Critical shear strain and sliding potential of rock joint under cyclic loading: Fid-Bau Portal

Critical shear strain and sliding potential of rock joint under cyclic loading

Soomro, Mairaj Hyder Alias Aamir / Indraratna, Buddhima / Karekal, Shivakumar

Abstract A new concept of critical shear strain $({ε_{τ}}_{critical})$ of rock joint under cyclic loading is presented, and the role of ${ε_{τ}}_{critical}$ in evaluating the sliding potential of rock joint is highlighted. A series of cyclic triaxial tests was conducted on a cylindrical rock joint specimen with a replicated rough surface representing a joint roughness coefficient $(J R C)$ value of 12.6 oriented at 60° with respect to the horizontal plane. The experimental results indicate that the onset of instability of rock joint is suppressed with increase in confining pressure and number of loading cycles $(N)$ until the normalized shear deformation increases beyond a threshold value of ${ε_{τ}}_{critical}$ . Generally, the critical strain of most rock types is considered in the proximity of 1% under small strain conditions , however, in this study, the critical strain concept is extended to the domain of rock joints, and a semi-empirical model to more rigorously quantify the critical shear strain $({ε_{τ}}_{critical})$ of rock joint is suggested considering the effect of joint roughness coefficient $(J R C)$ , cyclic loading amplitude, and the number of loading cycles $(N)$ . Also, a rational classification of Joint Sliding Potential (JSP) based on the ${ε_{τ}}_{critical}$ and normalized total shear strain $({ε_{θ}}_{N})$ of rock joint is proposed to characterize the cyclic loading induced sliding instability of a rock discontinuity.