This document summarizes a differential free swell test conducted to determine the swelling potential of a soil sample. The test involves drying and sieving the soil, then placing 10g of soil in two measuring cylinders filled with kerosene and distilled water, respectively. After 24 hours, the soil levels in the cylinders are recorded. The differential free swell index is calculated as a percentage based on the difference in soil volumes. This index indicates the soil's degree of expansiveness, which is important for designing structures on expansive soils to prevent cracking and settlement issues.

1. Experiment No.: 09 Date:
DIFFERENTIAL FREE SWELL TEST
Object and scope:
To determine the swelling potential of a given soil in term of differential free swell index.
Reference:
I.S. 2720 (Part 40) – 1977
Equipment:
1) 90 micron IS sieve
2) Electronic balance
3) Two 100 ml capacity borosil measuring cylinders
4) Thermostatically controlled oven
5) Stirring rod
Theory:
Most of the clayey soils have swelling potential. But some clayey soils like black cotton soils have high
swelling potential. Such soils are considered as problematic soils by civil engineers. The structures
constructed on such type of soils develop cracks and face other problems like settlement. Therefore in
order to design a structure swelling potential of soils needs to be ascertained. This test is used to find the
swelling potential.
Preparation of test specimen:
Soil to be tested is dried in an oven at 100-105 degree celcius.Then it is taken out, allowed to cool down
and sieved through 90 micron IS sieve.
Procedure:
1) 10 gm of soil is taken in two measuring cylinders of 100 ml capacity.
2) One cylinder is filled with distilled water and another cylinder is filled with kerosene up to 100 ml
mark. Then using a rod the soil in both cylinders is stirred.
3) After stirring, the two cylinders are kept for 24 hours without any disturbance.
4) After 24 hours the soil level in both the cylinders are recorded and tabulated below.
Observation Table:
Weight of Soil sample = 10 gm.
Sr. No. Time of
Start
Time
Elapsed
(hrs.)
Volume of soil in
cylinder containing
Kerosene (Vk) cc
Volume of soil in cylinder
containing Distilled water
(Vd) cc
Calculations:
Differential free swell index (DFSI) (%) = [
(Vd−Vk )
Vk
× 100]

2. Result:
Differential free swell index of given soil is __________
Hence its swelling potential is
Table No. 1. Relation between differential free swell (%) and degree of expansiveness for soils
Differential free swell (%) Degree of expansiveness
< 20 Low
20-30 Moderate
35-50 High
> 50 Very High

3. Fig. Differential Free swell test.