Significance and Use
5.1 Density is a key element in the phase relations, phase relationships, or mass-volume relationships of soil and rock ( ). When particle density, that is, specific gravity (Test Methods ) is also known, dry density can be used to calculate porosity and void ratio (see ). Dry density measurements are also useful for determining degree of soil compaction. Since water content is variable, total/moist soil density provides little useful information except to estimate the weight of soil per unit volume, for example, grams per cubic centimeter, at the time of sampling. Since soil volume shrinks with drying of swelling soils, total density will vary with water content. Hence, the water content of the soil should be determined at the time of sampling.
5.2 Densities and unit weights of remolded/reconstituted specimens are commonly used to evaluate the degree of compaction of earthen fills, embankments, and the like. Dry density values are used to calculate dry unit weight values to create a compaction curve (Test Methods and ).
Note 2: 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 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice does not in itself assure reliable results. Reliable results depend on several factors; Practice provides a means of evaluating some of these factors.
1.1 These test methods describe two ways of determining the total/moist/bulk density, dry density, and dry unit weight of intact, disturbed, remolded, and reconstituted (compacted) soil specimens ( ). Intact specimens may be obtained from thin-walled sampling tubes, block samples, or clods. Specimens that are remolded by dynamic or static compaction procedures are also measured by these methods. These methods apply to soils that will retain their shape during the measurement process and may also apply to other materials such as soil-cement, soil-lime, soil-bentonite or solidified soil-bentonite-cement slurries. It is common for the density to be less than the value based on tube or mold volumes, or of in situ conditions after removal of the specimen from sampling tubes and compaction molds. This change is due to the specimen swelling after removal of lateral pressures.
Note 1: The adjectives total, moist, wet or bulk are used to represent the density condition. In some professions, such as Soil Science and Geology, the term “bulk density” usually has the same meaning as dry density. In the Geotechnical and Civil Engineering professions, the preferred adjective is total over moist and bulk when referring to the total mass of partially saturated or saturated soil or rock per unit total volume. For more detailed information regarding the term density, refer to Terminology .
1.1.1 Method A (Water Displacement)—A specimen is coated in wax and then placed in water to measure the volume by determining the quantity of water displaced. The density and unit weight are then calculated based on the mass and volume measurements. Do not use this method if the specimen is susceptible to surface wax intrusion.
1.1.2 Method B (Direct Measurement)—The dimensions and mass of a specimen are measured. The density and unit weight are then calculated using these direct measurements. Usually, the specimen has a cylindrical or cuboid shape. Intact and reconstituted/remolded specimens may be tested by this method in conjunction with strength, permeability/hydraulic conductivity (air/water) and compressibility determinations.
1.2 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.2.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In the system, the pound (lbf) represents a unit of force (weight), while the units for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations are involved.
1.2.2 It is common practice in the engineering/construction profession to concurrently use pounds to represent both a unit of mass (lbm) and of force (lbf). This practice implicitly combines two separate systems of units; the absolute and the gravitational systems. It is scientifically undesirable to combine the use of two separate sets of inch-pound units within a single standard. As stated, this standard includes the gravitational system of inch-pound units and does not use/present the slug unit of mass. However, the use of balances and scales recording pounds of mass (lbm) or recording density in lbm/ft3 shall not be regarded as nonconformance with this standard.
1.2.3 The terms density and unit weight are often used interchangeably. Density is mass per unit volume, whereas unit weight is force per unit volume. In this standard, density is given only in SI units. After the density has been determined, the unit weight is calculated in SI or inch-pound units, or both.
1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice , unless superseded by this test method.
1.3.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.