ASTM D425-17

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D425 − 88 (Reapproved 2008) D425 − 17
Standard Test Method for
Centrifuge Moisture Equivalent of Soils
This standard is issued under the fixed designation D425; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This test method covers the determination of the moisture equivalent of soil in the laboratory by means of a centrifuge
technique.
1.2 This test method is limited to disturbed specimens of coarse-grained soils having sandy soils having a maximum particle
size of less than 2.00 mm and with fines of low plasticity plasticity. Soils having a unified soil classification, based upon procedures
outlined in Practice D2488 such as SP, SW, SC-SM, or SM soils. The test is limited to soils passing the 2.00-mm sieve or that
fraction of a soil passing a 2.00-mm sieve. are considered acceptable for the test method.
NOTE 1—Test Method D3152 or Test Method D2325 should be used to evaluate the capillary-moisture relations of fine-grained soils and coarse-grained
soils having fines of medium to high plasticity, undisturbed soils, and soils at specific desired units weights.
1.2.1 For soils that are predominantly fine-grained, coarse-grained soils with medium to high plasticity, intact specimens or soils
being tested at a specific density or unit weight refer to Test Methods D6836.
1.3 TheThis test method is temperature-dependent, and consistent comparable results can be obtained only if the tests are
performed under a constant-temperature condition.intended to be performed in a constant temperature environment. Variations in
temperature exceeding the range outlined in 8.7 may influence the test data.
1.4 Units—The values stated in SI units are to be regarded as the standard.standard except for sieve designations, which also
include the “alternative” system in accordance with E11.
1.5 All recorded and calculated values shall conform to the guide for significant digits and rounding established in Practice
D6026.
1.6 The procedures used to specify how data are collected/recorded and 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 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 commensurate with these considerations. It is
beyond the scope of these test methods to consider significant digits used in analysis methods for engineering design.
1.7 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2325D2487 Test Method for Capillary-Moisture Relationships for Coarse- and Medium-Textured Soils by Porous-Plate
ApparatusPractice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) (Withdrawn 2007)
D2488 Practice for Description and Identification of Soils (Visual-Manual Procedure)
D3152D3740 Test Method for Capillary-Moisture Relationships for Fine-Textured Soils by Pressure-Membrane ApparatusPrac-
tice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.03 on Texture, Plasticity
and Density Characteristics of Soils.
Current edition approved Feb. 1, 2008Jan. 15, 2017. Published March 2008January 2017. Originally approved in 1935. Last previous edition approved in 20012008 as
D425 – 88 (2008). (2001). DOI: 10.1520/D0425-88R08.10.1520/D0425-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D425 − 17
Design and Construction (Withdrawn 2007)
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D6026 Practice for Using Significant Digits in Geotechnical Data
D6836 Test Methods for Determination of the Soil Water Characteristic Curve for Desorption Using Hanging Column, Pressure
Extractor, Chilled Mirror Hygrometer, or Centrifuge
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
3. Terminology
3.1 All definitions are in accordance with Terminology D653. Terms of particular significance are as follows:Definitions:
3.1.1 For definitions of common technical terms used in this standard, refer to Terminology D653.
3.2 capillary fringe zone—the zone above the free water elevation in which water is held by capillary action.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 capillary fringe zone—the zone above the free water elevation in which water is held by capillary action.
3.2.2 centrifuge moisture equivalent—the water content of a soil after it has been saturated with water and then subjected for
one hour to a centrifugal force equal to 1000 times that of gravity.
3.2.3 specific retention—the ratio of the volume of water that cannot be drained from a saturated soil under the action of force
of gravity to the total volume of voids.
3.2.4 water-holding capacity—the smallest value to which the water content of soil or rock can be reduced by gravity drainage.
3.3 centrifuge moisture equivalent—the water content of a soil after it has been saturated with water and then subjected for one
hour to a centrifugal force equal to 1000 times that of gravity.
3.4 specific retention—the ratio of the volume of water that cannot be drained from a saturated soil under the action of force
of gravity to the total volume of voids.
3.5 water-holding capacity—the smallest value to which the water content of soil or rock can be reduced by gravity drainage.
