Specific gravity of soil by density bottle ( Pycnometer)

Determination of specific gravity of soil particles of both fine-grained and coarse-grained soils by using a pycnometer. The specific gravity of soil will help in the calculation of void ratio, degree of saturation, and other different soil properties.

Test Standard : IS 2720-Part 3/Sec1: 1980, Reaffirmed 2011

Test Apparatus :

1. Two density bottles of approximately 50 ml capacity with stoppers.
2. Water bath
3. Hot air oven
4. Weighing balance of accuracy 0.001gm,
5. A vacuum pump, spatula, wash bottle.

Test Procedure :

1. The complete density bottle with stopper, shall be dried at 105 to 1100C, cooled in the desiccator and weighed to the nearest 0.001gm ( Say m1).
2. Take 50gm of soil sample and if necessary ground to pass a 2.0 mm IS test sieve, 5 to 10 gm of subsample shall be taken and oven dried at 105 to 110°C. This sample shall be transferred to the density bottle direct from the desiccator in which it has been cooled. The bottle and contents together with the stopper shall be weighed to the nearest 0.001gm (Say m2).
3. Sufficient air-free distilled water shall be added so that the soil in the bottle is just covered. The bottle containing the soil and liquid, but without the stopper, shall be heated using water bath to remove the entrapped air. After removal of entrapped air, sufficient air free distilled water shall be added until the bottle is full.
4. The stopper shall then be inserted. The stoppered bottle shall be immersed upto the neck in a constant temperature bath for approximately one hour or until it has attained the constant temperature of the bath. If there is an apparent decrease in volume of the liquid the stopper shall be removed and further liquid added to fill the bottle and the stopper replaced.
5. The bottle shall then be returned to the bath and sufficient time shall be allowed to elapse after this operation to ensure that the bottle and its contents again attain the constant temperature of the bath.
6. If the bottle is still not completely full this process shall be repeated. The stoppered bottle shall then be taken out of the bath, wiped dry and the whole weighed to the nearest 0.001gm (Say m3).
7. The bottle shall then be cleaned out and filled completely with air free liquid, the stopper inserted and then the whole immersed in the constant temperature bath for 1 hour or until it has attained the constant temperature of the bath.If there is an apparent decrease in the volume of the liquid, the stopper shall be removed and further liquid added to fill the bottle and the stopper replaced.
8. The stoppered bottle shall then be returned to the batch and sufficient time shall be allowed to elapse after this operation to ensure that the bottle and its contents again attain the constant temperature process shall be repeated. If the bottle is still not completely full this the bottle shall then be taken out of the bath, wiped dry and the whole weighed to the nearest 0.001gm (Say m4).

Result Calculation :

Specific gravity of the soil shall be calculated as

 G = GL x (m2-m1)/[(m4-m1)-(m3-m2)] 

Where 

CL = specific gravity of the liquid used, at the constant temperature.