Consistency properties of Soil

The consistency properties of a fine-grained soil mass refers to its firmness, and it varies with the water content level of the soil.

The gradual homogenic increase in water content level may causes the soil to change from solid state to semi-solid to plastic to liquid states. The water content level at which the consistency changes from one state to the another state are called consistency limits (or Atterberg limits).

These basic three described limits are known as the

  1. shrinkage limit (WS),
  2. plastic limit (WP),
  3. liquid limit (WL) The values of these limits can be obtained from laboratory experimental tests.

Two of these three limits are commonly utilised in the classification of fine soils:

Liquid limit (WL) – change of consistency from plastic state to liquid state.
Plastic limit (WP) – change of consistency from brittle/crumbly state to plastic state.

The basic difference between the liquid limit state and the plastic limit state is known as the plasticity index (IP), and in this range of water content level that the soil mass has a plastic consistency level. The consistency of most soil mass in the field will be plastic or semi-solid state.