Determination of Specific Gravity

Testing objectives:
Determination of the specific gravity of soil fraction passing 4.75 mm I.S sieve by Volumetric flask.

Need and Scope:
The knowledge of specific gravity is required in calculation of soil properties like void ratio, degree of saturation and also weight-volume relationship.

Definition:

Specific gravity G is defined as the ratio of the unit weight ( or density ) of soil solids only to unit weight (or density ) of water.

 Apparatus Required:

 

 Test  Procedure:

1. Clean and dry the Volumetric flask.  

2. Carefully fill the flask with de-aired, distilled water up to the 500 ml mark (bottom of the meniscus should be at the 500 ml mark).

3. Measure the mass of the flask and the water filled to the 500 ml mark (W1).

4. Insert the thermometer into the flask with the water and determine the temperature of the water T= T1oC.

5. Put approximately 100 grams of air dry soil into an evaporating dish.

6. In the case of cohesive soil, add water (de-aired and distilled) to the soil and mix it to the form of a smooth paste.  keep it soaked for one-half to one hour in the evaporating dish. (Note: this step is not necessary for granular , i.e., non-cohesive, soils.)

7. Transfer the soil (if Granular) or the soil paste (if cohesive) into the volumetric flask.

8. Add distilled water to the volumetric flask containing the soil (or the soil paste) to make it about two-thirds full.

9. Remove the air from the soil-water mixture. this can be done by applying vacuum by a vacuum pump or aspirator until all of the entrapped air is out. Notice that this is an extremely important step. Most of the errors in the results of the test are due to entrapped air which is not removed.

10. Add de-aired, distilled water to the volumetric flask until the bottom of the meniscus touches the 500 ml mark. also dry the outside of the flask and the inside of the neck above the meniscus.

11. Determine the combined mass  of the bottle plus soil plus water (W2).

12. Pour the soil and water into an evaporating dish.  Use a plastic squeeze bottle and wash the inside of the flask .  Make sure that no soil is left inside.

13. Put the evaporating dish into a oven to dry to a constant weight.

14. Determine the mass of the dry soil in the evaporating dish (Ws).

 

  Calculations:  

S. No.   Observation Number 

 

 1

 

 2

 

 3

 
1 Weight of flask + Water filled to mark, W1 ( g )      
2 Weight of flask + Water filled to mark + soil, W2 ( g )      
3 Weight of dry soil, Ws ( g )        
4 Weight of equal volume of water as the soil solids, W w ( g) = ( W1 +Ws ) - W2        
5 Gs (T1oC ) = Ws / Ww  

 
6 Gs (20oC ) = Gs (T1oC ) * A 

 

      
7 Average specific gravity at 20 0C        



Interpretation and Reporting the Results:

  Average specific gravity at 20 0 C,  Gs =   ..............................

       The specific gravity of the soil particles lie within the range of 2.65 to 2.85. Soils containing organic matter and porous particles may have specific gravity values below 2.0. Soils having heavy substances may have values above 3.0.

 

 

Photos:

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Step 2