群桩基础桥桩单边开挖稳定性精细化数值模拟分析

Refined Numerical Simulation Analysis on Stability of Single Side Excavation of Bridge Piles of Pile Group Foundation

航道升级开挖会对既有桥梁桩基产生复杂的不安全影响。由于缺乏相应的设计计算理论,因此优化设计困难。文中针对桥桩嵌入河岸和远离河岸2种典型情况,考虑群桩桩土接触效应和钻孔灌注桩施工特点,采用侧壁阻力反算摩擦系数的方法,建立地基-桥桩整体三维精细化数值模拟模型,对存在软弱夹层的河床地层开挖后桥桩的内力和位移影响进行研究。结果表明,由于河床开挖回弹和河岸边坡的综合效应,桥桩与河岸分离时,桥桩产生的内力与位移大于嵌入式模型,桩基产生了1.66 MPa的拉应力,桩顶最大水平位移9.5 mm,大于规范允许值6 mm,建议进行加固预处理。三维精细化数值模拟能有效反映桩土摩擦效应、开挖引起的整体位移场效应、复杂地层分布,以及复杂边界效应。

The factors concerning safety of existing bridge pile foundation caused by channel upgrade excavation are complex.Due to the lack of the corresponding calculation theory in the design phase,it is difficult to carry out the optimization design.In this paper,considering the pile-soil contact effect of pile group and the construction characteristics of bored piles,two typical cases that bridge piles are embedded in the river bank and far away from the river bank are discussed.In addition,the friction coefficient is back calculated by the side resistance,and the three-dimensional refined numerical simulation model of the whole foundation-pile is established to study the internal force and displacement of the bridge pile after excavation of the riverbed stratum with weak interlayer.The results show that when the bridge piles are separated from the river bank,owing to the comprehensive effect of riverbed excavation rebound and river bank slope,the internal force and displacement of the bridge pile are slightly larger than that of the embedded model.Simultaneously,one of the piles generates tensile stress with the maximum value of 1.66 MPa and the maximum horizontal displacements value of 9.5 mm on its top,which is greater than the allowable value of 6 mm in Code.Consequently,it is recommended to carry out pre-reinforcement treatment.What can be effectively reflected in the three-dimensional refined numerical simulation are the pile-soil friction effect,the overall displacement field effect caused by excavation,the complex stratum distribution,and the complex boundary effect.