6. SOIL CLASSIFICATION
Soil is that portion of the earth’s crust, which is fragmentary, rock dust or such that some individual particles of a dried sample may be readily separated by agitation in water; it includes boulders, cobbles, gravel, sand, silt, clay and organic matter. Soils are identified and classified according to their particle size and distribution for coarse grained soils, and their plasticity for fine grained soils, which are based on soil laboratory testing, and the Unified Soil Classification System.