堆载作用下桥梁桩基偏移及处治分析

Analysis on Bridge Pile Foundation Offset and Measures Under Surcharge Load

针对桥梁桩基偏移问题,以一座受非对称堆载影响的公路桥梁为例,对桩基础偏移和偏移成因进行分析。通过建立有限元模型,分析该公路桥梁桩基础受堆载影响前、堆载影响后、堆载高度、卸载纠偏处治后等多个工况下的力学特性。根据现场桥梁上下部检测情况、土体处治监控情况和有限元数值分析,结果表明:非对称堆载是桩基础产生偏移的主要原因,桥梁周边的非对称堆载对桩基础周边的土体产生一定的扰动,使土体对桩基础产生水平的推力,从而引起桩基础的偏移。对堆载土体进行卸载直至土体变形趋于稳定,可在一定程度上改善既有桩基础的受力状态,起到一定的纠偏作用。通过增设反力锚直接作用外力于桥墩结构,控制纠偏方向,来提供对桥梁桩基的纠偏力,并在桩基顺桥向和横桥向布置应力释放孔,有效释放土体侧向挤压应力,减小土体侧向变形对桩基的影响。同时对偏移的桩基础,采用在原桩基础位置两侧进行对称性群桩加固后,桩基础的横桥向位移、弯矩和轴力大幅度降低,纠偏作用效果明显,使桥墩恢复到正常使用状态。以实际桥梁工程为例,对受非对称堆载影响的桩基础采用钻孔卸压、开挖卸载、桥梁横向加强、桥墩纵向复位和加桩加固等综合纠偏方案,结果表明纠偏方案效果良好。

In view of the pile foundation offset problem,taking a highway bridge affected by asymmetric surcharge load for an example,the pile foundation offset causes and reasons were analyzed.The finite element model was established to analyze the mechanical properties of bridge pile under multiple working conditions,e.g.,before and after being affected by surcharge load,the height of surcharge load,and after unloading correction and treatment.Based on the on-site inspection of upper and lower parts of bridge,soil treatment monitoring,and finite element numerical analysis,the result indicates that the asymmetric surcharge load is the main reason for pile foundation offset.The asymmetric surcharge load around bridge has a certain disturbance to the soil around pile.This causes the soil to have horizontal thrust to the pile foundation,thus causes the pile foundation offset.Unloading the pile-loaded soil until the soil deformation becomes stable can improve the bearing state of existing pile foundation to a certain extent,and play a certain role in rectifying the deviation.By adding reaction anchors to directly apply external forces to the bridge pier structure,and controlling correction direction,the corrective force on bridge pile foundation is provided.The stress release holes are arranged in the longitudinal and transverse directions of pile foundation to effectively release the lateral compressive stress of soil,and reduce the influence of lateral deformation of soil on the pile foundation.Simultaneously,after strengthening the symmetrical pile groups on both sides of original pile foundations,the transverse displacement,bending moment and axial force of pile foundation are greatly reduced.The effect of correcting deviation is obvious,so that the bridge pier can return to the normal state of use.Taking an actual bridge project for an example,the pile foundation,affected by asymmetric surcharge load,is adopted with comprehensive deviation correction schemes,e.g.,drilling pressure relief,excavation unloading,bridge transverse reinforcement,pier longitudinal restoration,and reinforcement by adding piles.The result shows that the deviation correction scheme is effective.