# Study on the Disturbance of Existing Subway Tunnels by Foundation Sloping Excavation
###### Abstract  
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 \(\theta\), 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 \(\theta\). existing tunnel; slope excavation; deformation analysis; slope release angle +
Footnote †: journal: Medical  
and considered the shearing effect of the surrounding soil on the tunnel. A Vlazov basis model was introduced to simulate the tunnel-soil interaction, and finally the parametric analysis was performed. The results reveal that the relative distance between the existing tunnel and the excavated pit, the soil strength and the tunnel burial depth all have a considerable influence on the existing tunnel deformation. [PERSON] et al. [6] constructed a three-dimensional model for the numerical calculation of the existing tunnel adjacent to the foundation excavation and studied the effect of foundation excavation on the stress-strain of the adjacent tunnel. The results indicate that the underground diaphragm wall can effectively reduce the tunnel deformation. The excavation of the foundation pit will result in compression on the upper surface and tension on the lower surface of the adjacent tunnel, and the stress redistribution is extremely complex. [PERSON] et al. [7] considered the shield tunnel joint discontinuity and the interaction between pipe joints and constructed a refined 3D model of the existing shield tunnel. The stress and deformation of the existing tunnel during the excavation of the foundation pit were studied. [PERSON] et al. [8] presented the case of a foundation excavation project and analyzed the construction excavation sequence and reinforcement measures on the disturbance of the existing tunnel deformation situation. In their studies, the results reveal that the bulge of the existing tunnels increases nonlinearly with the increase in the excavation width of each tunnel when the excavation volume is small. [PERSON] et al. [9] presented a case study of a deep foundation excavation project in soft soils in Shanghai, with a subway and railroad tracks adjacent to the excavation area of the foundation pit. The effects of the excavation sequence and reinforcement measures on the control of the subway tunnel and the railroad track are discussed in detail. [PERSON] et al.