Abstract:

It is very important to study the stress and deformation law of pile foundation caused by tunnel excavation when the existing pile foundation is located in different positions around the tunnel. Firstly, the soft soil around the shield section project of left line of North StationTiedong Road Station on Tianjin Metro Line No. 3 is divided into 8 zones according to the radial and tangential positions of pile end by ABAQUS software. And then a twodimensional finite element model considering soft soil modified Cambridge constitutive relation is established to study the lateral friction resistance and displacement of pile body under design load and ultimate load after excavation of tunnel. Finally, the influence zone of tunnel excavation on the behavior of adjacent single pile is established. The results show that: (1) Tunnel excavation will cause negative friction resistance on the side near the tunnel of pile foundation; and the maximum negative friction resistance increases with the decrease of radial distance between pile and tunnel, and increases with the increase of pile length. (2) The excavation of the tunnel will lead to the reduction of the ultimate lateral friction resistance of the pile body; and when the pile end is located on both sides of the tunnel, the decrease amplitude is much higher, ranging from 10% to 15%. (3) When the pile end is located on both sides of the tunnel, the bottom and the top of the tunnel, the tunnel excavation mainly affects the inclination of the pile body, the deflection of the pile body and the settlement of the pile top. (4) The inddices that can evaluate the behavior of existing single pile after tunnel excavation are put forward; when the pile end is located in zone 3, the comprehensive influence of shield tunneling on single pile is the largest, and construction monitoring measures should be strengthened.

Key words: soft soil, shield tunnel, single pile, influence partitions, numerical simulation