How to Determine Specific Gravity of Soil by Pycnometer Method?
The Pycnometer is used for determination of the specific gravity of soil particles of both fine grained and coarse grained soils. The specific gravity of soil is determined using the relation:
Where M1=mass of empty Pycnometer,
M2= mass of the Pycnometer with dry soil
M3= mass of the Pycnometer and soil and water,
M4 = mass of Pycnometer filled with water only.
G= Specific gravity of soils.
Equipment for Pycnometer Test:
- Pycnometer of about 1 litre capacity
- Weighing balance, with an accuracy of 1g.
- Glass rod
- Vacuum pump
Procedure for Specific Gravity of Soil by Pycnometer:
1. Clean and dry the Pycnometer. Tightly screw its cap. Take its mass (M1) to the nearest of 0.1 g.
2. Mark the cap and Pycnometer with a 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 place about 200 g of oven dried soil in the Pycnometer. Screw the cap. Determine the mass (M2).
4. Unscrew the cap and add sufficient amount of de-aired water to the Pycnometer so as to cover the soil. Screw on the cap.
5. Shake well the contents. Connect the Pycnometer to a vacuum pump to remove the entrapped air, for about 20 minutes for fine-grained soils and about 10 minutes for coarse-grained soils.
6. Disconnect the vacuum pump. Fill the Pycnometer with water, about three-fourths full. Reapply the vacuum for about 5min till air bubbles stop appearing on the surface of the water.
7. Fill the Pycnometer with water completely upto the mark. Dry it from outside. Take its mass (M3).
8. Record the temperature of contents.
9. Empty the Pycnometer. Clean it and wipe it dry.
10. Fill the Pycnometer with water only. Screw on the cap upto the mark. Wipe it dry. Take its mass (M4).
Table: Observations and calculations for Specific Gravity of Soil:
Observations an Calculations
Mass of empty Pycnometer (M1)
Mass of Pycnometer and dry soil (M2)
Mass of Pycnometer, soil and water (M3)
Mass of Pycnometer and water (M4)
M2 – M1
M3 – M4
Calculate G using formula
Results of Pycnometer Test:
Specific gravity of soil at ___0C = _____.
Read More on Geotechnical Lab Tests on Soils