| Unified Soil
Classification (USC) System (from ASTM D 2487) |
| |
| Major Divisions |
Group Symbol |
Typical Names |
|
Course-Grained
Soils More than 50% retained on the 0.075 mm (No. 200)
sieve |
Gravels 50% or more of
course fraction retained on the 4.75 mm (No. 4)
sieve |
Clean Gravels |
GW |
Well-graded gravels and
gravel-sand mixtures, little or no fines |
|
GP |
Poorly graded gravels and
gravel-sand mixtures, little or no fines |
|
Gravels with
Fines |
GM |
Silty gravels, gravel-sand-silt
mixtures |
|
GC |
Clayey gravels, gravel-sand-clay
mixtures |
|
Sands 50% or more of
course fraction passes the 4.75 (No. 4) sieve |
Clean Sands |
SW |
Well-graded sands and gravelly
sands, little or no fines |
|
SP |
Poorly graded sands and gravelly
sands, little or no fines |
|
Sands with
Fines |
SM |
Silty sands, sand-silt
mixtures |
|
SC |
Clayey sands, sand-clay
mixtures |
|
Fine-Grained
Soils More than 50% passes the 0.075 mm (No. 200)
sieve |
Silts and Clays Liquid
Limit 50% or less |
ML |
Inorganic silts, very fine
sands, rock four, silty or clayey fine sands |
|
CL |
Inorganic clays of low to medium
plasticity, gravelly/sandy/silty/lean clays |
|
OL |
Organic silts and organic silty
clays of low plasticity |
|
Silts and Clays Liquid
Limit greater than 50% |
MH |
Inorganic silts, micaceous or
diatomaceous fine sands or silts, elastic silts |
|
CH |
Inorganic clays or high
plasticity, fat clays |
|
OH |
Organic clays of medium to high
plasticity |
|
Highly Organic
Soils |
PT |
Peat, muck, and other highly
organic soils |
|
Prefix: G =
Gravel, S = Sand, M = Silt, C = Clay, O = Organic
Suffix: W = Well Graded, P = Poorly Graded, M = Silty, L = Clay, LL
< 50%, H = Clay, LL > 50% |