Specific gravity of soil

The specific gravity of soil is defined as the unit weight of the soil mass divided by the unit weight of distilled water at 4°C. It is some times required to compare the density of the soil solids to the density of water. This comparison is in the form of ratio and is termed as the specific gravity of the soil.

1. Presentation on
Specific Gravity of Soil Determination
Submitted by:-Abhishek M Chavan, Roll no:-04
Class:-Second Year, Div:-B Prn no:-190101062004
Subject:-Geotechnical Engineering, Guided by:-Prof Swati Patil
SPECIFIC GRAVITY OF SOIL DETERMINATION TUESDAY, 7 APRIL 2020 PAGE OF 116

2. Index
•Introduction
•Specific gravity of Soil by Pycnometer
•Theory
•Apparatus
•Procedure
•Observation table
•Safety and health
•Conclusion
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3. Introduction
Soil specific gravity G, refers to the mass of solid
matter of a given soil sample as compared to an
equal volume of water. The Gs of soils was used
not only for soil classification but also in calculation
other soil properties such as void ratio, degree of
saturation and porosity. Besides that the Gs is also
strongly related to the weight and volume
relationships. During the process of determining
the Gs, it is really important for the operator to
ensure the air is removed out from the sample in order to get an accurate result
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4. Specific Gravity of Soil by Pycnometer
Theory
The specific gravity of solid particles is defined as the ratio of the mass of given
volume of solids to the mass of equal volume of distilled water at 4 C. Both weights
are in air
Mass specific gravity:- It is defined as the ratio of the mass density of the
soil to the mass density of water
:-ρ/ρw

The value of the mass specific gravity of a soil is much smaller than the value of
specific gravity of solids
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5. Absolute Specific Gravity:- 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 void space in the total mass and not a part of soil
solids. The remaining volume is true or the absolute volume of the solids
the mass density of the absolute solids is used for determination of the absolute
specific gravity of solids.
:-(ρs) a/ρw
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6. Scope
This method of test which is modification of AASHTO (American Association of
State Highway and Transportation Officials) Designation T 100, is used for the
determination of the specific gravity of soils by means of a pycnometer.
When the soil contains particles retained on the 4,75mm sieve, the sample shall be
separated on the 4.75mm sieve and the apparent specific gravity of the retained 4.75mm
sieve material shall be determined in accordance with California Test 2006. The specific
gravity value for the soil shall be the weighted average of the two values,
Purpose
This test is performed to determine the specific gravity of soil by pycnometer.
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.
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7. Standard Reference
ASTM D 854-00- Standard test for Specific Gravity of Soil Solids by Water
Pycnometer.
Significance
The specific gravity of a soil is used in the phase relationship of
air, water and solids in a given volume of the soil.
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8. Apparatus
1.Pycnometer
2.Weighing balance with accuracy of 1 gm
3.Glass rod
4.Vacuum pump
5.Oven
6.Distilled water
7.Thermometer
8.Desiccators
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9. Pycnometer Weighing Balance Oven
Thermometer
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10. Procedure:
1.Clean and dry the pycnometer, tightly screw its cap. Take its mass M1
2.Mark the cap and pycnometer with vertical line parallel to the axis of the
pycnometer to ensure that the cap is screwed to the same mark each time
3.Unscrew the cap and fill the pycnometer with 200 to 400 gm or one third with
oven dried soil taken directly from the desiccator and screw the cap. Determine the
mass m2
4.Unscrew the cap and add sufficient amount of de-aired water to pycnometer so as
to cover the soil. Screw on the cap
5.Shake well the contents, to remove the entrapped air, for about 20 min for fine
grained soils and for about 10 min for coarse grained soils
6.Fill the pycnometer with water, about three fourth or full
7.Fill the pycnometer with water completely, up to the mark. Dry it fromqoutside.
Take it as mass M3.
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11. 8.Empty the pycnometer. Clean it and wipe it dry
9.Fill the pycnometer with water only. Screw on the cap up to the mark. Wipe it dry.
Take it as mass M4
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12. Observation table
Sl. No. Observations an Calculations
Determination No.
1 2 3
Observation
1Pycnometer No.
2Room Temperature
3Mass of empty Pycnometer (M1)
4Mass of Pycnometer and dry soil (M2)
5Mass of Pycnometer, soil and water (M3)
6Mass of Pycnometer and water (M4)
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13. Calculations
Specific Gravity (G)= Mass of given volume of solid particles/ mass of vol of water
Specific gravity (G)= M2-M1
————————
(M2-M1) - (M3-M4)
where,
M1- mass of the empty pycnometer
M2- mass of pycnometer + soil
M3- mass of pycnometer + soil + distilled water
M4- mass of pycnometer + distilled water
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14. Typical values of ‘G’
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.In-organic clay:- 2.68-2.80
6.Organic clay:- variable, may fall below 2
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15. Safety & Health
Soils and water may contain bacteria and/or organisms which can be harmful to
one’s health. Please be sure to clearly identify those soils and waters which may contain
contaminates. The wearing of dust masks and protective gloves when handling
materials is advised
If boiling off air from soil suspension, use caution when handling hot flasks and
beware of steam emanating from the mouth of a pycnometer while water is boiling.
The use of tongs or heat resistant gloves is recommended.
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16. Conclusion
Specific gravity of soil at ___0C = _____. Unless specified, the specific gravity
values of the soil will be reported at 27-degree Celsius. The specific gravity of soil
particles will come within the range of 2.65 and 2.85. If the soils consist of porous and
organic materials, a specific gravity value of less than 2 will be obtained. A specific
gravity value greater than 3 will be shown by soils that have heavy substances.
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