Seismically-induced failure mechanisms in massive rock slopes

Abstract

This article presents a study of seismically-induced failure of massive steep rock slopes. A dynamic implementation of the bonded particle model (BPM) for rock is used to simulate the dynamic response and initiation of fracture in the slopes. Observation of forces that develop within the model in response to wave transmission and dynamic excitation provides insight into the fundamental mechanisms at work in seismically induced rock slope failure. Five distinct mechanisms of failure initiation are identified using non-destructive simulations and confirmed with destructive simulations. Three distinct modes of rock mass movement enabled by the failure mechanisms are identified. The predominant co-seismic failure mode was a shallow, highly-disrupted cliff collapse. Cliff collapse is initiated by relatively low levels of shaking. Shallow failures are also triggered at higher levels of shaking prior to the initiation of deeper, more coherent failures in the same seismic event. The results of the numerical study agree with qualitative historical surveys of seismically-induced rock slope failure trends and provide insight into the mechanisms behind observed co-seismic rock slope behavior. The frequently observed shallow failures are triggered by high compression stresses near the cliff toe combined with shallow subhorizontal ruptures behind the cliff face. These mechanisms are not well-captured by simplified analysis methods which may lead to underprediction of shallow co-seismic events. Deeper failure surfaces from stronger shaking create a base-isolation effect, slowing further disruption in the failure mass. Slope dynamic response and damage accumulation were shown to be interdependent and complex, emphasizing the importance of further research into the interaction between rock mass strength, slope geometry, structure, and ground motion characteristics.