In order to determine the characteristics of soils, lab tests must be conducted. Once the test results are known, then soils are classified according to the results, and grouped with soils of similar characteristics.   A particle size analysis is conducted to determine the distribution of various particle sizes in the soil. Usually, this is conducted by screening on a mechanical screen. Certain nomenclature is associated with various soil sizes, as shown below: Name  Particle Size (mm)  Gravel  76.2 to 20  Coarse Sand  20 to 0.42  Fine Sand  0.42 to 0.075  Silt Size  0.075 to 0.002  Clay Size  Finer Than 0.002   Colodial  Less Than 0.001

The consistency limits of the soil are controlled by the pore fluid pressure. The fluid in a unconsolidated material promotes inter-granular cohesion. Fluid in a soil will promote excess pressure to cause fluid like behavior of the soil. The liquid limit of a soil is the moisture content of the soil at which the soil ceases to behave as a plastic and begins to flow like a liquid. The plastic limit of a soil is the moisture content of a soil when it ceases to behave like a plastic and begins to behave as a brittle solid. The Plasticity index (PI) of a soil is the numerical difference between the liquid limit and the plastic limit (PI= LL-PL). These soil characteristics are illustrated below:

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