TITLE: DETERMINATION OF SPECIFIC GRAVITY OF SOIL
OBJECTIVE: To Determine the Specific Gravity(G) of soil solids by Pycnometer method.
APPARATUS REQUIRED:MATERIAL REQUIRD:
THEORY:
The Specific Gravity of soil is defined as the ratio of the unit weight or unit mass of solids or solid particles to the unit weight or unit mass of the water at the standard temperature (4 degree celcious). it is also defined as the ratio of the mass of a given volume of solids to the mass of an equal volume of water at 4 degree celcious. it is denoted by G or Gs. Thus, the specific gravity is given by;
G=Ys/Yw
or, G=Ps/Pw
This is known as absolute specific gravity or grain specific gravity and is unit less quantity.
The specific gravity of soils for most natural soils falls in the general range of 2.65 to 2.80.
The typical values of specific gravity of soil particles for selected types of soils are presented in the following table.
Types of soil value of G
Gravel 2.65-2.68
sand 2.65-2.68
silty sands 2.66-2.70
silt 2.66-2.70
inorganic clays 2.68-2.80
organic soils variable may fall below 2.00
The specific gravity of soil is determined using pycnometer tube in the Laboratory.
let,
M1=mass of empty pycnometer
M2=mass of pycnometer +dry soil
M3=mass of pycnometer +soil+ water
M4=mass of pycnometer filled with water only
then, we use the following formula,
G=(M2-M1)/((M2-M1)-(M3-M4))
PROCEDURES:
1.The pycnometer was completely dry and was cleaned with paper or cloths.
2.it's cap was tightly screwed and it's mass was taken (M1).
3.The cap was unscrewed and about 200 gm of oven dried soil was placed in the pycnometer. The cap was screwed and it's mass was taken (M2).
4.Distilled water was poured to the sample until it is full but prevent from spill over the pycnometer and was shaken well such that no air is preserved inside pycnometer.
5.The cap was tighten well and upper part of cone was filled completely with drops of water ,pycnometer was rotated to eliminate air bubbles by placing finger on the apex of cone.
6.The outer surface was wiped out and again mass was taken (M3).
7.The pycnometer was emptied and was cleaned & was wiped.
8.Now, the pycnometer was refilled with water only and was tighten well and apex or cone was filled with drops of water completely.
9.The outer surface was wiped and dried & the mass was taken (M4).
10.specific gravity (G) was calculated using formula,
G=(M2-M1)/((M2-M1)-(M3-M4))
OBSERVATIONS AND CALCULATIONS:
Pycnometer no: 2
Room temperature:26 degree cel.
mass of empty pycnometer (M1): 620 gm=0.620 kg
mass of pycnometer and dry soil (M2) :820 gm=0.820 kg
mass of pycnometer , soil and water (M3) :1.637 kg
mass of pycnometer and water (M4) :1.517 kg
Now,
G=(M2-M1)/((M2-M1)-(M3-M4))
=(0.820-0.620)/((0.820-0.620)-(1.637-1.517))
G =2.5
RESULT:
Thus, from the above lab experiment the specific gravity of given soil sample was found to be 2.5.
This value indicates the ratio of density of soil sample to the density of water at standard temperature.
CONCLUSION:
The specific gravity of a soil sample is a crucial parameter in geotechnical engineering and soil mechanics. A specific gravity value of 2.5 indicates that the soil sample is denser than water. In practical terms, a specific gravity of 2.5 suggests that the soil sample may contain a significant amount of heavy minerals or aggregates. This implies that for an equal volume of soil and water, the soil sample will exert more weight or mass. Understanding the specific gravity helps in various engineering applications, including soil classification, compaction, and stability analysis.
PRECAUTIONS:
1.cleanliness of all equipment should be ensured.
2.soil samples should be Handled carefully to prevent contamination.
3.soil samples should be adequately to remove moisture.
4. should use distilled water to avoid impurities.
5. measurement of masses should be precise to minimize errors.
6.the pycnometer should fulfill air tight and complete.
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