Deformation Stability Response of Adjacent Subway Tunnels considering Excavation and Support of Foundation Pit

TLDR

Adjacent foundation pit excavation threatens tunnel safety, necessitating study of tunnel deformation during excavation. The study investigates how various support methods (pile, bolt, pile‑bolt, shotcrete‑bolt) affect tunnel stability for tunnels located right or below a foundation pit, using full‑process numerical simulation to identify the most beneficial support. Numerical simulation shows that for a tunnel below the pit, stresses and displacements are minimal, whereas for a tunnel to the right, pile‑bolt support reduces soil displacement, limits stress magnitude and area, and controls tunnel movement. Both one‑step and multistep excavations significantly affect tunnel displacement, with greater impact on tunnels to the right of the pit; multistep excavation is recommended for shallow tunnels adjacent to the pit.

Abstract

Abstract Since the safety and stability of the original tunnel structure are easily affected by the adjacent foundation pit excavation, it is strongly necessary to study the deformation evolution of tunnels during the adjacent foundation pit excavation. With regard to the two cases that tunnel is adjacently located at the right and bottom of foundation pit, the influence of different supporting methods, including pile support, bolt support, pile-bolt support, and shotcrete-bolt support, on the tunnel stability was investigated on the basis of the whole excavation process numerical simulation of deep foundation pit for determining the best foundation pit supporting beneficial to the stability of adjacent tunnel. The results indicate that both one-step excavation and multistep excavation have great influences on the displacement of adjacent tunnels, wherein the influences on the tunnel located at the right of foundation pit are greater than those at the bottom of foundation pit. Multistep excavation is recommended for the foundation pit adjacent to shallow tunnel. In the case of the tunnel located on the bottom of the foundation pit, the maximum stress generated around the tunnel is small, the maximum stress area is limited, and the displacement of tunnel monitoring points is also small. For the tunnel located at the right of the foundation pit, the pile-bolt supporting can effectively limit the displacement of soil between the tunnel and the foundation pit, reduce the maximum stress and the maximum stress distribution area, and effectively control the tunnel displacement.