Soil Solids Specific Gravity Testing

Soil Specific Gravity Test Procedure

• Calibrating the Specific Gravity Meters

At BOC Sciences, we generally calibrate our hydrometers only once.

• First, our experts weigh each dry hydrometer five times in succession
• Then, the hydrometer is filled with deoxygenated water to allow it to reach thermal equilibrium and maintain it for a period of time
• Immediately afterwards, one hydrometer at a time was removed from the container and the water level was adjusted to the calibration mark
• The mass and temperature of each cuvette were measured and recorded
• Finally, the calibration volume of each cuvette is calculated and recordeds

Figure 1. Specific Gravity Test of Soil

• Preparing the Sample

We have designed the specific gravity test method for soils that can pass through a No. 4 (4.75 mm) sieve. For soils containing larger particles, we use the ASTM C127 method to determine the specific gravity of the soil retained on the No. 4 test sieve. For some highly plastic, fine-grained or organic soils, we chose the wetting procedure.

• First, we add the appropriate mass of water to disperse the soil, and mix it into a slurry, which is then transferred to a specific gravity meter
• For oven-dried soils, the dried sample is placed directly into the hydrometer, then water is added and stirred into a slurry
• The slurry is degassed by boiling, vacuum, or a combination of both, and then de-oxygenated water is added to bring it close to the final calibration volume
• Finally, the hydrometer with the prepared sample is placed in an insulated vessel overnight to allow it to reach thermal equilibrium

• Measuring Mass and Temperature
• We remove the hydrometer from the container and make final adjustments to the calibrated water level and weigh the hydrometer on a laboratory balance
• Record the temperature to the nearest 0.1°C using the same equipment used to calibrate the hydrometer

• Calculating the Specific Gravity of the Soil
• We rinse the entire suspension into a graduated pan, and cool it in an oven to determine the dry mass of the soil solids
• Finally, the final specific gravity value is calculated according to the soil specific gravity formula in the standard method of the test

Figure 2. Specific gravity by pycnometer. (Bhashakhetre, C. S.; et al. 2017)

Specific Gravity Laboratory Equipment & Apparatus

• Specific Gravity Meter
• Temperature Measuring Device - Our thermometers have a readability of 0.1°C and an accuracy of ± 0.5°C
• Entrapped Air Removal - Degassing of water and soil slurry can be accomplished by boiling, applying a partial vacuum or both
• Desiccator - BOC Sciences is equipped with a desiccator with desiccant plates and desiccant to cool the sample to room temperature after drying in the oven
• Insulated Containers - During calibration and testing, our pycnometers are stored in an insulated container for temperature equilibration
• Densitometer Filler Tube - Avoid turbulence or the introduction of air into the liquid when adding de-oxygenated water to the pycnometer during calibration or testing
• Blender - Mixing the soil with water in a blender to disperse the sample into a slurry. We recommend the use of a soil dispersion mixer for preparing soil specimens for hydrometer analysis
• Balance. Our laboratory balances meet the requirements of ASTM D4753, and have a minimum capacity of 1,000 grams and a readability of 0.01 grams
• Drying Oven: Moisture determination and final drying of test solutions is performed in a standard laboratory oven capable of maintaining a uniform temperature of 110 ± 5°C
• Test Sieve. The test method requires that the sample particle size pass through an ASTM E11 No. 4 (4.75 mm) mesh sieve

Figure 3. Determination of Specific Gravity of Soils.