Study On Failure Mechanism And Methodology Of Safety Assessment Of The Lower Yellow River Dike

By combining the practical problems and the information from historical archives of lower Yellow River dikes, this thesis presents a study on the failure mechanism for dike, the risk analysis models for dike structure, calculating the failure probability of typical dike sections and the major impact factors on dike safety from which an index system for the dike safety assessment for lower Yellow River was developed. The accelerating genetic algorithm and analytic hierarchy process (AGA-AHP) were used in the safety assessment for the lower Yellow River dikes. The main contents of the study are described as follows:(1) The existing hidden defects and significant past dangerous situations of the lower Yellow River dikes were studied by collecting the information from the historical archives for the dangerous situations, the geological exploration, the survey of hidden defects, the design and the field monitoring.(2) The major impact factors on the safety of lower Yellow River dikes were identified. The impacts of the dike body, dike foundation and boundary conditions, which were considered as a complex interactive system, on the dike safety were discussed. The types of foundation for lower Yellow River dikes were classified according to the characteristics of the ground and the dangerous situations.(3) The occurrence, development and impact factors of piping in the lower Yellow River dikes were analyzed based on the characteristics of dangerous situations. Subsequently, the failure mechanism, triggering conditions and major impact factors for bank erosion of lower Yellow river dikes were systemically studied. At the same time, the occurrence, development process and failure mechanism of bank erosion were described in details.(4) A series of risk analysis models, such as seepage, piping, and landslide were established for the lower Yellow River dikes which were closely related to the practical problems in the lower Yellow river. The failure probability of the dike was calculated by the Monte-Carlo finite element method (FEM). The computational method for the general failure probability of lower Yellow River dikes was discussed.(5) The characteristics of the consequences of lower Yellow River dike failures were analyzed and a computational model for the consequences of dike failures was established. The risk criteria of lower Yellow River dike engineering were discussed by considering the state of arts in the risk analysis.(6) An index system for the safety assessment of lower Yellow River dikes was established. A methodology based on the accelerating genetic algorithm and the analytic hierarchy process, was used to evaluate the safety of lower Yellow River dikes is evaluated. The methodology was validated by case studies.