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

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.

Terms such as gravel, sand, silt, and clay are used to indicate grain sizes. These terms are used only as a designation of particle size.

Particle size classification used only as a designation of particle sizes, and do not signify the naturally occurring types which are mixtures of a particle of different sizes.

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

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.

Based on HRB system, the soil is divided into 7 primary groups, designated as A-1, A-2…A-7.

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.

Group index of soil usually varies by

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