Determining the Liquid Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 77

with distilled or demineralized water on the glass plate or mixing
dish using the spatula. If desired, soak the material in a
mixing/storage dish with a small amount of water to soften the ma-
terial before the start of mixing. If using Method A (see page 80),
adjust the water content of the material to bring it to a consistency
that would require about 25 to 35 blows of the liquid limit device to
close the groove (Note 1). For Method B (see page 82), the number
of blows should be between about 20 and 30 blows.
(1.1.2) If, during mixing, a small percentage of material is encoun-
tered that would be retained on a 425-µm (No. 40) sieve, remove these
particles by hand (if possible). If it is impractical to remove the
coarser material by hand, remove small percentages (less than about
15%) of coarser material by working the material (having the above
consistency) through a 425-µm sieve. During this procedure, use a
piece of rubber sheeting, rubber stopper, or other convenient device
provided the procedure does not distort the sieve or degrade material
that would be retained if the washing method described in (1.2) were
used. If larger percentages of coarse material are encountered during
mixing, or it is considered impractical to remove the coarser material
by the procedures just described, wash the sample as described in
(1.2). When the coarse particles found during mixing are concretions,
shells, or other fragile particles, do not crush these particles to make
them pass a 425-µm sieve, but remove by hand or by washing.
(1.1.3) Place the prepared material in the mixing/storage dish,
check its consistency (adjust if required), cover to prevent loss of
moisture, and allow to stand (cure) for at least 16 h (overnight).
After the standing period and immediately before starting the test,
thoroughly remix the soil.
Note 1 —The time taken to adequately mix a soil will vary
greatly, depending on the plasticity and initial water content.
Initial mixing times of more than 30 min may be needed for
stiff, fat clays.
(1.2) Material Containing Particles Retained on a 425 -µ m (No. 40)
Sieve:
(1.2.1) Place the specimen (see first paragraph in this section) in a
pan or dish and add sufficient water to cover the material. Allow
the material to soak until all lumps have softened and the fines no
longer adhere to the surfaces of the coarse particles (Note 2).
Note 2 —In some cases, the cations of salts present in tap water
will exchange with the natural cations in the soil and signifi-
cantly alter the test results if tap water is used in the soaking
and washing operations. Unless it is known that such cations
are not present in the tap water, distilled or demineralized
water should be used. As a general rule, water containing more
than 100 mg/L of dissolved solids should not be used for
washing operations.