Numerical Investigation of Underlying Curved Tunnel Heave during a New Foundation Pit Excavation

Abstract

Excavations of foundation pits around tunnels can induce alterations in stress and deformation within the tunnel, thereby influencing the safety of pre-existing tunnels, especially those with curved tunnel segments. This study focuses on investigating the effects of excavation processes and diverse construction methods on underlying curved tunnels, including excavation sequencing, reinforcement techniques, and support strategies. The efficacy of different construction methods in controlling deformation was assessed by a numerical analysis using finite difference software. The results show that adopting a skip excavation approach, positioned at a distance three times that of the excavation width, effectively diminishes heaving at the foundation pit bottom. In situations where tunnels intersect foundation pits at small angles, the generation of the hoop effect through intermittent reinforcement minimizes lateral extrusion forces, thereby enhancing control over both vertical and horizontal deformation of the curved tunnel. Deformation control within the tunnel, ranked from the least to the most effective, includes configurations of discontinuous reinforcement without a bottom plate, discontinuous main reinforcement, no reinforcement, damaged lining with discontinuous reinforcement, discontinuous reinforcement, and portal reinforcement. Moreover, the incorporation of a bottom plate in conjunction with discontinuous reinforcement methods proves efficient in restraining tunnel heave within safety limits. This study provides insights into safeguarding curved tunnels during irregular foundation pit excavation, offering potential time and cost savings through improved protective measures.