Incorporating Roughness Degradation Within the Critical State Framework: Modeling the Shear Behavior of Rock Joints

Abstract

ABSTRACT: Rock masses are characterized by numerous structural discontinuities, such as joints and faults, which exert a significant influence on their deformation responses. Therefore, it is important to develop a constitutive model that can accurately anticipate the mechanical response of rock joints. A previous study proposed an elastoplastic constitutive model based on the critical state framework originally developed in soil mechanics. The fundamental assumption of this model is that a rock joint reaches a critical state, where the shear stress and aperture is uniquely determined relative to the applied normal stress, after a large shear displacement. This model accounts for the joint matching by evaluating the difference in joint aperture between the current and the critical state. However, its applicability to rock joints remains incomplete, particularly in accommodating the influence of roughness degradation. Roughness degradation on joint surfaces can lead to a reduction in the asperity angle, resulting in a decrease in aperture at the critical state and a dilatancy response. In this study, we extend the aforementioned model by introducing a state parameter to account for the changes in critical state aperture. The proposed model effectively captures alterations in the shear response associated with the roughness degradation, providing a more comprehensive understanding of the mechanical behavior of rock joints. 1. INTRODUCTION The precise anticipation of rock mass behavior is critical in designing and maintaining rock structures such as tunnels, dam foundations, geological repositories for radioactive waste, and energy storage facilities. Within the rock mass, numerous discontinuities, such as faults and joints, characterized by reduced stiffness and strength compared to the rock materials, exert a significant influence on the overall rock mass behavior. In addition, alterations in stress conditions within the rock mass resulting from subsurface activities can induce slippage of these discontinuities, precipitating the failure or collapse of the entire rock mass. Therefore, comprehending and managing the slip behavior of discontinuities, particularly those surrounding underground structures, represents one of the critical challenges in rock engineering. Although various studies have explored slip/shear behavior, the surface roughness (Barton, 1973) and interlocking (Zhao, 1997a) of rock joints are important factors influencing shear behavior under applied stress conditions common in rock engineering. Numerous numerical methodologies have been proposed to forecast the behavior of discontinuities in rock. Nevertheless, enhancing constitutive models to incorporate geological characteristics of in-situ joints remain imperative.