1、Designation: D6572 12Standard Test Methods forDetermining Dispersive Characteristics of Clayey Soils bythe Crumb Test1This standard is issued under the fixed designation D6572; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 Two test methods are provided to give a qualitativeindication of the natural dispersive characteristics of clay
3、eysoils. Method A is for natural soil clumps and method B forremolded soil.1.2 These test methods are not applicable for soils with lessthan 12 % finer than 0.005 mm and with a plasticity index lessthan or equal to 8.1.3 The crumb test method has some limitations in itsusefulness as an indicator of
4、dispersive clay. A dispersive soilmay sometimes give a non-dispersive reaction in the crumbtest. Soils containing kaolinite with known field dispersionproblems have shown non-dispersive reactions in the crumbtest (1)2. However, if the crumb test indicates dispersion, thesoil is probably dispersive.1
5、.4 Oven-dried soil should not be used to prepare crumb testspecimens, 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
6、with apinhole test and a double hydrometer test, Test Methods D4647and D4221, 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 All obse
7、rved and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.6.1 The method used to specify how data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in desig
8、n or otheruses, or both. How one applies the results obtained using thisstandard is beyond its scope.1.7 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.8 This standard does not purport to address all of thesafety concerns, i
9、f 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and C
10、ontainedFluidsD1193 Specification for Reagent WaterD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and Constructio
11、nD4221 Test Method for Dispersive Characteristics of ClaySoil by Double HydrometerD4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD4647 Test Method for Identification and Classification ofDispersive Clay Soils by the Pinhole TestD6026 Practice for Using Significant Di
12、gits in GeotechnicalDataE1 Specification for ASTM Liquid-in-Glass ThermometersE11 Specification for Woven Wire Test Sieve Cloth and TestSievesE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids3. Terminology3.1 Definitions:1These test methods are under the ju
13、risdiction 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, 2012. Published December 2012. Originallyapproved in 2006. Last previous edition approved in 2006 as D4186 06.
14、DOI:10.1520/D6572-12.2The 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
15、 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, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 For definitions of other terms used in these testmethods, r
16、efer to Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 dispersive clayssoils that disperse (deflocculate)easily and rapidly without significant mechanical assistance inwater of low-salt concentration.3.2.1.1 DiscussionSuch soils usually have a high propor-tion of their ads
17、orptive capacity saturated with sodium cationsalthough adsorbed lithium and magnesium may also play a role(4). Such soils also generally have a high shrink-swellpotential, have low resistance to erosion, and have lowpermeability in an intact state.4. Summary of Test Method4.1 A cube of remolded soil
18、 approximately 15 6 5mm(58614 in.) on each side (about the size of a single die in a pairof dice) or a natural soil crumb of approximately similarvolume is placed on the bottom of a container containing 300mL of distilled water.4.2 Temperature of the water is recorded and visual deter-minations of d
19、ispersion grade are made and recorded at 2 min6 15 s, 1 h 6 8 min, and 6 h 6 45 min. Determination of gradeis based on the formation, extent, and turbidity of a dense“cloud” or halo of colloidal-sized particles extending from thesoil crumb.4.3 Determinations consist of: Grade 1 (Non-dispersive),Grad
20、e 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 identification of a dispersive clay soil.The internal erosion failures of a number of homogeneousearth dams, erosion along
21、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 The crumb test method, as originally developed byEmerson (6), was called the aggregate coherence test and hadseven
22、 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 areobserved during the test. The crumb test is a relatively accuratepositive indicator of the presence of dispersive p
23、roperties in asoil. The crumb test, however, is not a completely reliablenegative indicator that soils are not dispersive. The crumb testcan seldom be relied upon as a sole test method for determiningthe presence of dispersive clays. The double-hydrometer test(Test Method D4221) and pinhole test (Te
24、st Method D4647)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 methods isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities
25、 used. Agencies that meet thecriteria of Practice D3740 are generally considered capable of competentand objective testing. Users of these test methods are cautioned thatcompliance with Practice D3740 does not in itself ensure reliable testing.Reliable testing depends on several factors; Practice D3
26、740 provides ameans of evaluating some of those factors.6. Interference6.1 Oven-dried soil shall not be used in performing thecrumb test as irreversible changes could occur to the soilpore-water physicochemical properties responsible for disper-sion (2).6.2 Using other than Type IV water in accordan
27、ce withSpecification D1193, 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 crumb. Dropping the crumbfrom the water surface can cause excessive slaking and mayresult in erroneous interpretation o
