DETERMINATION OF SPECIFIC GRAVITY OF SOIL

1. Objective

The value of specific gravity is needed in calculation of soil properties like void ratio, degree of saturation, particle size analysis by hydrometer test etc. The value of specific gravity is sometimes used to determine the suitability of the soil as fill material.

2. Apparatus required

Balance

Fig. 2.1: Density Bottle

Two density bottles (pycnometers) of 50 ml with stopper, having capillary hole.
Balance

Fig. 2.2: Water Bath

A water-bath maintained at a constant temperature of 27± 0.20C.
Balance

Fig. 2.3: Weigh Balance

Balance to weigh the materials (accuracy 0.001g).

Balance

Fig. 2.4: Wash Bottle

Wash Bottle with distilled water.

    2.5 Vacuum desiccators

    2.6 Hot Air Oven, thermostatically controlled, capable of maintaining temperature of 1050 to 1100C.

    3. Reference

      IS 2720 (Part-3/Sec-2): 1980 (Reaffirmed 2021) “Method of test for soil: Determination of Specific Gravity, Section-1, Fine Grained Soils.”

    4. Procedure:

      4.1. Clean and dry the density bottle. Wash the bottle with water and allow it to drain. Wash it with alcohol and drain it to remove water. Wash it with ether to remove alcohol and drain ether. Weigh the empty bottle with stopper (W1).

      4.2. Take about 5 to 10 gm of oven dried soil sample which is cooled in desiccator. Transfer it to the bottle. Find the weight of the bottle and soil (W2).

      4.3. Put 10 ml of distilled water in the bottle to allow the soil to soak completely. Leave it for about 2 hours.

      4.4. Again fill the bottle completely with distilled water put the stopper and keep the bottle under constant temperature water bath (Tx0C). Take the bottle outside and wipe it clean and dry note. Now determine the weight of the bottle and the contents (W3).

      4.5. Now empty the bottle and thoroughly clean it. Fill the bottle with only distilled water and weigh it. Let it be (W4) at temperature (Tx0C)

      4.6. Repeat the same process for 2 to 3 times.

    5. Observations:

    Sr.No. Weight 1 2 3
    1 Weight of density bottle (W1, g)
    2 Weight of density bottle + dry soil (W2, g)  
    3 Weight of density bottle + dry soil+ water at temperature TXoC (W3, g)  
    4 Weight of density bottle + water (W4, g) at temperature TXoC  
    5 Specific Gravity G at TXoCAverage Specific Gravity at TXoC  
    Average Specific Gravity at TXoC  

    6. Calculations :

      Specific gravity of Soil = (Weight of Soil)/(Weight of water of equal volume at 270C)

      = (W2 - W1)/[W4 - W1) - (W3 - W2)]

      = (W2 - W1)/[W2 - W1) - (W3 - W4)]

7. Reporting :

    Unless or otherwise specified, specific gravity values reported shall be based on water at 270C. The average of the values obtained shall be as the specific gravity to the nearest of 0.01. If the two results differ by more than 0.03 the test shall be repeated.

    Specific Gravity at 270C = K x Specific Gravity at TX0C

    Where, K= (Density of water at TX0C /Density of water at 270C) 

                                   Table: Values of “K”
    Temperature TX0C K27 Temperature TX0C K27
    15 1.0026 28 0.9997
    16 1.0024 29 0.9994
    17 1.0023 30 0.9991
    18 1.0021 31 0.9988
    19 1.0019 32 0.9985
    20 1.0017 33 0.9982
    21 1.0015 34 0.9979
    22 1.0013 35 0.9975
    23 1.0010 36 0.9972
    24 1.0008 37 0.9968
    25 1.0005 38 0.9964
    26 1.0003 39 0.9961
    27 1.0000 40 0.9957