Specific Gravity Test of Soil IS: 2720–Part 3 | Geotechnical Engineering

Specific Gravity Test of Soil IS: 2720–Part 3, Section 1 - 1980, Reaffirmed in 2002

Theory:

Specific gravity of a soil is the ratio of mass of a given volume of soil solids to the mass of an equal volume of de-aired water both measured at a stated temperature. This is an important property and from it, many parameters of soils can be obtained, including density, porosity, and in hydrometer analysis test and oedometer tests. Specific gravity can give an idea of the content composition of the soil. The lower values-near 2 or less-might suggest organic content, while the higher values-2.75–2.85-indicate that the minerals are heavy, such as iron.

Need and Scope

Determination of Specific Gravity Specific gravity is quite useful for the following reasons:

Hydrometer test and oedometer test: The value of specific gravity is one of the required inputs in the laboratory tests for soil.

So, the knowledge about specific gravity is useful in determining phase relations which mean relative percentages of the same specimen of soil composed of solids, water, and air. Indication of soil composition: Specific gravity can be a marker of the organic matter or metal content in soil. A very low value of specific gravity might indicate an organic soil while higher values might indicate metallic components.

Apparatus Required

1. Glass specific gravity bottle (50 ml or 100 ml capacity).
2. Glass stopper with a hole to allow air to escape.
3. Precision balance (with 0.001 g accuracy).
4. Oven capable of maintaining 105°C ± 1°C.
5. Thermometer.
6. Funnel.
7. Sand bath for heating. 

8. 

   Density bottles for specific gravity

   
   
   

Procedure

1. Weigh the empty specific gravity bottle: Measure the weight of the dry bottle and record it as W1.

2. Add dry soil: Place approximately 10 g of oven-dried soil (for a 50 ml bottle) or 20 g (for a 100 ml bottle) into the bottle and weigh it again. Record this as W2.

3. Add water: Fill the bottle about three-quarters full with water and gently boil or place under partial vacuum to remove any trapped air bubbles. Occasionally roll the bottle to assist in air removal.

4. Cool and fill: Allow the bottle to cool to room temperature and fill it completely with water up to the mark.

5. Weigh the filled bottle: Clean the exterior of the bottle and weigh it, recording this value as W3.

6. Weigh the bottle with water only: After cleaning the bottle, fill it entirely with de-aired water, ensuring it is filled exactly to the mark, and weigh it. Record this as W4.

7. Data and calculations:

      Calculate the specific gravity using the formula: 

       

Tabulation and Results

Test No.	Temp (°C)	Bottle No.	W1 (g)	W2 (g)	W3 (g)	W4 (g)	Specific Gravity (Gs)
1
2
3

Specific Gravity at 27°C

If the test is not conducted at 27°C, you can correct the specific gravity by multiplying the measured specific gravity by a temperature correction factor, K27:

$$G_s (27^\circ C) = K_{27} \times G_s$$

Refer to Table 1 for the correction factor at your test temperature.

Table 1: Correction Factor for Specific Gravity of Water Due to Temperature

Temperature (°C)	K27
15	1.0026
16	1.0024
17	1.0023
18	1.0021
19	1.0019
20	1.0017
21	1.0015
22	1.0013
23	1.0010
24	1.0008
25	1.0005
26	1.0003
27	1.0000
28	0.9997
29	0.9994
30	0.9991
31	0.9988
32	0.9985
33	0.9982
34	0.9979
35	0.9975
36	0.9972
37	0.9968
38	0.9964
39	0.9961
40	0.9957

Conclusion

Range of Specific Gravity of different soils 

This is especially significant with regard to the content, in terms of organic matter or mineral content. A low specific gravity value is less than 2, and higher values close to 2.75–2.85 indicate mineral-rich soils, such as soils containing iron. Such data are considered important in various geotechnical evaluations, including hydrometer and consolidation tests.