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