Study On Safety Evaluation Of Steel Sheet Pile Cofferdam During Construction Of Bridge Deep Water Foundation

With the overall promotion of national infrastructure construction in the 14 th Five-Year Plan,bridge projects will step into new development areas such as new type,large scale and complex technology,and the difficulty of deep-water foundation construction will also increase.Steel cofferdam is a temporary water barrier component that runs through the construction stage of bridge deep water foundation,and its safety state directly affects the construction of deep water foundation.In the past bridge construction,the safety state of steel cofferdam is often ignored.On the one hand,in the process of deep-water foundation construction,there is a lack of heavy machinery,construction personnel and construction technology to control the influence of steel cofferdam safety,resulting in the damage of steel cofferdam and the destruction of the bridge foundation.On the other hand,steel cofferdam structure type,scale,construction and application environment will directly affect its safety state,often due to improper control of steel cofferdam construction and scale does not meet the requirements of the accident.Once the steel cofferdam is damaged,it not only has a direct impact on the bridge deep water foundation construction and water environment,but also affects the life safety of the construction personnel around the cofferdam,resulting in irreversible losses.Therefore,it is urgent to scientifically and reasonably evaluate the safety condition of steel cofferdam in the construction stage of bridge deep water foundation,so as to provide theoretical basis for the application of steel cofferdam in the construction stage of deep water foundation.Steel plate pile cofferdam is the most widely used in our country.This paper uses steel plate pile cofferdam as main object to study its safety condition during the construction of bridge in deep water foundation.Firstly,combined with the application characteristics of steel sheet pile cofferdam in th e construction stage of bridge deep water foundation,similar project data,relevant specification and standard documents and cofferdam accident cases in recent years,the factors that may affect the safety state of steel sheet pile cofferdam in the constr uction process of deep water foundation are analyzed and identified,and the influencing factors are identified by WBSRBS method to preliminarily determine the safety evaluation index.In order to improve the accuracy of evaluation indexes,indexes were screened based on the contribution rate,independence and sensitivity of influencing factors,and a safety evaluation index system of steel sheet pile cofferdam containing 5 first-level indexes and 24 second-level indexes was finally established.Then,by comparing the common index weighting methods and the safety evaluation methods,considering the characteristics of the safety system evaluation of steel sheet pile cofferdam,the improved G1-entropy weighting method was selected as the index weighting method,and the safety evaluation model was constructed based on the set pair extension coupling algorithm.A matter-element system for the safety evaluation of steel sheet pile cofferdam in the construction stage of bridge deep water foundation is constructed by using matter-element transformation.The set pair and extension set theory domain formed between the evaluation index quantity value and standard discussion level are carried out the same and different inverse analysis,and then the corresponding relati on membership function is constructed.Combined with the comprehensive weight of evaluation index determined by the improved G1-entropy weight method,The comprehensive relation membership degree and coupling coefficient of steel sheet pile cofferdam safety grade are obtained,and the safety grade of steel sheet pile cofferdam is determined according to the maximum pairing potential principle and confidence criterion,and the security situation and change trend of the cofferdam system are analyzed based on the coupling coefficient.Finally,taking Zhongweixia River Highway Bridge along the Yellow River as an application example,the evaluation model established in this paper is used to evaluate the safety of steel sheet pile cofferdam in the construction of pier 16# cap.The results show that the evaluation results of the model are in good agreement with the situation of steel sheet pile cofferdam on site,which verifies the applicability and feasibility of the established safety evaluation index system and evaluation model.The results can provide theoretical basis for the application management,maintenance and reinforcement decision of steel sheet pile cofferdam in the construction stage of bridge deep water foundation.