An anisotropic elastoplastic Cosserat continuum model for shear failure in stratified geomaterials

Abstract In this article, we formulate an anisotropic elastoplastic Cosserat continua model for shear failure in stratified geomaterials. Considering the dip angle between local and global coordinates of a formation, a Cosserat elastic anisotropy constitutive matrix under plane strain condition is derived, and cohesion anisotropy is reflected using a microstructural tensor combined-stress invariant method. A Cosserat continuum finite element model and consistent algorithm are developed to consider the characteristics of elastic anisotropy, strength anisotropy, and strain softening. The simulation of a stratified geomaterial sample under uniaxial compression condition shows that the elastic anisotropy has an evident influence on the deformation pattern. It is also demonstrated that dip angle could significantly impact macroscopic failure modes, uniaxial compressive strength, and macroscopic equivalent elastic modulus. The stability analysis of a layered slope demonstrates that the strength anisotropy has a considerable influence on the overload safety factor of the slope and can be a trigger of the formation of shear bands in such slopes. Furthermore, the dip angle of the structural plane also affects the stability of the stratified slope, which is controlled by both the block and structural surface. By comparing the numerical results of the classical continuum model and the Cosserat continuum model, it is proved that the numerical model considering the elastoplastic anisotropy and strain softening under the Cosserat continuum theory overcomes the ill-posedness of mesh sensitivity and maintains the well-posedness of the strain localization problem. Thus, the proposed model is useful for modeling shear failure in stratified geomaterials.