Specific Gravity of Soil | Soil mechanics

Specific Gravity | Soil mechanics 

Civil engineers and geotechnical studies rely on exact measurements in order to make sure that a structure would be stable and consistent. One very important property that engineers often measure is the specific gravity of soil. Sounds very complicated, right? Understanding specific gravity can help you evaluate soil behavior, design foundations, and manage your construction materials on time, effectively, and with lowest cost possible.

What is Specific Gravity?

Specific gravity refers to the ratio between the density of a material and that of water. Specific gravity is the ratio of the density of soil solids to the density of water. In general, the formula used to calculate specific gravity, Gs is as follows: 

Specific Gravity

In practice, the density of water is usually measured to be about 1 g/cm³ or 1000 kg/m³. Thus, the specific gravity of soil is a dimensionless number representing how much heavier a soil particle is compared to water.

Why is Specific Gravity Important?

1. Classification of Soils :

Specific gravity helps in classifying soils and gives an idea about the composition. Different types of soils-sand, silt, clay are different regarding their specific gravities, which influence their engineering properties and behavior.

2. Compaction and Strength : 

Knowing the specific gravity of soil will help the engineers know how compacted the soil is and predict its strength. Higher specific gravity indicates denser soil particles; it often contributes to greater soil strength and stability.

3. Volume Computations: 

The specific gravity applies to the computation of volumes and weights of soil. It enables engineers and builders to calculate the volume of soil required in construction and what load the soil could bear.

4. Quality Control: 

Specific gravity is one of the first quality control criteria applied during construction and testing of materials. If the soil samples collected from the sites fail to meet the standard specific gravity value, engineers can be assured that the tested material has qualities as promised by the manufacturer.

How to Measure Specific Gravity?

Specific gravity is measured in the laboratory using several methods such as:

Pycnometer Method: 

Here, the volume of soil particles is measured with the help of a pycnometer by displacement of water. This method is accurate and very much in use for fine soils.

Water Displacement Method: 

For larger particles like gravels or coarse sand, the water displacement method basically displaces water, and the soil is dipped into water; afterward, the displaced volume of water is measured.

 Conclusion

It is important that civil engineers and construction personnel understand and measure specific gravity. Specific gravity gives vital information concerning soil density and composition, which might be very critical in the design and construction of safe and durable structures. In integration of such data on specific gravity into an assessment, engineers make better decisions while ensuring that materials used for construction are sound, and have all the qualities required.