Determining the Shrinkage Limit of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 108

evaporating dish and rest the soil pat on the surface of the mercury
(it will float). Using the glass plate with the three prongs, gently
press the pat under the mercury and press the plate firmly over the
top of the cup to expel any excess mercury. Observe that no air is
trapped between the plate and mercury and, if there is, repeat the
process starting from (6.1). Measure the volume of the mercury dis-
placed into the evaporating dish either by means of the glass gradu-
ate or by dividing the measured mass of mercury by the mass density
of mercury. Record the volume in cubic centimeters (cubic feet) of the
dry soil pat, V o .

Data collected in this test should include the following:

DATA

Mass of dish coated with petroleum jelly, M T
Mass of dish coated with petroleum jelly plus wet soil, M w
Mass of dish coated with petroleum jelly plus oven-dried soil, M D
Volume of dish, V (which is equal to the volume of the wet soil pat)
Volume of oven-dried soil pat, V o

From the known mass of the dish coated with petroleum jelly, M T , mass
of the dish coated with petroleum jelly plus wet soil, M w , and mass of the
dish coated with petroleum jelly plus oven-dried soil, M D , the water con-
tent of the wet soil pat, w , can be computed using the following equa-
tions [1]:

CALCULATIONS

Initial wet soil mass M

M w M T

(9-3)

1 2

Dry soil mass 1 M o 2 M D M T (9-4)

a M

M o
M o

w 100 (9-5)

b

With the water content known, the shrinkage limit can be computed
using equation [1]:

c 1

V V o 2

ρ w

SL w d 100 (9-6)

M o

where:
SL shrinkage limit (expressed as a percentage)
w water content of wet soil in the shrinkage dish (expressed
as a percentage)
V volume of wet soil pat (same as volume of shrinkage dish), cm 3
V o volume of oven-dried soil pat, cm 3
ρ w approximate density of water equal to 1.0 g/cm 3
M o mass of oven-dried soil pat, g