To determine the water content in soil by calcium carbide
method as per IS: 2720 (Part II) - 1973.
It is a method for rapid determination of water content from the
gas pressure developed by the reaction of calcium carbide with
the free water of the soil. From the calibrated scale of the
pressure gauge the percentage of water on total mass of wet soil
is obtained and the same is converted to water content on dry
mass of soil.
METALLIC PRESSURE VESSEL
i) Metallic pressure vessel, with a clamp for sealing the cup,
alongwith a gauge calibrated in percentage water content
ii) Counterpoised balance, for weighing the sample
iii) Scoop, for measuring the absorbent (Calcium Carbide)
iv) Steel balls - 3 steel balls of about 12.5mm dia. and 1 steel
ball of 25mm dia.
v) One bottle of the absorbent (Calcium Carbide)
PREPARATION OF SAMPLE
Sand - No special preparation. Coarse powders may be ground
Cohesive and plastic soil - Soil is tested with addition of steel
ball in the pressure vessels.
The test requires about 6g of sample.
i) Set up the balance, place the sample in the pan till the
mark on the balance arm matches with the index mark.
ii) Check that the cup and the body are clean.
iii) Hold the body horizontally and gently deposit the levelled,
scoop-full of the absorbent (Calcium Carbide) inside the
iv) Transfer the weighed soil from the pan to the cup.
v) Hold cup and chamber horizontally, bringing them together
without disturbing the sample and the absorbent.
vi) Clamp the cup tightly into place. If the sample is bulky,
reverse the above placement, that is, put the sample in the
chamber and the absorbent in the cup.
vii) In case of clayey soils, place all the 4 steel balls (3 smaller
and 1 bigger) in the body alongwith the absorbent.
viii) Shake the unit up and down vigorously in this position for
about 15 seconds.
ix) Hold the unit horizontally, rotating it for 10 seconds, so that
the balls roll around the inner circumference of the body.
x) Rest for 20 seconds.
xi) Repeat the above cycle until the pressure gauge reading is
constant and note the reading. Usually it takes 4 to 8
minutes to achieve constant reading. This is the water
content (m) obtained on wet mass basis.
xii) Finally, release the pressure slowly by opening the clamp
screw and taking the cup out, empty the contents and clean
the instrument with a brush.
REPORTING OF RESULTS
The water content on dry mass basis,
w=(m/(100-m)) X 100 %