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dBasement (Geotechnical)
2 Feb 09 13:49
I need a "quick and dirty" method to determine clay content in soils.  Can the sand equivalent test give me a percentage clay content?  Or do I stick with a hydrometer test?  

When doing the hydrometer. I have tried cutting back the number of readings so I just end up around the 2 micron and use the wash to determine the fines content.  It still is a time-consuming test when all I need is the clay content, not a full gradation curve.
woofar (Geotechnical)
3 Feb 09 2:12
There is an Australian Standard method for doing that but I haven't personally done one for 20 years or more.

I could look up the reference to the standard for you but it would take a little research time.

The method involves putting a small amount of the soil in a test tube and adding a 3% salt solution, then agitating it vigorously, then allowing it to settle. The clay and fine silt content can then be measured and calculated from the layers that can be seen visually.

It's the agitating that does the dispersing of the particles. The saline solution stops the clay particles from going into suspension in the water.

HTH
Michael

 
iandig (Civil/Environmental)
3 Feb 09 11:26
There was a site test used in lots of sand & gravel pits similar to what Woofar suggests which was done to check the clay silt content. The salt from memory was done to act as a floculant [cation excahange?] and distribute the clay fines, as well as increasing the density of the water. From memory it was 'calibrated' against lab data, i.e. when you had xmm of clay/silt, this was equal to x% from a hydro/pippette test. The site kit was typically a jam jar, not very technical, but a decent gas jar with a volume of around 1000ml should work well. Key is to check the real value in a lab against the site observations.
 
fattdad (Geotechnical)
3 Feb 09 22:27
How do you use the "percent clay" data?

f-d

¡papá gordo ain't no madre flaca!

dBasement (Geotechnical)
4 Feb 09 10:45
Thanks fatdad,  

It's for USDA classification of soil for use in septic field applications.  We use the test to ascertain whether a soil is sandy loam, loamy sand etc. (shudder).

I know there are agricultural soil testing labs that use a shortened method for determination of clay content, but I'm not sure of the methodology they use.

It is not an engineering application where we use the Modified Unified method for soils classification.  For those applications we use the full grain-size chart.

The salt method has my interest peaked.


 
bmike (Geotechnical)
4 Mar 09 13:38
You might want to consider the methylene blue test on the fines.  This is used by Quebec Ministry of Transport as a method of evaluating the overall specific surface of the fines, which is a pretty good way of determining the principal clay mineral.

It won't tell the clay percentage, per se, but would help to flag whether the fines are clay or silt, or the predominant clay mineral, which can have a large role to play in its behaviour.

Have a look at http://www.astm.org/Standards/C837.htm

   

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