How to Determine USCS Soil Classification

The Unified Soil Classification System is a method of categorizing soils for use in engineering and geological applications. Soils are classified in USCS groups that are designated by a group symbol and a corresponding group name. The governing standard is ASTM D2487.

Classification Groups

The following are the soil classifications:

Symbol Description
GW Well graded, sandy gravel
GP Gap graded or uniform gravel
GM Silty gravel
GC Clayey gravel
SW Well graded gravelly sand
SP Gap graded or uniform sand
SM Gravelly sand
SC Clayey sand
ML Low plasticity silt
CL Low plasticity clay
OL Low plasticity organic silt/clay
MH High plasticity silt
CL High plasticity clay
OH High plasticity organic silt/clay
Pt Peat

 

How to Determine USCS Classification

The USCS classification of a soil is determine via sieve tests and plasticity tests, and the following chart. Start at the left and proceed to the right.

Major Divisions
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
GP
Gravels with Fines GM
GC
Sands
50% or more of course
fraction passes
the 4.75
(No. 4) sieve
Clean Sands SW
SP
Sands with Fines SM
SC
Fine-grained Soils
More than 50% passes
the 0.075 mm
(no. 200) sieve
Silts and Clays
Liquid Limit 50% or less
ML
CL
OL
Silts and Clays
Liquid Limit greater than 50%
MH
CH
OH
Highly Organic Soils PT
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