28、f the dispersion grade.6.4 Jarring or moving the soil specimen or container oncethe test method has begun can cause excessive turbidity andmay result in erroneous interpretation of the dispersion grade.6.5 The use of natural, irregular-shaped soil crumbs mayresult in a specimen that is not represent
29、ative of the totalsample. Therefore, several crumb test specimens should beselected to ensure that representative test results are obtained.The total number of test specimens should be determinedduring the test program and will depend on the degree ofagreement of individual test results.6.6 These te
30、st methods are not applicable to soils with lessthan 12 % finer than 0.005 mm and with a plasticity index lessthan or equal to 8, refer to Test Method D4318.7. Apparatus7.1 Specimen ContainerAn evaporating container with aminimum capacity of 300-mL.NOTE 3Plastic bowls or cups can also be used but th
31、ey 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, 0.1C divisions, con-forming to the requirements of Specification E1. Temperaturemeasuring devices such as RTDs, th
32、ermistors, or liquid-in-glass thermometers (e.g. Specification E2251) conforming toSpecification E1, and the temperature range and accuracy maybe used.7.3 Sieve(s), 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 Spe
33、cification D1193 with apH between 5.5 and 7.0 should be used for conducting the testmethod and preparing remolded specimens. Distilled water ispreferred.9. Sampling and Test Specimens9.1 SamplingObtain a representative soil sample passing4.75-mm (No. 4) sieve. Depending on the percentage of coarsesa
34、nd in the material, approximately 25 to 75 g of material isneeded to perform a crumb test method and approximately 400to 500 g of material is needed to perform the crumb, pinhole,and double-hydrometer tests.D6572 1229.1.1 Water content of the sample prior to specimen prepa-ration should be determine
35、d using either in situ, air-dried, orwater content as specified in Test Method D2216.9.2 Test Specimens:9.2.1 Test specimens may be 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 me
36、thod should be selected as soonas possible after obtaining the soil sample.9.2.2 Test Method ANatural Soil Crumbs:9.2.2.1 A natural, irregularly shaped soil crumb is selectedfrom a homogeneous soil sample with an abundance ofaggregated soil lumps suitable for crumb test specimens thathas been preser
37、ved at in situ or as-received water content oronly allowed to air-dry. This soil crumb should be approxi-mately the same volume as a cube 15 6 5mm(58 614 in.)on each side (about the size of a single die of a pair of dice).If no one crumb is equivalent to a cube approximately 15 6 5mm (58 614 in.) on
38、 each side, a series of smaller cubes canbe used. Crumb volume should not be less than equivalent to acube 7 6 3mm(14 618 in.) on each side.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 specim
39、ens be tested to ensurethe total sample is represented. 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 6 5mm(58 614 in.) oneach side, is prepared from moist soil which has passed a 2-mm(No. 10) sieve.9.2.3
40、.2 If the crumb test method is being done in conjunc-tion with the pinhole test method (Test Method D4647), thecube can be prepared from material cured to the moisturecontent desired for compacting the pinhole specimen.Alternatively, air-dried soil or soil at natural moisture can bepassed through a
41、2-mm (No. 10) sieve and formed into thecube. If additional moisture is needed to form the cube, TypeIV water in accordance with Specification D1193 can be addeduntil the cube can be formed.9.2.3.3 Results of the crumb test methods can be altered bymixing portions of a sample that have dispersive pro
42、pertieswith a portion of the sample with non-dispersive properties. Ifremolded crumbs are used for testing, minimize the mixing ofvisually nonhomogeneous soil to obtain the material for theremolded crumb to avoid mixing dispersive and non-dispersivesegments of the sample.10. Conditioning10.1 Preserv
43、e crumb test specimens at in situ or as-receivedwater content, if possible, or allow specimens to air-dry. Do notoven-dry crumb test specimens.11. Procedure11.1 Record data on a “Crumb Test” form.An example of anacceptable form is shown in Fig. 1.11.2 Place a suitable 300 ml non-porous container tha
44、t canfully immerse the sample on a horizontal working surface,which will be relatively free of vibration for the next 6 h.NOTE 4Placing 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 app
45、roximately 250 mL of Type IV water inaccordance with Specification D1193 into the container andallow the water temperature to stabilize to 21 6 6 degrees andmaintained throughout the test.11.4 Record the applicable test specimen information on thecrumb test form as shown in Fig. 1. Information shoul
46、d be inaccordance with Practice D6026.11.5 Prepare a crumb test specimen using one of two testmethods.11.5.1 Test Method A: Natural Soil Crumbs:11.5.1.1 Anatural soil crumb equivalent in volume to a cubeapproximately 15 6 5mm(58 614 in.) on each side isselected.NOTE 5When using natural crumb specime
47、ns, 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:11.5.2.1 Prepare a crumb test specimen by lightly compress-ing a moist soil sample into a cube approximately 15 6 5mm(58 614 in.) on each side. Use the thumbs an
48、d index fingerto gently form the cube.11.6 Carefully place the specimen in the water and gentlyrelease it only after placing it directly on the bottom 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
49、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-sized particles to deflocculate and gointo suspension.NOTE 6The 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. TheFIG. 1 Example of Data Sheet for Crumb Test for Dispersibility ofClayey SoilsD6572 123colloidal“ cloud” is influenced by soil color, tha
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