General

• Index properties are used in the identification and determination of soils for engineering purposes. In this chapter we are going to deal with the determination the index properties of the soils, Here is the list of index properties of soils.

  1. Water Content

  2. Specific Gravity

  3. In-situ Density

  4. Density Index

  5. Consistency Limits

  6. Particle Size Distribution

Water Content

• This is the list of the mehthods which are used to determine the water content of a soil sample.

  1. Oven drying method

  2. Sand bath method

  3. Alcohol method

  4. Calcium Carbide method

  5. Pycnometer method

  6. Radiation method

  7. Torsion balance method

1. Oven Drying Method

• This is the most accurate and preferable method of determining the water content and is therefore extensively used in the laboratory.

Procedure:

1. A container with an interior of non-corroding  material is taken and its mass is found with its lid, on a balance accurate to 0.01 g. (M1)

2. The mass of a specimen of the moist soil sample is taken by placing it in the container along with its lid on it. (M2)
   Note: add table

3. Now, the lid is removed and the container is placed in the thermostatically controlled oven for drying in which the temperature is maintained between 105℃ to 110℃ for 24 hrs.
   Note: For complete drying of,
   Sandy soils: about 4 hrs.
   Fat clays; 14-16 hrs.

For highly organic soils, such as Peat: 60℃ is preferable to prevent oxidation of organic matter.
For soils containing Gypsum: 80℃ but longer duration to prevent loss of water of crystallisation in it. (as per IS:2720 Part-II 1969)

• Usually, the sample is dried for 24 hrs to ensure complete drying.

• Temperature higher than 110℃ may break the crystalline structure of clay particles, resulting in the loss of chemically bonded structural water, especially in fat clay soils.