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Determining Water Content In Soil – Calcium Carbide Method

This test is done 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.

Apparatus required :-
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)

Sand – No special preparation. Coarse powders may be ground and pulverized. Cohesive and plastic soil – Soil is tested with addition of steel ball in the pressure vessels. The test requires about 6g of sample.

Procedure to determine Water Content In Soil By Calcium Carbide Method
carbon-carbide-methodi) 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 chamber.

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 along with 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.


The water content on dry mass basis,
w=m/[100-m] * 100%

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Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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22 comments on "Determining Water Content In Soil – Calcium Carbide Method"

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mohanlal says:

i always prefer to calculate the moisture content through rapid moisture meter but unfortunately the scoop measurment spoon has lost so i want to know that what quantity of calc. carbide use. if the qty. of the chemical varries other than specified what variations may occur in the test results.

Randhir Singh says:

Please ordered for new scoop as for safety as well as excat quantity it is must

sangita says:

hi…please anyone help me.

should we use the steel balls for clayey soils only?

for other soils,do we need to start shaking the system vertically with the gauge pointing downwards?

Randhir Singh says:

Yes as per IS 2720 part II you have to use steel balls for clayey soils onlyIn case of clayey soils and pastes, place the 3 smaller and one bigger steel balls in the body along with the absorbent and place the soil sample into the cup & seal up the unit as usual. Hold the rapid moisture meter vertical with the cup downwards and allow the absorbent with the balls to fall into the cup. Shake the unit up and down vigorously in this position for about 15 seconds. Now invert the unit and allow the material to fall into the body. Now holding the unit horizontally, rotate it for 10 seconds so that the balls are rolled round the inside circumference of the body. Rest for 20 seconds. Repeat the rotation–rest cycle until the gauge reading is constant (usually this takes 4 to 8 min). Note the reading as usual.

rana rizwan says:

i want to get labell diagram of every part of apparatus….plzZ help me in doing so……..!

Randhir Singh says:

Please refer to handbook of quality assureance part II published by MORD

Kalla sankararao says:

sir i want to know method of rapid moisture meter calibration

mehul nair says:

for which type of soils calcium carbide methods cannot be used?please send me a very clear answer

deepakkumar says:

for which type of soils calcium carbide methods cannot be used?please send me a very clear answer

Rosa Rodriguez says:

Does the apparatus need to be calibrated? How? How often?

Sudha pichaipilai says:

i want to test the clay soil for the following test liquid limit, plastic limit, determination of CaCo3 and specific surface area(blue methylen test). plz give the which places the lab are available and what about the cost.

kenneth ononiwu says:

I quite appreciate the contributors on this site ,keep it up.


thanx a lot………………………………….

Raghavendra Belavanki says:

How the Gauge of Rapid Moisture meter(Calcium Carbide Method) is calibrated?

deepakkumar says:

if the soil is not clay for eg. silty sand, fine sand c.t.c the how many bolls are uses to ditermine moistur in soil

Engr. Adeyemo says:

wanna knw more on soil mechanics pls

ravi says:

what type of materials can be used in rapid moisture meter calibration I.e sand or soil, if sand can be used then what is the size limits?

Sathish says:

what is the IS code for calibration of rapid moisture meter?

Chandresh sharma says:

If the number of balls get varies then how it will affect the test results.

Jaiprakash Mhetre says:

I Want to know if the result obtained ie degree
Of compaction is more than 100% in such condition what would u consist me

Debadatta says:

Soil formula used to iron ore fine.. kindly help me

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