Modeling surface roughness degradation of rock joint wall during monotonic and cyclic shearing

Abstract

Based on previously proposed surface roughness description parameters (k a, θs, SRs, DRr, a 0), two generalized rock joint surface roughness degradation models were proposed to predict the variation of joint surface degradation during shearing under both constant normal stress (CNS) and constant normal stiffness (CNK) loading conditions. The first model was developed based on the evolution of secondary roughness (an extension of an existing model) and the second was developed based on the concept of “average asperity probable contact angle.” Model variables can be initial normal stress (σn0; k n ≥ 0), normal stiffness (k n; σn0 ≥ 0), accumulated shear displacement u s-tot (monotonic or cyclic shearing), and surface roughness amplitude a 0. Good agreement between experimental and predicted degradation was observed. The models also allow prediction of surface degradation in large-scale shear fractures. Both models are semi-incremental, readily implemented in a numerical code, and adaptable to existing elastoplastic joint behavior models.