lab sheet - atterberg limits

CIVIL ENGINEERING DEPARTMENT

CC304 – GEOTECHNICAL 1

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NO. PARTICAL WORK :

TITLE OF PARTICAL WORK : ATTERBERG LIMITS

OBJECTIVE :

These tests are conducted to obtain the liquid and plastic limits of a soil sample for the purpose of

identification and classification of the soil. The determination of these limits is also used to predict the sheer

strength and settlement of soil. THEORY :

The engineering behaviors of fine-grained soil depend on factors other than particle size distribution. It is

influenced primarily by their mineral and structural composition and the amount of water they contain, which

is referred to as water content (or moisture content). The liquid and plastic limits tests characterize the

effects of water content on fine-grained soils and help to classify fine-grained soils and to assess their

mineral composition and engineering properties.

Water Content :

Soils are made of solid particles with voids between. These voids are generally filled with air and

water. The water content w of a soil iso

w = Ww x 100 (%)

Ws

Where Ww is the weight of water removed from the soil by oven drying at 105 o to 110oC and Ws is

the weight of the dried soil. A soil is considered to be dry when its mass does not change by oven

drying, which may usually require about 12 to 24 h.

Liquid and Plastic Limits

The mechanical properties of a clay are altered by changing the water content. A clay softens when

water is added, and with sufficient water, forms a slurry that behaves as a viscous liquid; this is

known as the liquid state. If the water content is gradually reduced by drying it slowly, the clay

eventually begins to hold together and to offer some resistance to deformation; this is the plastic

state. With further loss of water, the clay shrink and its stiffness increases until it becomes brittl e;

this is the semisolid state. As dring continues, the clay continues to shrink until it reaches a constant

minimum volume. Beyond that point, further drying causes no further decrease in volume; this is the

soild state. These four states are shown in figure 1. The change from one state to the next is not

abrupt, but gradual.



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These smooth transitions are empirically defined by introducing the liquid limit LL, plastix limit PL,

and shrinkage limit SL. The moisture content between PL and LL is the plasticity index PI:

PI =LL – PL

PI is a measure of the plasticity of a clay.

The liquid and plastic limit tests provide a means of measuring and describing the plasticity

range of clay soils. Liquid and plastic limits are also referred to as Atterberg limits, after the Swedish

Scientist A. Atterberg, who first defined them for the classification of agricultural soils in 1911.

Originally, the limits were determined by simple tests using an evaporating dish (Bauer, 1959) The

procedures were defined more precisely for engineering purposes by Casagrande (1932)The

mechanical device he designed for determining the liquid limit is still known as the Casagrande

apparatus (Casagrande, 1958).

Equipment : The equipment for determination of liquid and plastic limits includes:

i. Casagrande Apparatus

ii. Moisture Content can

iii. No. 36 Sieve (0.425mm)

iv. Porcelein dish

v. Glass plate

vi. Distilled water

PROCEDURE :

This experiment is divided into two parts.



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A. Determination of Liquid Limit

1. Prepare about 250g of soil passing through 0.425 sieve.

2. Check the drop of the casagrande bowl using the spacer gage on the grooving tool

handle. This 10mm thick steel block should just pass between cup and base when the

cup is at its maximum height. Tighten the locknut after adjus tment and recheck the

maximum height with the gage.

3. The soil used for Atterberg limits should not be dried prior to testing but may be air -dried

if necessary. Mix the soil sample with distilled water on a glass plate by using a spatula

until the mixture is uniform and behaves as a soft paste that can be shaped with a

spatula. Separate approximately 30g soil mixture and place in a closed container for

liquid limit determination.

4. Put some of the soil-water mixture into the casagrande bowl and level the surface using

a spatula. Using a grooving tool, cut through the sample from back to front dividing it into

two equal halves. The grooving tool must be kept normal to the cup and its chamfered

edge in the direction of movement. The tip of the tool should scrape the bowl lightly. The

completed groove must be clean and sharp.

5. Turn the crank handle at a steady rate of two revolutions per second so that the bowl is

lifted and dropped. Continue turning until the two halves of the soil pat come in contact

at the bottom of the groove along a distance of 13mm, as shown in Figure 2. During the

test, the soil should slump and flow plastically in the bowl. Record the number of blows

required to close the groove.

6. Take about 10g soil from the bowl to determine the moisture content. The extra soil is

removed and placed into a porcelain dish. The casagrande bowl must be cleaned.

7. Mix the extra soil with more distilled water. Steps 3 to 6 are to be repeated at least 4

times to obtain a specimen between 50 to 10 blows.

8. Plot a graph, moisture content vs no. of blows on a semilog graph that produces a

straight line and determine the liquid limit at 25 blows

Reporting of results: The liquid limit shall be expressed to the nearest whole number. The percentage of material passing

the 425µm BS test sieve shall be noted.

The history of the sample shall also be noted, i.e. natural state, air dried, unknown. The method

used to obtain the result shall also be stated, i.e. one point method using the Casagrande

apparatus.

B. Determination of Plastic Limit

1. Divide the soil sample separated from procedure A to 4 samples and shape them into small

balls (1-2 cm diameter).

2. Form the balls into threads by rolling them under your fingers against the glass plate

surface. Use just enough pressure to roll the soil into a thread 3mm in diameter. If the thread



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gets smaller than 3mm without crumbling, fold and knead the thread into a ball again and

repeat the rolling process. Knead and roll the soil thread until it has dried to the point of

crumbling and breaking into numerous pieces about 3 to 9mm in length when the thread

diameter reaches approximately 3mm.

3. As soon as the soil thread crumbles, collect part of it and determine its water content.

Repeat step 2 for the rest of the soil sample and check that two successive rums give

approximately the same plastic limit.

Reporting of result: The average of the moisture contents determined shall be taken as plastic limit (PL) of the soil and

shall be expressed to the nearest whole number. If the two results dif fer by more than 0.5% moisture

content, the test shall be repeated. The percentage of material passing the 425µm BS test sieve

shall be noted. The history of the sample shall also be noted.

C. Determination of the plasticity index

The plasticity index can be calculated from the equation:

PI = LL - PL

RESULT :

Use Form 2.D of the BS 1377

Plot the Moisture content vs number of blows on the semi log graph attached.



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JKA Laboratory area, Politechnic Kota Kinabalu

A B C D

24 31 22 19

E



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CONCLUSION :

REFERENCE(S)

1. BS 1377-2:1990 – Page 9 – 14, Form 2.D at page 53.

lab sheet - atterberg limits

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