The various properties of soils which would be considered as index properties are:
The size and shape of particles.
The relative density or consistency of soil.
The index properties of soils can be studied in a general way under two classes. They are:
- Soil grain properties.
- Soil aggregate properties.
The principal soil grain properties are the size and shape of grains and the mineralogical
character of the finer fractions (applied to clay soils). The most significant aggregate property of
cohesionless soils is the relative density, whereas that of cohesive soils is the consistency. Water
content can also be studied as an aggregate property as applied to cohesive soils. The strength and
compressibility characteristics of cohesive soils are functions of water content. As such water
content is an important factor in understanding the aggregate behavior of cohesive soils. By
contrast, water content does not alter the properties of a cohesionless soil significantly except when
the mass is submerged, in which case only its unit weight is reduced.