Determining the Liquid Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 79

(2) Dry Preparation:

(2.1) Dry the specimen at room temperature or in an oven at a tem-
perature not exceeding 60°C until the soil clods will pulverize read-
ily. Disaggregation is expedited if the material is not allowed to
completely dry. However, the material should have a dry appear-
ance when pulverized.

(2.2) Pulverize the material in a mortar with a rubber-tipped pes-
tle or in some other way that does not cause breakdown of individ-
ual particles. When the coarse particles found during pulverization
are concretions, shells, or other fragile particles, do not crush these
particles to make them pass a 425-µm (No. 40) sieve, but remove by
hand or other suitable means, such as washing. If a washing pro-
cedure is used, follow (1.2.1)-(1.2.4).

(2.3) Separate the sample on a 425-µm (No. 40) sieve, shaking the
sieve by hand to assure thorough separation of the finer fraction. Re-
turn the material retained on the 425-µm (No. 40) sieve to the pul-
verizing apparatus and repeat the pulverizing and sieving
operations. Stop this procedure when most of the fine material has
been disaggregated and material retained on the 425-µm sieve con-
sists of individual particles.

(2.4) Place material remaining on the 425-µm (No. 40) sieve after
the final pulverizing operations in a dish and soak in a small amount
of water. Stir this mixture and transfer it to a 425-µm (No. 40) sieve,
catching the water and any suspended fines in the washing pan.
Pour this suspension into a dish containing the dry soil previously
sieved through the 425-µm sieve. Discard material retained on the
425-µm sieve.

(2.5) Proceed as described in (1.2.3) and (1.2.4).

The liquid limit device should be inspected prior to use to ensure that it
is in good working order. In particular, the height to which the cup is
raised prior to dropping it onto the base should be checked. At the raised
position, the distance from the bottom of the cup (measured from the
point where it touches the base when dropped) to the base should be
10 ± 0.2 mm (0.3937 ± 0.0079 in.) (see Figure 7-5). If the distance is
incorrect, the device should be adjusted accordingly.

ADJUSTMENT OF
MECHANICAL
DEVICE

As mentioned previously, the liquid limit is identified in the laboratory
as that water content of the soil at which a groove of standard width is
closed a distance of 1 ⁄ 2 in. when jarred in a standard manner by exactly
25 drops (or blows) from a height of 1 cm in a liquid limit device. Hence,
the general procedure is to place a sample in the brass cup of the liquid
limit device, cut the standard groove, and then count the number of drops
of the device that are required to close the groove. If the number of drops
turns out to be exactly 25, the water content of the sample could be de-
termined, and it would be the liquid limit. This would happen only by

PROCEDURE