Vertical mechanical response of axial loaded pile to tunneling-induced pile exposure

Construction of tunnels in urban cities may inevitably pass frontally through existing piles, causing pile exposure. This tunneling-induced pile exposure will cause the loss of soil resistance and redistribution of ground stress, posing a risk to the safety of existing pile. However, few studies have been carried out on such cases. This study conducted a theoretical analysis based on the two-stage method to clarify the mechanical response of pile due to tunneling-induced exposure, which calculates the tunneling induced ground settlement and the ground settlement induced pile response in two separate stages. The displacement compatibility equation of the pile at the exposure part was adjusted to account for the loss of pile-soil interaction. The results show that the overall pile deformation behaves as a uniform settlement. The additional skin friction is negative above the exposed part and positive below, resulting in the whole pile being under pressure. The axial force increases with depth above the exposed part and decreases below, while remaining unchanged at the exposed part. The pile vertical response is strongly affected by both the pile top load and the ground loss. Limiting the pile's exposed length can significantly reduce the adverse effects of tunnel excavation.