1、Designation: D425 17Standard Test Method forCentrifuge Moisture Equivalent of Soils1This standard is issued under the fixed designation D425; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in pa
2、rentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the mois-ture equivalent of soil in the laboratory by means of acentrifuge technique.1.2 This test me
3、thod is limited to specimens of coarse-grained sandy soils having a maximum particle size of less than2.00 mm and with fines of low plasticity. Soils having a unifiedsoil classification, based upon procedures outlined in PracticeD2488 such as SP, SW, SC-SM, or SM are consideredacceptable for the tes
4、t method.1.2.1 For soils that are predominantly fine-grained, coarse-grained soils with medium to high plasticity, intact specimensor soils being tested at a specific density or unit weight refer toTest Methods D6836.1.3 This test method is intended to be performed in aconstant temperature environme
5、nt. Variations in temperatureexceeding the range outlined in 8.7 may influence the test data.1.4 UnitsThe values stated in SI units are to be regardedas the standard except for sieve designations, which alsoinclude the “alternative” system in accordance with E11.1.5 All recorded and calculated value
6、s shall conform to theguide for significant digits and rounding established in PracticeD6026.1.6 The procedures used to specify how data are collected/recorded and calculated in this standard are regarded as theindustry standard. In addition, they are representative of thesignificant digits that gen
7、erally should be retained. The proce-dures used do not consider material variation, purpose forobtaining data, special purpose studies, or any considerationsfor the users objectives; and it is common practice to increaseor reduce significant digits of reported data to commensuratewith these consider
8、ations. It is beyond the scope of these testmethods to consider significant digits used in analysis methodsfor engineering design.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establis
9、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil
10、 and Rock by MassD2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)D3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil
11、and Rock asUsed in Engineering Design and ConstructionD4753 Guide for Evaluating, Selecting, and Specifying Bal-ances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD6026 Practice for Using Significant Digits in GeotechnicalDataD6836 Test Methods for Determination of the
12、 Soil WaterCharacteristic Curve for Desorption Using HangingColumn, Pressure Extractor, Chilled Mirror Hygrometer,or CentrifugeE11 Specification for Woven Wire Test Sieve Cloth and TestSieves3. Terminology3.1 Definitions:3.1.1 For definitions of common technical terms used in thisstandard, refer to
13、Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 capillary fringe zonethe zone above the free waterelevation in which water is held by capillary action.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcom
14、mittee D18.03 on Texture, Plasticityand Density Characteristics of Soils.Current edition approved Jan. 15, 2017. Published January 2017. Originallyapproved in 1935. Last previous edition approved in 2008 as D425 88 (2008).DOI: 10.1520/D0425-17.2For referenced ASTM standards, visit the ASTM website,
15、www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive,
16、 PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issue
17、d by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.2 centrifuge moisture equivalentthe water content of asoil after it has been saturated with water and then subjected forone hour to a centrifugal force equal to 1000 times that ofgravity.3.2.3 specific retentionthe ra
18、tio of the volume of waterthat cannot be drained from a saturated soil under the action offorce of gravity to the total volume of voids.3.2.4 water-holding capacitythe smallest value to whichthe water content of soil or rock can be reduced by gravitydrainage.4. Summary of Test Method4.1 The centrifu
19、ge moisture equivalent of soils is deter-mined by initially air-drying the soil sample. Two 5-g testspecimens are selected from the sample and thoroughly soakedin distilled or deionized water. The specimens are centrifugedfor1hataforce equal to 1000 times that of gravity at aconstant temperature of
20、20 6 1C. The moisture content isdetermined after centrifuging in accordance with Test MethodsD2216. The average of the two water contents is the moistureequivalent of the soil.5. Significance and Use5.1 All water contained in a saturated soil cannot beremoved by gravity drainage alone. The amount of
