lab sheet - specific gravity

7/29/2019 Lab Sheet - Specific Gravity

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CIVIL ENGINEERING DEPARTMENT

CC304 – GEOTECHNICAL 1

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NO. PARTICAL WORK :

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.





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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).

Table 2 : Coeffient of temperature

Temperature (oC) Coefficient

4 1.0000

15 0.9999

20 0.9982

25 0.9971

30 0.9957

35 0.9941





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RESULT :

Name Group

Reg No. Date

Type of Soil /

Colour

Test No. 1 2 3

Mass of empty flask, W1 (g)

Mass of flask + dry soil, W2 (g)

Mass of flask + soil + water, W 3 (g)

Mass of flask + water, W4 (g)

Specific Gravity, Gs

Average value of Gs

Coefficient of Temperature (α)

Final Specific Gravity of Soil, G s





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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





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CONCLUSION :

REFERENCE(S)

1. BS 1377-2:1990 – Part 2

lab sheet - specific gravity

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