Risk Analysis of Tunnel Construction Scheme Change based on Field Monitoring and Numerical Analysis

Because of the surrounding environment restriction, some sections Lanzhou Metro Line 2 were forced to change original open excavation method concealed method. Among them, ingate is transitional section connecting shaft and cross passage, which accompanied by force conversion structure during plan process, accidents are prone occur. Combining this project situation, a construction scheme for turning from passage into mine line was proposed, finite element software used simulate scheme. Numerical analysis shows that stability tunnel supporting structure, shaft, all meet design requirements. The final ground settlement caused proposed 7.1 mm, vault 11.97 mm. It also turns out causes less deformation, can be applied conversion. rationality numerical model further verified comparison between monitored data surface sinking simulation results. Finally, modified compared. concluded superior in terms schedule, safety, economic benefits, impact on environment. indicates it good choice replace early if necessary. successful implementation provide reference similar urban subway projects.