Abstract:

An improved Hvorslev envelope-based three-dimensional elastoplastic model for overconsolidated clay was proposed by Yao et al (2009). The return mapping algorithm is adopted in order to implement the model into a finite element analysis software ABAQUS through the user material subroutine (UMAT) interface. By coupling the model with Biot’s consolidation theory, three dimensional coupled analyses of an overconsolidated clay specimen in triaxial compression and extension and plane strain stresses are performed. The numerical results show that, different stress paths are seen inside and outside the shear band. The elements in the vicinities of the shear band take on volume contraction, dilatancy and contraction due to being sucked, while the elements inside the shear band keep the dilatancy during shearing. Dilatancy is accompanied by the development of the shear band, so the negative pore pressure appears inside the shear band and their vicinities. The changes in the pore pressure and volumetric strain in plane strain are between triaxial compression and extension stresses and depend on the shear velocity, but the shear bands early occur in plane strain condition. The migration of the pore water controls the formation and development of the shear band. The confining pressure and location of the weak element also play an important effect on the formation of shear bands.

Key words: overconsolidated clay, pore pressure, dilatancy, three-dimensional stress, shear band