For determination of specific gravity of soil solids by pycnometer method.
Equipment & Apparatus
- Sieve(4.75 mm)
- Vacuum pump
- Weighing balance
- Glass rod
After receiving the soil sample it is dried in oven at a temperature of 105 to 1150C for a period of 16 to 24 hours.
- Dry the pycnometer and weigh it with its cap(W1)
- Take about 200 g to 300 g of oven dried soil passing through 4.75mm sieve into the pycnometer and weigh again(W2)
- Add water to cover the soil and screw on the cap.
- Shake the pycnometer well and connect it to the vacuum 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 up to 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=Empty weight of pycnometer
W2=Weight of pycnometer + oven dry soil
W3=Weight of pycnometer + oven dry soil + water
W4=Weight of pycnometer + water full
The result of the specific gravity test is reported to the nearest two digits after decimal.
Safety & Precautions
- Soil grains whose specific gravity is to be determined should be completely dry.
- 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.
IS : 2720 (Part 4) – 1985 – Method of test for soil (Part 4-Grain size analysis)