Experiment No. 5: Soil Atterberg Limits
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Determination of the liquid and plastic limits of a soil.

Liquid limit device and grooving tools, Metal rod of 3 mm diameter, Apparatus for moisture content determination, Porcelain evaporating dish, Spatula, Wash bottle filled with distilled water, Measuring cylinder, Glass plate.

Procedure for Liquid Limit
1. Take about 150 gm of dry soil passing 425 micron sieve, and mix it with distilled water in a porcelain dish to form a uniform paste.

2. Place a portion of the paste in the cup of liquid limit device with a spatula, press the soil down to remove air pockets, spread it to a maximum depth of 10 mm, and form an approximately horizontal surface.

3. By holding a grooving tool perpendicular to the cup, carefully cut through the sample from back to front, and form a clean straight groove in the centre by dividing into two halves.

4. Turn the crank handle of the device at a steady rate of two revolutions per second. Continue turning until the two halves of the groove is closed along a distance of 13 mm. Record the number of blows to reach this condition.

5. Take about 15 gm of the soil from the joined portion of the groove to a moisture can for determining water content.

6. Transfer the remaining soil from the cup into the porcelain dish. Clean and dry the cup and the grooving tool.

7. Repeat steps 2 to 6, and obtain at least four sets of readings evenly spaced out in the range of 10 to 40 blows.

Procedure for Plastic Limit
1. Use the remaining soil from the porcelain dish.

2. Take about 10 gm of the soil mass in the hand, form a ball, and roll it between the palm or the fingers and the glass plate using complete motion of the hand forward and reverse.

3. Apply only sufficient pressure to make a soil thread, and continue rolling until a thread of 3 mm diameter is formed. Comparison can be made with the metal rod.

4. If the diameter becomes less than 3 mm without cracking, turn the soil into a ball again, and re-roll. Repeat this remoulding and rolling process until the thread starts just crumbling at a diameter of 3 mm.

5. Gather the pieces of crumbled thread and place them in a moisture can for determining water content.

6. Repeat steps 2 to 5 at least two more times with fresh samples of 10 gm each.

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