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Soil Classification: USCS
PT to SW
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 | aashto equivalent | cbr typical pct (%) | cc max | cc min | cu min | drainage class | fines pct passing 200 | group name | plasticity index max (%) | plasticity index min (%) | standard | typical engineering behavior |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| USCS | PT | — | <1 | — | — | — | Impervious (saturated) | >50 | Peat | — | — | ASTM D2487-17; Das 2021; Coduto 1999 | Very poor; not suitable as foundation material; extremely high compressibility and secondary settlement; very low strength |
| USCS | SC | A-2-6 to A-6 | 5-15 | — | — | — | Poor to Fair | >12 | Clayey sand | — | <7 | ASTM D2487-17; Das 2021 | Fair to poor; plastic fines reduce permeability; susceptible to swelling if high PI |
| USCS | SM | A-2-4 to A-2-5 | 10-20 | — | — | — | Fair | >12 | Silty sand | <4 | NP | ASTM D2487-17; Das 2021; Coduto 1999 | Fair; permeability variable; frost susceptible; compacts to moderate density |
| USCS | SP | A-3 | 10-25 | <1 or >3 | — | — | Good | <5 | Poorly graded sand | 0 | NP | ASTM D2487-17; Das 2021 | Fair; uniform particle size; susceptible to piping; loose deposits liquefy |
| USCS | SW | A-1-b | 20-40 | 3 | 1 | 6 | Good | <5 | Well-graded sand | 0 | NP | ASTM D2487-17; Das 2021; Holtz & Kovacs 1981 | Good foundation; densifies well under compaction; excellent subbase material |
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