USCS 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.
- G for gravel
- O for organic soil
- M for silt
- C for the clay
- S for sand
Symbol chart of a unified soil classification system.
| Major divisions | Group symbol | Group name | ||
| Coarse-grained soils
more than 50% retained on or above No.200 sieve | gravel
> 50% of coarse fraction retained on No.4 (4.76mm) sieve | clean gravel <5% smaller than No.200(0.0029mm) Sieve | gw | well-graded gravel and fine course to coarse gravel |
| GP | poorly graded gravel course. | |||
| gravel course with >12% fines | gm | silty gravel course | ||
| GC | clayey gravel course | |||
| Sand ≥ 50% of coarse fraction passes No.4 (4.76mm) sieve | clean sand course | SW | well-graded sand and fine to sand coarse | |
| sp | poorly graded sand course | |||
| sand with >12% fines course | sm | silty sand course | ||
| sc | clayey sand course | |||
| Fine-grained soils 50% or more passing the No.200 (0.0029mm) sieve | silt and clay of liquid limit < 50 | Inorganic material | ml | silt |
| cl | the clay of low plasticity and lean clay | |||
| Organic material | ol | organic silt and organic clay material | ||
| silt and clay of
Liquid limit ≥ 50 | Inorganic material | MH | the silt of high plasticity and elastic silt material | |
| ch | the clay of high plasticity and fat clay | |||
| organic | oh | organic clay and organic silt material | ||
| Highly organic soils material | pt | Peat material |
ASTM D-2487
| Soil classification Group Symbols and Group Names Using Laboratory Tests | Soil Classification | ||||
| Group Symbol | Group Name | ||||
| COARSE-GRAINED SOILS material
More than 50% retained on No.200 (0.0029mm)Sieve | Gravels
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 | gw | Well-graded gravel course |
| Cc < 1/ Cc > 3 & Cu < 4 | GP | Poorly graded gravel course | |||
| Gravels with Fines course
More than 12% fines course | Fines course classify as ml or mh | gm | Silty Gravel course | ||
| Fines classify as cl/ch | GC | Clayey gravel course | |||
| Sands
50% or more of coarse fraction passes No.4 (4.76mm)sieve | Clean Sands Less than 5% fines course | 1 ≤ Cc ≤ 3 and Cu ≥ 6 | SW | Well-graded sand course | |
| Cc < 1/Cc > 3 & Cu < 6 | sp | Poorly graded sand course | |||
| Sands with Fines More than 12% fines course | Fines classify as ml / mh | sm | Silty sand course | ||
| Fines classify as cl/ch | sc | Clayey sand course | |||
| FINE-GRAINED SOILS material
50% or more passes the no. 200 (0.0029)Sieve | Silts and Clays course
less than Liquid limit <50 | Inorganic material | PI > 7 and plots or above A-line | cl | Learn clay course |
| PI < 4 & plots below A-line | ml | Silt course | |||
| Organic material | Liquid limit oven-dried to< 0.75 | ol | Organic clay course | ||
| The liquid limit does not dry | ol | Organic silt course | |||
| Silts and Clays course
Liquid limit 50 or <more | Inorganic material | pi plots / above A-line | ch | Fat clay course | |
| pi plots below the A-line | MH | Elastic silt | |||
| Organic material | Liquid limit to be oven-dried < 0.75 | oh | Organic clay | ||
| The liquid limit does not dry | oh | Organic silt | |||
| HIGHLY ORGANIC SOILS material | pt | Peat |
USCS soil classification chart.
