STANDARD
- IS: 2720 (Part 40) 1977.
DEFINITION
- Free Swell Index is the increase in volume of a soil, without any external constraints, on submergence in water.
APPARATUS
- 425 micron IS sieve.
- Graduated glass cylinders 100 ml capacity 2Nos (IS: 878 -1956).
- Glass rod for stirring.
- Balance of capacity 500 grams and sensitivity 0.01 gram.
PROCEDURE
- Take two representative oven dried soil samples each of 10 grams passing through 425 micron sieve.
- Pour each soil sample in to each of the two glass graduated cylinders of 100ml capacity.
- Fill one cylinder with kerosene and the other with the distilled water up to the 1 00ml mark.
- Remove the entrapped air in the cylinder by gentle shaking and stirring with a glass rod.
- Allow the samples to settle in both the cylinders.
- Sufficient time, not less than 24 hours shall be allowed for soil sample to attain equilibrium state of volume without any further change in the volume of the soils.
- Record the final volume of the soils in each of the cylinders.
CALCULATIONS
Free Swell Index, (%) = ((Vd-Vk)/Vk)x 100
Vd= Volume of the soil specimen read from the graduated cylinder containing distilled water.
Vk = Volume of the soil specimen read from the graduated cylinder containing kerosene.
REPORT
- Read the level of the soil in the kerosene graduated cylinder as the original volume of the soil samples, kerosene being non polar liquid does not cause swelling of the soil.
- Read the level of the soil in the distilled water cylinders as free swell level.
- Record the individual and the mean results to the nearest second decimal.
PRECAUTION
- In the case of highly expansive soils such as Sodium Betonites. the sample size may be 5 grams or alternatively a cylinder of 250 ml capacity for 10 grams of sample may be used.
DETERMINATION OF FREE SWELL INDEX
IS:2720(Part4O) 1977
| Description | Test 1 | Test 2 | Average |
| Weight of the soil sample gms | |||
| The volume of soil specimen read from the graduated V, cc cylinder containing distilled water | |||
| The volume of soil specimen read from the graduated Vk cc cylinder containing kerosene | |||
| Free Swell Index = (Vd-Vk) x100 | |||
| Specified Limit: For Embankment and Subgrade is maximum 50% | |||
| Remarks: | |||