The effect of joint orientation and spacing on the dynamic stability of persistently-jointed rock slopes

Abstract

Rock slopes with a dominant, persistent joint set are naturally occurring and have two common failure mechanisms: flexural toppling and cross-joint shear. Although the static stability of this slope category has been well studied, the stability of these slopes during earthquakes has remained opaque. In this study, the dynamic stability of persistently-jointed rock slopes is investigated using a dynamic implementation of the bonded particle model. In response to the dynamic motions, the slopes experience dynamic forces that break interparticle bonds and begin to fail. The study shows that the behavior of the slope is sensitive to the frequency content of the input ground motion. Further, the nature of the frequency sensitivity is dependent on the initial failure mechanism and the accumulation of damage over time. Persistently-jointed rock slopes that fail in flexural toppling are sensitive to low-frequency dynamic loading. Slopes failing in cross-joint shear are sensitive to tuning ratio. The nature of the frequency sensitivity has implications for the applicability of simplified (e.g., pseudostatic) analysis methods. Increased damage accumulation in rock slopes results in softening, which decreases the slope’s natural frequency and, therefore, the critical input frequency.