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Soil Classification: AASHTO
A-7-5 to A-8
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 | liquid limit min (%) | plasticity index min (%) | standard | typical engineering behavior |
|---|---|---|---|---|---|---|---|---|---|
| AASHTO | A-7-5 | <5 | Poor | >36 | Clayey soil - high elastic | >40 | 11 | AASHTO M 145; Das 2021 | Very poor; high plasticity; elastic swell; poor as subgrade; GI up to 20 |
| AASHTO | A-7-6 | <3 | Poor | >36 | Clayey soil - expansive | >40 | 11 | AASHTO M 145; Das 2021; Holtz & Kovacs 1981 | Very poor; expansive clay; high swell pressure; GI up to 20 |
| AASHTO | A-8 | <1 | Impervious (saturated) | — | Highly organic soils | — | — | AASHTO M 145; Das 2021 | Very poor; peat and muck; not suitable as subgrade; must be removed or bridged |
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