ASTM_D_8295_-_19.pdf

Designation:D829519Standard Test Method forDetermination of Shear Wave Velocity and Initial ShearModulus in Soil Specimens using Bender Elements1This standard is issued under the fixed designation D8295;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.1.Scope1.1 This test method covers the laboratory use of piezo-ceramic bender elements to determine the shear wave velocityin soil specimens.A shear wave is generated at one boundaryof a soil specimen and then received at an opposite boundary.The shear wave travel time is measured,which over a knowntravel distance yields the shear wave velocity.From this shearwave velocity and the density of the soil specimen the initialshear modulus(Gmax)can be determined,which is the result ofprimary interest from bender element tests.1.2 This shear wave velocity determination involves verysmall strains and is non-destructive to a test specimen.As such,bender element shear wave velocity determinations can bemade at any time and any number of times during a laboratorytest.1.3 This test method describes the use of bender elements ina triaxial type test(for example,Test Methods D3999,D4767,D5311,or D7181),but a similar procedure may be used forother laboratory applications,like in Direct Simple Shear(TestMethod D6528)or oedometer tests(for example,Test MethodsD2435 and D4186).Shear wave velocity can also be deter-mined in unconfined soil specimens held together by matrixsuction.1.4 Shear wave velocity can be determined in differentdirections in a triaxial test,for example vertically and horizon-tally.Shear waves generated to determine shear wave velocitycan also be polarized in different directions,for example ahorizontally propagating shear wave with either vertical orhorizontal polarization.This test method describes the use ofbender elements mounted in the top platen and base pedestal ofa triaxial test specimen to measure shear wave velocity in thevertical direction.With additional bender elements mounted onopposite sides of a triaxial specimen,a similar procedure maybe used to determine horizontal shear wave velocity.1.5 A variety of different interpretation methods to evaluatethe shear wave travel time in a soil specimen have beenproposed and used.This test method only describes two ofthese,Start to Start and Peak to Peak using a single sine wavesignal sent to the transmitter bender element.Other interpre-tation methods producing similar results may also be used.1.6 Bender element measurements may not work very wellin some situations,like in extremely stiff soils where thegenerated shear wave amplitude may be exceedingly small.1.7 This test method does not cover the determination ofcompressional wave velocity in soil specimens.This measure-ment requires a different type of piezo-ceramic elementconfiguration,and such determinations are generally not usefulin saturated soft soil specimens as the earliest identifiablecompressional wave arrival at the receiver end of a saturatedspecimen will likely have been transmitted through the(rela-tively incompressible)specimen pore water rather than the(compressible)soil skeleton.1.8 UnitsThe values stated in SI units are to be regardedas standard.No other units of measurement are included in thisstandard.1.9 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026,unless superseded by this test method.1.9.1 The procedures used to specify how data are collected/recorded and calculated in the standard are regarded as theindustry standard.In addition,they are representative of thesignificant digits that generally should be retained.The proce-dures used do not consider material variation,purpose forobtaining the data,special purpose studies,or any consider-ations for the users objectives;and it is common practice toincrease or reduce significant digits of reported data to becommensurate with these considerations.It is beyond the scopeof these test methods to consider significant digits used inanalysis methods for engineering data.1.10 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.1.11 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 D18.09 on Cyclic andDynamic Properties of Soils.Current edition approved Nov.1,2019.Published December 2019.DO