桥梁桩基主动托换中顶升荷载的简化计算

Simplified calculation of jacking load in active underpinning of bridge piles

以福州地铁1号线盾构隧道下穿洗马桥的桩基主动托换工程为依托,针对桥梁上部结构-桩身-土体三者共同组成的复杂超静定结构,运用数值模拟方法和现场实测数据,分析了在不同顶升荷载作用下复杂超静定结构的内力与位移响应,重点讨论了托换过程中上、下部结构的相对刚度及其对顶升荷载的影响;根据顶升荷载作用点以下桩身轴力接近0的条件,确定了桥墩盖梁与薄壁桥台梁两种典型工况下的桩基顶升荷载分别为1 800 k N和2 600 k N。现场监测结果表明,顶升过程中上部结构的位移值和桩身轴力变化值,均与计算结果吻合较好。在此基础上,提出基于上、下部结构刚度比的顶升荷载简化计算方法,研究结果可为类似复杂超静定结构的桩基主动托换工程提供参考和借鉴。

Based on the pile active underpinning project of Xima Bridge in Fuzhou Metro Line I shield tunnel, considering the complex hyperstatic structures composed by bridge superstructure, bridge piles and soil masses, the numerical simulation and the field monitoring data are utilized jointly to study the inner force and displacement responses of hyperstatic structures under different jacking loads. The influences of superstructure stiffness and substructure stiffness on the determination of jacking load are emphasized. The reasonable jacking loads for two typical conditions （the piles under cap beam and abutment beam） are 1800 kN and 2600 kN respectively, which make the axial forces of underpinned piles reduce to zero. The field monitoring is also carried out during construction, and the displacement of bridge superstructure and the axial force of bridge pile from monitoring data are consistent with their counterparts from numerical simulations. Based on these results from numerical simulation and field monitoring, a simplified analytical method is further proposed to calculate the reasonable active jacking load by considering the stiffness ratio between the superstructure and substructure, which can provide some reference for the pile underpinning projects under similar scenarios.