The specific gravity of any material is the ratio of its density to that of water. To determine the specific gravity of soil only its solid phase is computed and is defined as the Specific gravity of solids, Gs: 

 

 

 

The standard method of measuring the specific gravity of solids that pass the 4.75-mm (No. 4) sieve, by means of a water pycnometer, (ASTM D854).  Using a calibrated glass flask known as a pycnometer, (see figure 4), solids are added to calculate the Gs of the solid. 

Before the Gs could be calculated, moisture content test (ASTM D2166) have to be measured. 

 

Using a small tin filled with soil the following moisture content (ω) was obtained, after the sample was placed in an oven at 110 ± 5°C and left to dry for 12 to 16 hours. Since the(ω) is the ratio of the mass of water divided by the mass of solid thus:
 

 

Thus using this equation 2 can be re-written for the purpose of having the moisture content determined using (ASTM D2166) method giving equation 3.

Data:

Mass of Tin can: 14.28g

Mass of Tin can + Sample: 93.79g

Mass of Tin can + Dry sample: 88.86g

 

 

 

Once the (ω) was determined, the value obtained from the pycnometer lab (ASTM D835) method is as follows;

 

Data:

 

Mass of Pycnometer:  173.31g

Mass of Soil: 50.81g

Mass of Pycnometer + Water: 671.38g

Mass of Pycnometer + Soil + Water: 701.02g

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Now equation 1 can be used to obtain the (Gs),

 

Thus:

 

 

 

Figure 1 was used to illustrate the phase diagram to resolve the relationship needed to obtain (Gs)

 

To justify the soil having a Gs= 2.64 Table 4.2 and Table 4.3 from GEOTECHNICAL ENGINEERING, 2nd ed. was compared with quartz. Many grades of sand and gravels are composed primarily of quartz with a value of 2.66.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 4 Glass pycnometer