Understanding the deformation mechanism and threshold reservoir level of the floating weight-reducing landslide in the Three Gorges Reservoir Area, China

More than 5000 landslides or potential landslides have been identified in the Three Gorges Reservoir (TGR) region since its impoundment in 2003. These hazards seriously threaten the continuation of reservoir operations and the safety of dams, waterways, and local residents. Understanding the deformation characteristics and kinematic evolution of these landslides can be helpful for assessing their stability and providing long-term landslide predictions. In this study, the deformation characteristics, influencing factors, sliding mechanism, and threshold reservoir level of the Muyubao landslide are revealed. Data from a professional monitoring network implemented in 2006 reveal that the deformation of this landslide is in a stage of creep characterized by overall movement, and the rate of creep is gradually slowing. The deformation mechanism is investigated by combining meteorological, hydrological, and reservoir level data with displacement measurements from surface cracks, manual and automatic GPS monitoring records, and field investigations and drilling surveys. The reservoir level is the main driving factor of deformation, whereas the filling-drawdown rate is not directly related to the deformation of the landslide. Furthermore, rainfall can promote deformation during periods with high reservoir levels. The deformation of the landslide follows a very distinctive pattern featuring large displacements after the reservoir level rises to a high level (from late October to early March of the following year) and a rapid transition to constant deformation as the reservoir level drops. The results indicate that the reservoir level of 172 m is the general threshold reservoir level of the Muyubao landslide. At present, the deformation rate of the Muyubao landslide is gradually decreasing, and the probability of large-scale sliding is low; however, the monitoring system must be strengthened and additional research must be performed on the deformation mechanism.