Study on the Disturbance of Existing Subway Tunnels by Foundation Sloping Excavation

Urban subway tunnels are located in a very complex operating environment, and the surrounding construction disturbances can lead to the deformation of existing tunnels or even produce tunnel disease issues. The disturbance of adjacent tunnels by pit excavation is an important geotechnical issue among scholars. In our study, the two-stage method is used to derive the deformation of the existing tunnel caused by the use of sloping excavation in the foundation pit. Subsequently, the correctness of the theoretical calculation formulae and the results are verified by constructing numerical calculation models. The effects of different slope footings θ, different slope widths b and different excavation depths H on the deformation of the existing tunnel are analyzed. The results show that: the excavation of the foundation pit can effectively reduce the tunnel deformation by using the sloping excavation method. The soil directly above the tunnel is the main factor causing the deformation of that tunnel. When the foundation pit spans a single-lane existing tunnel, the sloping excavation method of excavating soil on both sides and reserving the middle core soil can be used. When the foundation pit spans a double-lane existing tunnel, the sloping excavation method of excavating the middle soil and reserving core soil on both sides can be adopted. The error between the theoretical calculation results and the numerical simulation results is small, which verifies the correctness of the theoretical calculation results. The load distribution width of the soil after sloping excavation can be taken as the median line width. The deformation of the existing tunnel is influenced, to a greater extent, by changes in the one-time excavation depth H and slope width b, and to a lesser extent, by changes in the slope angle θ.