Research On Flood Analysis Method And Erosion Test Of Barrier Lake

The landslide dam is mostly loose with broadly-graded soil,uneven structure,and more easier erosion.It is hard to predict the disaster on the downstream once the dam burst.It is important to build reasonable breach model of barrier lake,for reducing disaster and saving lives and property of the downstream people due to the failure of barrier lake.There is a barrier lake crashed on an unprecedented scale since the literature records,in April 9,2000 at 20:05 pm,occurred at Bomi county in Tibet Plateau(30°14'N,94° 53'E).Suppoted by the National Basic Research Program of China(2013CB036400)and the National Natural Sciences Foundation of China fund project(51579208),this paper investigates the breach mechanism of the Yigong barrier lake through experiment and numerical simulation.The main results and conclusions are as follows:(1)Through field survey and data collection,this paper modified the bottom elevation in 2000,water storage-elevation relationship and breaching discharge of Yigong barrier lake.This modified breaching discharge is 94810.34 m3/s,the entire breaching process lasted for about 24 hours,the total volume of water released from the reservoir is 2.11×109 m3,and the bottom elevation is 2186.41m.(2)This paper uses the material of Yigong material,based on Cylindrical Rotating Erosion Apparatus,to provide a better method--small fan-shaped erosion determination for measuring the erosion rate of the large particle soil.This research breaks through the existing methods limts which includes not carrying out large-scale soil erosion test,needing to detemine the start-up time of erosion,and needing artificial control.(3)This research uses Cylindrical Rotating Erosion Apparatus and small fan-shaped erosion determination method to research on the relationship between critical velocity,erosion rate and shear stress of single particle and mixed particle from Yigong.Experimental studies on critical velocity and erosion rate of different diameters have shown that the measurement values are reliable for erosion-shear stress analysis.The relationship between the critical velocity,the erosion rate and the shear stress is explored through determining the accurate calculation formula of the shear stress of the apparatus.It is found that the relationship between the critical velocity and the erosion rate is a hyperbolic function,the relationship between the critical velocity and the shear stress is an exponential function,the relationship between the erosion rate and the shear stress is a hyperbolic function.This research verifies the hyperbolic model between the soil erosion rate and shear stress.(4)Since the analysis contains tedious procedures(e.g.,modeling of a vertical toe cutting and stepped collapsing,searching for the critical slip surface by Bishop's simplified method and applying a total stress and effective stress analysis method),a spreadsheet for computing the lateral enlargement process,namely,the DBS-IWHR,based on VBA combines hydraulic and geological approaches,has been developed.This research confirms that the above 4-step computations on lateral enlargement can be automatically conducted by an Excel spreadsheet with the VBA programming with very little manual calculations.The spreadsheets are transparent and self-explanatory,and allow for secondary development.(5)It is proved that the improved analysis model is better based on the improved the method of flood analysis which includes erosion model,lateral enlargement numerical model and hydraulic model,the revised DB-IWHR program and back analysis of the Yigong barrier lake Sensitivity analysis shows that the erosion rate model has a significant impact on the results of the analysis.Then,ratio of water head drop,coefficient of broad-crested weir flow and the lateral enlargement factor have little effect on the results of the failure analysis.