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Organic Content of Silts and Clays

Organic Content of Silts and Clays

This may be more of a question for the lab guys, but we were discussing how to properly quantify the organic content in silts and clays. Per ASTM D2487-06, the sample must have a second oven dried sample for testing of the Atterberg Limits. My question is, if you oven-dry the second sample at 110 degrees Celcius, how are you supposed to treat the first sample? Do you ove-dry it at a lower oven temperature or do you run it as is right of the bag, no sieving or drying. I have compared both the ASTM D4318 - 10 to the ASTM D2487-06 and haven't really noticed a difference. Any help would be great. Thanks in Advance

RE: Organic Content of Silts and Clays

You only use the oven-dried method for the liquid limit test. You have to get it through the No. 40. I'm pretty sure you can air-dry the sample - just not oven dry it. If there is no plus 40, just take the sample from the bag for your first go at the liquid limit (I'd also do the plastic limit). Oven dry as much as you need for the sieve.


¡papá gordo ain’t no madre flaca!

RE: Organic Content of Silts and Clays

An interesting note about the Atterberg limits is that Holtz and Kovacs both do not recommend the use of the ASTM method (which requires air-dried samples for limits test) because they produce inconsistent results for some types of soils. They recommend performing the Atterberg limits test at the natural moisture content.

Rey Villa, MS, PE

RE: Organic Content of Silts and Clays

What is the meaning of performing an LL test at natural moisture content? The purpose of the test is the determine the moisture content defining the boundary of plasitc and liquid soil behaviors.

The cited procedure (ASTM D 4318) does not determine the organic content. The ratio of air dry to oven dry liquid limit is merely for soil classification purposed (OL, OH, CL, CH, etc.). The is an organic content test if you are interested in the organic "content". ASTM D 2487 is only a soil classification procedure are not a test procedure.

RE: Organic Content of Silts and Clays

Running the liquid limit at the natural moisture content is clearly an oversimplification, but I understood the intent. ASTM allows taking the soil and hydrating it for LL testing without first air drying the sample.

I'd rather use the ASTM method for organic soil classification than the organic content test. I recognize the value of both; however.


¡papá gordo ain’t no madre flaca!

RE: Organic Content of Silts and Clays

molerat2210 you misunderstood the point. You run the Atterberg test first with out air drying.

Rey Villa, MS, PE

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