Specific Gravity of Soil Test – Procedure, Result & Calculation
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What Is Specific Gravity of Soil
The Specific Gravity of Soil is defined as the ratio of the weight of a given volume of the material to the weight of an equal volume of distilled water.
It is an important parameter in soil mechanics for the calculation of the weight-volume relationship.
This specific gravity, G” is defined as
Gs = Unit weight (or density) of soil sample only / Unit weight (or density) or water
The general values for specific gravity for different soils are given in Table -1. This method of determining the specific gravity of soil given here is applicable for soils composed of particles smaller than 4.75 mm (No.4 U.S. sieve) in size.
General Specific Gravity of Soil Range for Various Soils
The Specific gravity of soil generally ranges from 2.60 to 2.90. Organic matter and porous particles may have specific gravity values below 2.0 and Soil which has heavy substances or particles may have values above 3.0.
Read More: Water Content of Soil Test – Procedure, Result & Report
Determination of Specific Gravity Test of Soil
Specific Gravity Test of Soil IS Code: IS 2720-3-2 (1980)
- Specific gravity bottle (500 ml).
- Thermometer graduated in O.soC division scale
- Balance sensitive up to 0.01 g
- Distilled water
- A vacuum pump or aspirator
- Evaporating dishes
- Plastic squeeze bottle
- Drying oven
The equipment for this experiment is shown in Fig. 3-1.
Specific Gravity Test Procedure
- Clean the specific gravity bottle well and dry it.
- Carefully fill the bottles with de-aired, distilled water up to the 500 ml mark.
- Determine the weight of the bottle and the water filled to the 500 ml mark (W1).
- Insert the thermometer into the bottle with the water and determine the temperature of the water T = T1 ºC.
- Fill approx 100gm of dry soil into an evaporating dish.
- In the case of cohesive soil, add water (de-aired and distilled) to the soil and mix it into the form of a smooth paste. Keep it soaked for about 1 hour at least in the evaporating dish.
- Now, Fill this soil (if granular) or the soil paste (if cohesive) into the volumetric specific gravity bottle.
- Add distilled water to the gravity bottle containing the soil (or the soil paste) to make it about two-thirds full.
- Remove excess air from the soil-water mixture. This can be done by:
- Gently boiling the specific gravity bottle containing the soil-water mixture for about 15 to 20 minutes. Accompany the boiling with continuous agitation of the flask. (Don’t use high flame otherwise, the soil may boil over.)
- The second option is to vacuum by a vacuum pump or aspirator until all of the entrapped air is out.
- This is the most important step for testing. If this entrapped air is not removed completely it can cause a result error.
- Bring the temperature of the soil-water mixture in the Bottle down to room temperature, i.e T1 ºC seen in Step 4. (This temperature of the water is at room temperature.)
- Now fill the distilled water into the bottle until the bottom of the meniscus touches the 500 ml mark. Also, clean the top and side of the bottle and remove any excess water.
- Find out the combined weight of the bottle + Soil + Water as (W2).
- Just as a precaution, check the temperature of the soil and water in the flask to see if it’s T1± 1 ºC or not.
- Empty Soil and water in an evaporating dish. Clean the bottle such that no soil particles are left on the side.
- Transfer evaporating dish into the oven to dry to a constant weight.
- Find out the mass of the dry soil in the evaporating dish (Ws).
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Specific Gravity of Soil Formula
The specific gravity of soil can be calculated by using the following formula,
G = Mass of soil / Mass of equal volume of water
Calculation Of Specific Gravity Of Soil Sample
Calculate the specific gravity
G = Mass of soil / Mass of equal volume of water
Mass of Soil = Ws
Mass of the same volume of water, Ww = (W1 + Ws) – W2
Gs (T1 º C) = Ws / Ww
Specific Gravity of Soil at Various Temperature
For more accurate results it is recommended to conduct tests 3 times on the same soil sample. Take an average of 3 values these values should not vary by more than 2 to 3%.
A sample calculation for the Specific Gravity of Soil is shown in the table given below :
Detail of soil: Light brown sandy Silt
The volume of the Bottle: 500 ml.
The temperature of the test: is 23 ºC.
Water Density (23ºC) = 0.9993 (Table-3) .
From the above table, we can say that the specific gravity of the soil sample is 2.68.
(Note: Specific gravity of any element is unit less parameter)
Specific Gravity of Soil Lab Report Discussion
Specific gravity of soil definition.
The Soil Specific Gravity is defined as the ratio of the weight of a given volume of the material to the weight of an equal volume of distilled water.
Specific Gravity of Soil
The Soil Specific Gravity is defined as the ratio of the weight of a given volume of the material to the weight of an equal volume of distilled water. It is denoted by “G”. It is an important parameter in soil mechanics for the calculation of the weight-volume relationship.
The specific gravity of soil can be calculated by using the following formula, G = Mass of soil / Mass of equal volume of water Where, Mass of Soil = Ws Mass of the same volume of water, Ww = (W1 + Ws) – W2 Gs (T1 º C) = Ws / Ww
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Measurement of Specific Gravity of Soils
Contents [ hide show ]
Introduction
Testing equipment, testing procedure, calculations.
Soil is a three-phase material that consists of solid particles and voids which are filled with water and air. The specific gravity (G S ) of a soil refers to the ratio of the solid particles’ unit weight to the unit weight of water. G S should not be confused with the soil density since it is a dimensionless unit and expresses the ratio of two particular densities.
G S is a significant parameter of soil mechanics since it can be associated with the soil’s mineral composition and weathering. It is also used to derive several important soil parameters such as the porosity, the dry and saturated density and the degree of saturation.
To derive the Specific Gravity of a soil, the following equipment is needed:
- Volumetric flask marked with a thin ring at a specific point of its neck (graduation mark)
- Balance sensitive to 0.01g
- Vacuum pump
- Distilled water
- Drying oven
The Specific Gravity is computed as the ratio of the weight in air of a given volume of soil particles at a stated temperature to the weight in air of an equal volume of distilled water at the same temperature. The procedure that is followed towards that goal is the following:
- Weigh the empty and clean volumetric flask ( W 1 ).
- Fill the flask with distilled water up to the graduation mark.
- Clean and dry the inside (above the water level) and the outer part of the flask and weigh it ( W 2 ).
- Empty and dry the Flask
- Weigh around 50 grams of soil material.
- Use the funnel to carefully place the soil into the flask and weigh it ( W 3 ).
- Fill around 2/3 of the flask with distilled water.
- Use a vacuum pump to gradually apply vacuum and remove the entrapped air while spinning the flask to remove the air bubbles. The procedure should last for about 2-3 minutes for sands and 10-15 minutes for clays.
- Remove the vacuum, clean and dry the flask and add distilled water up to the mark.
- Weigh the flask ( W 4 ).
- Use the thermometer to derive the temperature of the water.
To better understand how the Specific Gravity is calculated, the aforementioned measured quantities are presented in Figure 1.
Based on the temperature of the water that was recorded in the last step, the density of the distilled water ρ w is derived through specific tables (i.e., ρ w =998.23 kg/m 3 at T=20 ° C)
Therefore, the Specific Gravity G S is calculated as:
A correction is utilized to adjust the results at a reference temperature T=20 ° C:
where K is the temperature correction factor.
The Specific Gravity of soils is usually between 2.65-2.80 with finer soils having higher values than coarser ones.
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