1、Designation: D 6572 06Standard Test Methods forDetermining Dispersive Characteristics of Clayey Soils bythe Crumb Test1This standard is issued under the fixed designation D 6572; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods provide a qualitative indication ofthe natural dispersive characteristics of clayey soils.
3、1.2 These test methods are not applicable for soils with lessthan 12 % fraction finer than 0.005 mm and with a plasticityindex less than or equal to 8.1.3 The crumb test method has some limitations in itsusefulness as an indicator of dispersive clay. A dispersive soilmay sometimes give a nondispersi
4、ve reaction in the crumb test.Soils containing kaolinite with known field dispersion prob-lems have shown nondispersive reactions in the crumb test(1)2. However, if the crumb test indicates dispersion, the soil isprobably dispersive.1.4 Oven-dried soil should not be used to prepare crumb testspecime
5、ns, as irreversible changes could occur to the soilpore-water physicochemical properties responsible for disper-sion (2).1.5 The crumb test method, while a good quick indication ofdispersive clay, should usually be run in conjunction with apinhole test and a double hydrometer test, Test MethodsD 464
6、7 and D 4221, respectively.NOTE 1In some cases, the results of the pinhole, crumb, anddouble-hydrometer test methods may disagree. Crumb test methods are abetter indicator of dispersive clays than of nondispersive clays (3).1.6 The values stated in SI units are to be regarded as thestandard. The val
7、ues given in parentheses are for informationonly.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 establish appro-priate safety and health practices and determine the applica-bility of re
8、gulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 1193 Specification for Reagent WaterD 2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 3740 Practice for Mi
9、nimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and ConstructionD 4221 Test Method for Dispersive Characteristics of ClaySoil by Double HydrometerD 4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD 4
10、647 Test Method for Identification and Classification ofDispersive Clay Soils by the Pinhole TestD 6026 Practice for Using Significant Digits in Geotechni-cal DataE1 Specification for ASTM Liquid-in-Glass ThermometersE11 Specification for Wire Cloth and Sieves for TestingPurposes3. Terminology3.1 De
11、finitions:3.1.1 dispersive clayssoils that disperse (deflocculate)easily and rapidly without significant mechanical assistance inwater of low-salt concentration.3.1.1.1 DiscussionSuch soils usually have a high propor-tion of their adsorptive capacity saturated with sodium cationsalthough adsorbed li
12、thium and magnesium may also play a role1These test methods are under the jurisdiction of ASTM Committee D18 on Soiland Rock and are the direct responsibility of Subcommittee D18.06 on Physical-Chemical Interactions of Soil and RockCurrent edition approved Nov. 1, 2006. Published December 2006.2The
13、boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Su
14、mmary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(4). Such soils also generally have a high shrink-swell poten-tial, have low resistance to erosion, and have low permeabilityin an intact state.3.2 For def
15、initions of other terms used in these test methods,refer to Terminology D 653.4. Summary of Test Method4.1 A cube of remolded soil approximately 15 mm (58 in.)on each side (about the size of a single die in a pair of dice) ora natural soil crumb of approximately similar volume is placedon the bottom
16、 of a white porcelain dish containing 250 mL ofdistilled water.4.2 Temperature of the water is recorded and visual deter-minations of dispersion grade are made and recorded at 2 min,1 h, and 6 h. Determination of grade is based on the formation,extent, and turbidity of a dense “cloud” or halo of col
17、loidal-sized particles extending from the soil crumb.4.3 Determinations consist of: Grade 1 (Nondispersive),Grade 2 (Intermediate), Grade 3 (Dispersive), and Grade 4(Highly Dispersive).5. Significance and Use5.1 The crumb test method provides a simple, quick methodfor field or laboratory identificat
18、ion of a dispersive clay soil.The internal erosion failures of a number of homogeneousearth dams, erosion along channel or canal banks, and rainfallerosion of earthen structures have been attributed to colloidalerosion along cracks or other flow channels formed in massesof dispersive clay (5).5.2 Th
19、e crumb test method, as originally developed byEmerson (6), was called the aggregate coherence test and hadseven different categories of soil-water reactions. Sherard (5)later simplified the test by combining some soil-water reactionsso that only four categories, or grades, of soil dispersion areobs
