HOW TO DETERMINE WATER CONTENT OF SOIL?

What is Water Content of Soil?

Water content of a soil mass is defined as the ratio of weight of water present in a given soil mass to the weight of dry soil.

i.e. water content = (weight of water in soil mass)/(weight of dry soil)

Water content is usually expressed in percentage (%).

water content of soil
water content of soil

How Much Sample Required for Test?

The minimum amount of sample required for the test is primarily dependent upon the maximum particle size present in that given soil mass. The table given below can be used as a reference for deciding minimum weight of moist soil sample required.

Maximum particle size in the soil (mm) Minimum weight of soil sample (g)
0.425 20
2.0 50
4.75 100
10.0 500
19.0 2500

Equipments Needed

  • Moisture cans (must be made of heat resistant material)
  • Oven with temp. control (1050c to 1100c)
  • Desiccator (used for cooling)
  • Balance (having a readability of 0.01 g for specimens having mass of 200 g or less and 0.1 g for specimens having mass of over 200 g.

Standard Test Procedure to Follow

  1. Determine the weight (g) of the empty moisture can plus cap (W1), and also record the can number.
  2. Place the required amount of moist soil in the can with its cap to avoid loss of moisture.
  3. Determine the combined weight of the can and moist soil (W2).
  4. Remove the cap from the top of the can and place it at the bottom of the can.
  5. Put the can with moist soil sample in the oven for 24 hours.
  6. After complete drying of soil mass, remove it from the oven and let it cool down to room temperature inside a desiccator. Determine the combined weight of the dry soil sample plus the can and its cap (W3).

Calculations Involved

Calculate the weight of moisture = W2-W3

Calculate the mass of dry soil = W3-W1

Calculate the water content (%) as given below

w (%) = [(W2-W3)/(W3-W1)]*100

How to Report Test Result?

Minimum of three numbers of specimens of the same sample should be tested. The average value of the 3 observations should be reported. The water content of the soil is reported to two significant figures.

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