Specific gravity of soil solid is the ratio between the unit weight of the soil solid to the unit weight of the water. In other words it is the density of the soil solid relative to water. Water is considered to be the reference which have specific gravity of ‘1’. The specific gravity of soil solid is that properly which helps in determining the void ration, density and water content.
The specific gravity of soil varies with respect to the variation in the soil type or grade of soil.
The values of specific gravity soil ranges as fallows:
- Coarse grained soils: 2.6 to 2.7
- Fine grained soil: 2.7 to 2.8
- Organic soil: 2.3 to 2.5
The specific gravity of soil can be easily determined by performing some laboratory experiments. some of the most commonly used experiment that are performed to determined the specific gravity of soil are mentioned below.
- Determination of specific gravity by Pycnometer method
- Determination of specific gravity by density bottle method
To Determine Specific Gravity of Soil Solids by Density Bottle Method
M1 = mass of empty bottle
M2 = mass of the bottle and dry soil
M3 = mass of bottle, soil and water
M4 = mass of bottle filled with water only.
1. 50ml density bottle with stopper
2. Oven (105 0 to 110 0C)
3. Constant temperature water bath (27 0C)
4. Vacuum desiccator
5. Vacuum pump
6. Weighing balance accuracy 0.001g
1. First and foremost job that is to be done is wash the density bottle and dry it in an oven at 105 0C to 100 0C. Cool it in the desiccator.
2. After the first step, Weigh the bottle, with stopper to the nearest 0.001g (M1).
3. Now take about 5 to 10g of the oven dried soil sample and transfer it the density bottle. Weigh the bootle with the stopper and the dry sample (M2).
4. Add de-aired distilled water to the density bottle just enough to cover the soil. Shake gently to mix the soil and water.
5. Place the bottle containing the soil and water after removing the stopper in the vacuum desiccator.
6. Evacuate the desiccator gradually by operating the vacuum pump and reduce the pressure to about 20 mm of mercury. Keep the bottle in the desiccator for at least 1 hour or until no further movement of air is noticed.
7. Now replace the vacuum and remove the lid of the desiccator. Stir the soil in the bottle carefully with a spatula. Before removing the spatula from the bottle, the particles of soil adhering to it should be washed off with a few drops of air free water. Replace the lid of the desiccator and again apply vacuum. Repeat the procedure until no more air is evolved from the specimen.
Note: In case of vacuum desiccator is not available, the entrapped air can be removed by heating the density bottle on a water bath or a sand bath.
8. Remove the bottle from the desiccator. Add air-free water until the bottle is full. Insert the stopper.
9. Immerse the bottle upto the neck in a constant-temperature bath for approximately 1 hour or until it has attained the constant temperature.
Note:If there is an apparent decrease in the volume of the liquid in the bottle, remove the stopper and add more water to the bottle and replace the stopper. Again place the bottle in the water bath. Allow sufficient time to ensure that the bottle and its content attain the constant temperature.
10. Take out the bottle from the water bath. Wipe it clean and dry it from outside. Fill the capillary in the stopper with drops of distilled water, if necessary.
11. Determine the mass of the bottle and its contents (M3).
12. Empty the bottle and clean it thoroughly. Fill it with distilled water. Insert the stopper.
13. Immerse the bottle in the constant-temperature bath for 1 hour or until it has attained the constant temperature of the bath.
If there is an apparent decrease in the volume of the liquid, remove the stopper and add more water. Again keep it in the water bath.
14. Take out the bottle from the water bath, dry and take the mass (M4).
Observations and calculations:
|Sl. No.||Observations an Calculations||Determination No.|
|1||Density bottle No.|
|2||Mass of empty density bottle (M1)|
|3||Mass of Mass of bottle dry soil (M2)|
|4||Mass of bottle, soil and water (M3)|
|5||Mass of bottle filled with water (M4)|
|6||M2 – M1|
|7||M3 – M4|
|8||Calculate G using formula|
Specific gravity of solids = _____.
- The soil sample that is to be used must be dry.
- Weighing of soil sample should be done accurately
What are the Importance of Specific Gravity of Soil?
- From the engineering point of view specific gravity of soil is an important property to be determined. This is because higher the specific gravity higher is the value of strength.
- This gives an idea about the extend of stability that the soil sample is able to offer for the proposed construction.
- Specific gravity of soil plays an important role in the construction of road and foundation.