1.Calibrate the hydrometer to be used in the test.
2.Determine the meniscus correction.
3.Take about 50 g of oven dried soil sample passing 75 µ IS sieve.
4. Subject the soil to pre-treatment to remove soluble salts or organic matter or calcium compounds, if necessary.
5. Dissolve 3.3 g of sodium hexa meta phosphate and 0.7 g of sodium carbonate in 100 ml distilled water. Transfer the solution to 1000 ml capacity jar and add distilled water to make the volume of the solution to 1000 ml (This dispersion agent solution is required for getting the composite correction).
6. Take the measured quantity of soil in a beaker. Add 100 ml of solution prepared by dissolving 3.3 g of sodium hexa meta phosphate and 0.7 g of sodium carbonate in distilled water to the beaker.
7. Warm the soil suspension gently for about 10 minutes.
8Transfer the soil suspension to the cup of a mechanical stirrer using about 100 ml of distilled water. Stir the suspension for about 15 minutes..
9. Transfer the stirred soil suspension to another 1000 ml capacity measuring jar. Add distilled water to the suspension to make its volume to 1000 ml.
10. Place suitable covers on the top of the two 1000 ml measuring jars – one containing the dispersion agent solution and the other containing the soil suspension. Shake the contents in the two jars vigorously and place them slowly on a level platform. Start a stop watch immediately.
11. Insert the hydrometer in to the jar containing the soil suspension slowly and allow it to float freely. Contd…. Geotechnical Engineering Lab Instruction Manual 8
12. Note down the hydrometer readings corresponding to upper meniscus after suitable time intervals or note down the time intervals corresponding to well defined hydrometer readings.
13. After 4 minutes reading, take out the hydrometer from the jar, rinse it with distilled water and allow it to stand in another 1000 ml jar containing distilled water.
14. Insert the hydrometer in to the jar containing soil suspension from time to time and note down the hydrometer readings and corresponding time intervals. After removing the hydrometer from the jar each time, rinse it with distilled water and store it in the jar containing distilled water.
15. Record the temperature of the soil suspension and the composite correction in the beginning of the test and also after each time the hydrometer reading is taken beyond 15 minutes period
16. Calculate the equivalent diameter of the soil particles corresponding to the noted time intervals (D) and also the corresponding values of percentage finer based on the dry mass of the soil sample taken for the test (N') and based on the total mass of the dry soil sample taken for the grain size analysis(N).
17. Carry out the test till the equivalent diameter of the particles is less than 2 µm.
18. Using the values of equivalent diameter of the particles (D) and the values of corresponding percentage finer (N), plot the grain size distribution curve. From the plotted curve, note down the percentage of silt size and clay size fractions present in the soil.