A consistent calibration process for the Matsuoka–Nakai friction angle under direct simple shear conditions for clay hypoplasticity

In geotechnical engineering, direct simple shear (DSS) tests are used to determine strength and stiffness parameters of a material. DSS predictions constitutive model influence failure mechanisms in plane-strain, finite-element applications. this article, we introduce closed-form solution the Matsuoka–Nakai equivalent critical friction angle from stress normal data. order apply it clay hypoplasticity (Mašín, 2013), carry out simulations investigate rotations principal stresses state at for plane-strain conditions. Finally, interpret different overconsolidation ratios demonstrate that location CSL vertical stress–void ratio plane coincides with mean effective plane.