Presentation on plastic limit

Presentation on Plastic limit

1. Department of Civil Engineering P. G. Section in Transportation Engineering & Planning Determination of Plastic Limit of Soil Sample Submitted by – Adersh TV P17TP008 Manish Choudhary P17TP007 Shubham Sharma P17TP002 Vivek Wagh P17TP011

2. 2 Plastic Limit The minimum water content at which a soil will just begin to crumble when it is rolled into a thread of approximately 3 mm in diameter . Reference IS : 2720 -Part V (1985)

3. Apparatus 3 Porcelain Evaporating dish – about 12 cm in diameter Spatula – Flexible with the blade about 8 cm long and 2 cm wide Glass plate about 20cm X 15 cm Containers – Airtight to determine moisture content Balance sensitive to 0.01g Oven – thermostatically controlled with interior of non corroding material to maintain the temperature between 105 C to 110 C Rod – 3 mm in diameter and about 10 cm long

4. Preparation of soil sample Soil sample passed through 425 micron IS –Sieve When both the liquid limit and the plastic limit of soil are to be determined, a quantity of soil sufficient for both the tests shall be taken for preparation of the soil At stage in the process of mixing soil and water at which mass becomes plastic enough to be easily shaped into a ball, sample must be taken for test. In case of clayey soils the plastic soil shall be kept for sufficient time(24 hours) for uniform distribution of moisture within soil

5. Procedure 5 A ball of about 8g of plastic mass is formed Ball is rolled between fingers and glass plate with sufficient pressure to roll soil mass into thread of uniform diameter throughout its length Rate of rolling = 80 to 90 Strokes/min 1 stroke = complete motion of the hand forward and back to starting point again Rolling shall be done till the threads are of 3 mm diameter

6. What if soil crushes at diameter more than 3 mm in first trial In such a case, Test must be conducted with a sample having more water content than that of previous sample

7. What if soil crushes at diameter less than 3 mm in first trial, say 2mm In such a case, the soil shall be kneaded together(crushed pieces) to a uniform mass and rolled again. This process of alternate kneading and rolling is continued till the thread crumbles under pressure required for rolling and soil can no longer be rolled into a thread Crumbling may occur when a thread has diameter greater than 3 mm At no time shall an attempt to be made to produce failure at 3 mm, by either reducing the rolling or pressure or both, and continuing the rolling without further deformation until thread falls apart

8. Determination of moisture content IS 2720: Part II -1973 – Indian Standard Method of test for soils Part II, Determination of water content Water content specimen should be discarded and should not be used for any other use Plastic Limit as an average of result from 3 specimen passing through 425 micron IS Sieve must be reported to nearest whole number. Size of particles more than 90 percent passing Minimum quantity of soil specimen to be taken for test (MASS in g) 425 micron IS Sieve 25 2 mm IS Sieve 50 4.75 mm IS Sieve 200 10 mm IS Sieve 300 20 mm IS Sieve 500 40 mm IS Sieve 1000

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10. Definition of Plasticity Index 10 Plasticity Index is the numerical difference between the Liquid Limit w% and the Plastic Limit w % w% LL PL PI = LL - PL plastic State

11. 11 Calculations Sample no Wt of wet soil (g) Wt of oven dried soil (g) Moisture content (g) Sample 1 25 20.53 21.77 % Sample 2 25 20.53 21.77% Plastic Limit as an average to nearest whole no. 22% 1. Moisture content = (Wt of Wet soil – Wt of Dry soil)*100/Wt of dry soil 2. Plasticity index = 38 – 22 = 16%

12. Plastic Limit of the given soil is 22 % Plasticity index of given soil is 16% Results Conclusions Since the Plastic Limit of the soil is <25%, as per MoRTH specifications for roads and bridges , the soil is fit to be used as a fill material, provided it satisfies the specifications for other soil parameters.

13. Factors affecting Plastic Limit Clay minerals in soil Rate of Rolling Non uniform mixing Clay content of soil Temperature

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