Research on the numerical simulation of two-stage landslide dam breach process and characterization of breach flow evolution
Under the influence of strong earthquakes,mountainous canyon regions are prone to experiencing land-slides that block rivers and forming cascading landslide dams.Once the one of these landslide dams breaches,it can trigger a chain reaction,leading to the successive failure of cascading landslide dams which poses a significant threat to the lives,property,and infrastructure downstream.Based on the three-dimensional Reynolds-averaged Navier-Stokes equations,turbulent renormalization group modeling,suspended and bed load transport equations,and con-sidering the unstable collapse of the dam breach slope,by using the Finite Volume Method,a numerical simulation method for calculating the cascading dam breach process has been developed.This numerical method can be used to simulate the hydraulic characteristics and the dam breach morphology evolution during the cascading failure process.A typical generalized model test on the breaches of two cascading landslide dams is chosen as the validation case.The comparison of measured and calculated results indicates that,the breach hydrograph and breach morphology evolution process of the upstream and downstream dams are generally consistent,and the relative errors of key breaching pa-rameters,such as peak breach flows of the upstream and downstream dams,and flood routing time between the inter-zone,are less than±5％.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that,there is an amplification effect of breach flood on the cascading landslide dam failures.Three key param-eters,such as distance between upstream and downstream dams,river channel slope,and downstream dam height,are selected to study the flood amplification effect.The parameter sensitivity analysis shows that,the peak breach flow at the downstream dam decreases with the increases of distance between the two dams and downstream dam height,and it follows a trend of increasing at first and then decreasing with the increase of river channel slope.When the flood caused by the upstream dam failure flowed to the downstream dam,it may produce surge that overtops and erodes the dam crest,resulting in a decrease in the dam crest elevation.This has a certain impact on the failure oc-currence time and peak breach flow of the downstream dam,and the influence of surge on the downstream dam failure process is related to the amount of water overtops the dam crest and the erosion characteristics of dam materials.The cascading dam failure cases of Xiaogangjian-upper and Xiaogangjian-lower are selected as the representatives for the validation.By comparing the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10％,which verify the rationality of the model's applica-tion in real-word cases.The proposed numerical simulation method can provide important technical support for casca-ding landslide dam failure risk assessment and emergency treatment.
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维普
