02 determination of specific gravity

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

Part Time Degree Course in Civil Engineering

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Determination of Specific Gravity (By Pycnometer)

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 specific gravity of soil grains by pycnometer.

Reference: I.S. 2720 (Part II & III)

Theory: The Specific gravity of solid particles (G) is defined as the ratio of the mass of

given volume of soils to the mass of equal volume of distilled water at 4 ْC. Both weights

are taken in air.

G= ρs/ρw

The mass density of water ρw at 4 ْC is 1 g/ml. The specific gravity of solids for most

natural soils falls in range of 2.65 to 2.80, the smaller values are of the coarse grained

soils. The specific gravity of the different particles in a soil mass may not be the same.

Whereas, when the specific gravity of the soil mass is indicated, it is the average value of

all the solid particles present in the soil mass.

Mass Specific Gravity (GM): It is defined as ratio of the mass density of the soil to the

mass density of the water

GM= ρ/ρw

The value of the mass specific gravity of a soil is much smaller than the value of specific

gravity of solids. The mass Specific gravity is also known as apparent specific gravity.

Absolute specific gravity (Ga): The soil solids are not perfect solids but contain voids.

Some of these voids are permeable through which water can enter, whereas others are

impermeable. Since permeable voids get filled when the soil is wet, these are in reality a

part of voids space in the total mass & not a part of soil solids. The remaining volume is

true or absolute volume of solids.

The mass density of absolute solids is used for determination of the absolute specific

gravity of solids.

Ga= (ρs)a/ρw

The absolute specific gravity is not of much practical use, as it is

difficult to differentiate between the permeable & impermeable voids

The specific gravity of solid particles can be determined in the laboratory

using following methods.

1) Density Bottle Method 4) Pycnometer Method

2) Gas Jar Method 5) Shrinkage Limit Method



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3) Measuring Flask Method 6) Voluminometer

Density bottle method is suitable for fine grained soils, with more than 90%

passing through 2mm-I.S. sieve. This method is also used for medium & coarse grained

soils if they are pulverized such that the particles pass through 2mm- I.S. sieve.

Pycnometer method is used for all types of soils, but is more suitable for medium

grained soils (Sand), with more than 90% passing through 20mm I.S. Sieve & for Coarse

grained soils with more than 90% passing through 40mm I.S. Sieve.

Measuring flask method is suitable for the fine grained and medium grained soils.

Specific gravity of very coarse fraction i.e., gravels, pebbles is calculated by using

voluminometer.

Applications: Specific gravity of soil grains is an important property & is used in

calculating void ratio, porosity, and degree of saturation if density & void ratio are

known. Its value helps to some extent in indication & classification of soils. It gives an

idea about the suitability of soil as a construction material, higher value of specific

gravity gives more strength for roads & foundations. It is used in computing the soil

particle size by hydrometer analysis. It is also used in estimating the critical hydraulic

gradient in soil when a soil boiling condition is being studied and in zero air void

calculations in the compaction theory of soils.

Its value ranges as follows: -

Coarse grained soils: 2.6 to 2.7.

Fine grained soils: 2.7 to 2.8.

Organic soils: 2.3 to 2.5.

Specific gravity of soil grains,

)M -M()M -(M

) M -M (

waterof volumeequal of Mass

soildry of MassGs

4 31 2

1 2

−

==

Where, M1 represents mass of the empty pycnometer

M2 represents mass of the pycnometer + dry soil

M3 represents mass of the pycnometer + dry soil + water

M4 represents mass of the pycnometer + water

Mass of soil grains Ms = M2 - M1

Mass of equal volume of distilled water

= (M2 - M1) – (M3 –M4)

Apparatus:

i. Pycnometer

ii. Weighing balance (accuracy 1g)

iii. Oven (interior of non corroding material, thermostatically controlled)

iv. Desiccator.

v. Glass rod

vi. Vacuum pump

vii. 4.75 mm I.S sieve.

viii. Distilled water.



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Procedure: i. Clean the pycnometer & dry it. Find the Mass of the pycnometer, brass cap &

washer, accurate to (M1) g.

ii. Take about 200 g to 400 g of oven-dried soil & put it in the pycnometer.

iii. Weigh the pycnometer plus soil etc (M2).

iv. Fill the pycnometer to half its height with distilled water & mix it thoroughly with

glass rod. Add more water & stir it. Replace the screw top and fill the pycnometer

flush with the hole in the conical cap. Dry the pycnometer from outside, & weigh

it (M3)

v. Empty the pycnometer; clean it thoroughly & fill it with distilled water, to the

hole of the conical cap and weigh it (M4)

vi. Repeat steps 2 to 4 for 2 or more determinations of specific gravity.

Observation Table:

Determination No. 1 2 3

Pycnometer No.

Mass of Pycnometer (M1) g

Mass of pycnometer. + dry soil (M2) g

Mass of pycnometer + dry soil +water (M3) g

Mass of pycnometer + water (M4) g

Specific Gravity (Gs)

Average Specific Gravity

Calculations: The specific gravity is calculated from the equation

)M -M()M -(M

) M -M (

waterof volumeequal of Mass

soildry of MassGs

4 31 2

1 2

−

==

Result: The Average Specific Gravity of a given soil sample is, Gs = ________%



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Questionnaire: 1. Explain what Specific Gravity of material is.

2. What is the significance of specific gravity of soil in civil engineering?

3. What is the principle of pycnometer method of determination of specific gravity of

soil?

4. What is the reason of using conical brass cap in pycnometer?

5. Which are the other tests by which you can determine specific gravity?

6. What are the applications/uses of specific gravity?

02 determination of specific gravity

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