Modelling the large deformations in stratified media - the Cosserat continuum approach

Methods employing continuum approximation in describing the deformation of layered materials possess a clear advantage over explicit models, However, the conventional implicit models based on the theory of anisotropic continu a suffers from certain difficulties associated with interface slip and inte rnal instabilities. These difficulties can be remedied by considering the b ending stiffness of the layers. This implies the introduction of moment (co uple) stresses and internal rotations, which leads to a Cosserat-type theor y. In the present model, the behaviour of the layered material is assumed t o be linearly elastic; the interfaces are assumed to be elastic perfectly p lastic. Conditions of slip or no slip at the interfaces are detected by a C oulomb criterion with tension cut off at zero normal stress. The theory is valid for large deformation analysis. The model is incorporated into the fi nite element program AFENA and validated against analytical solutions of el ementary buckling problems in layered medium. A problem associated with buc kling of the roof and the floor of a rectangular excavation in jointed rock mass under high horizontal in situ stresses is considered as the main appl ication of the theory. Copyright (C) 1999 John Wiley & Sons, Ltd.