Fatigue degradation characteristics and energy evolution of phyllite under combined actions of dynamic and static loading

Earthquakes may inflict varied levels of damage on mountains. Understanding the deformation properties of earthquake-damaged rock masses is critical for evaluating rocky slope stability over time. Taking the phyllite of the Xinmo Village rockslide as the research object, the degradation features of the phyllite are investigated through laboratory tests, and a discrete-element numerical approach that fully accounts for the progressive rock deterioration is presented. The approach is then used to investigate the evolution characteristics of phyllite under various dynamic and static loading circumstances. Results show that the remaining strength of rock decreases with increasing dynamic cyclic loading (DCL) amplitude and times but increases with increasing frequency. As the dynamic damage degree increases, rock failure modes become more complex, and microcracks expand in a more preferential orientation, as well as a denser spatial distribution. Dynamic damage cracks act as the dominant paths for the macroscopic failure surface of the rock. The results indicate that the input energy and dissipated energy increase with fluctuating and linear trends with the advance of the DCL, respectively. The peak strain energy and acoustic emission (AE) magnitude decrease with increasing dynamic damage degrees, and the distribution of AE events displays temporal dispersion and spatial clustering characteristics, which is attributed to a decrease in the rock's potential for storing energy.