Determining the Shrinkage Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 106

Glass plate (with three metal prongs; see Figures 9-2 and 9-3)
Graduate (glass) (see Figure 9-3)
Balance (with accuracy to 0.1 g)
Mercury
Petroleum jelly
Shallow pan [about 20 by 20 by 5 cm (8 by 8 by 2 in.) deep, nonmetallic
(preferably glass) pan used to contain accidental mercury spills]

ASTM D 421 gives specific instructions for preparing soil samples for
particle-size analysis (see Chapter 10) and determining soil constants,
including shrinkage limit. The general soil preparation procedure is to
air-dry samples first and then pulverize them. A pulverized sample is
passed through a No. 40 sieve, and the portion of the sample that passed
through is used for determining the shrinkage limit. Approximately 80 g
should be used in finding the shrinkage limit of a soil.

PREPARATION OF
TEST SAMPLE

The general procedure for determining shrinkage limit is begun by plac-
ing the sample in an evaporating dish and mixing it with enough dis-
tilled water to fill the soil voids completely. After the shrinkage dish is
coated with petroleum jelly, wet soil is taken from the evaporating dish
with the spatula and placed in the shrinkage dish. This should be done
in three parts, with steps taken each time to drive all air out of the soil.
After the shrinkage dish and wet soil are weighed, the soil is set aside
to dry in air. It is then oven-dried overnight, after which the shrinkage
dish and dry soil are weighed again. After the oven-dried soil pat is
removed from the shrinkage dish, its volume can be determined by mer-
cury displacement. The weight and volume of the empty shrinkage dish
must also be determined. The latter (i.e., the volume of the shrinkage
dish) is also done by mercury displacement, and it is the same as the vol-
ume of the wet soil pat. With these data known, the shrinkage limit and
shrinkage ratio can be determined by formulas.
The actual step-by-step procedure is as follows (ASTM D 427-04 [1]):

PROCEDURE

(1) Place the soil in the evaporating dish and thoroughly mix with
distilled water. The amount of water added should produce a soil of
the consistency somewhat above the liquid limit (Chapter 7) based
on visual inspection. In physical terms, this is a consistency that is
not a slurry but one that will flow sufficiently to expel air bubbles
when using gentle tapping action. It is desirable to use the mini-
mum possible water content. This is of some importance with very
plastic soils so that they do not crack during the drying process.

(2) Coat the inside of the shrinkage dish with a thin layer of petro-
leum jelly, silicone grease, or similar lubricant to prevent the adhe-
sion of the soil to the dish. Determine and record the mass in grams
of the empty dish, M T .