USCS soil classification

USCS (unified soil classification system) soil classification

The USCS (unified soil classification system) is a soil classification system used in geology and engineering material to describe the soil texture and grain soil size. The classification system can be applied by unconsolidated material and represented by two-letter symbols.

            First letter                       Second letter 

Letter                definition                                   Letter                definition

  O                      organic                                           P                  poorly graded

  M                      silt                                                   L                   low plasticity

  C                       clay                                                 W                  well graded

  G                       gravel                                             H                   high plasticity

  S                        sand

The (uscs) is based on the soil classification system airfield developed by Casagrande tools during World War Two. With some modification, it was jointly adopted by several United States of America government agencies in 1952. It is used in the united state of America and many countries of the world for geotechnical work other than roads and highways used in AASHTO Soil Classification. Additional refinements standardized as ASTM D 2487-93. The USCS is designated by a two-letter symbol. the first one found the primary component of the soil and the second describes its plasticity characteristics of grain size. For example, SP designated poorly graded sand and CL for the low plasticity clay.used 5 first-letter symbols.

  1. G for gravel
  2. O for organic soil
  3. M for silt
  4. C for the clay
  5. S for sand
classification chart

 Symbol chart of a unified soil classification system.

Major divisionsGroup symbolGroup name
Coarse-grained soils


more than 50% retained on or above No.200 sieve



> 50% of coarse fraction retained on No.4 (4.76mm) sieve

clean gravel <5% smaller than No.200(0.0029mm) Sievegwwell-graded gravel and fine course to coarse gravel
GPpoorly graded gravel course.
gravel course with >12% finesgmsilty gravel course
GCclayey gravel course
Sand ≥ 50% of coarse fraction passes No.4 (4.76mm) sieveclean sand courseSWwell-graded sand and fine to sand coarse
sppoorly graded sand course
sand with >12% fines coursesmsilty sand course
scclayey sand course
Fine-grained soils 50% or more passing the No.200 (0.0029mm) sievesilt and clay of liquid  limit < 50Inorganic material mlsilt
clthe clay of low plasticity and lean clay
Organic materialolorganic silt and organic clay material
silt and clay of


Liquid  limit ≥ 50

Inorganic material MHthe silt of high plasticity and elastic silt material 
chthe clay of high plasticity and fat clay
organic ohorganic clay and organic silt material
Highly organic soils material  ptPeat material 

ASTM D-2487

Soil classification  Group Symbols and Group Names Using       Laboratory TestsSoil Classification
Group SymbolGroup Name


More than 50% retained on No.200 (0.0029mm)Sieve



More than 50% of the coarse fraction on No. 4 (4.76mm)Sieve

Clean Gravels


Less than 5% fines course

1 ≤ Cc ≤ 3 & Cu ≥ 4 gwWell-graded gravel course
Cc < 1/ Cc > 3 & Cu < 4GPPoorly graded gravel course
Gravels with Fines course


More than 12% fines course

Fines course classify as ml or mhgmSilty Gravel course
Fines classify as cl/chGCClayey gravel course


50% or more of coarse fraction passes No.4 (4.76mm)sieve

Clean Sands Less than 5% fines course 1 ≤ Cc ≤ 3 and Cu ≥ 6SWWell-graded sand course
Cc < 1/Cc > 3 & Cu < 6spPoorly graded sand course
Sands with Fines More than 12% fines courseFines classify as ml / mhsmSilty sand course
Fines classify as cl/chscClayey sand course


50% or more passes the no. 200 (0.0029)Sieve

Silts and Clays course


less than Liquid limit <50

Inorganic materialPI > 7 and plots or above  A-lineclLearn clay course
PI < 4 & plots below A-linemlSilt course
Organic materialLiquid limit oven-dried to< 0.75olOrganic clay course
The liquid limit does not dryolOrganic silt course
Silts and Clays course


Liquid limit 50 or <more

Inorganic materialpi plots / above A-linechFat clay course
pi plots below the  A-lineMHElastic silt
Organic materialLiquid limit to be oven-dried < 0.75ohOrganic clay
The liquid limit does not dryohOrganic silt

USCS soil classification chart.

uscs soil plasticity chart
flow chart
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