water content of soil

Water Content of Soil | Moisture Content of Soil | Oven Drying Method4 min read

What Is Water Content of Soil

The water content of the soil is defined as the percentage of water present in soil mass by its weight. Water content data is required for the majority of soil parameter calculations.

w = weight of dry soil

Water content is usually expressed in percent.

For better results, the minimum size of most soil specimens should be approximate as given in Table -1. These data constitute ASTM Test Designation D-2216.

Maximum Particle Size in the Soil (mm) U. S. Sieve No. Minimum Mass of Soil Sample (g)
0.425 40 20
2.0 10 50
4.75 4 100
9.5 3/8  in. 500
19.0 3/4  in. 2500

IS Code For Water Content of Soil: IS 2720-2 (1973)


Equipment For Moisture Content of Soil Test

1. Moisture can(s):

Moisture cans are available in various sizes [for example, 2-in. (50.S mm) diameter and % in. (22.2 mm) high, 3.5-in. (S8.9 mm) diameter and 2 in. (50.S mm) high).

2. Oven with Temperature Control:

For drying of soil, the temperature of the oven is kept between 105°C to 110°C. A higher temperature of the oven should be avoided by the burning of organic matter in soil.

3. Balance:

The weight balance should have an accuracy of 0.01 gm for specimens having a mass of 200 g or less.


Moisture Content Test Procedure

Procedure for the Water Content of Soil test given below,

water content of soil
Moisture Content Test

1. Find out the weight empty container (W1) and also record the number.

2. Take a representative sample of soil in the container. Close the container with its cap to avoid loss of moisture.

3. Take the weight of the combined mass (g) of the closed container and moist soil (W2).

4. Remove the cap from the top of the can and place it on the bottom (of the can).

5. Put the container (Step 4) in the oven to dry the soil to a constant weight. In most cases,

24 hours of drying is enough.

6. Determine the combined mass (g) of the dry soil sample plus the can and its cap (W3).


Calculating Water Content

1. Mass or Weight of Moisture = W2 W3

2. Weight of dry soil = W3 W1

3. Water Content =

W (%) = (W2 W3) * 100 ) x W3W1

Calculate water to an accuracy of 0.1 % as appropriate based on the size of the specimen.

A sample representative calculation is given in table – 2,

Description of Soil=

Sample No=

Location=

Tested by =

Date of Test =

Observation Table

Items Container Container Container
  1 2 3
Container No: 42 31 54
Weight of container, W1 17.31 18.92 16.07
Weight of container + Wet Soil, W2   (g) 43.52 52.19 39.43
Weight of Container + Dry Soil, W3   (g) 39.86 47.61 36.13
Weight of Moisture, W2 W3 (g) 3.66 4.58 3.30
Weight of dry Soil, W3 W1 (g) 22.55 28.69 20.06
Moisture Content, w (%)= (W2 W3) * 100                                             W3 W1     16.2   16.0   16.5

Take Average of above three results =(16.2 + 16.0 + 16.5)/3 = 16.23 %

Moisture Content Formula, w (%)= (W2 W3) * 100 / (W3 W1)  

The Final Water Content of Soil is 16.23%


Important Notes

  • Most natural soils, which have gravel and sandy in nature, may have water contents up to about 15 to 20%. In natural silty or clayed soil water content can be found about 50 to 80% can be found. However, in highly organic soil and peat with water contents up to about 500% is not uncommon.
  • Different organic soil particles get decompose during oven drying at 110°C. An oven heating temperature of 110° may be too high for soils containing gypsum, as this material slowly dehydrates. As per ASTM, a drying temperature of 60°C is more appropriate for such soils.
  • It is recommended the Cooling the dry soil after oven drying (Step 5) in a desiccator. It helps to prevents the absorption of moisture from the atmosphere.

Some standard values of water content of soil for various types of natural soils in a saturated state are shown in Table 2

Soil Natural Water Content in Saturated State (%)
Loose uniforll sand 25-30
Dense uniform sand 12-16
Loose angular-grained silty sand 25
Dense angular-grained silty sand 15
Stiff clay , 20
Soft clay 30-50
Soft organic clay 80-130
Glacial till 12-16

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