Effects of Large-Scale Twin Tunnel Excavation on an Existing Pile Group: Three-Dimensional Centrifuge Modeling

Existing piles are commonly encountered during tunnel construction in congested underground areas. Tunnel-soil-pile interaction has recently attracted considerable research attention; however, previous studies have mainly focused on the pile response owing to small-scale tunnel excavation. In this study, we conducted a three-dimensional centrifuge test to investigate the deformation mechanisms of a pile group owing to largescale twin tunnel excavation. Pile group settlement increases almost linearly with tunnel advancement in response to a decrease of the tunneling-induced stress. A shorter distance between the monitoring point and new tunnel results in higher pile group settlement. A maximum pile group settlement of 0.23% of the tunnel diameter (D) is observed directly above the tunnel centerline upon completion of a single tunnel excavation. After twin tunnel excavation, the maximum pile group settlement increases to 0.32% D and the location of the maximum pile group settlement shifts to the centerline between the two tunnels. As the tunnel face approaches the monitoring section, the existing pile group tilts rapidly toward the tunnel face. Tilting of the existing pile group decreases as the tunnel face passes through the monitoring section. The measured tilting of the pile group reaches a maximum when the tunnel face is located directly beneath the monitoring section. This demonstrates the three-dimensional deformation mechanisms of the pile group owing to tunnel excavation. If the tunnel excavation is simplified to a two-dimensional problem, tilting of the pile group along the longitudinal tunnel direction is ignored, which is on the nonconservative side.