| At present,the urban transportation system tends to be underground.As a new type of transportation tool,subway has made great contribution to alleviate the urban traffic pressure.The interstation connecting passage plays an important role in disaster prevention,drainage and connection of metro engineering.In the process of subway construction,artificial freezing reinforcement technology is more and more widely used in the construction of connecting passage.The freezing method of shield tunnel is characterized by high risk,especially in the underground undercurrent and silty sand stratum,which often faces the geological disaster of mud bursting and sand gushing.Therefore,it is necessary to establish a risk assessment system and analyze the key risks quantitatively.The purpose of this paper is to establish the construction risk evaluation system of Lanzhou freezing method subway connecting passage,identify the key risk factors in the construction process of Lanzhou special stratum freezing method,so as to provide the basis for the construction risk control research.First of all,relying on the construction of the connecting passage between the yingma section of Lanzhou Rail Transit Line 1,this paper describes the engineering conditions of the project,including the ground traffic conditions,building density,population density and structure conditions.Through the investigation and analysis,the possible risk events in the construction of the freezing method of the connecting channel are listed,and the cause and effect analysis of these events is carried out,the statistical table of risk events is established,and the fault tree model of the four construction stages of the freezing method is established based on the fault tree method of the risk identification model.The fault tree model is hierarchical,and the risk hierarchy index system of freezing method construction is established.According to the questionnaire survey,the judgment matrix is determined,the consistency test and relative weight calculation are carried out with Yaahp software,and then the weight is transformed into the influence degree score according to,corresponding to five levels: Level I(very low),level II(low),level III(medium),level IV(high)and level V(very high);at the same time,the fault tree is transformed into Bayesian network model,which is obtained through questionnaire survey The prior probability of the root node,the conditional probability of the intermediate node determined by the chain rule,and finally by the help of Genie 2.0 software to obtain the probability grade of evaluation indexes.The probability grade is also divided into five grades: Grade I(impossible),grade II(rare),grade III(occasional),grade IV(possible)and grade V(frequent);according to the final risk probability score and impact score,according to the risk evaluation grade in the regulations on risk management of urban rail transit underground engineering construction The final risk index grade is determined in the table.The risk grade is divided into four grades: Grade I(low degree),grade II(medium degree),grade III(high degree)and grade IV(extremely high degree).Finally,the construction risk of freezing method for connecting passage between yingma section of Lanzhou Rail Transit Line 1 is determined,and the biggest risk factor is the fracture of freezing pipe.The research results show that the risk assessment of freezing method is not only easy to implement,but also high accuracy.Finally,the key risk factors identified,combined with specific projects,put forward risk avoidance measures and risk mitigation measures,hoping to provide reference for similar projects in the future. |
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