Mechanical Responses of Adjacent Pile Foundations to Superlarge Slurry Shield Tunneling: A Full-Scale Field Case Study

Abstract This case study presents a full-scale field test on the impact of superlarge diameter slurry shield tunneling on adjacent pile foundations during the construction of the Zhanjiang Bay subsea tunnel. Through systematic in situ monitoring of four full-scale test piles at the tunnel exit portal, this study elucidates the disturbance mechanisms that arise from superlarge diameter slurry shield tunneling in ultrashallow overburden strata. For this purpose, an innovative monitoring framework combining a self-anchored loading system with high-resolution densely distributed optical fiber sensor array is developed, enabling both load application and continuous internal force measurement during shield advancement. Key findings indicate that shield tunneling induces significant axial stress redistribution in adjacent piles, particularly during the critical advancement stage with shield cutterhead at the position of 0.0 D ± 0.5 D (where D is the excavation diameter of shield tunnel), with disturbance zones extending up to + 2.0 D in unreinforced strata. Furthermore, prereinforcement strategies were found to substantially alter the responses of the piles: reinforced zones exhibited higher axial forces but lower bending moments compared to their unreinforced counterparts. The vertical spatial relationship between pile tips and adjacent tunnels plays a crucial role in governing disturbance patterns, with peak axial forces generally shifting downward as pile length increases, whereas bending moments escalate in proportion to relative excavation ranges. Safety assessments confirm that control measures effectively limit surface settlements to less than 12 mm, pile head displacements to less than 8 mm, and anchor force loss to lower than 6%, thereby ensuring compliance with safety thresholds.