21、 waterretained after gravity drainage is usually expressed as the waterholding capacity or specific retention of the soil. These valuesmay be influenced by elapsed time, the particle-size distribu-tion and the plasticity of the soil. In most cases, as the plasticityincreases so does the moisture equ
22、ivalent value.5.2 The centrifuge moisture equivalent is determined byapplying a centrifugal force great enough to reduce thecapillary fringe zone sufficiently so that it can be ignoredwithout introducing error. The centrifical force is maintainedsufficiently low as not to withdraw a large proportion
23、 of thewater that is held securely above the capillary fringe (see Note1).5.3 It has been determined that for at least medium-texturedsoils (sandy to silty particle-size distribution) the centrifugemoisture equivalent approximates the water holding capacityand when combined with the bulk density can
24、 be used tocalculate an approximate specific retention and specific yield.These properties when combined with porosity can be used toestimate aquifer storage coefficient.NOTE 1If a soil will hold water 100 mm by capillarity acting againstgravity, the soil will theoretically be able to hold the water
25、 only 0.1 mmagainst a centrifugal force that is 1000 times greater than the force ofgravity.NOTE 2The statements on precision and bias contained in this testmethod; the precision of this test method is dependent on the competenceof the personnel performing it, and the suitability of the equipment an
26、dfacilities used. Agencies that meet the criteria of Practice D3740 aregenerally considered capable of competent and objective testing. Users ofthis test method are cautioned that compliance with Practice D3740 doesnot in itself assure reliable testing. Reliable testing depends on manyfactors; Pract
27、ice D3740 provides a means of evaluating some of thesefactors.6. Apparatus6.1 CentrifugeA centrifuge capable of generating a forceequal to 1000 times the force of gravity on the center of gravityof the soil specimen for a period of 1 h. The centrifuge chambershall be capable of maintaining a control
28、led temperature of 206 1C. In place of a temperature controlled chamber, the entirecentrifuge may be operated in a controlled environment ca-pable of meeting the temperature requirement of 20 6 1C.6.1.1 The revolutions per minute, N, required to provide acentrifugal force of 1000 times gravity is de
29、termined from theequation:N 5RCF0.00000111 rm(1)where:N = revolutions per minute,RCF = relative centrifugal force (1000),r = radius of rotation to center of gravity of the testspecimen, mm, andm = mass of the body, taken as unity.For most standard centrifuges, N will equal approximately2300 rpm.6.2
30、Gooch CrucibleTwo procelain Gooch crucibles hav-ing a capacity of approximately 25 mL, and a diameter at thebottom of the crucible of about 20 mm (Fig. 1). The crucibleshall have a perforated bottom and be compatible for use withthe centrifuge being used.6.3 Babcock Trunnion CupsAt least two centrif
31、uge cupswith caps and with a crucible holder for supporting the Goochcrucible above the bottom of the cup (Fig. 1). The holder shallhave sufficient clearance to fit fully within the cup and supportthe cup in such a manner that the water removed during thecentrifuging operation does not come in conta
32、ct with thecrucible and soil. Cups and crucible holders shall be balancedin pairs opposite each other in the centrifuge.6.4 Filter PaperA circular piece of filter paper of suffi-cient size to cover the inside bottom of the Gooch crucible (seeNote 3).NOTE 3A medium speed, high wet strength (hardened)
33、 filter paper isrecommended.6.5 BalanceA balance having a readability of 0.01 g, andaccurate to 60.03 g, conforming to Specification D4753.6.6 HumidifierA cabinet or large jar with water in thelower half of the container. A shelf positioned above the levelof the water should be covered with moisture
34、 resistant fabric onwhich to store the crucibles and soil specimens.6.7 OvenA thermostatically controlled drying oven, pref-erably of the forced-draft type, capable of maintaining auniform temperature of 110 6 5C throughout.6.8 Water Content ContainersSuitable containers made ofmaterial resistant to
35、 corrosion and change in mass uponrepeated heating, cooling, and cleaning. Containers shall haveclose-fitting lids to prevent loss of moisture from the soil priorto the initial weighing and to prevent absorption of moisturefrom the atmosphere following oven drying and before finalD425 172weighing. O
