Objective

Student should be able to:-

Determine the liquid and plastic limit of soil samples for identification and classification of dried soil.

Knowing that the determination of these limits is also used to predict the shear strength and sediment of soil.

Theory

The Atterberg limits can be used to distinguish between silt and clay, and it can distinguish between different types of silts and clays. These limits were created by Albert Atterberg, a Swedish chemist. They were later refined by Arthur Casagrande. These distinctions in soil are used in picking the soils to build structures on top. Soils when wet retain water and expand in volume. The amount of expansion is related to the ability of the soil to take in water and its structural make up (the type of atoms present). These tests are mainly used on clay or silty soils since these are the soils that expand and shrink due to moisture content. Clays and silts react with the water and thus change sizes and have varying shear strengths. Thus these tests are used widely in the preliminary stages of building any structure to insure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents.

Plasticity index

The plasticity index (PI) is a measure of the plasticity of a soil. The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. The PI is the difference between the liquid limit and the plastic limit (PI = LL-PL). Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay.

PI and their meanings

0 – Non-plastic

(1-5)- Slightly plastic

(5-10) - Low plasticity

(10-20)- Medium plasticity

(20-40)- High plasticity

40 Very high plasticity

EQUIPMENT

equipment picture

Apparatus Casagrande

Can

Sieve # 36 (0425 mm)

Porcelain bowl

Spatula

Distilled Water

Glass plate

Pan Balance – sensitive to 0.1 gram

PROCEDURE

A. Determination of liquid limit

Description PicturePrepare about 250 grams of ground 0425 mm sieve transparent.

Check drop tray (bowl casagrade) using a calibration block size of 10 mm thick.

3) Mix the soil with distilled water earlier in the porcelain bowl until smooth with a spatula. Alliance mixture (paste) occurs when it looks creamy and uniform colour. Separate the mixture about 30 grams of mixture and place in sealed containers for plastic limit test.Fill in the earlier part of the soil mixture into the porcelain bowl until smooth the soil surface casagrade with a spatula. By using the tools for creating grooves, one groove are lined along the centre line axis through the centre of the bowl. Groove maker to be held upright to the surface of the bowlThe spin being spun at a rate of 2 cycles per second and number of blows to close the groove along the 13 mm was recorded.

Take 10 grams of soil in the valleys which are closed to determine moisture content. More land is brought out and put in bowl porcelain again. Wash and dry the bowl casagrade

The excess land in the bowl of porcelain mixed with a small increase distilled water. Repeat steps 3 to 6 at least 5 times for a total impact of between 50 and 10. Plot a graph of a straight line for moisture content versus number of blows on semi-log graph paper and determine the liquid limit the impact of land 25 times

B. Determination of plastic limit

Description Picture Divide the land which has been separated from the first program to the same three examples make it spherical.

Soil ball then rolled up with a finger on a glass plate until it forms a cylinder diameter of 3 mm. If the land has not been split, fold and roll the land ceases to be a cylinder 3mm. This is repeated until the land is split on the cylinder diameter of 3mm. Keep the Soil in a covered container for moisture content.Repeat step 2 remaining soil example

Data and analysis

Liquid limitsNo of Can 1 2 3 4 5Number of Impact

49 41 23 18 15

Can + Wet Soil Weight (g)

0.067 0.061 0.064 0.060 0.063

Can + dry soil weight (g)

0.063 0.058 0.062 0.059 0.062

Water weight (g) 0.004 0.003 0.002 0.001 0.001Can Empty Weight (g)

0.050 0.48 0.050 0.049 0.051

Dry soil weight (g)

0.066 0.057 0.059 0.057 0.059

Moisture content (%)

30.1 30 16.67 10 10

Moisture content=(Canweight+wet soil)−(Canweight+dry soil )(Canweight+dry soil)−(Canweight)

Example : (0.067−0.063)(0.063−0.050)

= 0.31

Mass of water Moisture content % = --------------------

x 100 Total weight of Solid massExample :

(0.067−0.063)(0.063−0.050)

= 0.31

0.31 x 100 = 30.1 %

Plastic limitsNo. of Can 1 2 3Can + Wet Soil Weight (g)

0.049 0.049 0.053

Can + dry soil weight (g)

0.048 0.048 0.052

Water weight (g) 0.001 0.001 0.001Can Empty Weight (g) 0.047 0.047 0.051Dry soil weight (g) 0.048 0.048 0.052Moisture content (%) 1 1 1Average Moisture content (%)

1

Moisture content=(Canweight+wet soil)−(Canweight+dry soil )(Canweight+dry soil)−(Canweight)

Example: (0.049−0.048)(0.048−0.047)

= 1

Mass of water Moisture content % = --------------------

x 100 Total weight of Solid massExample:

(0.049−0.048)(0.048−0.047)

= 1

1 x 100 = 100 %

Plasticity index = (LL – PL)

=17-1

=16 %

DiscussionThe importance of the liquid limit test is to classify soils. Different soils have varying liquid limits. Also to find the plasticity index of a soil you need to know the liquid limit and the plastic limit.

The values of these limits are used in a number of ways. There is also a close relationship between the limits and properties of a soil such as compressibility, permeability, and strength. This is thought to be very useful because as limit determination is relatively simple, it is more difficult to determine these other properties. Thus the Atterberg limits are not only used to identify the soil's classification, but it allows for the use of empirical correlations for some other engineering properties.

Different types of clays have different specific surface areas which controls how much wetting is required to move a soil from one phase to another such as across the liquid limit or the plastic limit. From this activity, it can predict the dominant clay type present in a soil sample. High activity signifies large volume change when wetted and large shrinkage when dried. Soils with high activity are very reactive chemically. Normally the activity of clay is between 0.75 and 1.25, and in this range clay is called normal. It is assumed that the plasticity index is approximately equal to the clay fraction (A = 1). When A is less than 0.75, it is considered inactive. When it is greater than 1.25, it is considered active.

Conclusion

The conclusion is, another method for measuring the liquid limit is the fall cone test. It is based on the measurement of penetration into the soil of a standardized cone of specific mass. Although the Casagrande test is widely used across North America, the fall cone test is much more prevalent in Europe due to being less dependent on the operator in determining the Liquid Limit.

The importance of the liquid limit test is to classify soils. Different soils have varying liquid limits. Also to find the plasticity index of a soil you need to know the liquid limit and the plastic limit.

Reference

University of Washington lecture notes Soil Physical Properties--Mechanics Seed, H.B. (1967). "Fundamental Aspects of the Atterberg

Limits". Journal of Soil Mechanics and Foundations Div., 92(SM4),

Das, B. M. (2006). Principles of geotechnical engineering. Stamford, CT: Thomson Learning College.

Geotechnical engineering from http://trid.trb.org/view.aspx?id=38900

Content

Atterberg limitsTest

no Title page

1 Objective 3

2 Theory 4

3 Equipment 5

4 Procedure 7

5 Data and analysis 9

6 Discussion 11

7 Conclusion 12

8 Reference 13