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Exp6 : Determination of specific gravity of soil particles

Introduction :

Specific gravity of soil particles is an important property and its determinationhelps in calculating void ratio, porosity and degree of saturation . Also the solids

contributes towards the weight of the soil substantially. Higher the value of specific

gravity of soil solids, higher will be the bulk density as well , through compaction playsan important role in it .

The specific gravity of soil particles , G, can be calculated by determining the ratio.

= weight of soil solids ( Ws )

Weight of equal volume of water ( Ww)

Objective :

To determine specific gravity of soil solids

BY PYCNOMETER

Apparatus1. Pycnometer it consist of glass cylinder of 1000 cc capacity over which a

conical cap of brass with a rubber seal can be attached .2. Water bottle made of plastic to which flexible plastic pipe for out let of water

can be attached .

3. Balance of 1 g accuracy

4. Glass rod5. Drying oven , tray etc.

Procedure

Sample : The soil sample should in dry powdered form . the sample my be air dried oroven dried.

6. Clean and dry the pycnometer thoroughly and weigh with the conical cap screwedon tightly . ( W1 )7. Make a vertical mark on cap and glass . The cap should always be tightened such

that both the marks coincide.

8. Unscrew the cap and put about 150 to 200 g of dry soil replace cap and recordthe weight . ( W2 )

9. Add water to fill about half of the pycnometer

10. Stir with glass rod for about 3-4 minutes so as to remove the air .

11. Add more water and stir it again.12. Screw on the cap to the vertical mark . Add more water by water bottle ( check

that the rubber gasket conical cap is in place and there is no leakage) .

13. Insert glass rod through the central hole in cap and gently stir it .14. Fill water up to top of the conical cap and weigh it ( W3 ).

15. Empty the pycnometer , clean it and fill it with water. Record the weight ( W4 )

16. Record all the observation in proforma and calculate the G value . Repeat at leastonce more and find the average up to second decimal point.

Record of observations :

PROFORMA

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Soil type .

Determination No. 1 2

Weight of pycnometer

W1 (g )Weight of pycnometer +

dry soil , w2 (g)

Weight of pycnometer +

soil + water , W3 (g)

Weight of pycnometer

full of water , W4 (g)

Weight of soil solids Ws =

W2 - W1

Wt of equal volume of

water

Ww = W2 + W4 W3 W1

Specific gravity of soil

particles = Ws

Ww

Mean =

Specific gravity of soil

particles , G =

Precautions :

17. The soil should be dried completely

18. Stirring should be continued till no more air bubble is released .

19. Always wipe off the excess water from outside of pycnometer by a drycloth before weighing it .

20. The conical cup should be tightened to same extent very time .

21. Use de-aired water .