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

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’.

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

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.

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

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.

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

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.

Group index of soil usually varies by

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