Cumulative damage effect on debris slopes under frequent microseisms.

Debris slopes are widely distributed across the Three Gorges Reservoir area in China, and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslides on such debris slopes. In this study, a cumulative damage model of debris slope with varying slope characteristics under the effects of frequent microseisms was established, based on the accurate definition of slope damage variables. The cumulative damage behaviour and the mechanisms of slope instability and sliding under frequent microseisms were thus systematically investigated through a series of shaking table tests and discrete element numerical simulations, and the influences of related parameters such as bedrock, dry density and stone content were discussed. The results showed that the instability mode of a debris slope can be divided into a vibration-compaction stage, a crack generation stage, a crack development stage, and an instability stage. Under the action of frequent microseisms, debris slope undergoes the last three stages cyclically, which causes the accumulation to slide out in layers under the synergistic action of tension and shear, causing the slope to become destabilised. There are two sliding surfaces as well as the parallel tensile surfaces in the final instability of the debris slope. In the process of instability, the development trend of the damage accumulation curve remains similar for debris slopes with different parameters. However, the initial vibration compaction effect in the bedrock-free model is stronger than that in the bedrock model, with the overall cumulative damage degree in the former being lower than that of the latter. The damage degree of the debris slope with high dry density also develops more slowly than that of the debris slope with low dry density. The damage development rate of the debris slope does not always decrease with the increase of stone content. The damage degree growth rate of the debris slope with the optimal stone content is the lowest, and the increase or decrease of the stone content makes the debris slope instability happen earlier. The numerical simulation study also further reveals that the damage in the debris slope mainly develops in the form of crack formation and penetration, in which, shear failure occurs more frequently in the debris slope. [ABSTRACT FROM AUTHOR]