TECHNICAL INFORMATION DOCUMENT
How to Use 0.002mm. as the Grain Size Silt/Clay Division
Last Revised 2.June.2011
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Several users have inquired as to how to set up their grain size test
so that it uses 0.002mm. as the breakpoint between silt and clay particle
sizes. There's two options for doing this; the "best"
option is subject to engineering judgement and the requirements of
the test you performed!
- If you're classifying the soil via AASHTO or USDA classification methods,
select either "AASHTO" or "USDA" as your grain size
test's "Classification system" (select "Window"
> "Sample Info." from the menu at the top of the screen,
then look for the "Classification system" box towards the
bottom of the screen).
- If you're sure that you want to use the divisions specified by the
USCS classification system (e.g., gravel is between 3/4" and 3",
sand between the #200 and the #4 sieve, etc.), but you want the silt/clay
division to be 0.002mm. instead of 0.005mm., firstly, make sure that you know
why you want to do so! 0.005mm. is the appropriate silt/clay division size for
the USCS/ASTM D 2487 soil classification method. We're finding that many times users
ask to switch to 0.002mm. because their DOT told them to use that division: One clue -- if it's
a state DOT making the request, it's because they use the AASHTO classification system's divisions
(see the previous paragraph).
If, after due diligence, you determine that you actually do need to modify the USCS classification
system to use a 0.002mm. silt/clay division, do the following:
- Open your grain size test, select
"Window" > "Sample Info." from the menu at
the top of the screen, then select "USCS with .002mm. instead
of .005 silt/clay division" as the test's "Classification
system" (look for the box towards the bottom of the screen).
- If you cannot find that option, close the program, visit the program's update page and
install the latest update, then go back to step 1.
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