Study On Identification And Evaluation Of Safety Risks In Shield Construction Of Subway Tunnel

With the continuous progress of shield technology,the adaptability of shield method to construction environment is also increasing,and it is widely used in the construction of subway tunnel.Although the shield tunneling method is relatively mature and has obvious advantages,there are still a large number of uncertain factors in the construction process,leading to the occurrence of construction safety accidents.In this paper,the shield tunneling construction stage of the M section tunnel of a large city subway project is taken as the research object.From the perspective of the construction unit,combined with the shield construction technology,and using relevant risk management theories,the safety risk assessment research of the shield construction of the M section tunnel is carried out.Firstly,this paper introduces the domestic and foreign research results from the aspects of risk identification and risk assessment,and makes a brief review,in order to get the inspiration for this study.Then,with the M project tunnel as the empirical background,the project overview,engineering machinery,construction preparation,construction scheme and other conditions of the tunnel in this area are discussed.Taking the tunneling stage as an example,the working structure of M project is decomposed,and the four-level working structure is determined.Through the decomposition of risk element structure,the risk element structure of three levels is determined,and the risk identification matrix is constructed.Through the research of project data,accident statistics and literature,the preliminary risk factors of 79 projects are determined.Through the correlation analysis of risk factors,36 risk factors are finally determined.From the identification results of risk factors,there is a clear hierarchical structure in the final risk factors.In order to make the results of safety risk assessment of M project reasonable and reliable,the index system of safety risk assessment of M project was established according to the hierarchical structure,and the factor sets composed of criterion layer and factor layer were constructed as the objects of FCE respectively.Then the evaluation set was established according to the relevant national standards,and then the weight was obtained by discriminating and calculating all levels of indicators with AHP.After obtaining the weight,experts in the field of shield are used to score the probability of occurrence of each risk event and the degree of loss,and the membership matrix of the probability of occurrence of risk and the degree of loss is established.After fuzzy operation,the occurrence probability membership vector Q and risk loss degree membership vector R of each index of M project are obtained.According to the classification standard of relevant national standards and the principle of maximum membership,the risk probability grade and risk loss grade of the index are determined.Finally obtains M project overall security risk situation as a "rare",once happened,is"serious",risk level for Ⅲ,belong to "acceptable".After the risk evaluation,the author briefly puts forward the countermeasures and suggestions for the improvement of risk management.Finally,the author puts forward the conclusion and prospect that the independence of risk factors should be further studied,and the risk response and control should also be discussed in depth.