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Appendix C: Determining Volumetric Moisture
Content
(Weight Method
–
In Laboratory)
Procedure Overview
The following procedure describes a method to determine the volumetric moisture content of a
soil sample. A soil sample of a known volume is taken, and its weight is recorded. The soil sam-
ple is dried. The loss of weight is due to loss of water, this can be used to calculate the volu-
metric moisture content.
Equipment Required
•
Soil sampling ring of known volume (see below for requirements)
•
Digital scale with minimum resolution of one tenth of a gram, e.g. 0.1 grams
•
Trowel
•
Plastic scraper / tongue depressors
•
Ceramic bowl
•
Microwave oven
Soil Sampling Ring Requirements
The soil sampling ring should be a thin-walled metal cylinder. A section of metal pipe may be
used, provided the wall thickness is no more than 1.5 mm (a wall that is too thick may cause
soil compaction as the cylinder is pressed into the soil, which could introduce errors in the
measurement)
Sampling Ring calculation
Calculate the volume of the sampling ring by measuring the interior diameter and cylinder
length. The pictured example has length of 3.80 cm and interior diameter of 3.35 cm, corre-
sponding to a volume of 33.5 cm3 or 33.5 ml:
Volume of a cylinder = π * radius2 * length = π *
(diameter/2)2 * length
V = π
* (3.35 cm/2)2 * 3.80 cm
V = 33.494 cm3 = 33.5 cm3 or 33.5 ml
Sampling Method
For the most accurate results, soil must have been allowed to sit for at least one hour after wa-
ter has been applied before any moisture measurements are taken. Also, for larger soil contain-
ers, take at least three soil samples and average the results.
The volumetric moisture percentage is calculated according to the following process: