Response of landslide deformation to flood and impoundment of the Dahuaqiao Reservoir: characteristics and mechanisms

Extreme climate events and reservoir impoundment may cause the reactivation of ancient landslides. Understanding the evolutionary mechanisms and triggers of these landslides is crucial for evaluating their stability. The spatial and temporal deformation characteristics and reactivation mechanisms of two ancient landslides in the Dahuaqiao Reservoir were researched in detail using field investigations and in situ monitoring. The Yingpan (YP) and Lagu (LG) landslides are retrogressive landslides mainly in the creeping stage, characterized by low velocities. Flooding and impoundment are triggers of two accelerated deformations of landslides based on correlation analysis, respectively. Flooding caused a reservoir water level rapid drawdown, resulting in a loss of buttressing effect and a continual increase in seepage force, which, combined with sustained scouring, shearing, and erosion, reactivated the two landslides. During the impoundment, increasing buoyancy of the LG landslide mass resulted in decreased normal stress on the sliding surface and diminished resisting force. The LG landslide entered another accelerated deformation phase. In contrast, the YP landslide, which had been reinforced with stabilizing piles and slope toe presses, did not experience acceleration during the impoundment. Owing to the different permeability characteristics of the two landslides, rainfall has a greater impact on the LG landslide than the YP landslide. The results from this study will be invaluable for reservoir landslide disaster prevention.