Abstract: An improved Hvorslev envelope-based three-dimensional elastoplastic constitutive model was proposed by Yao et al. (2008) for overconsolidated clays. The return mapping algorithm is adopted in order to implement the constitutive model into a finite element analysis software ABAQUS through the user material subroutine interface. By coupling the model with the Biot’s consolidation theory, coupled analyses of the localized deformation on overconsolidated clay specimens under undrained boundary conditions in triaxial compression and extension and plane strain stress states are performed. The numerical results show that the same stress paths are seen for the elements inside and outside the shear band. The elements in the vicinities of the shear band behave volume contracted, while the elements inside the shear band keep shear dilatancy during shear. The shear dilatancy is accompanied by the development of the shear band, and negative pore pressure appears inside the shear band and their vicinities. The changes in the pore water pressure and volumetric strain in the plane strain are between triaxial compression and extension stresses, but shear bands early occur in the plane strain.