Determination of Plastic Limit

AIM

To determine the plastic limit of the soil

THEORY
Soil is used for making bricks , tiles , soil cement blocks in addition to its use as foundation for structures.

APPARATUS 
Porcelain dish, Glass plate for rolling the specimen, Air tight containers to determine the moisture content, Balance of capacity 200gm and sensitive to 0.01gm, Oven thermostatically controlled with interior of non-corroding material to maintain the temperature around 1050 and 1100C.

PROCEDURE
1. Take about 20gm of thoroughly mixed portion of the material passing through 425 micron I.S. sieve obtained in accordance with I.S. 2720 (part 1).
2. Mix it thoroughly with distilled water in the evaporating dish till the soil mass becomes plastic enough to be easily molded with fingers.
3. Allow it to season for sufficient time (for 24 hrs) to allow water to permeate throughout the soil mass
4. Take about 10gms of this plastic soil mass and roll it between fingers and glass plate with just sufficient pressure to roll the mass into a threaded of uniform diameter throughout its length. The rate of rolling shall be between 60 and 90 strokes per minute.
5. Continue rolling till you get a threaded of 3 mm diameter.
6. Kneed the soil together to a uniform mass and re-roll.
7. Continue the process until the thread crumbles when the diameter is 3 mm.
8. Collect the pieces of the crumbled thread in air tight container for moisture content determination.
9. Repeat the test to atleast 3 times and take the average of the results calculated to the nearest whole number.

OBSERVATION 
Compare the diameter of thread at intervals with the rod. When the diameter reduces to 3 mm, note the surface of the thread for cracks.

Container No.
Wt. of container + lid,W1
Wt. of container + lid + wet sample,W2
Wt. of container + lid + dry sample,W3
Wt. of dry sample = W3 - W1
Wt. of water in the soil = W3 - W2
Water content (%) = (W3 - W2)100 /(W3 - W1)

RESULT

Average Plastic Limit=...............
Plasticity Index(Ip) = (LL - PL)=............ 

Toughness Index =Ip/IF

Geotechnicial Engineering laboratory test

1. Physical properties of minerals
2. Determination of natural moisture of soil
3. Determination of specific gravity of soil
4. Sand replacement method
5. Sieve analysis-Grain distribution
6. Hydrometer analysis of soil
7. Determination of liquid limit
8. Determination of Plastic limit
9. Determination of Shrinkage limit
10. Direct shear test
11. Proctor test