SCREWS. Manipulate the screws to adjust the
height to which the cup is lifted. The point on the
cup that comes into contact with the anvil of the
machine should be exactly 1 cm above the anvil
(the upper surface of the hard-rubber base of the
machine). Check the adjustment by turning the
crank at a rate of two drops per second. You
should hear a slight click when the adjustment is
correct.
Steps in the test procedure are as follows:
1. From the prepared test material, take a
sample that weighs about 100 g and place a por-
tion in the cup above the spot where the cup rests
on the base. Squeeze the sample and spread it with
as few strokes of the spatula as possible, taking
care to prevent the air bubbles from getting
trapped within the mass. With the spatula, level
the soil as you trim it to a depth of 1 cm at the
point of maximum depth. Divide the soil in the
cup by making a groove with the grooving tool
along the center line of the cam follower or hook
that holds the cup. When you make the groove,
hold the cup in your left hand with the hook up-
ward, and draw the grooving tool, beveled edge
forward, through the material downward away
from the hook. With some soils (especially
sandy soils and soils containing organic matter),
it is not possible to draw the grooving tool through
the specimen without tearing the sides of the
groove. In such cases, make the groove with
a spatula, using the tool only for final shaping.
When made correctly, the groove is wedge-shaped
in section; it is open at the bottom for a dis-
tance equal to the width of the tip of the grooving
tool.
2. Attach the cup to the carriage and turn the
crank at a rate of two revolutions per second.
Count the blows as you continue to turn the crank
until the two halves of the soil cake come into con-
tact at the bottom of the groove along a distance
of about 1/2 in. (fig. 15-35). Record the number
of blows required to close the groove in this
manner.
After you record the number of blows, re-
move the cup from the testing device. Remix
and regroove the sample. Place the cup again
in the testing device and repeat the test. If
the number of blows on the second test dif-
fers from the number on the first by one or
less, record both numbers on the data sheet
and consider the test finished. If the number of
blows on the second test differs by more than one,
repeat the test until three successive tests give a
reasonably consistent sequence. The average of
the three is taken as the number required for the
closure.
3. Remove a slice of soil approximately the
width of the spatula (say about 10 g), extending
from the edge of the soil cake at right angles to
Figure 15-35.-Liquid limit test.
15-31
