CIVIL ENGINEERING DEPARTMENT CC304– GEOTECHNICAL 1 1 NO. PARTICAL WORK : TITLE OF PARTICAL WORK : DETERMINATION OF SPECIFIC GRAVITY OBJECTIVE : Determining specific gravity of a soil sample for weight-volume relationships. THEORY : The Specific Gravity, G s of a soil is the ratio between the unit masses of soil particles and water. Gs is useful for determining weight-volume relationships. Equipment : The equipment for determination of specific gravity includes: i. Volumetric flasks (100ml) ii. No.7 Sieve (2.36mm) iii.Rubber mortar and pastel iv. Vacuum pump v. Distilled deaired watervi. ThermometerPROCEDURE : 1) Prepare a dry and clean volu metric flask and meas ure its weight. (W1) 2) Take a sample of 100g– 120g of air-dried soil and place it into a mortar. Use the pastel to break the soil grains into pieces small enough to go into the flasks. 3) Put the sample into a 2.36mm sieve and the sample pass ing through the s ieve is to be used for the test. The mass for the sample to be tested bust be between 5-10g. 4) Put some of the soil into the volum etric flask and measure the weight. (W 2) 5) Pour the dis tilled deaired water into the flask u ntil all soil is soaked. Place the flask into the desiccator vacuum. 6) Reduce the air pressure to 2cm m ercury. Be careful so that the soil-water mixture does not boil. Remove the vacuum after all the air in the mixture is released.
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TITLE OF PARTICAL WORK : DETERMINATION OF SPECIFIC GRAVITY
OBJECTIVE : Determining specific gravity of a soil sample for weight-volumerelationships.
THEORY :
The Specific Gravity, Gs of a soil is the ratio between the unit masses of soil
particles and water. Gs is useful for determining weight-volume relationships.
Equipment : The equipment for determination of specific gravity includes:
i. Volumetric flasks (100ml)ii. No.7 Sieve (2.36mm)iii. Rubber mortar and pastel
iv. Vacuum pumpv. Distilled deaired water
vi. Thermometer
PROCEDURE :
1) Prepare a dry and clean volumetric flask and measure its weight. (W1)
2) Take a sample of 100g – 120g of air-dried soil and place it into a mortar. Use the
pastel to break the soil grains into pieces small enough to go into the flasks.
3) Put the sample into a 2.36mm sieve and the sample passing through the sieve is tobe used for the test. The mass for the sample to be tested bust be between 5-10g.
4) Put some of the soil into the volumetric flask and measure the weight. (W2)
5) Pour the distilled deaired water into the flask until all soil is soaked. Place the flask
into the desiccator vacuum.
6) Reduce the air pressure to 2cm mercury. Be careful so that the soil-water mixture
does not boil. Remove the vacuum after all the air in the mixture is released.
7) Fill up the flask with distilled water and place into the vacuum. Repeat step 6.
8) Measure the weight of the flask (W3)
9) Empty the flask and fill up with distilled water. Place it into the dessicator vaccumand repeat step 6. Measure the weight of the flas with the distilled water. (W4)record the temperature of the water during the test.
10) Repeat the test to calculate additional values of Gs until the values of Gs are within
2% of each other.
*NOTE
The temperature of water affects its value of density, so use the prepared distilled water only. Use thecorrection factor to determine the specific gravity of the soil sample.
Computation :
Specific Gravity (Gs) Formula
Gs = W2-W1
(W4-W1) – (W3 – W2)
For the correction of calculation based on the water temperature, the value of G s obtained must be multiplied
with the coefficient of temperature. (Refer to Table 2).
REVIEW QUESTIONS :1. Define Specific Gravity of soil.
2. What are the typical values for the specific gravity for soils?3. Can you apply the technique described in this section to measure the specific gravity of
material lighter than water?
4. Why do we use vacuum while determining the specific gravity of soils>5. What is the effect of water temperature on the determination of the specific gravity of soils?
APPENDIX :
Figure 3 : Graph bearing capacity against the no. of blows /0.3m