Determination of water content for soil

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 index properties of the Soil. The natural moisture content will give an idea of the state of soil in the field.

---

Apparatus

1. Container: Any suitable noncorrodible airtight container.
2. Balance: of sufficient sensitivity to weigh the soil samples to an accuracy of 0.04 percent of the weight of the soil taken for the test
3. Oven: thermostatically controlled, with interior of non-corroding material to maintain the temperature at 110 ± 5°C.
4. Desiccator: A desiccator with any suitable desiccating agent.

---

Soil Specimen

The soil specimen taken shall be representative of the soil mass. The size of the specimen selected depends on the quantity required for good representation, which is influenced by the gradation and the maximum size of particles, and on the accuracy of weighing.

Recommended quantities for general laboratory use:

Sr.	Size of Particles More Than 90 Percent Passing	Minimum Quantity of Soil Specimen to be Taken for Test, Mass in g.
1	$425~\mu m$ IS Sieve	25 g.
2.	2-mm IS Sieve	50 g.
3.	4.75-mm IS Sieve	200 g.
4.	9.5-mm IS Sieve	300 g.
5.	19-mm IS Sieve	500 g.
6.	37.5-mm IS Sieve	1000 g.

Procedure

Clean the container with lid, dry and weigh ( W₁). Take the required quantity of the soil specimen in the container crumbled and placed loosely, and weigh with lid ( W₂). Then keep it in an oven with the lid removed, and maintain the temperature of the oven at 110 ± 5°C (see Note). Dry the specimen in the oven for 24 h. Every time the container is taken out for weighing, replace the lid on the container and cool the container in a desiccator. Record the final mass (W₃) of the container with lid with dried soil sample.

Note: Oven-drying at 110 ± 5°C does not result in reliable water content values for soil containing gypsum or other minerals having loosely bound water of hydration or for soil containing significant amounts of organic material. Reliable water content values for these soils can be obtained by drying in an oven at approximately 60 to 80°C.

---

The percent of water content shall be calculated as follows:

$w = \frac{(W_2-W_3)}{(W_3-W_1)}\times 100$

Where,

• w is Water Content Percent
• W₁ is mass of container (bowl) in gram
• W₂ is mass of container (bowl) with wet soil in gram
• W₃ is mass of container (bowl) with dry soil in gram