
Unified Soil Classification System
Criteria | Group Symbol | Group Name | ||
---|---|---|---|---|
Gravels
> 50% retained on No. 4 Sieve |
Clean Gravels
< 5% fines |
Cu ≥ 4 & 1 ≤ Cc ≤ 3 | GW | Well-graded gravel |
Cu < 4 and/or Cc < 1 or Cc > 3 | GP | Poorly graded gravel | Gravels with Fines
> 12% fines |
Fines ML or MH | GM | Silty gravel |
Fines CL or CH | GC | Clayey gravel | ||
Sands
> 50% of coarse fraction passed No. 4 Sieve |
Clean Sands
< 5% fines |
Cu ≥ 6 and 1 ≤ Cc ≤ 3 | SW | Well-graded sand |
Cu < 6 and/or Cc < 1 or Cc > 3 | SP | Poorly graded sand | Sands with Fines
> 12% fines |
Fines ML or MH | SM | Silty sand |
Fines CL or CH | SC | Clayey sand | ||
Silts and Clays
LL < 50 |
Inorganic | PI > 7 and plots on or above "A" line | CL | Lean clay |
PI < 4 or plots below "A" line | ML | Silt | Organic | PI ≥ 4 and plots on or above "A" line | OL | Organic clay |
PI < 4 or plots below "A" line | OL | Organic silt | ||
Silts and Clays
LL ≥ 50 |
Inorganic | PI plots on or above "A" line | CH | Fat clay |
PI plots below "A" line | MH | Elastic silt | Organic | Plots on or above "A" line | OH | Organic clay |
Plots below "A" line | OH | Organic silt | ||
Highly Organic Soils | PT | Peat |
Reference
ASTM D2487-06 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
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