Soil Classification: AASHTO
USCS and AASHTO soil classification group symbols with grain size criteria, plasticity limits, drainage class, and typical engineering behavior for geotechnical design
| classification system | group symbol | cbr typical pct (%) | drainage class | fines pct passing 200 | group name | notes | plasticity index max (%) | plasticity index min (%) | typical engineering behavior |
|---|---|---|---|---|---|---|---|---|---|
| AASHTO | A-1-a | >=80 | Excellent | <=25 | Stone fragments gravel and sand | Passing No.10<=50%; Passing No.40<=30%; Passing No.200<=15%; PI<=6 | 0 | NP | Excellent subgrade; excellent subbase; high stability and low compressibility |
| AASHTO | A-1-b | >=60 | Excellent | <=35 | Coarse sand | Passing No.40<=50%; Passing No.200<=25%; NP to PI<=6 | 0 | NP | Excellent subgrade; good for subbase; slightly more fines than A-1-a |
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