20、erved during the test. The crumb test is a relatively accuratepositive indicator of the presence of dispersive properties in asoil. The crumb test, however, is not a completely reliablenegative indicator that soils are not dispersive. The crumb test,can seldom be relied upon as a sole test method fo
21、r determiningthe presence of dispersive clays. The double-hydrometer test(Test Method D 4221) and pinhole test (Test Method D 4647)are test methods that provide valuable additional insight intothe probable dispersive behavior of clay soils.NOTE 2The quality of the result produced by these test metho
22、ds isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D 3740 are generally considered capable of competentand objective testing. Users of these test methods are cautioned thatcompliance wit
23、h Practice D 3740 does not in itself ensure reliable testing.Reliable testing depends on several factors; Practice D 3740 provides ameans of evaluating some of those factors.6. Interferences6.1 Oven-dried soil shall not be used in performing thecrumb test as irreversible changes could occur to the s
24、oilpore-water physicochemical properties responsible for disper-sion (2).6.2 Using other than Type IV water in accordance withSpecification D 1193, can interfere with dispersion of thecolloidal clay particles.6.3 Carefully place the cube or crumb directly on the bottomof the dish when submerging the
25、 crumb. Dropping the crumbfrom the water surface can cause excessive slaking and mayresult in erroneous interpretation of the dispersion grade.6.4 Jarring or moving the soil specimen or porcelain dishonce the test method has begun can cause excessive turbidityand may result in erroneous interpretati
26、on of the dispersiongrade.6.5 The use of natural, irregular-shaped soil crumbs mayresult in a specimen that is not representative of the totalsample. Therefore, several crumb test specimens should beselected to ensure that representative test results are obtained.The total number of test specimens s
27、hould be determinedduring the test program and will depend on the degree ofagreement of individual test results.6.6 These test methods are not applicable to soils less than12 % fraction finer than 0.005 mm and with a plasticity indexless than or equal to 8, refer to Test Method D 4318.7. Apparatus7.
28、1 Specimen ContainerDish, porcelain, evaporating,300-mL capacity.NOTE 3Plastic bowls or cups can also be used but they should bewhite or clear to help in distinguishing the colloidal cloud. The containershould be at least 85 mm (3 in.) across the bottom if flat-bottomed.7.2 Thermometer0 to 50C range
29、, 0.1C divisions, con-forming to the requirements of Specification E1.7.3 Sieve, 4.75-mm (No. 4) and 2-mm (No. 10) sieve, inaccordance with Specification E11.8. Reagents and Materials8.1 Purity of WaterType IV of Specification D 1193 witha pH between 5.5 and 7.0 shall be used for conducting the test
30、method and preparing remolded specimens. Distilled water ispreferred.9. Sampling, Test Specimens, and Test Units9.1 SamplingObtain a representative soil sample of4.75-mm (No. 4) soil. Depending on the percentage of coarsesand in the material, approximately 25 to 75 g of material isneeded to perform
31、a crumb test method and approximately 400to 500 g of material is needed to perform the crumb, pinhole,and double-hydrometer tests.NOTE 4Do not use oven-dried material for the crumb test methodbecause irreversible changes may occur to the soil pore-water physico-chemical properties responsible for di
32、spersion. Soil at natural moisture orat specified compaction moisture is preferred.9.1.1 Water content of the sample prior to specimen prepa-ration should be determined using either natural, air-dried, orwater content as specified in Test Method D 2216.99.2 Test Specimens:9.2.1 Test specimens may be
33、 from natural, irregularlyshaped soil crumbs (Test Method A) or may be remolded frommaterial passing a 2-mm (No. 10) sieve (Test Method B).Material for the crumb test method should be selected as soonas possible after obtaining the soil sample.9.2.2 Test Method ANatural Soil Crumbs:D65720629.2.2.1 A
34、 natural, irregularly shaped soil crumb is selectedthat has been preserved at natural moisture or only allowed toair-dry. This soil crumb should be approximately the samevolume as a cube 15 mm (58 in.) on each side (about the sizeof a single die of a pair of dice). Smaller soil crumbs down toa volum
