-Q&A Q.I understand that the following conversion has to be made when soil element simulation is done by FLIPSIM on the triaxial undrained cyclic test: 【strain amplitude: double amplitude axial strain εa=(εv-εh)×0.5×1.5， for example εa=５％⇒5／2×1.5=3.75%（single amplitude）】　【shear stress ratio: τ／σm=1.5×σdl／２σc　σdl: axial stress difference σdl(=σｖ-σh)，　σｃ: confining stress 】. Is my understanding correct?

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I understand that the following conversion has to be made when soil element simulation is done by FLIPSIM on the triaxial undrained cyclic test: 【strain amplitude: double amplitude axial strain εa=(εv-εh)×0.5×1.5, for example εa=５％⇒5／2×1.5=3.75%（single amplitude）】　【shear stress ratio: τ／σm=1.5×σdl／２σc　σdl: axial stress difference σdl(=σｖ-σh),　σｃ: confining stress 】. Is my understanding correct?

In triaxial undrained cyclic test, double amplitude of strain is defined in terms of axial strain, not axial strain difference. Because it is undrained condition, volumetric strain is unchanged and εv+εh+εh=0 holds.

Consequently, shear strain in triaxial undrained cyclic test becomes εv-εh=εv+εv/2=1.5εv（double amplitude shear strain）. Single amplitude shear strain is γ=0.75εv. For εv=5%, γ=3.75% holds.

Shear stress ratio is σdl/(2σc')=(σdl/2)/σc'=τ/σc'（τ is shear stress at a plane with 45° inclination）. Consequently no conversion is required.