4. Summary of Test Method
4.1 The centrifuge moisture equivalent of soils is determined by initially air-drying the soil, selecting two 5-g test specimens,
thoroughly soaking each test specimen, and then determining the water content of each specimen after it has been soil sample. Two
5-g test specimens are selected from the sample and thoroughly soaked in distilled or deionized water. The specimens are
centrifuged for 1 h at a force equal to 1000 times that of gravity at a controlledconstant temperature of 20 6 1°C. The moisture
content is determined after centrifuging in accordance with Test Methods D2216. The average of the two water contents is the
moisture equivalent of the soil.
5. Significance and Use
5.1 Not all All water contained in a saturated soil cancannot be removed by gravity drainage. drainage alone. The amount of
water retained after gravity drainage is usually expressed as the water holding capacity or specific retention. It varies with time,
and with retention of the soil. These values may be influenced by elapsed time, the particle-size distribution and the plasticity of
the soil (in general, increasing in value with increasing plasticity index). soil. In most cases, as the plasticity increases so does the
moisture equivalent value.
5.2 The centrifuge moisture equivalent is determined by applying a centrifugal force great enough to reduce the capillary fringe
zone sufficiently so that it can be ignored without introducing error. The centrifical force is maintained sufficiently low as not to
withdraw a large proportion of the water that is held securely above the capillary fringe (see Note 1).
5.3 In general, the centrifuge moisture equivalent is based on the theory of applying a centrifugal force great enough to reduce
the capillary fringe zone enough that it can be ignored without introducing much error, even in small specimens, and yet not so
great as to withdraw a large proportion of the water that is held securely above the capillary fringe. For example, if a soil will hold
water 100 mm by capillarity acting against gravity, the soil will theoretically be able to hold the water only 0.1 mm against a
centrifugal force that is 1000 times greater than the force of gravity. It has been determined that for at least medium-textured soils
(sandy to silty particle-size distribution) the centrifuge moisture equivalent approximates the water holding capacity and when
combined with the bulk density can be used to calculate an approximate specific retention and specific yield. These properties when
combined with porosity can be used to estimate aquifer storage coefficient.
NOTE 1—If a soil will hold water 100 mm by capillarity acting against gravity, the soil will theoretically be able to hold the water only 0.1 mm against
a centrifugal force that is 1000 times greater than the force of gravity.
NOTE 2—The statements on precision and bias contained in this test method; the precision of this test method 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 test method are cautioned that compliance with Practice D3740 does not in itself assure reliable
testing. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of these factors.
D425 − 17
6. Apparatus
6.1 Centrifuge—A centrifuge capable of such a size and so driven that a generating a force equal to 1000 times the force of
gravity may be exerted on the center of gravity of the soil specimen for a period of 1 h. The centrifuge chamber shall be capable
of maintaining a controlled temperature of 20 6 1°C. The revolutions per minute, In place of N, required to provide a centrifugal
force of 1000 times gravity is determined from the equation:a temperature controlled chamber, the entire centrifuge may be
operated in a
RCF
N 5Π(1)
0.0000111 rm
controlled environment capable of meeting the temperature requirement of 20 6 1°C.
where:
N = revolutions per minute,
RCF = relative centrifugal force (1000),
r = radius of rotation to center of gravity of the test specimen, cm, and
m = mass of the body, taken as unity.
6.1.1 The revolutions per minute, N, required to provide a centrifugal force of 1000 times gravity is determined from the
equation:
RCF
N 5Π(1)
0.00000111 rm
where:
N = revolutions per minute,
RCF = relative centrifugal force (1000),
r = radius of rotation to center of gravity of the test specimen, mm, and
m = mass of the body, taken as unity.
For most standard centrifuges, N will equal approximately 2300 rpm.
For normal equipment installation, N will equal approximately 2300 rpm.
6.2 Gooch Crucible—ATwo procelain Gooch cruciblecrucibles having a perforated bottom, a capacity of approximately 25 mL,
and a diameter at the bottom of the crucible of about 20 mm (Fig. 1). Crucibles should be number
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