Unified Soil Classification
This system was originally developed by A.Casagrande (1940) and was used for airfield construction. Later it was slightly modified to make it applicable to other constructions like foundation, earth dams, etc.
In this system, coarse-grained soils are classified on the basis of their grain size distribution and the fine-grained soils are classified on the basis of their plasticity.
This system classifies various soils into four major groups and 15 subgroups. The major group is:
- Organic soils
The type o soil is indicated by a suitable combination of symbols such as GW, SP, SC, CL, SM, etc.
For example, SC indicates clayey sand, SM indicates silty sand.