Conducting Subsurface Environmental Investigations in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 147

Unified Soil Classification and Symbol Chart

Coarse-grained soils
(more than 50% of material is larger than No. 200 sieve size.)
Clean gravels (less than 5% fines)

Well-graded gravels, gravel-sand
mixtures, little or no fines

GW

Gravels
More than 50%
of coarse
fraction larger
than No. 4
sieve size

Poorly-graded gravels, gravel-sand
mixtures, little or no fines

GP

Gravels with fines (more than 12% fines)

GM Silty gravels, gravel-sand-silt mixtures

GC Clayey gravels, gravel-sand-clay mixtures

Clean sands (less than 5% fines)

Well-graded sands, gravelly sands,
little or no fines

SW

Sands
50% or more
of coarse
fraction smaller
than No. 4
sieve size

Poorly graded sands, gravelly sands,
little or no fines

SP

Sands with fines (more than 12% fines)

SM Silty sands, sand-silt mixtures

Clayey sands, sand-clay mixtures

SC

Fine-grained soils
(50% or more of material is smaller than No. 200 sieve size)
Inorganic silts and very fine sands, rock
flour, silty of clayey fine sands or clayey
silts with slight plasticity
Inorganic clays of low to medium
plasticity, gravelly clays, sandy clays,
silty clays, lean clays

ML

Silts and
clays
liquid limit
less than
50%

CL

Organic silts and organic silty clays of
low plasticity

OL

Inorganic silts, micaceous or
diatomaceous fine sandy or silty soils,
elastic silts

MH

Silts and
clays
liquid limit
50%
or greater

Inorganic clays of high plasticity, fat clays

CH

Organic clays of medium to high plasticity,
organic silts

OH

Highly
organic
soils

Peat and other highly organic soils

PT

FIGURE 4.19
Unified Soil Classification System. (From Virginia Department of Transportation, Unified soil classification sys-
tem. http://www.occ.state.ok.us/Divisions/PST/Forms/Technical%20Forms/Orbca%20Guidance/unified%20
soil%classification.pdf (accessed July 4, 2010), 2003.)