Analysis Of Reservoir Headwork Structure Safety Based On Fault Tree

With the increase of agricultural irrigation demand in Vietnam,reservoir plays an important role in the development of the country.The existing dams are generally designed in the traditional way,and the technical specifications are only based on the discharge and load of the reservoirs.The impact of each project on the overall structural safety of the project is not taken into account.In addition,because of stochastic appearance and uncontrolled characteristics of natural factors,the safety factors of dam structure are uncertain.Currently,most of the studies on the dam safety analysis and assessment in Vietnam did not take into account the relationships of safety factors and their uncertainty characteristics.Therefore,this paper analyzes the characteristics and mechanism of dam accident.The Monte Carlo,probability reliability theory and fault tree are used to assess the structural safety of reservoir headworkof Vietnam Reservoir project,aiming to provide the scientific basis for the design,restoration and safety management of hydraulic engineering in Vietnam.The main research contents are summarized as follows:(1)To establish the model of safety probability calculation,this paper introduces the structure of reservoir headwork of irrigation system in detail,and analyzes five main factors of structural damage: natural factors,design factors,construction factors,management factors and deliberate destruction.Moreover,the uncertainty of these factors is completely considered.After that,the damage mechanism of each building in reservoir headwork is analyzed.(2)The reservoir headworksystem is decomposed into several sub-structures,such as main dam,spillway,diversion tunnel,etc.The process and causes of structural damage of these key building are deeply analyzed.To quantify the structural damage mechanism of each key building,fault tree is first used to describe the relationship between the causes,and structural damage process.Then,the probability reliability theory is applied to construct the safety probability function of structural damage in the main dam,spillway,and diversion tunnel.At last,based on the parallel relationship between structural safety factors,the safety evaluation function of reservoir headwork structure is established without considering the randomness of safety factors.(3)Because of the uncertainty of safety factors,the probability density function of each safety factor is determined according to historical experience,statistical data,and normative standards.A model of evaluating the safety situation of reservoir headwork structure is built.The model takes full account of the uncertainty and theparallel relation of the structural safety factors.The randomness of the factors in the model is simulated through Monte Carlo.Because of the complexity of model calculation,a software-SYPRO2018 that can evaluate the structural safety of the main dam,spillway and diversion tunnel is developed by using C++.The above theory and the software are applied in the Phu Ninh Reservoir's headwork in Vietnam.The methods without and with considering factors' uncertainties are compared when calculating the stability of the main dam and spillway,and the results show that:a)The two main damages that seriously affect the operation of the project are downstream slide and overtopping.b)The structural safety of each key building is evaluated to reasonably arrange the maintenance and upgrading.The calculation results show that the main dams and the auxiliary dams have the greatest impact on the safety of the system,followed by the underground sewers and spillway.c)The safety coefficient calculated by the conventional method is higher than the result calculated by the method of considering the uncertainty of safety factors.