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 calculation.
w = weight of dry soil
Water content is usually expressed in percent.
For better results, the minimum size of the most soil specimens should be approximate as given in Table -1. These data constitute with ASTM Test Designation D-2216.
|Maximum Particle Size in the Soil (mm)||U. S. Sieve No.||Minimum Mass of Soil Sample (g)|
IS Code For Water Content of Soil : IS 2720-2 (1973)
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 matters of soil.
The weight balance should have an accuracy of 0.01 gm for specimens having a mass of 200 g or less.
Water Content Test of Soil
Procedure for water content of soil test given below,
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 W3– W1
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_____________________________________________
|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 %
The Final Water Content of Soil is 16.23%
- 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 organic clay||80-130|