In urban subway construction, shield tunneling inevitably passes in close proximity to existing pile foundations, inducing adverse effects on their internal forces and deformations. Taking the twin shield tunnels with small clearance adjacent to the bridge piles as the engineering background, this study establishes a three-dimensional finite element numerical model to investigate the deformation and internal force responses of the adjacent pile foundations under different pile lengths, twin-tunnel construction sequences, and tunnel face pressure conditions. The findings indicate that the primary influence zone affected by twin-tunnel excavation extends approximately twice the tunnel diameter (2D) before and after the pile foundation location. Compared with short piles, longer piles exhibit smaller vertical displacements. Meanwhile, the lateral displacements, additional axial forces and bending moments of medium and long piles increase, with their maximum values occurring near the tunnel centerline. For the near pile, when the right tunnel is excavated first, compared with the condition of the left-tunnel-first excavation, the lateral and vertical displacements slightly increase. In addition, the maximum additional axial force increases by 38.8%, while the maximum additional bending moment decreases by approximately 21%. Tunnel face pressure exerts a moderate influence on the vertical displacement of both the surrounding soil and pile foundation, while its effect on lateral displacement and internal forces is relatively insignificant. The tunnel face pressure within the range of 200 kPa to 300 kPa provides optimal control over pile foundation deformation.
Guo et al. (Mon,) studied this question.