Unified Soil Classification System

The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):More than 50% retained on No.200 SieveMore than 50% of coarse fraction on No. 4 SieveLess than 5% finesMore than 12% fines50% or more of coarse fraction passes No.4 sieveLess than 5% finesMore than 12% fines50% or more passes the no. 200 SieveLiquid limit less than 50Liquid limit 50 or more The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt): If the soil has 5–12% by weight of fines passing a #200 sieve (5% < P#200 < 12%), both grain size distribution and plasticity have a significant effect on the engineering properties of the soil, and dual notation may be used for the group symbol. For example, GW-GM corresponds to 'well-graded gravel with silt.' If the soil has more than 15% by weight retained on a #4 sieve (R#4 > 15%), there is a significant amount of gravel, and the suffix 'with gravel' may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to 'poorly graded SAND with silt' or 'poorly graded SAND with silt and gravel.'