Study On Coupling Effect Of Shield Lanuching Safety Risk In Water-Rich Sand Layer

Shield lanuching construction is the first stage of subway tunnel construction by shield method.Many risks occur at this stage,such as water and sand gushing,gate collapse,kowtowing of shield,attitude control of shield,ground settlement,construction deformation,reaction frame instability and so on.Especially in the water-rich sandy soil layer,the selfstability of soil is poor and groundwater is abundant,which leads to the risk of water and sand gushing at the portal,the risk of collapse when the portal is broken,the risk of surrounding surface settlement and deformation of construction structures is higher.In many cases,risks are caused by the coupling effect of various risk factors.Therefore,the coupling effect of safety risk of shield lanuching construction in water-rich sand soil layer is selected as the research object in this paper.The degree of risk coupling effect and key influencing factors in the lanuching process are studied.Through the simulation of risk coupling effect,The magnitude law of coupling effect and the sensitivity of risk factors to the occurrence of risk events are revealed,and the decoupling principle and method are proposed.Through the control of important and high risk factors,the purpose of reducing the safety risk of shield launching construction in water-rich sand soil layer is achieved.Firstly,the basic process of shield launching construction was introduced.According to the characteristics of water-rich sand layer,the risk identification and risk classification of shield lanuching construction in water-rich sand layer are carried out by using expert investigation and evaluation method.The risk factors were classified according to human,machine,environment,management and method.Their coupling effects were qualitatively analyzed,and the coupling action path diagrams of 26 groups of risk factors were obtained.Secondly,combining with the characteristics of shield lanuching engineering and risk factors,the adaptability of the quantitative research method based on coupling degree model and system dynamics model for shield lanuching risk coupling in water-rich sand layer was analyzed and the model construction and key simulation steps were also introduced in detail.On this basis,according to the decoupling principle of reducing the degree of correlation between risk coupling,the decoupling path and measures was put forward,which can reduce the chance of risk coupling action in time or space,reduce the speed of coupling between risk factors and destroy the vector of risk factors.Finally,the application analysis was carried out in combination with the shield lanuching project with water-rich sand layer.By using the coupling degree model,the coupling degree values of 26 different risk factor combinations in practical engineering were obtained.Only the "human-ring" risk coupling which is the largest coupling degree was selected as the simulation object of system dynamics.Through simulation and sensitivity analysis,it was concluded that the key influencing factors of the human-environment risk coupling system are personnel’s professional technical ability and hydrogeological conditions.Combined with the principle and path of risk decoupling,the key decoupling measures for "human-environment " risk coupling system were first proposed.Combined with the qualitative analysis of the "mechanism-management-methed" risk coupling in the second chapter,the corresponding control measures were also proposed.The practical construction results verified the feasibility of the research method and decoupling measures.