Study On Countermeasures And Risks Analysis In The Shield Tunnel Construction Of Lanzhou Metro

Because of abundant groundwater,high water pressure,more gravel quantity,the local distribution of more boulders and rock in stratum in the Lanzhou subway Line 1,especially,Yellow River-crossing project,shield construction is very difficulty,is a world-class technical problem.The paper studies the risk factors of Lanzhou metro shield construction,and puts forward the corresponding control measures.Firstly,the paper introduces the background,significance and purpose of research,expounds the present situation of tunnel risk at home and abroad,and reviews the current situation of domestic tunnel risk,puts forward the research content and method.At the same time,the concept,principles and steps of risk and construction risk management are discussed,and the theoretical basis of construction construction risk management and risk management method.Secondly,the paper introduces the history of shield method,the advantages and disadvantages of shield construction technology,the use of shield construction flow chart method,the risk breakdown structure method,the use of expert survey method from the environmental geology,equipment,materials,construction management in all three aspects This paper analyzes the risk factors of shield construction in Lanzhou subway,and analyzes and estimates the main risks of shield construction in Lanzhou subway,and establishes the risk system of shield construction in Lanzhou subway.Thirdly,using the Delphi method to determine the level of risk factors at all stages of shield construction in Lanzhou subway by using the risk analysis method(R = P × L)qualitative analysis of the risk factors of Lanzhou subway,on the basis of this,the Analytic Hierarchy Process(AHP)Subway shield construction at all stages of the risk factors were calculated,followed by the results of expert qualitative evaluation and quantitative calculation of the results of a comparative analysis,and finally determine the Lanzhou subway shield construction risk level.Finally,on the basis of risk research,we further study the risk control measures of shield construction,especially the special technical problems encountered in the construction of Lanzhou Metro Line 1,Embedded channel of the disease mechanism to do the study,and for the first time in the domestic proposed embedded channel insulation layer of technical indicators and anti-alkaline test indicators.Then,the strength and stability of the shielded steel pipe are measured.At the same time,the measures of extending the tool life of the EPB shield in the construction of large size sand and gravel strata are put forward.Through the practice and research of the project,the optimization scheme of the earth pressure balance shield and the composite mud shield design of the large particle size sand and gravel stratum is put forward.The optimized shield has achieved good results in the following construction of the first stage of Lanzhou Metro Line 1.It shows that the optimized improvement scheme of the shield is feasible and is worth popularizing in sandy cobble stratum.