Determining the Liquid Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 81

from the soil pat but form the pat with as few strokes as possible.
Keep the unused soil in the storage dish. Cover the storage dish
with a wet towel (or use other means) to retain the moisture in
the soil.
(2) Form a groove in the soil pat by drawing the tool, beveled edge
forward, through the soil on a line joining the highest point to the
lowest point on the rim of the cup. When cutting the groove, hold
the grooving tool against the surface of the cup and draw in an arc,
maintaining the tool perpendicular to the surface of the cup
throughout its movement. In soils where a groove cannot be made
in one stroke without tearing the soil, cut the groove with several
strokes of the grooving tool. Alternatively, cut the groove to slightly
less than required dimensions with a spatula and use the grooving
tool to bring the groove to final dimensions. Exercise extreme care
to prevent sliding the soil pat relative to the surface of the cup.
(3) Verify that no crumbs of soil are present on the base or the un-
derside of the cup. Lift and drop the cup by turning the crank at a
rate of 1.9 to 2.1 drops per second until the two halves of the soil
pat come in contact at the bottom of the groove along a distance of
13 mm ( 1 ⁄ 2 in.).
Note 1 —Use of a scale is recommended to verify that the
groove has closed 13 mm ( 1 ⁄ 2 in.).
(4) Verify that an air bubble has not caused premature closing of
the groove by observing that both sides of the groove have flowed
together with approximately the same shape. If a bubble has
caused premature closing of the groove, re-form the soil in the cup,
adding a small amount of soil to make up for that lost in the groov-
ing operation and repeat (1) to (3). If the soil slides on the surface
of the cup, repeat (1) through (3) at a higher water content. If, after
several trials at successively higher water contents, the soil pat
continues to slide in the cup or if the number of blows required to
close the groove is always less than 25, record that the liquid limit
could not be determined, and report the soil as nonplastic without
performing the plastic limit test.
(5) Record the number of drops N required to close the groove.
Remove a slice of soil approximately the width of the spatula, ex-
tending from edge to edge of the soil cake at right angles to the
groove and including that portion of the groove in which the soil
flowed together, place in a weighed container, and cover.
(6) Return the soil remaining in the cup to the dish. Wash and dry
the cup and grooving tool and reattach the cup to the carriage in
preparation for the next trial.
(7) Remix the entire soil specimen in the dish adding distilled
water to increase the water content of the soil and decrease the
number of blows required to close the groove. Repeat (1) through
(6) for at least two additional trials producing successively lower