For determination of free swell index of soils

Reference Standard

IS: 2720(Part 40)-1985- Methods of test for soils: Determination of free swell index of soil.

Equipment / Apparatus

  • Oven(1050C to 1100C, min)
  • Balance (0.01g accuracy)
  • Sieve [425 micron]
  • Graduated glass cylinder [100ml capacity]

Preparation sample

The soil passing 425 micron sieve is used in this test.


  1. Two no. of 10 g oven dried soil specimens passing through 425 micron IS sieve is taken.
  2. Each soil specimen is poured in each of the two glass graduated cylinders of 100 ml. capacity.
  3. Then one cylinder is filled with kerosene oil and the other with distilled water up to the 100 ml. mark.
  4. It is to be stirred with a glass rod to remove entrapped air and allowed to settle for 24 hours.
  5. After completion of 24 hours the final volume of soils in each of the cylinder is read out.


The free swell index of the soil is to be calculated as follows :

Free swell index, percent = ((Vd-Vk) / Vk)*100


Vd = The volume of soil specimen read from the graduated cylinder containing distilled water.

Vk = The volume of soil specimen read from the graduated cylinder containing kerosene


The free swell index is reported to the nearest whole number.

Safety & Precautions

  • Clean the sieves with the help of a brush, after sieving
  • While weighing put the sieve with soil sample on the balance in a concentric position.
  • Check the electric connection of the sieve shaker before conducting the test.
  • Use hand gloves while removing the soil sample from oven, after switching off the oven.

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