Engineering Reports Examples

Liquid Limit and Plastic Limit

Description of Test Methodology:
Liquid Limit:
In this lab experiement eight equipments have been used and they are Casagrande liquid limit device, Grooving tool, Moisture cans, Porcelain evaporating dish, Spatula, Oven, Balance sensitive up to 0.01 g, Plastic squeeze bottle and paper towels.
At first the weight of three moisture cans were evaluated. Then about 250 g of air-dry soil, passed though No. 40 seived, was put into an evaporating dish. Water was added from the plastic squeeze bottle and soil was mixed to form of a uniform paste. A part of paste was placed in brass cup of the liquid limit device. Then, using the spatula, the surface of the soil in cup was smoothened so that the maximum depth of the soil is about 8 mm. After this, a groove was cut along the centre line of soil pat in the cup by grooving tool. The crank of Casagrande device was turned at the rate of about 2 revolutions per second allowing the liquid limit cup to rise and drop through a vertical distance of 10 mm oce in a revolution. Soil from two sides of cup began to flow toawards centre. The number of blows, N, was counted for the groove in soil to close through a distance 0.5 inch. After closing the cover of can, the weight of can was determined. After this, the rest of soil paste was removed from the cup to evaporatinf dish and paper towels were used to thoroughly clean the cup. These steps were repeated and three moisture cans were put in the oven to dry to constant weight (W3).

Plastic limit:

At first approx. 20 grams of samplw was put in to porcelain dish and water was added and mixed with the sample. Weight of moisture can was taken and recorded as W1. From the moist soil several ellipsoidal-shaped soil masses was prepared by squueezing the soil with fingure. After this, the soil mass was rolled on a ground glass plate using palm of hand. The rolling was done at rate about 80 strokes per minute. When the diameter of the thread became 1/8 inch, it was broke into several small pieces and squeezed with fingers to form an allipsoidal mass gain. These steps were repeated until the thread crumbled into several pieces. In the next step, small crumbled pieces were collected in moisture can and closed. After taking the combined weight of moisture can plus wet soil (W2), the cap was removed from the top of can and the can was placed on oven. After about 24 hours, the can was removed from the oven and the weight of the can plus dry soil ( W3) were taken.

Test Results:

Liqui limit test:
Following graph of Moisture content (%) vs. No. of Blows can be found from above table.

Liquid limit (LL) : 25.4

Flow Index: F = w1(%) – w2 (%) /( log N2 – log N1) = (23.7 -27.1)/( log 23 – log 30) = 29.06

Plastic limit test:

Average plastic limit = PL = (16.7 + 14.6)/2 = 15.65
Plasticity Index = PI = LL – PL = 25.4 – 15.65 = 9.75

Discussion:

Conclusion:
The experiment was carried out safely. By performing the experiment, the procedure to determine liquid limit, plastic limit, plasticity index, flow index of a particular soil sample was known. However, experimental value deviated from the theoretical value due to some probable sources of errors. If we would take care to eradicate those error during the experiment, expected results could be achieved.