Water Content of Soil by Oven Drying Method

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Water Content of soil is the quantity of soil contained in a sample of soil. Generally this is expressed in ratio.
Here : s-soil (dry), v-void (pores filled with water or air),w-water, a-air. V is volume, M is mass.
Volumetric Water Content is defined by
where V w is the volume of water and V T = V s + V v = V s + V w + V a is the total volume (that is soil volume + water volume + air space).
Gravimetric water content is expressed by mass(weight) as follows:
where m w is the mass of water and m t is the bulk mass.The bulk mass is taken as the total mass, except for geotechnical and soil science applications where oven-dried soil ( m s , see the diagram) is conventionally used as m t
By Oven Drying Method we can determine the Gravimetric water content in soil as per IS: 2720 (Part II) - 1973.
PRINCIPLE
The water content (w) of a soil sample is equal to the mass of water divided by the mass of solids.
APPARATUS
i) Thermostatically controlled oven maintained at a temperature of 110 ± 5 o C
ii) Weighing balance, with an accuracy of 0.04% of the weight of the soil taken
iii) Air-tight container made of non-corrodible material with lid
iv) Tongs
SAMPLE
The soil specimen should be representative of the soil mass. The quantity of the specimen taken would depend upon the gradation and the maximum size of particles as under:
Size of particles 90 percent passing through IS Sieve
Minimum quantity of soilspecimen to betaken for test(g)
425μm
2.0mm
4.75mm
9.50mm
19mm
37.5mm
25
50
200
300
500
1000
PROCEDURE
i) Clean the container, dry it and weigh it with the lid (Weight 'W 1 ').
ii) Take the required quantity of the wet soil specimen in thecontainer and weigh it with the lid (Weight 'W 2 ').
iii) Place the container, with itslid removed, in the oven till its weight becomes constant (Normally for 24hrs.).
iv) When the soil has dried, remove the container from the oven, using tongs.
v) Find the weight 'W 3 ' of the container with the lid and the dry soil sample.
REPORTING OF RESU LTS
The water content,

An average of three determinations should be taken.
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