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.

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

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

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

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

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

A triangle, having equal length of sides (i.e. Equilateral triangle) is used in textural classification chart.

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.