Risk Evaluation Of Xiamen Metro Line 3 Undersea Tunnel Shield Construction Based On Bayesian Network Method

In recent years,as an effective means to relieve urban land and traffic pressure,the subway has ushered in rapid development with the process of urbanization in China.As one of the main methods for subway construction,the shield construction method has also been widely used.Generally,the shield construction method in China is a shallow shield with high risk and many accidents.In particular,for the Xiamen Metro Line 3 undersea tunnel project,there are adverse geologic risk factors such as upper soft and lower hard strata(bedrock bulge),solitary rocks,weathered deep troughs,and strong weathered formations.The hydrogeological conditions for the construction are complex and tunnel leakage risk accidents can easily be triggered,and the undersea construction of shallow overburden may lead to the penetration of seawater through the instability of the excavation surface,resulting in accidents such as collapse.Construction risk management is an important task to ensure the smooth implementation of the project,and risk evaluation is a key part of it.Therefore,this paper uses the Bayesian network method to study the risk evaluation of Xiamen Metro Line 3 undersea tunnel shield construction:Through literature research and statistical analysis of accident cases,based on the thought of causal Bayesian network and the three-dimensional model of shield construction risk identification,the corresponding relationship between the basic units of construction process and the risk factors was established using the WBS-RBS method,and on this basis,the undersea tunnel shield construction risk index system has been built and a Bayesian network model of risk index system has been structured.Through the questionnaire,combined with Bootstrap,the questionnaire as a small sample was repeatedly sampled,and the prior probability distribution corresponding to the risk level of each risk factor was estimated.The Bayesian network model was constructed by GeNle software and was used to predict reasoning.It was concluded that the shield construction risk rating of Xiamen Metro Line 3 undersea tunnel was on Level I;and through diagnostic reasoning the influence coefficient of the related nodes was calculated,the maximum possible path for the construction risk of the project and the risk factors that most easily lead to the risk accident have been found.Then from which,identified the poor scheme and effect of the end reinforcement;the upper soft and lower hard(base rock raised),soft soil and severe weathering and other special formations;sudden encounter of underground obstacles;unsuccessful assembly of segments;improper management of muddy water systems;improper control of grouting systems;chamber opening and cutting tool replacement;and so on,are the most critical risk factors.Finally,the evaluation result of this paper is compared with the risk assessment report of Xiamen Metro Line 3 undersea tunnel shield construction.It is believed that the evaluation result is reliable,and corresponding control measures are put forward.