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Determine Water Content of Soil by Oven Dry and Pycnometer Methods

Water Content of soil

Water Content of soil

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What is Water Content of Soil?

The water content of soil is is the ratio of mass of water to mass of soil which is expressed in percentage. Oven Dry Method and Pycnometer Method are commonly used to determine the water content of soil in laboratory.

1. Water Content of Soil by Oven Dry Method

The oven dry method is widely used laboratory method determine the water content or moisture content of given soil sample. It gives very accurate results.

Apparatus Required for Oven Dry Method

To determine water content by oven dry method following equipment is required.

Minimum Soil Sample Quantity

The soil sample collected from the field should be of required quantity to find the water content. The quantity of soil required is depends upon the maximum particle size and gradation of soil sample. Below table shows the soil quantity required for test based on the sieve analysis.

Table 1: Minimum Quantity of Soil Required for Water Content Determination

Size of particles more than 90% of passing Minimum Quantity ( grams)
425 micron sieve 25
2 mm sieve 50
4.25 mm sieve 200
10 mm sieve 300
20 mm sieve 500
40 mm sieve 1000

Fig 1: Wet Soil Sample

Test Procedure of Oven Dry Method

The test procedure of Oven Dry method to find the moisture content of soil consists following steps.

Fig 2: Placing Containers in Oven

Observations and Calculations of Oven Dry Method

The data collected during the test is noted in below data sheet. From this data the water content of given soil sample is calculated by the below shown formula Where     M1= Mass of empty container with lid, M2= Mass of the container with wet soil and lid, M3= Mass of the container with dry soil and lid. Table 2: Observations and Calculations of Oven Dry Method
Sl. No. Observations and Calculations Determination No.
1 2 3
Observation
1 Container No.
2 Mass of empty container (M1)
3 Mass of container + soil (M2)
4 Mass of container + dry soil (M3)
Calculations
5 Mass of water Mw= M2 – M3
6 Mass of solids, Ms= M3 – M1
7 Water content= (5)/(6)x100

Result of Oven Dry Method

Water content of the given soil sample = ______%.

2. Water Content of Soil by Pycnometer Method

Pycnometer method is also useful to determine water content. But this is used when the specific gravity of the given soil sample is already known. However, Specific gravity can also be determined using pycnometer. Read also: Specific Gravity of Soil by Pycnometer Method

Apparatus Required for Pycnometer Method

Apparatus used in pycnometer method are

Fig 3: Pycnometer Bottle

Test Procedure of Pycnometer Method

Test procedure of pycnometer method is as follows

Observations and Calculations of Pycnometer Method

The water content (w) of the soil sample using pycnometer method is calculated from the below formula Where   M1=mass of empty Pycnometer, M2= mass of the Pycnometer with wet soil M3= mass of the Pycnometer and soil, filled with water, M4 = mass of Pycnometer filled with water only. G= Specific gravity of solids. Table 2: Observations and Calculations of Pycnometer Method
Sl. No. Observations and Calculations Determination No.
1 2 3
Observation
1 Mass of empty pycnometer (M1)
2 Mass of pycnometer + wet soil (M2)
3 Mass of Pycnometer soil filled with water (M3)
4 Mass of Pycnometer filled with water only (M4)
Calculations
5 M2 – M1
6 M3 – M4
7 (G – 1) / G
8 w (using above formula)

Result of Pycnometer Method

Water content of the given soil sample = _______%.
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