A CONTINUUM MODEL OF LAYERED ROCK MASSES WITH NONASSOCIATIVE JOINT PLASTICITY

Layered rock masses can be modelled either as standard, orthotropic co ntinua if the layer bending can be neglected or as Cosserat continua i f the influence of layer bending is essential. This paper presents a f inite element smeared joint model based on the Cosserat theory. The la yers are assumed to be elastic with equal thickness and equal mechanic al properties. All the cosserat parameters are expressed through the e lastic properties of layers, layer thickness and joint stiffness. Plas tic-slip as well as tensile-opening of layer interface (joint) are acc ounted for in a manner similar to the conventional non-associative pla sticity theory. As an application, the behaviour of an excavation in a layered rock mass is examined. The displacement and stress fields giv en by smeared joint models based on the Cosserat continuum and the con ventional anisotropic continuum approaches are compared with those obt ained from the discrete joint model. The conventional anisotropic cont inuum model is found to break-down completely when the effective shear modulus in the direction parallel to layering is low in comparison to the shear modulus of the intact layer, whereas the Cosserat model is found to be capable of accurately reproducing complex load-deflection patterns irrespective of the differences in shear moduli. (C) 1998 Joh n Wiley & Sons, Ltd.