Determination of water content

 Determination of water content with various method:-

• Water content is an important parameter of the soil, which influences the behaviour of soil.
• Water content and unit weight changes during transportation and storage. Hence it is important to determine it before doing any other tests.
• Water content is a quantitative measure of the wetness of the soil mass.
• Water content can be determined with high accuracy.
• Water content is also important because some physical properties are calculated using water content following the practical measurements of others. e.g. dry unit weight from bulk unit weight.
• The water content of a soil can be determined by anyone of the following method-

            1) Oven Drying Method

            2) Torsion Balance Method

            3) Pycnometer Method

            4) Sand Bath Method

            5) Alcohol Method

            6) Calcium Carbide Method

            7) Radiation Method

 

1) Oven Drying Method:-

• It is a standard laboratory method of determining water content.
• It is the simplest and most accurate method.
• Oven drying can remove all water (Gravity water, Capillary water and Hydroscopic water) in the soil except structural water.
• The soil sample is taken in a small, non-corrodible, airtight container.
• The mass of the sample and container is obtained by a weighing balance.
• The quantity of the sample to be taken for the taste depends upon the gradation, the maximum size of the particle and the degree of wetness.
• More quantity of sample shall be taken for drier soil.
• The soil sample in the container is then dried in an oven at a temperature of 105⁰ -110⁰C for 24 hours.
• The temperature higher than 110⁰C may cause breaking down of the crystalline structure of the soil and loss of chemically bond structural water.
• The temperature lower than 110⁰C may not cause complete evaporation of water from the soil.
• Highly organic soil is dried in an oven at a lower temperature of 60⁰Cbecause at higher temperature organic matter get oxidised.
• The soil containing Gypsum is dried at a temperature of 80⁰C, because at a higher temperature gypsum loses its structural water.
• For complete drying, sandy soil takes about 4 hours and fat clays take about 14 to 16 hours.
• Usually, the sample is dried for about 24 hours in the oven to assure complete drying.
• A clean non-corrodible container with lid is taken and its weight is found as W₁.
• A sample of moist soil is placed in the container and the lid is replaced. The weight of the container with the sample is found as W₂.
• The container is then placed in an oven for drying with the lid removed at a temperature of 110⁰C for 24 hours.
• After drying, the container is removed from the oven and allowed to cool. The weight of the container with dry soil is found as W₃.
• The water content can be calculated as-

                               Water content, 

           Where-

                       W1 = Weight of clean container

                       W2 = Weight of clean container + Moist sample

                       W3 = Weight of clean container + Dry sample