Liquid limit and plasticity index of soil by cone penetrometer method | LL and PI Test of Soil
Test Standard : IS 2720-Part 5:1985, Reaffirmed 2010
- Cone penetrometer
- Evaporation dishes
- Air tight containers
- Spatula, 425 micron IS sieve
- 45cm square and 10mm thick glass plate, pallet knives,
- Balance of 0.1 gm accuracy,
- Oven thermostatically controlled.
Liquid limit of Soil :
- Take 150gm of soil from the material sieved from 425micron IS sieve in evaporation dish and mix with water thoroughly to form paste.
- Place a portion of paste in the cylindrical cup of cone penetrometer apparatus insuring no air in trapped in this wet soil. Level this wet soil up-to the top of the cup and paced on the base of the cone penetrometer apparatus.
- Adjust the penetrometer so that the cone point just touches the surface of the soil paste in the cup clamped in this position. Adjust initial reading to zero. Release the vertical clamp allowing the cone to penetrate into soil paste under its own weight.
- Note the penetration of the cone after 5 seconds to the nearest millimetre. Repeat the test with suitable adjustments to moisture either by addition of more water or exposure of the spread paste on a glass plate for reduction in moisture content if the difference in penetration lies between 14 and 28 mm. Repeat the test atleast to have four sets of values of penetration in the range of 14 to28 mm. From each set of sample some soil shall be kept in different containers for determination of moisture content.
Prepare a graph for Liquid Limit
- Take 30gm of soil from the above representative soil, mix with water on the glass plate till the soil mass becomes plastic enough to be easily moulded between fingers.
- A ball weighing approx. 8gm shall be formed, rolled between fingers and the glass plate with just sufficient pressure to roll the mass of soil to form a uniform diameter of 3mm throughout its length, at a rate of 80-90strokes/minute. The soil is kneaded together to a uniform mass and rolled again this process of kneading and rolling shall be continued until the thread of 3mm diameter just crumbles with no pressure and the soil no longer can be rolled.
- The pieces of crumbled threads are to be collected in an airtight container and moisture content is to be determined.
Two tests are to be done on each soil sample.
Plasticity Index (%) = Liquid Limit (%) – Plastic Limit (%)
- Liqiud limit test by Casagrande Apparatus
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