DETERMINATION OF SPECIFIC GRAVITY OF SOIL SAMPLE BY
PYCNOMETER METHOD
Aim:
To determine the specific gravity of soil solids by Pycnometer bottle method.
Specific gravity is the ratio of the mass of unit volume of soil at a stated
temperature to the mass of the same volume of gas-free distilled water at a stated
temperature.
Specification:
This test is specified in IS: 2720 (Part 4) — 1985. A soil's specific gravity largely
depends on the density of the minerals making up the individual soil particles.
However, as a general guide, some typical values for specific soil types are as follows:
• The specific gravity of the solid substance of most inorganic soils varies
between 2.60 and 2.80.
• Tropical iron-rich laterite, as well as some lateritic soils, usually have a specific
gravity of between 2.75 and 3.0 but could behigher.
• Sand particles composed of quartz have a specific gravity ranging from 2.65 to
2.67.
• Inorganic clays generally range from 2.70 to 2.80.
• Soils with large amounts of organic matter or porous particles (such as
diatomaceous earth) have specific gravities below 2.60. Some range as low as
2.00.
Equipments Required:
a) Pycnometer of about 1 litre capacity.
b) Balance accurate to lg, glass rod, de-aired distilled water etc.
Theory:
Specific gravity of soil solids is defined as the weight of soil solids to weight of
equal volume of water. In effect, it tells how much heavier (or lighter) the
material is than water. This test method covers the determination of the specific
gravity of soil solids that pass 4.75 mm sieve.
Equation for specific gravity, G:
Where, Wi=weight of Pycnometer in grams.
W2=weight of Pycnometer + dry soil in grams.
W3=weight of Pycnometer + soil+ water grams.
W4=weight of Pycnometer + water grams.
Note: This method is recommended for coarse and fine grained soils
Procedure:
a) Clean and dry the pycnometer and weigh it along with the conical cap (WI in
gm).
b) Select about 300 gm of dry soil free of clods and put the same into the pycnometre.
Weigh it (W2 in g) with cap andwasher.
c) Fill the pycnometer with de-aired water up-to its height and . Fit the screw cap and
fill the pycnometer flush with the hole in the conical cap and take the weight (W3 in
g).
d) Remove all the contents from the pycnometer, clean it thoroughly and fill it with
distilled water. Weigh it (W4 in g).
e) Now use the above equation for determining G.
f) Repeat the same process for additional tests.
Table:
Table 1: Weights of pycnometer
SI No Particulars Test No I Test No 2 Test No 3
Weight of Pycnometer bottle
(W1), g
2 Weight of Pycnometer + dry
soil (W2), g
3 Weight of Pycnometer + soil
+ water, (W3), g
4 Weight of Pycnomerter +
water (W4), g
5 Calculation of specific
gravity , G
6 Average G =(G1+G2+G3)/3
Specimen Calculation:
Result:
Average G=
Conclusion:
The experiment is conducted as per the procedure laid down. The specific gravity
of soil solids obtained is This value falls in the range 2.6 to 2.75. Hence the type of soil
