Determination of Specific Gravity of Soil

Purpose of test

To determine the specific gravity of soil fraction passing 4.75 mm sieve by pycnometer.

Use of specific gravity value

The knowledge of specific gravity is needed in calculation of soil properties like void ratio, degree of saturation etc.

Definition

Specific gravity G is defined as the ratio of the weight of an equal volume of distilled water at that temperature both weights taken in air.

Apparatus

1. Pycnometer
2. Balance to weigh the materials.
3. Wash bottle with distilled water.
4. Alcohol and ether.

PROCEDURE

1. Clean and dry the pycnometer
2. Wash the pycnometer with water and allow it to drain.
3. Wash it with alcohol and drain it to remove water.
4. Wash it with ether, to remove alcohol and drain ether.
5. Weigh the pycnometer (W1)
6. Take about 200 gm of oven-dried soil sample which is cooled in a desiccator. Transfer it to the pycnometer. Find the weight of the pycnometer and soil (W2).
7. Put 10 ml of distilled water in the pycnometer to allow the soil to soak completely. Leave it for about 2 hours.
8. Again fill the pycnometer completely with distilled water put the stopper and keep the pycnometer under constant temperature water baths.
9. Take the pycnometer outside and wipe it clean and dry it. Now determine the weight of the pycnometer and the contents (W3).
10. Now empty the pycnometer and thoroughly clean it. Fill the pycnometer with only distilled water and weigh it. Let it be W4 at the same temperature.

Observations

Calculations

Average specific gravity:

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