ASTM_D_7608_-_18e1.pdf

Designation:D7608181Standard 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 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.1NOTEThe standard was editorially updated in January 2022.1.Scope1.1 This test method provides a procedure for performing 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 strength 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)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 grained 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,the 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 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 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,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 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 stresses 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 parentheses 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 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 the1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.05 on Strength 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/D760818E01.2Skempton,A.(1970).“First-time slides in over-consolidated clays.”Gotechnique,20(3),320324.3Skempton,A.(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 Design”ASCE Journal of Geotechnical andGeoenvironmental Engine