盾构法施工对近距离侧穿桥梁桩基的影响分析

盾构法施工地铁隧道近距离侧穿高速公路桥梁桩基时,引起地层移动和应力调整,导致桩基位移和内力发生变化,给上部结构带来安全隐患。以杭州地铁3号线工大站—留和站盾构区间双线施工为依托,运用三维有限元软件模拟盾构开挖施工的全过程,研究开挖过程对地层沉降及邻近桥梁桩基影响规律。结果表明,先行隧道开挖导致地表形成沉降槽,后行隧道开挖沉降曲线向后行线扩展;桩基竖向呈现刚体位移,单线开挖时在横向(Y方向)上嵌入土体桩基上半部分向隧道内倾移,下半部分背离隧道方向倾移,在纵向(X方向)上桩基呈现拱形弯曲,双线开挖时桩基横向位移发生反向叠加效应,导致最终横向位移基本接近初始状态,纵向上弯曲位移发生正向叠加效应;双线隧道先后开挖使桩基产生附加摩阻力和附加轴力,在隧道顶面分界线以上桩基总侧摩阻力较初始状态不断减小,分界线以下增加,位于-2.5 m以上桩基轴力较初始状态减小,以下增加;单线开挖时桩基弯矩变化明显,双线开挖弯矩出现反向叠加效果,基本保持初始状态。

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, 3D 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-2.5m 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.