Determining the Liquid Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 78

(1.2.2) When the material contains a large percentage of material
retained on the 425-µm (No. 40) sieve, perform the following wash-
ing operation in increments, washing no more than 0.5 kg (1 lb) of
material at one time. Place the 425-µm (No. 40) sieve in the bottom
of the clean pan. Transfer without any loss of material the soil-
water mixture onto the sieve. If gravel or coarse sand particles are
present, rinse as many of these as possible with small quantities of
water from a wash bottle, and discard. Alternatively, transfer the
soil-water mixture over a 2.00-mm (No. 10) sieve nested atop the
425-µm (No. 40) sieve, rinse the fine material through, and remove
the 2.00-mm (No. 10) sieve. After washing and removing as much
of the coarser material as possible, add sufficient water to the pan
to bring the level to about 13 mm ( 1 ⁄ 2 in.) above the surface of the
425-µm (No. 40) sieve. Agitate the slurry by stirring with the fin-
gers while raising and lowering the sieve in the pan and swirling
the suspension so that fine material is washed from the coarser
particles. Disaggregate fine soil lumps that have not slaked by gen-
tly rubbing them over the sieve with the fingertips. Complete the
washing operation by raising the sieve above the water surface and
rinsing the material retained with a small amount of clean water.
Discard material retained on the 425-µm (No. 40) sieve.
(1.2.3) Reduce the water content of the material passing the
425-µm (No. 40) sieve until it approaches the liquid limit. Reduction
of water content may be accomplished by one or a combination of the
following methods: ( a ) exposing to air currents at ordinary room
temperature, ( b ) exposing to warm air currents from a source such
as an electric hair dryer, ( c ) decanting clear water from the surface
of suspension, (d) filtering in a Büchner funnel or using filter can-
dles, or (e) draining in a colander or plaster of paris dish lined with
high retentivity, high wet-strength filter paper. If a plaster of paris
dish is used, take care that the dish never becomes sufficiently sat-
urated that it fails to absorb water into its surface. Thoroughly dry
dish between uses. During evaporation and cooling, stir the sample
often enough to prevent overdrying of the fringes and soil pinnacles
on the surface of the mixture. For materials containing soluble salts,
use a method of water reduction such as ( a ) or ( b ) that will not elim-
inate the soluble salts from the test specimen.
(1.2.4) If applicable, remove the material retained on the filter pa-
per. Thoroughly mix this material or the above material on the
glass plate or in the mixing dish using the spatula. Adjust the wa-
ter content of the mixture, if necessary, by adding small increments
of distilled or demineralized water or by allowing the mixture to dry
at room temperature while mixing on the glass plate. If using
Method A, the material should be at a water content that would
require about 25 to 35 blows of the liquid limit device to close the
groove. For Method B, the number of blows should be between
20 and 30. Put, if necessary, the mixed material in the storage dish,
cover to prevent loss of moisture, and allow to stand (cure) for at
least 16 h. After the standing period, and immediately before start-
ing the test, thoroughly remix the specimen.