33 / 2021-11-02 10:34:23

A new simulation method for prediction of landslide dam overtopping failure

landslide dam; overtopping failure; large-scale experiment; numerical simulation

The breaching of landslide dams is a severe geological disaster, and the resulting breaching floods significantly threaten people in downstream areas. In this study, a large-scale physical model was constructed in a natural river channel using unconsolidated dam material with a wide grain size distribution. Terrestrial laser scanning was used to capture three-dimensional geometric information of the landslide dam during the breaching process. The results showed that the dominant erosion pattern during dam breaching was surface progressive erosion. The breaching process could be divided into three stages based on different erosion characteristics: headward erosion, rapid erosion, and attenuated erosion. Longitudinal and lateral evolution models were proposed based on the field test results. The longitudinal evolution model describes the erosion at the dam crest and the sedimentation at the dam toe during the breaching process by defining the erosion and rotation points. The lateral evolution model revealed different lateral erosion characteristics at different cross-sections. Both the longitudinal and lateral evolution models were validated using two dam break events of the Baige landslide. Based on the analysis of the breach mechanism, a new simulation method for landslide dam breaching is proposed. The model simulates the breach process of landslide dam by setting initial parameters and calculations of five modules, including hydraulic module, material erosion module, downstream sedimentation module, longitudinal evolution model, and lateral enlargement model. The simulation method successfully revealed the phenomena of the headward erosion and dam toe sedimentation during the dam breach. Additionally, the simulated breach morphology matches well with the actual observation, reflecting the changes of slope failure mode from toppling failure to shear planar failure. The model does not need to set the residual dam height and is able to predict the final depth of the breach by the decrease of flow shear force. The relative errors of the measured and simulated results, including peak discharge, time to peak, and final breach size, are less than 2%, indicating that the rationality and accuracy of the proposed method are satisfactory. The evolution models and simulation method proposed in this study provide a scientific reference for numerical simulations of dam breaching and the prevention and mitigation of landslide dams.