Ex 3 specific gravity by pycnometer

Geo-technical Engineering

1. Experiment No.: 03 Date:
SPECIFIC GRAVITY DETERMINATION BY PYCNOMETER
Object and scope:
To determine the Specific gravity of soil sample by Pycnometer.
Reference:
IS: 2720 (Part III) - 1964
Theory:
Specific gravity is defined as the ratio of mass of a given dry soil to mass of equal volume of water
displaced by the soil. Also defined as the ratio of density of soil solids to density of water. It is
dimensionless quantity denoted by ‘Gs’. It is an average value of all the particles present in soil mass. It
is correlated with other properties of soil like density, dry density, voids ratio, degree of saturation, etc.
Specific gravity of soil is found using following methods
a) Pycnometer method
b) Density bottle method
c) Gas Jar method
d) Measuring Flask method
e) Voluminometer.
Pycnometer method is used for all types of soils, but is more suitable for medium grained soils (sand),
with more than 90% passing through 20 mm I.S. sieve and for coarse grained soils with more than 90%
passing through 40 mm I.S. sieve. Density bottle method is suitable for fine-grained soil. Measuring
flask method is suitable for fine grained and medium grained soils. Voluminometer is suitable for
finding specific gravity of coarse fraction i.e. gravels and pebbles
Equipments:
1) Pycnometer is glass jar of 900 ml capacity with a conical brass cap having 6 mm diameter hole in
the center, screwed with a rubber washer
2) Weighing Balance with accuracy of 0.1gm
3) Glass rod
4) De-aired distilled water.
5) Thermostatically controlled oven.
Procedure:
1) Clean the Pycnometer and dry it. Find the mass (M1) of the pycnometer, brass cap and washer
accurate to 1gm.
2) Take about 200 gm to 400 gm of oven-dried soil and put it in the pycnometer. Find the mass of the
pycnometer + soil. (M2).
3) Fill the pycnometer to its half height with distilled water and mix it with soil thoroughly with glass
rod. Add more water and stir it. Replace the screw top and fill the pycnometer flush with hole in the
conical cap. Dry the pycnometer from outside, and find the mass (M3).

2. 4) Empty the pycnometer, clean it thoroughly and fill it with distilled water to the hole of the conical
cap and find the mass (M4).
5) Repeat step 2 to 4 for two more determinations of specific gravity.

Observation Table:
Sr.
No.
Description Sample - 1 Sample - 2 Sample - 3
1 Pycnometer No.
2 Mass of Empty Pycnometer
(M1) gm

3 Mass of Pycnometer + soil
(M2) gm

4 Mass of Pycnometer + soil + water
(M3) gm

5 Mass of Pycnometer + water
(M4) gm

6 Specific gravity (G)
7 Average Specific Gravity
Calculations:
Specific gravity G =
(M
2−M
1
)
(M
4−M
1
)−(M
3−M
2
)


Result:
Specific gravity of given soil sample is =
Use of Specific Gravity:
1) To determine voids ratio of soil by knowing its water content
2) To determine unit weight of soil
3) For mineral classification
4) To determine particle’s size by Stoke’s law.
Table No. 1. Typical values of specific gravity ‘GS’
Sr. No. Soil Type Specific Gravity
1 Gravel 2.65-2.68
2 Sand 2.65-2.68
3 Silty Sand 2.66-2.70
4 Silt 2.66-2.70
5 Inorganic Clay 2.68-2.80
6 Organic Soil < 2.0

3. Fig. 1 Pycnometer


Fig. 2 Diagrammatic representation of the experimental procedure