Multi-effects of tunneling and excavation on pile group in clay

Existing studies predominantly investigate the impacts of tunnel or excavation on pile foundations in isolation, whereas actual engineering projects often involve sequential or simultaneous excavation of tunnels and excavation. This study focuses on the effects of combined tunnel and excavation unloading on adjacent pile groups in clay strata. Constant-gravity physical scaled model tests and three-dimensional numerical simulations are conducted, accounting for the time-dependent effects of clay excavation unloading and soil stiffness characteristics under small-strain conditions. The additional responses of pile foundations and the evolution of excess pore water pressure dissipation during excavation unloading are systematically analyzed. The results reveal that the type of pile foundation surrounding tunnels and foundation pits has a minor influence on surface settlement. Both tunnel and excavation induce tilting of pile groups toward the unloading zone: the tilt increases continuously to 0.12% of the pile spacing during tunnel excavation, gradually decreases to 0.05% of the pile spacing during excavation, and a net tilt toward the tunnel side persists in the end. Pile foundation type affects the axial force variation pattern of piles. Owing to the shielding effect of rear piles in the group, the maximum negative bending moment of the pile group is approximately 29% smaller than that of a single pile, with a large bending moment occurring near the pile head. The presence of excavation support structures and existing pile foundations alters seepage paths of pore water, thereby influencing the dissipation time of excess pore water pressure.