In the particle soil classification system, soils are arranged to the grain size.

To use the textural classification chart, for a given percentage of three constituents forming a soil, lines are drawn parallel to three sides of the equilateral triangle.

Highway research board classification system is also known as public road administration (PRA) system.

Since properties of clay soils is less dependent on particle size distrubution(textural classification) and more dependent on size it is best suited for clay soil.

Since the textural classification is based on the percentages of sand, silt, and clay size making up the soil. Such a classification is more suitable for describing coarse-grained soil.

HRB classification system, also known as public road administration (PRA) is based on both the particle-size composition and plasticity characteristics.

The purpose of soil classification is to arrange various types of soils in to groups according to their engineering or agricultural properties.

As group index is a mean of rating the value of soil as a sub-grade material. It can be used for finding the performance and quality of the soil.

Soil occurring in nature is composed of a different percentage of sand, silt, and clay size particles.

As the system is classified based on size, it is preferable to use the word ‘silt size’ and ‘clay size’ in place of simply ‘silt’ or ‘clay’.