. I don't like the terms, "trace silt" or "trace clay" - how the heck do you figure that out and what difference does it make - just do a wash 200 and an Atterberg limit and follow the ASTM.
Just a stubborn middle-age engineer, I guess. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Non Plastic silt soil
I am not a big fan of ASTM. In many ways, I think that they complicate descriptions too much - and when you get down to it, their descriptions rely "heavily" on percentages of the constituent parts too - they just couch the wording in a different way.
In thinking that only the ASTM way "works" one sells out many pioneering geotechnical firms - they didn't use the USCS; used the "percentage" way were involved in building very very many very very important projects. I started work for Geocon in Canada (a long established firm) in 1977 and am familiar with almost all of their early reports (1954 to 1977) from before joining them. They never used "elastic silt", "fat clay" or any of the other terms bandied about by ASTM. Still, their history of major projects in the mining, pulp and paper, steel mill, ports and wharves for the St. Lawrence Seaway, oil refineries (Sarnia, for example) were built with success. Most of Golder's founders were indoctrinated at Geocon before starting Golders and in reports that I saw of theirs when I was with them and subsequently, again, no mention in the logs of their reports the ASTM terminology. Both firms and many others lived with clayey silt, trace sand; silty clay; etc. See attached page from Soderman and Quigley as found in the Canadian Geotechnical Journal (CGS - don't be mad!) - notice that they use clayey silt. This is found, too, in the original USCS charts (as found in Lambe and Whitman among others). See also the Canadian Guide to the Field Description of soils - they also indicate the use of clayey silt (a term not found in ASTM). Review the borehole logs and descriptions form the Canadian Geotechnical Journal articles in the 1960s, 1970s; see the example borehole logs in Fang's Foundation Engineering Handbook. I admit that with the younger set "growing up with ASTM" there is a shift towards the ASTM nomenclature (hell, I never even read an ASTM testing spec for 20 years after I started - we used Lambe's Soil Testing book for our testing). Still, we must give credit to the developers of geotechnical engineering. They did fine without ASTM.
One argues that ASTM is a "behavoural" classification system - if so, then why so much reliance on %ages of constituents as I indicated above. See Fig 1a in D2487 - you need to know 30%, 15%, 50%. Say I have a soil that is fine grained. Less than 15% is "plus #200 sieve". I decide to do two Atterbergs on the same sample. One test gives LL = 51; the also gives LL = 49. The plasticity index of the first is 23, and the second is 21. By ASTM the first is to be called a Fat Clay. The second a Silt. Now, to be honest, these two terms, to me, are diametrically opposite, yet they are the same sample. What is the behavoural difference of the two? I couldn't say. It is similar as what is the "line you draw in the sand" to apply the consistency descriptor - or the relative density descriptor. Anyone venture a guess on that? And how do you classify a varved clay? or is it a varved fat clay? or a varved silt? or a varved ???????
The bottom line, and I think that fattdad, I, and others will agree, is that one must have the experience and "feel" of knowing the material at which you are looking, touching (tactile) and smelling to have the right appreciation of whether a material is one way or the other. A common descriptor system is useful in data-base work but as I pointed out in my little example above, very slight differences in the Atterberg limits may very well slant one's view immensely.
RE: Non Plastic silt soil
I guess to me it's a matter of being consistent. To the original post, I would repeat. If you are using ASTM then anything non-plastic cannot have the word "clay" in the name.
Otherwise, I think I'm with BigH and others.
Enjoy your 4th (i.e., if you're in USA).
f-d
¡papá gordo ain't no madre flaca!
RE: Non Plastic silt soil