Optimization To The Composite Lining Structure Of Large-scale Underground Culvert For Water Conveyance

Large-scale underground culvert for water conveyance is widely used in municipal water conservancy project. The design and selection of the composite lining structure of the culvert is closely related to engineering safety. Furthermore, it is also essential to control the project investment. The structure of the culvert is under complicated stress due to impact of geological structure and construction technology. To date, there are no explicit theory and method in calculating stress for the structure. The applied configuration, calculating theory and method vary in different projects, which usually lead to waste of investment, potential security problems, as well as different results.This study systematically discussed the key design point in construction technology and selection of structral style of the large-scale underground culvert for water conveyance. Based on the case of shallow-buried and underground-excavated water-conveyance tunnel in the project of Beijing west fourth-ring underground culvert, one of the middle parts of the South-to-North-Water Diversion Project, the study carried on research in the structral style, construction technology, design theory and calculating method of structure, and material monitoring of the double lining structure. It then raised the new idea in structural design and optimizing of the large-scale underground culvert for water conveyance, which are engineering analogy, structural mechanics and finite element calculation, finite element analysis and optimization, and inversion of monitored data, respectively. Firstly, according to the project scale and geological condition, it applied the engineering analogy method to determine key structural parameters of shoring thickness, strength, reinforcing bars during initial period. The steps and support measures of construction were also protocalled. Secondly, it testified the rationality of the structal parameters and steps selected during initial periods using the structural mechemics method. Meanwhile, it established theoretical model that are appropriate for different geological condition and single lining type, to deduce the theoretical calculation method that are suitable for real project. It also analyzied the inner force of lining and theory of reinforcing bars in different operating condition. Thirdly, the study established 2D and 3D finite element model to analyze the structure of the water-conveyance culvert, and obtained the stress-strain rule of the whole water-conveyance culvert. The study also analyzed and reviewed the results calculated using structural mechanics method, and provided basis for the optimizing of the composite lining structure of the culvert. As a result, it obtained the optimizing values and parameters of the engineering structures. Fourthly, the study carried on comprehensive comparison, and adjusted the structural parameters. Through computation, the study tried to explore the feasibility in optimizing structure design of both single and double tunnel linings of the composite ling structure. The study also analyzed the sensitivity of the calculating result to parameters, and the power transmission characteristics of the composite ling structure under multiple stresses. It then illuminated the the focus in waterproof design of the water-conveyance culvert structure. Furthermore, we discussed the strained condition and mechanisms of the deformation and stress of the composite lining structures through analysis of observed data from both construction and operation periods, to further verify the safety of the structure and rationality of the hypothesis. Based on the analysis of observed and calculated values, we obtained the stressed ratio of the single and double lining structures, as well as the structural optimization path. The result showed that the stress ratio on the double lining structures can be decreased form 54% to 34%. The combination of different methods ensures the safety and rationality of the designed structures. The study proposed the safety degree and optimization capability of engineering project.The study should provide reference value for designers in hydraulic, subway, and municipal institutes. The method and result of this study have guiding significance in theory and method.