ABSTRACT:

This paper is devoted to constitutive modeling of induced anisotropic damage in stratified sedimentary rocks. The emphasis is put on the coupling between initial and induced anisotropies in general loading conditions. A new coupled plasticity-damage model based on fabric tensor and discrete approach is proposed. Fabric tensor is used to characterize the inherent orientation-dependent properties of materials. Macroscopic plastic deformation and damage are considered as the result of frictional sliding along weakness sliding planes and growth of these ones. The coupling phenomenon between inherent and induced anisotropy is discussed. A series of numerical simulations are performed in order to verify the predictive performance of the proposed model.

1 INTRODUCTION

Plastic deformation and induced damage by micocrack growth are two essential mechanisms of inelastic behaviors and failure in rock materials. A number of constitutive models have been so far developed for modeling of anisotropic plastic deformation and damage in geomaterials like concrete and rocks. However, most of them are formulated for initially isotropic materials and only induced anisotropy was taken into account. In stratified sedimentary rocks like hard cay rocks, there is significant structural anisotropy due to existence of bedding planes. The mechanical properties such as elastic modulus and failure strength are strongly dependent on loading orientations. Further these materials are also sensitive to nucleation and propagation of oriented microcracks. There is thus coupling between induced and inherent anisotropy, which will control failure mechanisms in these rocks. Inspired by multi layer models in soil mechanics, an original model is proposed in this work by developing a discrete approach for plastic and damage modeling in initially anisotropic rocks. The macroscopic mechanical responses are assumed to be inherently related to local deformation behaviors in a finite number of weakness sliding planes (WSPs).

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