ASIAN DEVELOPMENT FOUNDATION COLLEGE
TACLOBAN CITY
CIVIL ENGINEERING DEPARTMENT
NAME:________________________________ COURSE AND YEAR: __________________
Date Performed: _________________________ Date Due: _____________________________
CE 202
MATERIAL TESTING
Experiment No. 5
LIQUID LIMIT AND PLASTIC LIMIT OF SOIL
OBJECTIVE:
To introduce the student to the procedure for determining the liquid limit and plastic limit
of soil.
EQUIPMENT:
Liquid limit device with grooving tool
moisture cups
plastic limit plate
soil mixing equipment
weighing scale
sieve no. 40
GENERAL DISCUSSION:
The liquid and plastic limit of soils has been widely used mainly for soil identification
and classification. Liquid limit is the water content of the soil when a pat of soil placed in a brass
cup, cut with a standard groove, and then dropped from a height of 1 cm will undergo a groove
closure of 12.7 mm when dropped 25 times. The test is affected by the following factors:
a. size of the soil pat in brass cup ( thickness and quantity)
b. rate of blows ( 120 rpm)
c. time the soil is in the cup before start of test and how clean is the cup
d. laboratory humidity and speed of performing the test
e. type of material used for liquid limit device base
f. accuracy of height of fall calibration
g. type of grooving tool
h. condition of the liquid limit device
These factors are operator-controlled.
The liquid and plastic limit tests are performed on soils passing no. 40 sieve. The soil
must be air dried. Oven drying may lower the values of both the liquid limit and plastic
limit. Since it is difficult to have the exact water content corresponding to 25 blows to
obtain a 12.7 mm groove closure, it is more convenient to have at least 4 trials using
different water content. The results are plotted on a semi-logarithmic paper with the
number of blows on a log scale and water content on the normal scale. To get the liquid
limit, the 25 blows is projected upward to intersect the plotted line then projected to the
vertical to obtain the value of the limit. For faster result, the one point method may be
used using the formula:
LL= wn ( N/25 ) 0.121
Good results can be obtained if the water content is taken for an N count between
20- 30. The liquid limit is a measure of the shear strength of soil at some water content..
Each blow to close a standard groove corresponds to about 1 gram per square cm of shear
strength. It was also found out that as the grain sizes decreases the liquid limit increases.
On the other hand, plastic limit is the lower boundary range of plastic behavior of
soil, tend to increase in numerical value as grain sizes decreases. It is defined as the water
content at which the soil start to crumble when rolled into 1/8 inch diameter thread at 80-
90 strokes per minute. The test is more or less subjective in the sense that it depends on
the observation of the performer ( when he considers as 1/8 inch and crumbling point).
The result might be checked by three or more technicians with the percentage difference
of between 1 to 3 %.
PROCEDURE:
A. LIQUID LIMIT TEST
1. Each group will pulverize a sufficient quantity of air dried soil to obtain a
representative sample passing no. 40 sieve. Be sure to discard the residue
remaining of the sieve into waste cans as this material are no longer
representative of soil passing no. 40 sieve.
2. Check the height of fall of the liquid limit device. It should be exactly 1.0 cm
measured from the worn spot on the base of the cup to the platform. Check the
condition of the apparatus.
3. Place about 250 grams of soil on a porcelain mixing dish, add a small amount
of water and mix thoroughly until the color is uniform. Continue to add more
water in small amounts mixing the soil to uniform color after each addition
until; stickiness is attained.
4. Place a small amount of soil to the correct depth of the grooving tool, well
centered in the cup with respect to the hinge. Smooth the surface of the soil
pat carefully, and using the grooving tool, cut a clean, straight grove that
completely separates the soil pat into two parts. See to it that the thickness of
the soil in the deepest portion is exactly 1.0 cm.
5. After making the groove, quickly attached the cup to the device and make the
blow count. Unnecessary delay will cause some error in the blow count. The
effect can be shown in the plotting of data which will produce an erratic locus
of points. Application of blows is done until a 12.7 mm groove closure is
attained.
6. Take a moisture sample form the closed part of the groove of about 40 grams.
Determine its moisture contents and record the corresponding number of
blows.
7. Place back the remainder of the soil to the porcelain dish. Wash and dry the
brass cup.
8. Add small amount of water to the soil in the porcelain dish and mix to
uniform color.
9. repeat procedure for additional test. Make four trials having blow counts
between 15 and 20, 20 and 25, 25 and 30.
10. Plot the result in a semi-log with the number of blows in the log scale and the
moisture content on the normal scale. Determine the liquid limit by projecting
the 25 blow point intersecting the average line connecting the points and
projecting it to the vertical axis obtaining the corresponding water content.
This is the liquid limit of the soil.
B. PLASTIC LIMIT.
1. Place about 250 grams of soil passing no. 40 sieve into a porcelain dish and
add a small amount of water then mix thoroughly to a uniform color. Add
small amounts of water mixing to uniform color for each addition until
stickiness.
2. Each group member will take a small lump soil from the porcelain dish and
then roll the soil between the fingers and a glass plate with sufficient pressure
to form a uniform diameter thread using about 80-90 strokes per minute.
When the diameter of the soil thread becomes 3.0 mm, break thread into
several pieces, reform into a ball and reroll. Continue this rolling and reballing
until the thread crumbles under the pressure of rolling and the soil can no
longer be rolled into thread.
3. Repeat this sequence several times adding each test to the moisture can. For
groups of several members, the test performed by each member will serve as
trials. Each member will place his tested soil into a common moisture can to
eliminate several weighings.
4. Determine the moisture content. This corresponds to the plastic limit.
5. Compute the plasticity index.
6. Fill up the data chart provided.
COMPUTATIONS:
DISCUSSION OF RESULT
CONCLUSION:
Checked by: ___________________
Date: ________________________
ATTERBERG LIMITS
A. Liquid Limit Test
1 2 3 4
Number of blows
Weight of container + wet soil
Weight of container + dry soil
Weight of water
Weight of container
Weight of dry soil
Water content, %
B. PLASTIC LIMIT TEST
1 2 3 4 5
Container number
Weight of the container + wet soil
Weight of the container + dry soil
Weight of water
Weight of the container
Weight of dry soil
Water content, %
RESULT:
Natural Moisture content : _________________________
Plastic Limit : _________________________
Liquid Limit : _________________________
Plasticity Index : _________________________
Liquidity Index : _________________________
Shrinkage Limit : _________________________
Remarks:
___________________________________________________________________________
