Analysis on the Influence of Shield Construction on Lateral and Closely Cross Bridge Pile Foundation

When the shield method is used to construct a subway tunnel that crosses the pile foundation of a highway bridge at a close distance, it causes stratum movement and stress adjustment, which leads to changes in pile foundation displacement and internal force, and brings safety hazards to the superstructure. Relying on the double-line construction of the shield tunnel between Gongda Station and Liuhe Station of Hangzhou Metro Line 3, 3 D finite element software was used to simulate the whole process of shield excavation, and the influence of the excavation process on ground settlement and adjacent bridge pile foundations was studied. The results show that the first tunnel excavation leads to the formation of settlement troughs on the ground surface, and the subsequent tunnel excavation settlement curve extends backward; the pile foundation exhibits a rigid displacement in the vertical direction, and the single-line excavation is embedded in the soil pile foundation in the transverse direction (Y direction). The upper part tilts into the tunnel, and the lower part tilts away from the tunnel direction. In the longitudinal direction (X direction), the pile foundation is arched and bent. Double-line excavation will cause the reverse superposition effect of the pile foundation lateral displacement, resulting in the final lateral displacement. Basically close to the initial state, the longitudinal bending displacement has a positive superimposition effect; the double-track tunnel excavation successively causes additional friction and additional axial force on the pile foundation. The total lateral friction resistance of the pile foundation above the boundary line of the tunnel top surface decreases compared with the initial state, and it increases below the dividing line. And the axial force of pile foundation above-2.5 m decreases compared with the initial state, but increases below; single-line excavation, the pile foundation bending moment changes obviously, and the double-line excavation bending moment has reverse superposition effect, basically keep the initial state.