Experiment 4 ( Plastic Limit Test)

EXPERIMENT NO 4 : PLASTIC LIMIT TEST INTRODUCTION Plastic Limit Test is conducted to determine the moisture content at the point of translation from plastic to semisolid state. The plastic limit is defined as minimum water content at which a soil will just begin to crumble when rolled into a thread of 3.2 mm in diameter.

OBJECTIVE The objective of this experiment is to determine the plastic limit of soil sample and then to calculate plasticity index.

PROBLEM STATEMENT Classification of a fine grained soil requires quantification of the soil plasticity index. Plastic limit is required for the determination of plasticity index. Hence accurate determination of soil plastic limit is required for determination of reliable plasticity index.

APPARATUS 1. 2. 3. 4. 5. 6.

Spatula Moisture containers Wash bottle containing distilled water Electronic balance sensitive to 0.1 g Large glass plate Drying oven

MATERIALS Fine grained soil sample

PROCEDURE

1. 50 g of dried soil were mixed with water sufficiently and soil paste were made. The soil paste were shaped into a ball shape, and rolled on to the glass plate with the hand pressure at rate 0f 80 – 90 strokes per minute. The rate of rolling have to be decreased for very fragile soils. 2. The mass was rolled into a thread of uniform diameter throughout its length until the thread reaches a diameter of approximately 3mm. The provided 3mm diameter rod was used as a reference. If at this point the thread begins to act brittle and crumbles then the plastic limit has been reached. If the plastic limit has not been reached then fold and knead the thread into a ball again and repeat the rolling process. The process was continued until the thread just crumble at 3mm diameter.

3. The soil thread that have been crumbled was collected and kept in the airtight container for water determination.

4. The test was repeated for two more determinations

DISCUSSION

The following moisture conditions - liquid unlit, plastic limit, along with shrinkage limit are referred to as the "Atterberg Limits", after the originator of the test procedures. Semi-Solid. StagySolid State Atterbera Limits and Indices. In this experiment, we determined the plastic limit of the soil. The plastic limit, also known as the lower plastic limit, is the water content at which a soil changes from the plastic state to a semisolid state. The following moisture conditions - liquid limit, plastic limit, along with shrinkage limit are referred to as the "Atterberg Limits", after the originator of the test procedures. Semi-Solid .Solid State Atterberg Limits and Indices. Its primary use is in association with the other Atterberg limits in soil identification and classification. In this experiment, we repeat the procedures for three times. We mixed the soil with water, ball it and rolled the ball gently until it form crumble. For the first and second, the value of water content was 23.81% and 26.67%. For the third time testing, the percentage of water content was 42.86%. From the values we can see that the percentage of water content in the third time testing shows extremely different from the first and second time testing. After calculate the average, we found that the plastic limit of soil was 31.11%. Atterberg limit is quite unreliable since the test method often give a wide range or error. When considering the plastic limit test, amount of finger pressure used and the shape of the tips of fingers varies to a great extent and, in addition, operators frequently do not carry out testing using the tips of the fingers (as specified in the Bristish Standard) since these are eminently unsuited to the task. The extensive use of plasticity testing can be most rewarding, however the low levels of accuracy coupled with high cost tend to discourage use. In order to avoid any mistakes, we should be more careful and follow all the procedures. We must consider any possibility of error that can be happen during the experiment. Besides that, we must be careful when using the apparatus in the lab in order to elude from any incident occurred in the lab. This is because we need to avoid any dangerous especially when using the oven or any chemical. We have to wear gloves when dealing with the hot oven. Wash the apparatus until it’s clean and throw the soil or any materials in the dustbin.

DATA AND OBSERVATION:

Determination No.

1

2

3

1

2

3

Mass of container + wet soil (g)

17.0

16.2

15.9

Mass of container + dry soil (g)

16.5

15.8

15.3

Mass of water (g)

0.5

0.4

0.6

Mass of container (g)

14.9

14.7

14.5

Mass of dry soil (g)

1.6

1.1

0.8

Water content (%)

23.81

26.67

42.86

Container number

1.

Sample Of Calculations: Water content for specimen of container no. 1, w

=

[(mass of water) / (mass of solids + mass of water)] x 100

=

[(0.5)/ (1.6 + 0.5)] x 100

w

=

23.81%

w

=

[(mass of water) / (mass of solids + mass of water)] x 100

=

[(0.4)/ (1.1 + 0.4)] x 100

w

=

26.67%

w

=

[(mass of water) / (mass of solids + mass of water)] x 100

=

[(0.6)/ (0.8 + 0.6)] x 100

=

42.86%

w 2.

The value plastic limit, PL is the average of the three water contents. Plastic limit,

3.

PL

=

(23.81 + 26.67 + 42.86) / 3

PL

=

31.11 %

Plasticity index, PL

=

Liquid Limit – Plastic Limit

=

40.23 – 31.11

=

13.12 %

CONCLUSION

Plastic limit is conducted to determine the moisture content at the point of transition from plastic to semisolid state. The plastic limit is defined as the minimum water content at which a soil will just begin to crumble when rolled into a thread of 3.2 mm in diameter. In this experiment, we determined the plastic limit of the soil. The plastic limit is the lower boundary range of the plastic behaviour of a given soil. Its primary use is in association with the other Atterberg limits in soil identification and classification. The four states of consistency in Atterberg limits are liquid, plastic, semisolid and solid. The dividing line between liquid and plastic states is the liquid limit; the dividing line between plastic and semisolid states is the shrinkage limit. If a soil in the liquid state is gradually dried out, it wills past through the liquid limit, plastic state, plastic limit, semisolid state and shrinkage limit and reach the solid stage. The liquid, plastic and shrinkage limits are therefore quantified in terms of the water content at which a soil changes from the liquid to the plastic state. The difference between the liquid limit and plastic limit is the plasticity index. Because the liquid limit and plastic limit are the two most commonly used Atterberg limits. For the first time testing, the percentage of water content was only 23.81%. For the second and third test, the value of water content was 26.67% and 42.86%. So, from all the values we can see that the percentage of water content not show the extremely different, and after calculate the average, we found that the plastic limit of soil was 31.11%. In the lab, we just do the experiment for liquid limit and plastic limit. We use Cassagrande method to determine the liquid limit of the sample soil. After plotting the graph, we found that the liquid limit of soil sample 44.23 % and it shows that the soil had a lot of water content.. After do the calculation using the formula, we found the plastic limit of sample soil is less than 50%. After we have done the experiment (Liquid Limit and Plastic Limit Tests), we found that the plastic index of the soil is equal to 13.12 %. From the chart we found that the type of soil was falling under silt intermediate (MI) (below A-line). So, we can conclude that the objectives of this experiment were achieved.

ATTACHMENT

Figure 1.0

Apparatus in experiment

Figure 2.0

Ellipsoidal soil mass.

Figure 3.0

Roll into uniform diameter.

Figure 4.0

Thread reach until 3mm

REFERENCES

1.

Soil Mechanics Laboratory Manual, Department of Civil Engineering Version 1 May

2. 3.

2013 R.F. Craig. Craig’s Soil Mechanics, 7th Edition. Spon Press. http://civilengineeringlaboratory.blogspot.com/2012/02/liquid-limit-and-plastic-limittests.html