SPECIFIC GRAVITY OF A SOIL SAMPLE EXPERIMENT

       

Determination of the Specific gravity of a soil sample

Specific gravity is the ratio of the mass (or weight) of a unit volume of a material – at a specific temperature – to the same volume of gas-free distilled water at the same temperature. Mathematically,

S.G. =                        _{Weight of water}

                                                         ^{Volume of material × density of water}                  

The aggregate particles contains pores and due to this the volume of a particle depends on how it was assessed; with or without the pore volume. In other words the quantity in the denominator is not the same when the pore volume has been include as in when it has been excluded from the volume calculation. In addition, the numerator i.e. the weight of the material will change with the amount of moisture content in the material. Because of these possibilities that exist in its measurement, the specific gravity of an aggregate should be associated with or qualified by the moisture content level and the method of measurement of the volume.

Specific gravity is made use of in the design and calculation of concrete mixes. With the specific gravity of each constituent known, its weight can be converted into solid volume and hence a theoretical yield of the concrete per unit volume can be calculated. Specific gravity is also useful in calculating the compacting factor in connection with the workability measurements. Also, specific gravity is required to be considered when dealing with light or heavy weight concrete. Average specific gravity for fine aggregates is between 2.0 and 2.6.

AIM         

To determine the specific gravity of soil sample.

                 APPARATUS
Apparatus used in the experiment included:

• Density bottle
• Electronic balance
• Container/pan
• Oven machine

PROCEDURE

After getting the apparatus and materials;

• The density bottle was prepared by cleaning and drying after which its weight was measured and recorded.
• The density bottle was filled completely with water and its stopper inserted to obtain a perfect level of water in the bottle.
• The weight of the bottle with water was measured and recorded.
• The density bottle was emptied, cleaned and filled with soil sample of known mass to about one-third of its capacity.
• This bottle was then filled with water and the level regulated with stopper.
• The weight of this mixture (of density bottle, sand and water) was measured and recorded.
• The procedure was repeated three times with each successive readings recorded.

DATA AND CALCULATION

Mathematically,

G = ɤs / ɤw

In a more general way,

G = [ GL(m2 – m1 ) ] / [ (m4  – m1 ) – (m3  – m2 ) ]

Where;

GL = specific gravity of the liquid used i.e for distilled water, then GL is assumed 1.00     m1 = mass of density bottle (g) = 26g.          m2 = mass of bottle + dry soil (g) = 47g     m3 = mass of bottle + soil + liquid (g)             m4 = mass of bottle + liquid only = 76g.

For the first experiment:

m3 = mass of bottle + soil + liquid (g) = 88g thus,

G = [ GL(m2 – m1 ) ] / [ (m4  – m1 ) – (m3  – m2 ) ]

=  [ 1*(47 – 26 ) ] / [ (76  – 26 ) – ( 88  – 47 ) ]

= 21 / (50 – 41) = 21 / 9

= 2.33

For the second experiment:

m3 = mass of bottle + soil + liquid (g) = 88 thus,

G = [ GL(m2 – m1 ) ] / [ (m4  – m1 ) – (m3  – m2 ) ]

=  [ 1*(47 – 26 ) ] / [ (76  – 26 ) – ( 88 – 47 ) ]

= 21 / (50 – 41) = 21 / 9

= 2.33

For the third experiment:

m3 = mass of bottle + soil + liquid (g) = 87 thus,

G = [ GL(m2 – m1 ) ] / [ (m4  – m1 ) – (m3  – m2 ) ]

=  [ 1*(47 – 26 ) ] / [ (76  – 26 ) – ( 87  – 47 ) ]

= 21 / (50 – 40) = 21 / 10

= 2.10

The average of the three values gotten:

= (2.33 + 2.33 + 2.10) / 3

= 2.25

Thus, the specific gravity of the soil sample is 2.25

                             

OBSERVATION

The volume of the soil sample in the density bottle was observed to drop when filled with water to the brim.

                                  PRECAUTION

The following care was taken during the course of the experiment:

• Parallax error was always ensured and avoided while taking readings.
• Any spillover on the surface of the bottle was cleaned before measuring.
• The same mass and type of the soil sample was used throughout.
• It was ensured that all entrapped air was removed.
• After placing the soil in the density bottle, it was ensured that the soil mass was not disturbed.
• Material used was ensured to be dried fine grained soil.
• All measurement were properly and accurately recorded.

                                            ERROR

Some of the various types of error that may undermine the outcome of the

Experimental result includes:

Human Error:

• Incorrect measurement of the sample
• Erratic error
• Parallax error

Instrumental Error

• Insensitivity of the electronic balance

Random Error

• Environmental air effect
• Laboratory experimental condition

CONCLUSION

The following conclusion can safely be drawn on the conclusion of the experiment.

• For any given soil material, its specific gravity can be determined as gives is a measure of its strength.
• This is necessary as it is used in calculating the phase relationships of soils, to calculate the density of the soil solids and other wide range of applications.