| The safety of dam occupies an important position in the national economy foundation industry, for the flood control, electricity generation, irrigation, water supply and marine products farming etc. created the huge social wealth and economic performance. The probability of the dam crash is very small, however, once it occurs , the destructiveness is huge, and will bring the loss of national economy and the people's life property. In this text, the Bishop method, the technique of random simulation, the risk analysis method and the flood regulation of reservoir are used to research the risk of dam failure due to overtopping and instability and a good result is obtained. The main works are summarized as follows:(1) The basic concepts, theories, the calculation method and the standard of risk analysis were introduced in detail. Because overtopping and landslide are the two most important reasons that the big dam crash, this text mainly carried on the risk analysis of overtopping and the risk analysis of instability for the Yuqiao reservoir dam.(2) According to the statistical characters of inflow into Yuqiao reservoir from 1960 to 2000, firstly a seasonal AR(1) model was used to simulate the flood flowing into Yuqiao reservoir. Then the risk probability of overtopping was calculated by flood regulating that makes use of the flood hydrograph and the principle of flood regulating. According to the allowed risk standard, risk analysis of overtopping was carried out. The results show that the risk rate of overtopping is raised from 3.125×10-7 to 1.125×10-6 when the limited flood water level of Yuqiao reservoir is raised from 19.87m to 21.16m, but both of them are less then 5.5×10-6 . If taking the function of wave protection wall into consideration, the risk will be smaller. So it explains that the risk can be accepted if raising the limited flood water level to 21.16 meter in the whole flood season. (3) According to the physical mechanics property of the dam's soil and water level of Yuqiao reservoir, firstly the Bishop method was used to calculate the minimum safety coefficient and to determine the most dangerous slippery arc. And then MC method was applied to calculate the risk probability of instability to analyze the risk of instability of Yuqiao earth dam according to the allowed risk standard. Through the analysis, we could find that the minimum safety coefficient of earth dam lowers gradually with the ascension of the water level, from 1.403 for the start water level declined to 1.3115 for the design water level. Contrary, the corresponding risk probability increase from 0.1×10-4 to 16.4×10-4. The risk of instability of Yuqiao earth dam is 984.77×10-6. Therefore it is thought that the engineering is in danger, and should be reinforced. |
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