Research On Diversion Risk Of High Earth-rock Cofferdam And Decision-making Method For Construction Diversion Scheme

The risk of diversion system with high rock-fill cofferdam, includes multiple risk modes such as overtopping, structural damage, schedule delay and so on, is the basic of diversion schemes decision and the key factor influencing the safety in water-power engineering construction and running. The paper systemically studies on the risk analysis and schemes decision of diversion system with high rock-fill cofferdam, which includes structural characteristics and structural risk analysis of high rock-fill cofferdam, schedule risk analysis, and the diversion scheme optimization. Conclusions are as follows:The analysis of structural failure form and mechanism of high rock-fill cofferdam indicates that the main damaging model are slope instability and seepage destruction. The influnce on high rock-fill cofferdam slope stability and seepage evolution, comes from construction process and dynamic boundaries, is researched according to the construction characteristics of the cofferdam, and the slope stability analysis model considered construction process and unsteady seepage analysis method of high rock-fill cofferdam are proposed on the basis of non-linear strength theory and unsteady seepage theory. The rationality and practicability of the proposed model and method are proved by engineering example, and provide high rock-fill cofferdam with stuctural analysis theory support.The random factors influnce cofferdam slope stability and seepage safety are analysed. The statistical characteristic of earth and rocks materials mechanical parameters, including eigenvalue and distribution, are determined with random fuzzy theory and hypothesis testing theory, and combined with hydrologic stochastic analysis, the comprehensive risk model for rock-fill cofferdam slope stability is established. The seepage failure fuzzy risk model is established on the basis of Monte-Carlo method and randomness analysis of exit seepage gradient and critical seepage gradient. Then the relativity between slope instability risk and seepage failure risk is discussed, and structural system risk calculation model of high rock-fill cofferdam is established with coupla function.The construction characteristic of diversion system with high rock-fill cofferdam is analyzed. The critical path in construction network is represented by critical chain according to theory of constraint, and the risk of construction schedule is measured with the randomness of project buffer on the basis of collective risk theory. The construction schedule risk calculation model considered logic relationship of process and resource constraint, and calculating the construction schedule risk with Monte-Carlo method.The decision-making indexes of diversion scheme optimization commonly used are always related with diversion risk, and the relevance is existed among them. The relevance of the indexes was characterized and decoupled with k-additive fuzzy measures on the base of the analysis and quantization of indexes, and the weights of indexes were determined according to maximum fuzzy measure entropy principle. The multi-objective decision-making model considered indexes relevance for diversion schemes is established, and the diversion schemes were ranked and optimum selected according to synthetic appraisal value schemes with choquet integral. The case study shows that the decision-making method is effective for characterizing the relevance of the indexes such as construction investment, construction period and dynamic risk rationally and enhancing the decision-making veracity, and provides a effective method for the diversion scheme decision of hydropower engineering.