35、e equivalent to a cube 7 mm (14 in.) on each side maybe used if larger ones are unavailable.9.2.2.2 Use of natural soil crumbs may result in a specimenthat is not representative of the total sample. Therefore, it isrecommended that several crumb specimens be tested to ensurethe total sample is repre
36、sented. The number chosen is depen-dent on the homogeneity of the total sample.9.2.3 Test Method BRemolded Specimens:9.2.3.1 A cube, approximately 15 mm (58 in.) on each side,is prepared from moist soil which has passed a 2-mm (No. 10)sieve.9.2.3.2 If the crumb test method is being done in conjunc-t
37、ion with the pinhole test method (Test Method D 4647), thecube can be prepared from material cured to the moisturecontent desired for compacting the pinhole specimen. Alterna-tively, air-dried soil or soil at natural moisture can be passedthrough a 2-mm (No. 10) sieve and formed into the cube. Ifadd
38、itional moisture is needed to form the cube, Type IV waterin accordance with Specification D 1193 can be added until thecube can be formed.NOTE 5Results of the crumb test methods can be altered by mixingportions of a sample that have dispersive properties with a portion of thesample with nondispersi
39、ve properties. If remolded crumbs are used fortesting, minimize the mixing of visually nonhomogeneous soil to obtainthe material for the remolded crumb to avoid mixing dispersive andnondispersive segments of the sample.10. Conditioning10.1 Preserve crumb test specimens at natural moisture, ifpossibl
40、e, or allow specimens to air-dry. Do not oven-dry crumbtest specimens.11. Procedure11.1 Record all data on a “Crumb Test Method” form. Anexample of an acceptable form is shown in Fig. 1.11.2 Place a 300-mL porcelain evaporating dish on a hori-zontal working surface, which will be relatively free ofv
41、ibration for the next 6 h.NOTE 6Placing the dish on the top edge of the crumb test formfacilitates easy identification of a number of specimens and reduces thepotential for misidentification.11.3 Pour approximately 250 mL of Type IV water inaccordance with Specification D 1193 into the porcelain dis
42、hand allow the water temperature to stabilize.11.4 Record the applicable test specimen information on thecrumb test form as shown in Fig. 1. Information should be inaccordance with Practice D 6026.11.5 Prepare a crumb test specimen using one of two testmethods.11.5.1 Test Method A: Natural Soil Crum
43、bs:11.5.1.1 Anatural soil crumb equivalent in volume to a cubeapproximately 15 mm (58 in.) on each side is selected from ahomogeneous soil sample with an abundance of aggregatedsoil lumps suitable for crumb test specimens. If no one crumbis equivalent to a cube approximately 15 mm on each side, aser
44、ies of smaller cubes can be used. Crumb volume should notbe less than equivalent to a cube 7 mm (14 in.) on each side.NOTE 7When using natural crumb specimens, it is better to use aseries of crumbs to ensure results representative of the entire sample.11.5.2 Test Method B: Remolded Soil Crumbs:11.5.
45、2.1 Prepare a crumb test specimen by lightly compress-ing a moist soil sample into a cube approximately 15 mm (58in.) on each side. Use the thumbs and index finger to gentlyform the cube.11.6 Carefully place the specimen in the water and gentlyrelease it only after placing it directly on the bottom
46、of the dish.Do not move or vibrate the dish or stir the water from specimenplacement until the end of this test method.11.7 Note and record the time of specimen placement on thecrumb test form and start the stopwatch.11.8 As the soil crumb begins to absorb water, observe thetendency for colloidal-si
47、zed particles to deflocculate and gointo suspension.NOTE 8The colloidal-sized particles are visible in the form of a dense“cloud” or halo that extends from the soil crumb. The extent and turbidityof the suspended clay particle “cloud” is visually interpreted. Thecolloidal“ cloud” is influenced by so
48、il color, that is, dark soils produce adarker, more distinctly visible “cloud.”11.9 At 2 min, 1 h, and 6 h, determine and record the soildispersion grade in accordance with to the following criteria:11.9.1 Grade 1, (Nondispersive)No reaction; the soil maycrumble, slake, diffuse, and spread out, but
49、there is no turbidwater created by colloids suspended in the water. All particlessettle during the first hour.FIG. 1 Example of Data Sheet for Crumb Test for Dispersibility ofClayey SoilsD657206311.9.2 Grade 2, (Intermediate)Slight reaction; this is thetransition grade. A faint, barely visible colloidal suspensioncauses turbid water near portions of the soil crumb surface orall around the surface. If the cloud is easily visible, assignGrade 3. If the cloud is faintly seen in only one small area,assign Grade 1.11.9.3 Grade 3, (Dispersive)Moderate reaction; a
