Significance and Use

The specific gravity value is used in many phase relation equations to determine relative volumes of particle, water, and gas mixtures.

The term soil particle typically refers to a naturally occurring mineral grain that is not readily soluble in water. Therefore, the specific gravity of soils that contain extraneous matter (such as cement, lime, and the like) or water-soluble material (such as salt) must be corrected for the precipitate that forms on the specimen after drying. If the precipitate has a specific gravity less than the parent soil grains, the uncorrected test result will be too low. If the precipitate has a higher specific gravity, then the uncorrected test value will be too high.

NOTE 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.

Scope

This test method covers the determination of the specific gravity of soil solids by means of a gas pycnometer. Particle size is limited by the dimensions of the specimen container of the particular pycnometer being used.

Test Method D854 may be used instead of or in conjunction with this test method for performing specific gravity tests on soils. Note that Test Method D854 does not require the specialized test apparatus needed by this test method. However, Test Method D854 may not be used if the specimen contains matter that can readily dissolve in water, whereas this test method does not have that limitation.

Summary of Test Method

This test method is used to determine the specific gravity of soil grains using a gas pycnometer. This test method also contains equations for correcting the initial specific gravity value for dissolved matter within the pore fluid.

Apparatus

Pycnometer—The gas pycnometer shall be one of the commercially available models that determines the volume of a solid by one of two methods. One measures the pressure drop that occurs after a gas at a known pressure is allowed to flow into another chamber (typically the first chamber contains the solid material being tested). The amount of pressure drop is related to the volume of soil present. The other type of instrument puts a known volume of gas into a chamber containing the specimen. The increase in pressure is related to the volume of the material. Either type of instrument is acceptable provided that the required accuracy of the instrument produces a volume measurement that is 60.2 % of the specimen volume.

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