Importance of Soil Classification:

1. A soil classification system is essentially to faciliate communication between different groups of engineers, widely separated.
2. The classification system does not eliminate the need for detailed soil investigation and testing.
3. The classifiaction based on grain size or texture.
4. Attterberg was the first to suggest properties other than which can be used for classification.
5. At that time, these were proposed for agricultural purpose but were later accepted in soil engeneering.

Traingular Soil Classification:

• Classification has been developed by US public roads Administration.
• Soil classification of composite soils exclusively based on the particle size distribution is known as textural classification.
• The classification is based on the percentage of sand, silt and clay size making up the soil.

• As properties of clay soils are less dependent on particle size distribution, this classification is more suitable for coarse grained soils.

• For given percentage of three constitutes forming a soil, lines are drawn parallel to the three sides of the equilateral triangle as shown by arrows in the key as shown in fig.

• For example, if a soil consists of 35% sand, 35% silt and 30% clay sizes the the three lines as drawn intersect at the point (p) situated in the sector designed as 'Clay'. Hence a soil will be termed as clay.