Dept of Civil Engg. Cusrow Wadia Institute of Technology, Pune

Part Time Degree Course in Civil Engineering

Page No.

Dept of Civil Engg. Cusrow Wadia Institute of Technology, Pune

Part Time Degree Course in Civil Engineering

Page No.

Determination of Differential Free Swell Index

Experiment No. Evaluation

Date of Experiment Timely / late / Attendance / 2

Signature of Teacher

with date

Performance / 2

Understanding / 3

Remarks

Lab Quiz / 2

Neatness / 1

/ 10

Aim: To determine the differential free swell index of soil, hence swelling potential of

the soil.

Reference: I.S. 2720 (Part 40) -1977

Theory: Generally the clayey and specially the black cotton soil have a tendency to sell

in small or more proportion when submerged in water. Free swell or differential free

swell is also termed as free swell index, & is the increase in volume of soil without any

external constraint when subjected to submergence in water. Such soil has a possibility to

damage the structure when the ground water table reaches the influence zone. It is

therefore, always essential to investigate the swelling or expansive nature of these clayey

soils which are likely to posses undesirable expansion characteristics.

Differential free swell (%) Degree of expansiveness

<20 Low

20-35 Moderate

35-50 High

>50 Very high

If the degree of expansiveness of soil at a site is damageable to the structure to be

constructed there, it is recommended to take suitable measures for foundation design of

the same. In such cases, the foundation should be constructed under the supervision of

geotechnical engineer.

Apparatus:

i. 425 micron IS sieve

ii. Oven

iii. Weighing Balance accurate to 0.01 gm

iv. Graduated glass cylinders-2no.s, each of 100 ml capacity

v. Kerosene and distilled water.

Procedure: i. Dry about 50 gm of soil in an oven at 100-110 degree, sieve soil through 425

micron IS sieve. Take two specimens of 10gm each. Fill one cylinder with

kerosene and one with distilled water (100ml).

ii. Pour gently one soil specimen in the first cylinder containing kerosene and the

other specimen containing distilled water. Remove the entrapped air by gently

shaking or by stirring with clean glass rod.

Dept of Civil Engg. Cusrow Wadia Institute of Technology, Pune

Part Time Degree Course in Civil Engineering

Page No.

iii. Leave the soil in both the cylinders to settle for 24 hours or more. Read the final

(constant) volume of the soil specimen in both the cylinders. Kerosene is a non-

polar liquid, causing no swelling of the soil. The level of soil specimen in the

graduated cylinder containing kerosene oil, therefore, is read as the original

volume of the soil sample.

iv. The level of the soil specimen in the second cylinder containing distilled water is

taken as the free swell level.

Precautions:

i. Pour the soil specimen in both the graduated glass cylinders gently, so that no soil

particle remains stuck to the wall of the cylinder

ii. Sufficient time should be taken to both the soil specimen to attain the final

equilibrium position of volume without any further change in soil volume. This

may take 24 hours or more.

iii. For highly swelling soils, the weight of soil specimen may be taken as 5 gm or

cylinders of 250 ml capacity may be used.

Observation Table:

Determination No. 1 2

Time of Start

Time of Finish

Time Elapsed (Usually total of 24hrs or more)

Volume of soil specimen read from the graduated

cylinder containing kerosene (V1) cc

Volume of soil specimen read from the graduated

cylinder containing distilled water (V2) cc

Calculations:

%_________

100V

V -V%index swell Free

1

1 2==×=

Result: Differential free swell is __________________

As the differential free swell is <20 / 20-35 / 35-50 / >50 , the swelling potential of the

soil is

________________.

Questionnaire: 1. What is free swell of soil? What is importance of word “free”?

2. Why and which soil swell? Which are the minerals responsible for this?

3. What is the significance of free swell index of soil in civil engineering?

4. What is the reason to use kerosene?

5. In field, how will you imply the knowledge of free swell?