【作者】 邢万波；

【导师】 徐卫亚；

【作者基本信息】 河海大学 ， 岩土工程， 2006， 博士

【摘要】 堤防安全评价是堤防设计和堤防除险加固的重要组成部分,是对所研究堤段防洪能力的综合检验和评价。但堤防工程是赋存于一定水环境中受水文和水力条件作用的岩土工程结构,而风险作为一种用来考虑和评价工程实践中诸多不确定和无法预测因素而导致工程失事的一种手段时,是所有岩土工程中先天固有的(Casagrande,1965)。传统定值设计方法由于很难考虑到堤防工程实际存在的不确定性,因而已不足以确切地表征工程的安全程度。将以概率论和可靠度为基础的风险分析方法引入堤防工程安全评价实践中具有重要意义。本文在广泛参阅国内外大量文献基础上,对堤防工程风险分析的理论、模型、方法以及应用进行了探讨研究,取得了以下研究成果: (1) 采用故障树分析方法对单元堤段失事破坏类型进行了分析,将单元堤段失事模式分为以下3个层次8种分项失事模式: Level Ⅰ:水文失事模式和结构失事模式; Level Ⅱ:将水文失事模式分为洪水漫溢失事模式和洪水漫顶失事模式,将结构失事模式分为渗透破坏失事模式、岸坡失稳模式和地震险情失事模式; Level Ⅲ:将地震险情失事模式分为岸坡地震失稳和地震液化,岸坡失稳模式分为临水面岸坡失稳模式和背水面岸坡失稳模式,岸坡地震失稳模式同样亦分为临水面岸坡地震失稳模式和背水面岸坡地震失稳模式。 (2) 依据所进行的单元堤段失事模式分析,分别推导建立了单元堤段分项失事模式风险率计算模型,并提出了分项失事模式功能函数及其功能函数中随机变量的估计方法;同时在建立分项失事模式的风险率计算模型时考虑了分项失事模式的失事后果严重程度,在洪水漫顶失事模式和地震液化失事模式的风险率计算模型中引入贡献权重函数K(h)来考虑其风险对综合失事风险的贡献;然后对单元堤段分项失事模式的风险率计算模型中的洪水位概率密度函数和分项失事风险率的表述方式进行了详细阐述,提出了风险率计算模型中积分计算方法(基于高斯—勒让德节点的离散化积分求解方法和函数拟合方法),给出了分项失事模式条件失事概率计算中随机变量的标准差估计方法,并建议将失事风险率计算结果用风险率与洪水位关系曲线来表示,以更好地表征堤防工程安全程度。 (3) 对单元堤段综合失事风险率计算的解析解、界限估计和近似估计方法进行了描述;建立了单元堤段失事事件之间的相关函数,以及堤防系统综合失事风险率计算的公式,并提出了堤防系统综合失事风险率计算步骤;分析了堤防失事后更多还原

【Abstract】 Safety evaluations on levees are systematic inspections and assessments on the performance of flood prevention of the studied reaches, and also are the main part of job before reinforcement design for levees. Levees are brim over with uncertainty, which are kind of geotechnical structures running under the circumstances of flood water and suffering from hydrological and hydraulic effect. However, risks are inherent in geotechnical engineering as tools to considering and evaluating the uncertainty or things hard to predict which could result in failure of the structure(Casagrande, 1965). As a result, traditional deterministic design approaches due to lack of consideration of existed uncertainty in practice, seems not good enough to represent the safety of levees. Therefore, it will be rather valuable to apply probability-and-reliability-based risk analysis procedure in safety assessment of levees. Based on referring on large numbers of correlative literature at home and abroad, this dissertation presents a groping study on foundations, models, approaches and applications of risk analysis for levees failures. And main conclusions of the study are drawn as follows:(1) Fault tree analysis(FTA) is adopted to analyze the failure types of levee reaches, and failure modes of levee reaches are classified into three levels:Level Ⅰ: Hydrological failure mode and structural failure mode.Level Ⅱ: Hydrological failure mode is classified into overflowing failure mode and overtopping failure mode. Structural failure mode is classified into seepage failure mode, slide instability failure mode and seismic disaster failure mode;Level Ⅲ: Seismic disaster failure mode is classified into seism-induced slide instability failure mode and seismic liquefaction failure mode. Both slide instability failure mode and seism-induced slide instability failure mode include the riverward slope and landward slope.(2) Calculating models for risk factor of each failure mode of levee reach are established, and accordingly performance function of each failure mode of levee reaches are proposed. Meanwhile an Contributing weight function K(h) is introduced into calculating models of overtopping failure mode and seimic liquefaction failure mode so as to considering of the contribution from risk of the two failure modes to comprehensive failure risk. Then an illustration to flood PDF in calculating model foreach failure mode and risk factor of each failure mode are described in detail. And a points-of-Gauss-Legender-quadrature-based discretized method for integral formula of calculating models is proposed, so it is with nonlinear curve fitting method. Furthermore, methods for estimating value of standard deviation of random variables are also discussed.(3) Analytical solution, bounds estimating and approximate estimating to comprehensive failure risk factor of each levee reach are described. In order to obtain failure risk factor of levee system, a correlative function of failure event between two levee reaches is established, and accordingly the formula and procedure of failure risk factor of levee system is proposed. Meanwhile, economic consequence assessment due to levee failure is described, and then the procedure to failure risk evaluation of levee system is proposed. In addition, over-level flood is defined, and procedure of calculating failure risk of levee system under over-level flood condition is brought forward.(4) One misapplication of Monte Carlo sampling method in practice is pointed out, and procedure of Monte Carlo sampling under correlation conditions is presented. Meanwhile, an extended geometrical optimized method(EGOM) is proposed, procedure of which under conditions of correlation and non-normal distribution variable is presented. Furthermore, EGOM and quadratic polynomial response surface method(RSM) are combined to solve the probabilistic problems with implicit performance function.(5) In allusion to the characteristic of each failure mode of levee reach, calculating approaches for conditional probability of each failure mode of levee reach are presented: EGOM-based RSM for conditional probability of seepage failure mode, a practical method to locate critical probabilistic surface and minimum (3 by Hassan and Wolff for conditional probability of slope instability failure mode. In addition, based on proposed calculating models of failure modes and calculating approaches for conditional probability of failure modes, the code LeveeRisk for failure risk factor of levee reach is developed.(6) Based on Banqiao river left levee reinforcement project, with proposed and presented foundations, approaches and code of risk analysis for levees, the risk factor and risk value of Banqiao river left levee are evaluated, and assessment about the calculating result is also made subsequently. According to its 1995’ failure case, critical risk factor and critical risk value for Banqiao river left levee are established. InLevee Engineering;Risk Analysis;Failure Mode;Acceptable Risk;Over-level Flood;External Qinhuai River Levee;Banqiao River Levee;Geomembance更多还原