Soil classification of composite soils exclusively based on the particle size distribution is known as textural classification.

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

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

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.

For general engineering purposes, soil can be classified in terms of particle size, textural and unified soil.

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

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

Triangular classification of U.S. public road administration is a commonly used system for textural classification.

Based on particle size, soil can be classified as

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.