Determining specific gravity of soil by Using Pycnometer
Determination of specific gravity of soil solids by pycnometer method.
IS : 2720 (Part 4) – 1985 – Method of test for soil (Part 4-Grain size analysis)
EQUIPMENT & APPARATUS
The major equipment used in this test is Pycnometer. It is a glass jar of 1 litre capacity that is fitted at its top by a conical cap made of brass. It has a screw type cover as shown.
- Sieve (4.75 mm)
- Vaccum Pump
- Weighing balance
- Glass rod
After receiving the soil sample it is dried in oven at a temperature of 1050C to 1150C for a period of 16 to 24 hours.
- Dry the pycnometer completely and weigh it with its cap (W1)Take its mass (M1) to the nearest of 0.1 g.
- Take about 300 g of oven dried soil passing through 4.75mm sieve into the pycnometer and weigh it again (W2).
- Unscrew the cap and add sufficient amount of de-aired water to the Pycnometer so as to cover the soil. Screw on the cap.
- Shake the pycnometer thoroughly and connect it to the vaccum pump to remove entrapped air for about 10 to 20 minutes.
- After the air has been removed, fill the pycnometer with water and weigh it (W3).
- Clean the pycnometer by washing thoroughly.
- Fill the cleaned pycnometer completely with water upto its top with cap screw on.
- Weigh the pycnometer after drying it on the outside thoroughly(W4).
The Specific gravity of soil solids (Gs) is calculated using the following equation.
W1=weight of empty pycnometer
W2=Weight of pycnometer + oven dry soil
W3=Weight of pycnometer + oven dry soil + water
W4=Weight of pycnometer + water full.
Specific gravity of soil at ___0C = _____.
Specific gravity of solids is defined as weight of solids in a given volume, to the weight of equivalent volume of water.
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.
SAFETY & PRECAUTIONS
- Completely dry the Soil grains whose specific gravity is to be determined.
- If on drying soil lumps are formed, they should be broken to its original size.
- Inaccuracies in weighing and failure to completely eliminate the entrapped air are the main sources of error. Both should be avoided.
- While cleaning the glass jar, please be careful as there may be glass grains projecting out and it may tear the skin.
- Make sure, you handle the glass jar and conical cap without falling on your legs or floor. Hence, handle the equipment with care.