1、Designation: D7608 18Standard Test Method forTorsional Ring Shear Test to Measure Drained FullySoftened Shear Strength and Stress Dependent StrengthEnvelope of Fine-Grained Soils1This standard is issued under the fixed designation D7608; the number immediately following the designation indicates the
2、 year oforiginal adoption or, in the case of revision, the year 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. Scope1.1 This test method provides a procedure for performin
3、g atorsional ring shear test under a drained condition to measurethe fully softened shear strength and stress dependent strengthenvelope of fine-grained soils (using a reconstituted normallyconsolidated specimen). The fully softened strength and thecorresponding stress dependent effective stress str
4、ength enve-lope are used to evaluate the stability of slopes that do not havea pre-existing shear surface but have been subjected to envi-ronmental conditions and shear stresses that lead to soilsoftening, deterioration of the soil fabric, and strength loss. Ithas been shown (Skempton 19702and 19773
5、) that under theseconditions and within the depth zones that have undergonesoftening, first-time slope failures can occur at effective stresslevels that correspond to a fully softened strength envelope. Ithas also been shown empirically (Skempton 19702and 19773)that fully softened strength of fine g
6、rained soils can beapproximated by the peak strength of a reconstituted andnormally consolidated specimen. In this test method, reconsti-tuted and normally consolidated specimens are sheared at acontrolled and constant displacement rate until the peak shearresistance has been obtained. Generally, th
7、e drained fullysoftened failure envelope is determined at three or moreeffective normal stresses. A separate test specimen must beused for each normal stress to measure the fully softenedstrength otherwise a post-peak or even drained residualstrength will be measured if the same specimen is used at
8、thesame or at another effective normal stress because of theexistence of a prior shear surface.1.2 The ring shear apparatus allows a reconstituted speci-men to be normally consolidated at the desired normal stressprior to drained shearing. The test results closely simulate thefully softened strength
9、 of stiff natural fine-grained soils(Skempton 19702and 19773) and compacted fills of fine-grained soils (Gamez and Stark 20144). This simulates themobilized shear strength in overconsolidated clays, claystones,mudstones, and shales in natural slopes and compacted fill inmanmade slopes, such as, dams
10、, levees, and highwayembankments, after the soil has fully softened and attained thefully softened strength condition.1.3 A shear stress-displacement relationship may be ob-tained from this test method. However, a shear stress-strainrelationship or any associated quantity, such as modulus,cannot be
11、determined from this test method because definingthe height of the shear zone is difficult and needed in the shearstrain calculations. As a result, the height of this shear zone isunknown, so an accurate or representative shear strain cantherefore not be determined.1.4 The selection of normal stress
12、es and final determinationof the shear strength envelope for design analyses and thecriteria to interpret and evaluate the test results are theresponsibility of the engineer or entity requesting the test.1.5 UnitsThe values stated in SI units are to be regardedas the standard.The values given in par
13、entheses are mathemati-cal conversions to inch-pound units that are provided forinformation only and are not considered standard.1.6 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
14、 appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for
15、theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.05 on Strengt
16、h andCompressibility of Soils.Current edition approved June 1, 2018. Published July 2018. Originally approvedin 2010. Last previous edition approved in 2010 as D726310. DOI: 10.1520/D760818.2Skempton, A. (1970). “First-time slides in over-consolidated clays.”Gotechnique, 20(3), 320324.3Skempton, A.
17、(1977). “Slope stability of cutting in brown London clay.” Proc.9th Int. Conf. on Soil Mechanics and Foundation Engineering, Society of SoilMechanics and Foundation Engineering, Tokyo, 261270.4Gamez, J. and Stark, T.D. (2014). “Fully Softened Shear Strength at LowStresses for Levee and Embankment De
18、sign” ASCE Journal of Geotechnical andGeoenvironmental Engineering, June, 140(9), 06014010-1-06014010-6.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recogn
19、ized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.12. Referenced Documents2.1 ASTM Standards:5D653 Terminology Relat
20、ing to Soil, Rock, and ContainedFluidsD854 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD2435 Test Methods for One-Dimensional ConsolidationProperties of Soils Using Incremental L
21、oadingD2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D2488 Practice for Description and Identification of Soils(Visual-Manual Procedures)D2974 Test Methods for Moisture, Ash, and Organic Matterof Peat and Other Organic SoilsD3740 Practice for M
22、inimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD6026 Practice for Using Significant Digits in GeotechnicalDataD6467 Test Method for Tors
23、ional Ring Shear Test to Deter-mine Drained Residual Shear Strength of Cohesive SoilsD6913 Test Methods for Particle-Size Distribution (Grada-tion) of Soils Using Sieve AnalysisD7928 Test Method for Particle-Size Distribution (Grada-tion) of Fine-Grained Soils Using the Sedimentation(Hydrometer) Ana
24、lysisE11 Specification for Woven Wire Test Sieve Cloth and TestSieves3. Terminology3.1 DefinitionsFor definitions of technical terms used inthis test method, refer to Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 consolidatedsoil specimen condition after primaryconsolidat
25、ion under a specific normal stress.3.2.2 fully softened shear forcethe shear force beingapplied to the specimen when the shear resistance begins todecrease with continued shear displacement.3.2.3 fully softened shear strengththe maximum shearresistance of normally consolidated and not presheared soi
26、l andequals the fully softened shear force divided by the cross-sectional area of the annular specimen.4. Summary of Test Method4.1 This test method consists of placing the soft reconsti-tuted specimen (paste) in the annular specimen container of aring shear device, applying a predetermined normal s
27、tressthrough the top loading platen, providing for wetting anddrainage of the specimen; consolidating the specimen under theapplied normal stress; applying a constant rate of sheardeformation for fully drained condition; and measuring theshearing force and angular shear displacement until a maxi-mum
