Field Classification of of Soils with < 25% Fines
Field Classification of of Soils with < 25% Fines
(OP)
We have some lab results that classify soil as SC without corresponding Atterburg limits. The sieve analysis show less than 25% passing a #200 sieve. When questioned how the classification was reached the respons was it was based on field observation. Is it reasonable or possible to discern between an SC and an SM soil with this percentage of fines by visual observation of samples during collection or is lab testing required?
Thanks,
Thanks,





RE: Field Classification of of Soils with < 25% Fines
Just how does the naming of the soil affect your project?
f-d
¡papá gordo ain't no madre flaca!
RE: Field Classification of of Soils with < 25% Fines
You could say you just know whit out having to measure it. It the same with soil classification, although the 100% correct way would be to measure it, but if you been playing with that same soil for twenty years, you just know.
One contractor told me one day, he the expert, dont question his field, that what we pay him to do.
RE: Field Classification of of Soils with < 25% Fines
The specification references ASTM D 2487 for soil classification. For our backfill SC soils or any dual classification with SC are not allowed while SM soils are suitable.
RE: Field Classification of of Soils with < 25% Fines
I've seen carpenters drive 1/2" bolts and mechanics use 16d nails as cotter pins and learned that experts come in many forms.
I've also found that 'experts' who are uncomfortable with being questioned usually aren't as proficient as they claim. If the decision may cost me $ I want the measure not the opinion.
RE: Field Classification of of Soils with < 25% Fines
If the specification cites D-2487 then the appropriate testing to qualify fill materials should conform to these criteria.
As an aside, it's a bad spec. There is likely nothing wrong with SC backfill especially if it's at the proper moisture content and it contains only 25 percent fines.
Excluding SC soils seems arbitrary. I'd like to have some technical basis to exclude SC soils before I'd cause undue harship to the project (i.e., delay or additional expense). If it's in your power to accept this fill, I'd accept it without reservation. First, however, I'd be yelling at the testing firm for stirring the pot in the absence of data.
f-d
p.s. to brownbag: One thing I try to get people to understand, if the specification calls for a test - DO IT! Any contractor that reacts unfavorably to questions has something to hide. Phooey!
¡papá gordo ain't no madre flaca!
RE: Field Classification of of Soils with < 25% Fines
Thanks for the help. I'm told that the SC soils are excluded due to liquifaction concerns during a siesmic event.
RE: Field Classification of of Soils with < 25% Fines
f-d
¡papá gordo ain't no madre flaca!
RE: Field Classification of of Soils with < 25% Fines
http://en.wikipedia.org/wiki/Soil_liquefaction
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
Mat, what part of this you dont understand
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
This is incorrect advice. ASTM D-2497 (the basis of this thread) has no provisions on classifying soils based on hydrometer or percent silt or clay content. It's amazing to me that a geotechnical engineer is unclear on the classification methods that are used in the profession and the basis for our correlation with engineering behavoir.
Soil scientists use weight percent but the ASTM does not provide for this at all.
End of rant. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Field Classification of of Soils with < 25% Fines
This is incorrect advice. ASTM D-2497 (the basis of this thread) has no provisions on classifying soils based on hydrometer or percent silt or clay content.
D 2497 Man-Made Organic-Base Filament Single Yarns
what does yarn have to do with classification of soil.
RE: Field Classification of of Soils with < 25% Fines
f-d
¡papá gordo ain't no madre flaca!
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
Soil will be placed as backfill at 95% modified proctor starting well below the water table up to final grade.
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
The original "Chinese criteria" (less than 15% smaller than 5 microns, LL<35, %w> 0.9 LL) have been shown by a number of researchers not to work, in part because of the limited data set used by Wang to develop them. Likewise, there is no fines content that can rule out liquefaction; there are a number of well-known cases where ~100% fines liquefied (Moss Landing, a loess deposit in Tajikistan, tailings, etc.).
95% of modified would be similar to or higher than what we use for large dams, where we typically require 98% of standard Proctor. Liquefaction can be ruled out DEFINITIVELY with that kind of density!
RE: Field Classification of of Soils with < 25% Fines
(and sancio is the author i was trying to think of)
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
RE: Field Classification of of Soils with < 25% Fines
But yes, you are correct to pay attention to decrease in strength w/ cyclic loadings if they will push the peak strength. In general, saturated clays show sensitivity, i.e., remolded strength less than peak, and will show decrease in strength with very large cyclic shear strains and buildup of excess PWP, but just loss of stiffness with smaller cyclic shear stresses that stay below the peak strength. Sensitivity ratio can be anywhere from 1.5 to VERY high in Scandinavian and Quebec quick clays, with 2 to 4 being most common. Idriss and Boulanger recently ~2007 published a big report on cyclic failure of clays, sensitive and otherwise. (I'm fairly sure that it's not in the public domain, so I can't post it for you, unlike that report I promised to post for McCoy last week.) Like their liquefaction red book, it will probably be considered the state of practice in the near future. They show cyclic failure eventually occurring with repeated loads that flirt with the monotonic peak strength but don't quite reach it (like 95%).
Funny you should bring this topic up. In a dynamic deformation analysis, the trick (OK, one of many tricks) is deciding how much deformation it takes to reduce the strength from peak to fully softened to remolded strength. I was considering posting a new question to see if anybody knew of any well analyzed case histories or centrifuge research or anything else that would provide a good analog. The one good case history I know of is the 4th Ave, Anchorage AK slide in 1964, on which I have papers by Idriss and by Stark and Contreras, and of course that is different geology, stress history, clay properties, etc. from the case I'm interested in.
Every time I turn around, this s(tuff) gets more complicated.
DRG
RE: Field Classification of of Soils with < 25% Fines
http://cee
RE: Field Classification of of Soils with < 25% Fines