Title
Atterberg Limit Tests
Introduction
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.
Figure (1)
This lab is performed to determine the plastic and liquid limits
of a fine grained soil. The liquid limit (LL) is arbitrarily
defined as the water content, in percent, at which a part of soil
in a standard cup and cut by a groove of standard dimensions will
flow together at the base of the groove for a distance of 13 mm
(1/2 in.) when subjected to 25 shocks from the cup being dropped 10
mm in a standard liquid limit apparatus operated at a rate of two
shocks per second. The plastic limit (PL) is the water content, in
percent, at which a soil can no longer be deformed by rolling into
3.2 mm (1/8 in.) diameter threads without crumbling.
The Swedish soil scientist Albert Atterberg originally defined
seven limits of consistency to classify fine-grained soils, but in
current engineering practice only two of the limits, the liquid and
plastic limits, are commonly used. (A third limit, called the
shrinkage limit, is used occasionally.) The Atterberg limits are
based on the moisture content of the soil. The plastic limit is the
moisture content that defines where the soil changes from a
semi-solid to a plastic (flexible) state. The liquid limit is the
moisture content that defines where the soil changes from a plastic
to a viscous fluid state. The shrinkage limit is the moisture
content that defines where the soil volume will not reduce further
if the moisture content is reduced.
A wide variety of soil engineering properties have been
correlated to the liquid and plastic limits, and these Atterberg
limits are also used to classify a fine-grained soil.
Theory
Liquid Limit test- The liquid limit of a soil is the moisture
content, expressed as a percentage of the weight of the oven-dried
soil, at the boundary between the liquid and plastic states of
consistency. The moisture content at this boundary is arbitrarily
defined as the water content at which two halves of a soil cake
will flow together, for a distance of in. (12.7 mm) along the
bottom of a groove of standard dimensions separating the two
halves, when the cup of a standard liquid limit apparatus is
dropped 25 times from a height of 0.3937 in. (10 mm) at the rate of
two drops/second.
Plastic Limit Test- The plastic limit of a soil is the moisture
content, expressed as a percentage of the weight of the oven-dry
soil, at the boundary between the plastic and semisolid states of
consistency. It is the moisture content at which a soil will just
begin to crumble when rolled into a thread in. (3 mm) in diameter
using a ground glass plate or other acceptable surface.
Apparatus
Liquid limit device
Porcelain (evaporating) dish
Flat grooving tool with gage
Eight moisture cans
Balance
Glass plate
Spatula
Wash bottle filled with distilled water,
Drying oven set at 105C.
Figure (2)
Experimental Procedure
Liquid Limit Determination
We were calibrated the liquid limit apparatus to 10mm, falling
height using the space gauge on the grooving tool hand.
Then we were taken 100g of moist soil passing through sieve
No.40 and mix it thoroughly with distilled water to form a uniform
paste.
Next we were placed a portion of the paste in the cup of the
liquid limit devices to smooth surface off to a maximum depth of
inch, holding the tool perpendicular to the cup at the point of
contact.
After that we were turned the crank handle at a rate of two
revolutions per second, and counted the blows necessary to close
the groove in the soil for s distance of inch.
The groove was closed by us because a flow of the soil and not
by slippage between the soil and cup.
We were obtained a consistent value in the range of 10 to 50
blows had been obtained, then we were taken approximately 10g of
soil from near closed groove for a water content determination.
We were added extra water of the soil and repeated steps.
Figure (3)
Plastic Limit Determination
We were mixed thoroughly about 15g of the moist soil used for
the liquid limit test.
Then we were rolled the soil on a glass plate with the hand
until it was approximately 3mm in diameter.
Next we were repeated the step 2 with changing water content
until a 3mm diameter thread shows signs of crumbling.
We were taken some of the crumbling material obtained in step 3
for the water content determination.
Finally we were repeated step 2-4 to obtain three determinations
which could be averaged to give a plastic limit.
Figure (4)
Conclusion
The subject of the study is the liquid limit that is an
empirically determined state at which transition from a softly
plastic to liquid state occurs, therefore after its achieving soil
starts to behave as a liquid substance. The liquid limit
measurement is principal especially for finding consistency
statesplaying
adecisiverolefordeterminingthekeystandardcharacteristicsofsoilsrepresentingimportant
geotechnical parameters of fine-grained soils for investigations of
the so-called first geotechnical category. In conclusion before
realization of the tests the sample set up for 24 hours for
thepurpose of even distribution of moisture.
After we have done the experiment (Liquid limit and Plastic
Limit tests), we found that the plastic index of the soil is equal
to and the liquid limit of the soil is equal to .
References
Terzaghi, K., Peck, R.B. and Mesri, G. (1996),Soil Mechanics in
Engineering Practice3rd Ed., John Wiley & Son.
Holtz, R. and Kovacs, W. (1981),an Introduction to Geotechnical
Engineering, Prentice-Hall, Inc.
Das, B.M., 2010. Principles of geotechnical engineering. Cengage
Learning, Stamfort, U.S.A., 666 p.
Coduto, Donald et al. (2011).Geotechnical Engineering Principles
and Practices. New Jersey: Pearson Higher Education.
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