28、 shear resistance is reached.5. Significance and Use5.1 The ring shear apparatus maintains the cross-sectionalarea of the shear surface constant during shear and shears thespecimen continuously in one rotational direction for anymagnitude of shear displacement and along the entire specimencross-sect
29、ional area.5.2 The ring shear apparatus allows a reconstituted speci-men to be consolidated at the desired normal stress prior todrained shearing. This simulates the field conditions underwhich complete softening develops in overconsolidated clays,claystones, mudstones, and shales that do not have a
30、 pre-existing shear surface, sheared bedding planes, joints, or faultsas described by Skempton (19702and 19773) and unfailedcompacted fill slopes (Gamez and Stark 20144) because thefully softened strength corresponds to the peak shear strengthof a normally consolidated fine-grained soil. The fully s
31、oftenedstrength is only applicable to the soil zones that are subject tothe environmental deterioration and applied shear stresses thatlead to soil softening, deterioration of soil fabric, and strengthloss, which may not be relevant to all slopes and all depths.Thefully softened strength should be u
32、sed in an effective stress/drained stability analysis using a stress dependent strengthenvelope for slopes with no prior shearing.5.3 The ring shear test is suited to the determination of thedrained fully softened shear strength because of the shortdrainage path through the thin specimen, small post
33、-peakstrength loss in a normally consolidated specimen, and theconstant cross-sectional area.5.4 The ring shear test specimen is annular so the angulardisplacement differs from the inner radius to the outer radius.This is not significant because a normally consolidated speci-men does not exhibit a l
34、arge post-peak strength loss so thedifference in peak shear resistance at the inner radius and outerradius at different displacements is not significant and the ratioof the inner to outer radii of the ring is greater than 0.5 inaccordance with Hvorslev (1936)6.NOTE 1Notwithstanding the statements on
35、 precision and bias con-tained in this test method: The precision of this test method is dependenton the competence of the personnel performing it and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD3740 are generally considered capable of competent t
36、esting. Users ofthis test method are cautioned that compliance with Practice D3740 doesnot ensure reliable testing. Reliable testing depends on several factors;Practice D3740 provides a means of evaluating some of those factors.6. Apparatus6.1 Shear Device, to hold the specimen securely betweentwo p
37、orous discs. The shear device shall provide a means for5For 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 Summary page onthe ASTM website.6Hvors
38、lev, M. J. (1936). “A ring shear apparatus for the determination of theshearing resistance and plastic flow of soils.” Proceedings of the 1st InternationalConference on Soil Mechanics and Foundation Engineering, 2, 125129.D7608 182applying a normal stress to the faces of the specimen, formeasuring c
39、hanges in thickness of the specimen, for permittingdrainage of water through the porous discs at the top andbottom boundaries of the specimen, and for submerging thespecimen in water. The device shall be capable of applying atorque to the specimen along a shear surface parallel to thefaces of the sp
40、ecimen.Anumber of different ring shear devicesare commercially available, in practice, or are being developedso a general description of a ring shear device is presentedwithout schematic diagrams. The location of the shear surfacedepends on the configuration of the apparatus. As a result, theshear s
41、urface may be located near a soil/porous disc interfaceor at the mid-height of the specimen if an upper ring can beseparated from a bottom ring as is done in a direct shear box.The device shall have low friction along the inner and outerwalls of the specimen container during shearing. Friction maybe
42、 reduced by having the shear surface occur at the top of thespecimen container, modifying the specimen container wallswith low-friction material, or exposing the shear surface byseparating the top and bottom portions of the specimencontainer. The frames that hold the specimen shall be suffi-ciently
43、rigid to prevent their distortion during shearing. Thevarious parts of the shear device shall be made of a materialsuch as stainless steel, bronze, or coated aluminum that is notsubject to corrosion by moisture or substances within the soil.Dissimilar metals, which may cause galvanic action, are not
44、permitted.6.2 Specimen ContainerA device containing an annularcavity for the soil specimen with an inside diameter not lessthan 50 mm (2 in.) and an inside to outside diameter ratio notless than 0.5. The container has provisions for drainage throughthe top and bottom. The initial specimen depth, bef
45、ore con-solidation and preshearing, is not less than 5 mm (0.2 in.) whenshearing occurs at the top soil/porous disc interface. Themaximum particle size is limited to 10 % of the initialspecimen height as stated in the test specimen description.6.3 Torque Arm/Loading Platen Assembly, may have differ-
46、ent bearing stops for the proving rings, load cells, or force ortorque transducers to provide different options for the torquemeasurement.6.4 Porous DiscsTwo bronze or stainless steel porousdiscs mounted on the top loading platen and the bottom of thespecimen container cavity to allow drainage from
47、the soilspecimen along the top and bottom boundaries. The discsshould have good contact between the porous disc and the soiland a surface or pattern that develops a strong interlock withthe soil specimen to aid in transfer of shear stress to the top andbottom boundaries of the specimen. The porous d
48、iscs must besufficiently serrated to develop a strong interlock with the soilspecimen so shearing occurs in the soil and not at the soil/discinterface, which will result in too low shear resistances. Thiscan be accomplished by minimizing the porous disc surfacearea in contact with the soil and havin
49、g part of the porous discpenetrate into the specimen. The hydraulic conductivity of thediscs shall be substantially greater than that of the soil, butshall be textured fine enough to prevent excessive intrusion ofthe soil into the pores of the porous disc. The outer and innerdiameters of the discs shall be 0.1 mm (0.004 in.) less, andgreater than those of the specimen annular cavity, respectively.The serration should have a depth of between 10 and 15% ofthe specimen height before shearing.NOTE 2Exact criteria for porous disc texture and hydraulic conduc-tivity have not
