Determination of Free Swell Index of Soil Calculate Free Swell Index of Soil

Free swell is the increase in volume of a soil, without any external onstraints, on submergence in water.
The possibility of damage to structures due to swelling of expensive clays need be identified, at the outset, by an investigation of those soils likely to possess undesirable expansion characteristics. Inferential testing is resorted to reflect the potential of the system to swell under different simulated conditions. Actual magnitude of swelling pressures developed depends upon the dry density, initial water content, surcharge loading and several other environmental factors.

Why need to determine Free swell index of Soil?

Free swell index determination of soil helps to identify the potential of a soil to swell which might need further detailed investigation regarding swelling and swelling pressures under different field conditions.

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Apparatus

1. Sieve - 425-micron IS Sieve.
2. Glass Graduated Cylinders - lOO-ml capacity 2 Numbers. (IS: 878 -1956).
3. Glass rod for stirring.
4. Balance of capacity 500 grams and sensitivity 0.01 gram.

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Procedure to determine Free Swell Index of Soil

1. Take two 10 g soil specimens of oven dry soil passing through 425 micron IS Sieve.
2. Each soil specimen shall be poured in each of the two glass graduated cylinders of 100 ml capacity.
3. One cylinder shall then be filled with kerosene oil and the other with distilled water up to the 100 ml mark. After removal of entrapped air (by gentle shaking or stirring with a glass rod), the soils in both the cylinders shall be allowed to settle. Sufficient time (not less than 24 h) shall be allowed for the soil sample to attain equilibrium state of volume without any further change in the volume of the soils.
4. The final volume of soils in each of the cylinders shall be read out.

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How to Calculate Free swell Index of soil?

The level of the soil in the kerosene graduated cylinder shall be read as the original volume of the soil sample & kerosene being a non-polar liquid does not cause swelling of the soil. The level of the soil in the distilled water cylinder shall be read as the free swell level.

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

Free swell index = $\frac{V_d-V_k}{V_k}\times 100$ %

Where,

• V_d is the volume of soil specimen read from the graduated cylinder containing distilled water
• V_k is the volume of soil specimen read from the graduated cylinder containing kerosene