Anisotropy of sedimentary rocks is mainly due to the geometrical arrangement of particles that depends on the orientation of applied load respect to the bedding plane. It is geologically due to micro-fabric created by the arrangement of the particles configured during deposition. Multi-plane based model of the contact areas of a joint implicated into the elastoplastic behaviour of shear/normal deformation along different directions. Laboratory observations clearly show that only the steepest polygon surfaces touch the other sample, the identification of the potential sliding areas only requires the determination of the polygons which are faced to the shear direction and which, among them, are steep enough to be involved. Accordingly, it has been postulated that through fractured/jointed rock, mainly, the polygons turned to the shear vector (τ i) are involved in the mobilization of shear resistance. Consequently, in order to locate the contact areas implicated into the shear-test it was firstly necessary to fix the shear direction. Moreover, since laboratory observations clearly show that only the steepest polygon surfaces touch the other sample, the identification of the potential sliding areas only requires the determination of the polygons which are faced to the shear direction and which, among them, are steep enough to be involved. The methodology to be discussed here is modeling of slip on the local and global levels due to the distribution of deformation procedure of the interaction in rock joint. More attention has been given to slip initiation and propagation through rock joint. In particular, softening in nonlinear behaviour of joint in going from the peak to residual strengths imparts a behaviour often associated with progressive failure. In this paper, a multi-plane based model capable of predicting the behaviour of geo-materials on the basis of sliding mechanisms, elastic behaviour of particles and possibilities to see the micro-fabric effects as inherent anisotropy as well as induced anisotropy is introduced. The model is capable of predicting the behaviour of rock under different orientation of bedding plane, history of strain progression during the application of any stress/strain paths. Examples comparing predictions based on sliding or opening/closing mechanism as computed from different activities of planes through netting analysis show both gross and local accuracies..
A noticeable feature of rock media failures is the appearance of slip surfaces or shear band, the characteristics of that are associated with deformation being concentrated in narrow zones and the surrounding material remaining intact. The concept of a distinct failure plane that forms a wedge of material allows a direct examination of force equilibrium of the system and is central to most stability calculation (Hoek and Bray 1981). This problem includes a certain behavior of a local joint in global level due to the development of sliding and shear band. The softening observed in going from peak to residual strengths imparts a behavior often associated with progressive failure (Palmer and Rice 1973).
