Effects of pile tip cutting due to shield TBM tunnel construction on pile behaviour under various reinforcement conditions

Existing piles, especially in urban areas, are at risk of being cut by new tunnel construction, potentially affecting their serviceability. This study examined the behaviour of piles under various reinforcement conditions subject to tip cutting resulting from tunnel excavation. For this, the construction of a tunnel using a shield tunnel boring machine adjacent to existing single and group piles was simulated. A three-dimensional finite element analysis was used to perform the simulations. Certain piles in the group were simulated by cutting the pile tips to mimic the effect of tunnel excavation, and the behaviour of the piles was studied by considering the effect of pile cap and ground reinforcements. A numerical analysis was used to examine the ground settlement caused by tunnel excavation, pile head settlement, axial pile force, and shear stress occurring at the pile–ground interface. The results revealed that for all piles with pile tips supported by weathered rock, the shear stress distributions demonstrated similar trends, whereas for piles with cut tips, tensile or compressive forces occurred simultaneously according to the relative position by pile depth. Additionally, when the pile tip was supported by weathered rock, approximately 70% of the support was due to shaft friction and the remaining 30% was provided by the pile tip. For piles without reinforcement, the final settlement was approximately 70% greater than that of piles with grouting reinforcement. These results indicate that pile and ground settlements are substantially influenced by pile tip cutting and reinforcement conditions.