Theory

The ratio of unit weight of the material to the unit weight of some reference material is called specific gravity of the material. The soil solids have permeable as well as impermeable voids of soil particles are the durability of the material. Material with high specific gravity do not differ in gravity are likely to break down and change their properties with time. It is importance to know the specific gravity to ratio, porosity unit weight degree of saturation etc. it is also used to determine the saturation line.


Application

The specific gravity is applicable in finding out degree of saturation, specific gravity of soils is useful in finding out the degree of saturation voids ratio and unit weight of moist soils. The unit weight is required in calculation of pressure settlement and stability problems in soil engineering. Specific gravity is also used in computing particle rise of soil in sedimentation analysis.


Items required

1.      The pycnometer of 500ml capacity with stoppers.
2.    Balance accurate to 0.0019
3.    Oven
4.    Dessicator
5.     Distilled are free water
6.    I.S. sieves 4.75mm and 2mm
7.     Soil sample passing 4.75mm and retained on 2mm sieve
8.    Wash bottole
9.    Glass rod


Diagram




Procedure

1.      The pynometers cleaned dried and weighted to the nearest 0.0019 (N1)

2.    About 200gm of oven dried sample passed through 4.75mm I.S. sieve and retained on 2mm is sieve in pycnometer and closed the stopper.

3.    Weighted the pycnometers with soil to the nearest 0.0019 (N2)

4.   Add sufficient distilled and cleared water to cover the soil in the pycnometer.

5.     Stirred the soil with glass rod to removed air.

6.    Filled the pycnometer completely with distilled water and weighted (N3)

7.  Cleaned the pycnometer and filled it completely with distilled water and its weighted to the nearest 0.0019 (N4)

8.    The step 1 to 7 was repeated with other two pycnometer.

9.    The average specific gravity was calcultated.


Precaution

1.    Mass N1,N2,N3 and N4 should be noted very carefully any error in mass gives large discrepancy in value of specific gravity.

2.    See that the stopper is properly fitted to the pycnometer causing no leakaged water.

3.    See that sil particals sticking to the stirring glass rod are not last.

4.    For greater accuracy the entrapped correction should be applied.

5.  For greater accuracy the entrapped air in water and soil should be removed by vaccum pump.

6. It the two results differ by more than 0.03 the test should be repeated.


Observation


SR.NO.
PARTICULAR
DETERMINATION NO.
SAMPLE
1
SAMPLE
2
SAMPLE
3
01
Pycnometer no.
A
B

02
Mass of Pycnometer (M1) gms
442 gms
442 gms

03
Mass of Pycnometer & dry soil (M2) gms
622 gms
614 gms

04
Mass of Pycnometer soil & water (M3) gms
1037 gms
1028 gms

05
Mass of Pycnometer when fully of water (M4) gms
930 gms
930 gms



Sample calculation


Specific gravity G = (M2 – M1)/(M4 – M1) – (M3 – M2)
                                = (622 – 442)/(930 – 442) – (1037 – 622)
                                = 2.74

Specific gravity G = (M2 – M1)/(M4 – M1) – (M3 – M2)
                                = (614 – 442)/(930 – 442) – (1028 – 514)
                                = 2.32

                    Mean = 2.74 + 2.32 / 2
                               = 2.53


RESULT

Specific gravity of the given soil sample was found G = 2.53