Explanation:

• The Unified Soil Classification system (USCS) is originally developed by Casagrande in 1948. The intention behind this development was to use airfield construction during World War II.
• The Unified soil classification system is almost similar to IS soil classification.

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According to USCS,

The coarse-grained soils are classified on the basis of their grain-size distribution and the fine-grained soils on the basis of their plasticity characteristics.​

Classification of fine-grained soil:

(i) In USSC, fine-grained soils are classified on the basis of plasticity chart and compressibility.

(ii) generally, soils are considered as fine soils, when 50% or more of the total material by weight pass 75 μ sieve.

(iii) Liquid limit and plastic limit are determined for 425 μ sieve fraction and corresponding plasticity index is find out

CASE 1: Low plastic soil (Low compressibility) (LL < 35%)

CL → Low plastic inorganic soil

ML → Low plastic inorganic silt

OL → Low plastic organic clay

CASE 2: Medium Plastic soil (medium compressibility) (35% < LL < 50%)

CI → Medium plastic inorganic soil

MI → Medium plastic inorganic silt

OI → Medium plastic organic clay

CASE 3: Highly plastic soils (High compressibility) (LL > 50%)

CH → High plastic inorganic soil

MH → High plastic inorganic silt

OH → High plastic organic clay