黄土山区冲沟地形对桥梁桩基有效桩长影响研究

Influence of Gulch Topography on Effective Length of Bridge Pile Foundationin in Loess Hilly Area

为全面了解黄土山区冲沟地形对桥梁桩基有效长度的影响,在对山西省典型黄土山区桥梁下部全面调查的基础上,依据黄土地区现场桩基静载试验,应用FLAC3D建立黄土山区地形桥梁桩基有限差分模型,分析了不同坡度、临坡距、桩长变化对桩基有效桩长的影响,揭示了桩基承载力、桩侧摩阻力、桩端阻力及有效桩长变化规律,并依据计算结果提出相关工程技术建议。研究结果表明:一定桩长时,斜坡坡度、临坡距变化对桩侧摩阻力产生不同程度影响,对桩端阻力影响不大;坡度越大,临坡距越小,桩侧摩阻力减小幅度越显著,最大为70.89%;坡度较小、临坡距较大时,增长桩长使桩侧摩阻力从95.99%提高至99.71%;桩侧摩阻力变化的根本原因是桩基有效长度发生改变,桩基有效桩长折减程度同斜坡坡度及桩基临坡距有关,与桩长无关;建立的桩基有效长度计算公式可为黄土山区冲沟地形条件桩基础设计提供技术借鉴。

Based on widely investigation on bridges foundation in loess area of Shanxi province and onsite pile static loading test,the parameters of slope gradient,slope distance and pile length were ana-lyzed to study the influence of gulch topography on effective length of bridge pile in loess hilly area. By means of the FLAC3D finite analysis,the change rules of ultimate bearing capacity,pile lateral fric-tion,tip resistance and effective pile length were obtained,and furthermore some suggestions for engi-neering were provided. The research shows that:with certain pile length,the slope gradient and slope distance have great influence on pile lateral friction,and has little influence on tip resistance. More-over,the lateral friction of the pile gradually reduces with increase of slope angle and decrease of dis-tance to the slope. The reduction can reach 70.89%. The lateral friction can rise from 95.99% to99.71% by elongating the pile length for the ground with small slope angle or long distance to the slope. The basic influence factor on lateral friction is the effective length of the pile. The reduction co-efficient of the effective length of the pile is independent of pile length,and closely related to the slope gradient and the distance to the slope. Finally,the calculation formula of pile effective length is provid-ed,which gives an effective technical reference for pile design in gulch topography of loess hilly area.