36、ne container is needed for each water contentdetermination. Containers should be 50-100 mL capacity (seeNote 4).NOTE 4It is recommended that the containers be numbered in pairs tocoincide with the crucible numbers.6.9 Mortar and PestleA mortar and rubber-tipped pestlesuitable for breaking up the soi
37、l aggregations.6.10 Sieve2.00-mm (No. 10) mesh sieve conforming toSpecification E11.6.11 A pan or container used to collect the sample oncepassed through the 2.00-mm (No. 10) sieve.7. Samples and Specimens7.1 Air dry the as-received soil sample. Break up theaggregations thoroughly using the mortar a
38、nd pestle. Dry sievethe sample through the 2.00-mm (No. 10) sieve.7.2 Thoroughly mix the sample and split by use of a samplesplitter or quartering method to obtain about 50 g of air-driedsoil.7.3 Obtain two 5-g specimens of material for testing. Thecrucibles shall be paired in such a way that the ma
39、sses of thecrucibles and contents meet the requirements of the manufac-turer of the centrifuge.8. Procedure8.1 Place a disk of wet filter paper on the bottom of the twocrucibles. The filter paper shall cover the entire bottom of thecrucible but not rest on the crucibles wall.8.2 Loosely and evenly p
40、lace the two soil specimens intothe paired crucibles.8.3 Place the crucibles in a pan of distilled or demineralizedwater to a depth at least 5 mm above the height of the soil inthe crucible. Allow the soil to absorb water until fully satu-rated.NOTE 5Eight hours or overnight is normally sufficient t
41、ime for thesoil to become saturated and is indicated by the presence of free watercovering the surface of the soil.8.4 Place the crucible and specimen in the humidifier todrain for at least 12 h to obtain uniform distribution of waterthroughout the soil mass.8.5 Pour or siphon off any water remainin
42、g above thesurface of the specimens.8.6 Place the paired crucibles into the centrifuge cups fittedas described in 6.2 and position opposite each other in thecentrifuge.8.7 Maintain the centrifuge environment at a temperature 206 1C and adjust the centrifuge to the required speed within 5min by five
43、incremental and equal steps.8.8 Maintain the centrifuge speed and temperature for 60min. The speed of the centrifuge shall exert a centrifugal force1000 times greater than that of gravity upon the center ofgravity of each of the test specimens.8.9 Following the 60 min centrifuging period, allow thec
44、entrifuge to come to rest with as little braking as possible, butnot to exceed a 5-min time interval.FIG. 1 Crucible, Trunnion Cup, and Cup HolderD425 1738.10 Immediately after centrifuging, transfer the soil fromthe two crucibles to water content containers as quickly aspossible to minimize moistur
45、e loss. It is not necessary toremove all of the soil from the crucibles.8.10.1 Determine the water content of each specimen inaccordance with Test Methods D2216.8.11 If water is observed on the top of the soil aftercentrifuging, the soil is said to have water-logged. The centri-fuge moisture equival
46、ent is not considered to be valid for thismaterial and the report should be so noted.8.12 A sample data sheet is shown in Fig. 2.9. Calculation9.1 Calculate the centrifuge moisture equivalent as theaverage of the water contents of the two specimens asdetermined by Test Methods D2216.10. Report: Test
47、 Data Sheet(s)/Form(s)10.1 The methodology used to specify how data are re-corded on the test data sheet(s)/forms(s), as given below, iscovered in 1.6.10.2 Record as a minimum the following information(data):FIG. 2 Centrifuge Moisture Equivalent Sample Data SheetD425 17410.2.1 Name of the person per
48、forming the test.10.2.2 Identification of sample including project number,project name, boring number, sample number, and depth ifappropriate.10.2.3 Description of the soil including the Unified SoilClassification following Practice D2487 or D2488.10.2.4 The average centrifuge moisture equivalent of
49、 thespecimen to the nearest 1 %.10.2.5 If one or both of the specimens were water-logged,the report shall state that the centrifuge moisture equivalentwas not valid for the soil tested.11. Precision and Bias11.1 PrecisionInformation on the precision of this testmethod is being gathered.312. Keywords12.1 centrifuge moisture equivalent; specific retention; spe-cific yield, storage capacity; water holding capacitySUMMARY OF CHANGESIn accordance with Committee D18 policy, this section identifies the location of changes to this standard sincethe last edit
