|Alternative Title||experimental study on the breaching processes of natural dams|
|Thesis Advisor||崔鹏 ; 王兆印|
|Place of Conferral||北京|
|Keyword||堰塞坝 溃决模式 水槽实验 溃决过程 数学模型|
The research of the breaching process of landslide dam is useful to understand the principle of dam failure, and predict the concerned factors during emergency such as the breaching modes of dam, the outflow discharge, the duration of dam failure, and the submerge area. Analyzing main characteristics of landslide dams by collecting representative historic data help to understand characteristics of landslide dams and provide details for laboratory experimental design. The influences of flume bed slopes, inflow discharges, dam geometrical shape, material, water content to the process of dam failure were analyzed. The relationships between governing factors and the outflow discharge, the size of dam breach, erosion ratio were discussed. The relationships between the width of dam breach and Froude number were also studied. Meanwhile the critical conditions of different mode of dam breach and outburst debris flow from natural dam failure were deduced. A mathematical model was developed to simulate natural dam failure in contain the theory of hydraulics and soil mechanics. These are main conclusions: (1)Based on the 68 detailed natural dams, the influence of the size, the geometric characters of dam, the soil intensity in dam, the rules of erosion and permeation, the influence of topographic feature to the capacity of lake were analyzed.(2)On the basis of flume experiments, we found critical condition of three dam failure modes. Overtopping mode could be easier happen while the median size and permeation ratio are small and inflow is large. Large permeation ratio, small inflow and permeation will cause pore water pressure increasing, erosion inside, which leads to slope failure.If the discharge of inflow equals seepage before water overtopping, the dam will not breach. Critical conditions between overtopping and slope failure and not failure were established considering influence of the inflow, soil permeation, soil strength, and soil gravity.(3)The processes of natural dam failure include: dam breach gradually developing (stage Ⅰ), dam breach rapidly enlarging stage (stage Ⅱ), and stable riverbed formed stage (stage Ⅲ). In the whole process, sediment movement change from suspended load motion to strong bed load motion. Eventually form an armoring layer, and a new water-sediment balance is reached. The slope of dam breach mainly fail in stage 2, which is more frequent and larger than other stages. (4)Burst discharge has a positive correlation with inflow discharge, upstream slope and downstream slope, median diameter and water content of dam material. However, outflow discharge increases first and then decreases with the increase of flume slope. Under the same other conditions, average erosion rate increases first and then decreases with the increase of flume slope then increases again. The increasing of inflow discharge, upstream slope and downstream slope, and water content will increase erosion rate. Median diameter of dam material has a negative correlation with erosion rate. The ratio of breach width and depth increases first and then decreases with the increasing of flume slope, and it has a positive correlation with inflow discharge, upstream slope and downstream slope, but it has a negative correlation with fine content and water content.(5)Larger flume slope, better gradation granular materials, more fine particle content lead to the debris flow formation easier. (6)A mathematical model which can describe natural dam overtopping burst has been established. The complicated dam breach is simplified and the formula of broad-crested weir is used to calculate burst discharge. The new erosion rate formula considering bed slope and particle size is used in the model. Meanwhile, probability function is used in the model to describe the heterogeneity and discontinuity of soils. The model is applied to failure process of Tangjiashan landslide dam, Xiaogangjian landslide dam and Mantaro landslide dam and small size natural dams tests. The results showed that the calculations of burst discharge, duration, breach width, and the water level variation of barrier lake and evacuation launder, which show a good agreement with observations.
|蒋先刚. 堰塞坝漫顶溃决过程实验研究[D]. 北京. 中国科学院大学,2016.|
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