WATER CONTENT DETERMINATION (BY OVEN DRYING METHOD)

OBJECTIVE

To determine the amount of water or moisture present in the given quantity of soil in terms of its dry weight.

NEED AND SCOPE OF THE EXPERIMENT

In almost all soil tests natural moisture content of the soil is to be determined. The knowledge of the natural moisture content is essential in all studies of soil mechanics. To sight a few, natural moisture content is used in determining the bearing capacity and settlement. The natural moisture content will give an idea of the state of soil in the field.

THEORY

Water content or moisture content determination is a routine laboratory test, the results of which are used in evaluation of different important engineering properties of soil. The determination of moisture content involves removing of soil moisture by oven-drying a soil sample until the weight remains constant. The moisture content is expressed in percentage and is calculated from the sample weight before and after drying.

Mathematically it can be written as;

W_w       = Weight of Soil Water

W_s        = Weight of Soil Solids

APPARATUS

1.     Moisture tins

2.     Weighing balance (Least count of 0.01 grams)

3.     Drying oven (temperature control at 110 ± 5 ^OC)

PROCEDURE

1.     Take empty, clean moisture tin and mark it with an identifying number or code.

2.     Weigh the container and record the weight as W₁ to the nearest 0.01 grams.

3.     Take representative wet soil sample (not less than 20 grams) and place it quickly in the moisture tin.

4.     Weight the moisture tin with wet soil sample to the nearest 0.01 gram and record this weight as W_2.

5.     Place the moisture tin with the wet soil sample in drying oven at constant temperature of 110 ± 5 ^OC for 24 hours.

6.     After 24 hours remove the moisture tin from drying oven and weigh it to the nearest 0.01 gram. Record this weight as W₃.

PRECAUTIONS

1.     If it is not possible to place the container carrying wet soil sample in drying oven immediately, cover the container with lid.

2.     If it is suspected that gypsum is present in the soil, the soil sample should not be subjected to a temperature beyond 60 ^oC. Otherwise gypsum will lose its water of crystallization affecting thereby the results of moisture content. Oven drying at 60^oC may, however, be continued for a longer time in order to ensure complete evaporation of free water present in the sample.

OBSERVATIONS AND CALCULATIONS

Where;

W₁ = Weight of tin                           =                                  (grams)

W₂ = Weight of moist soil + tin       =                                  (grams)

W₃ = Weight of dried soil + tin        =                                  (grams)

Can No.
Wt. of wet soil + can (grams)
Wt. of dry soil + can (grams)
Wt. of can (grams)
Wt. of dry soil (grams)
Wt. of moisture (grams)
Water content (%)

Moisture content, w =     %

REFERENCE

ASTM D2216-98

Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass.

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