In the course of teaching my Soil Mechanics class, I’ve tried numerous different charts and methods for teaching the Unified system of soil classification. Probably the most success I’ve had is with the one from NAVFAC DM 7, and it’s below. (I’ve included the plasticity chart for completeness.)
This chart is reproduced (with better typography) in my book Soils in Construction. Unfortunately ASTM has been messing with this procedure, and for that reason I have had to shift to it in the last years of teaching Soil Mechanics. I still prefer this NAVFAC chart because it reduces soil classification to a straight-up process of elimination rather than the “decision tree” approach ASTM apparently prefers. NAVFAC DM 7.1, the newer edition, has gone with a narrative description of the system (except for the plasticity chart) which is even harder to follow for those just learning the system.
An example of how this works is here.
NAVFAC DM 7 remains a popular reference book for geotechnical engineers, and ordering information is here.
