# To Determine the Specific Gravity of Soil

**ASTM Designation: C128**

## Apparatus

Sieve #4, balance, electric oven, pycnometer.

## Theory

Specific gravity is defined as the ratio of the weight of given volume of material to the weight of an equal volume of water.

G = density of soil/density of equal volume of water

G = mass of dry soil/mass of and equal volume of water.

## Procedure

- Take at least 25g of soil which has been passed through sieve#4 and place it in an oven at fixed temperature of 105-110 °C for 24 hours to dry it completely.
- Clean and dry the pycnometer thoroughly and find its mass (M1).
- Find the mass (M2) of pycnometer by placing dried soil in it.
- Add sufficient quantity of water to fill the pycnometer up to the given mark and then find mass of the pycnometer ( m
^{3}) and its content. - Empty the pycnometer then fill it with water up to the same level. Now find the mass (M4) of the pycnometer having water in it.
- Determine the specific gravity of the given soil sample.

## Precautions

- The graduated cylinder used should be cleaned.
- Dry the coarse aggregate so that it does not absorb moisture otherwise it will not give the desired results.
- All the readings of mass should be noted carefully.

## Practical applications

- The value of specific gravity helps us to some extent in identification and classification of soil.
- It gives the idea about the suitability of a given soil as a construction material.
- It is utilized in calculating voids ratio, porosity, and degree of saturation if the density or unit weight and water content are known.

Let us know in the comments what you think about the concepts in this article!