Index Properties of Soil

The properties of the soil on which their classification and identification are based are known as index properties. The index properties that are used are:

  • Grain size distribution
  • Consistency limits
  • Plasticity index

Grain size distribution (sieve analysis)

The sieves are arranged, keeping the thinner ones below and the thicker ones above. A defined amount of soil is dried in an electric oven (for 24 hours at 105 ° C) and placed in the upper sieve. The cover is placed on the upper sieve and a tray under the lower sieve. Then, the sieves are placed on the agitator and stirred for a few minutes. The weight of the soil thus retained in each sieve is determined and converted into a percentage.

Soil consistency

Soil consistency is the physical state of the soil with respect to the moisture content present at that time. By consistency is meant the relative ease with which the soil can be deformed. The consistency is related to the fine-grained soil.

Limits of consistency or limits of Atterberg

The moisture content in which the soil changes from one state to another is called consistency limits or Atterberg limits. There are four different soil states:

  1. Solid State
  2. Semi solid state
  3. Plastic state
  4. Liquid state

When water is added to the dry soil mass, its change from the solid state to the liquid state passes through the semi-solid and plastic state. Atterberg identifies some other limits that are more useful for engineering purposes.

  1. Limit of liquid
  2. Plastic limit
  3. Shrinkage limit

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