In this article, we explained how to determine free swell index of soil in laboratory, what is the practical uses of it, aim, apparatus, precautions, etc.
Table of Contents
Aim of Free swell index test :
To determine free swell index of expansive nature soil
Apparatus of Free swell Index test :
Free swell is the increase in volume of soil, Without any external constraints on submergence in water. The possibility of damage to structures due to swelling of expansive clay need be identified by an investigation of those soil likely to possess undesirable expensive characteristics. This testing is provided to reflect the potential of the soil to swell under different simulated conditions. For the given clay the free swell index in percent can be calculated as follows:
Free swell index (%) = (Vd – Vk/ Vk) x 100
Where, Vd = The volume of soil specimen read from the graduated cylinder containing distilled water, ml
Vk = The volume of soil specimen read from the graduated cylinder containing kerosene, ml
Free swell index test Procedure :
Take two 10gm soil specimen of oven dry soil passing through 425 micron IS Sieve.
Pour each of the specimen in each of the two glass graduated cylinders of 100ml capacity.
Fill one cylinder with kerosene oil and the other with distilled water upto the 100ml mark. After removal of entrapped. Air (by gentle shaking or stirring with a glass rod), allow soils in both the cylinders to settle.
Allow sufficient time (not less than 24hrs) for the soil sample to attain equilibrium state of volume without any further change in the volume of the soils.
On completion of swelling, read out the final volume of soils in each of the cylinders.
Do the necessary calculation and find out the free swell index.
Also Read: Shrinkage Limit Test For soil
Precautions in free swell index test :
To determine the evaporation losses, both the cylinders should be e bless away from any source of heat and wind.
Practical Utility of free swell index:
As stated in theory, this test gives the idea about potential of the soil to expand when it submerged in the water. Thus possibility of damage to the structure due to swelling can be identified and possible precaution can be taken. For guideline table 8 of IS code has been given below.
| Liquid Limit (%) | Plasticity Index (%) | Shrinkage Index (%) | Free Swell (%) | Degree of Expansion | Degree of Severity |
|---|---|---|---|---|---|
| 20-35 | <12 | <15 | <50 | Low | Non-Critical |
| 35-50 | 12-23 | 15-30 | 50-100 | Medium | Marginal |
| 50-70 | 23-32 | 30-60 | 100-200 | High | Critical |
| 70-90 | >32 | >60 | >200 | Very High | Severe |
Also Read: Plastic and Liquid Limit test for soil
Observations in Free Swell Index:
1. Volume of the soil specimen read from the graduated cylinder containing distilled water, Vd = ___________ ml.
2. Volume of the soil specimen read from the graduated cylinder containing kerosene, Vk = _______________ ml.
3. Free swell index = (Vd – Vk/ Vk) x 100 (%) = ______________ x 100
Reference : IS : 2720 (Part -40) – 1977
Results : Free Swell Index = __________%
Also Read: Field and Lab Test on Cement