反复水平荷载下斜坡段桥梁基桩桩土受力变形特性及其计算方法研究

The behavior of piles and soils of bridge foundation in sloping ground is more complicated than that in level ground. Currently, there is no systematic design and calculation method. Combining with laboratory model tests, numerical simulations and a theoretical model, this project tends to investigate variations of cumulative pile deformations and weakening of surrounding soils under low-cyclic lateral loads, and propose the corresponding theoretical method. To develop the understanding among cumulative pile deformation and slope angle, loading times and magnitudes, a model test of a single pile in sloping ground under low-cyclic lateral loads will be conducted based on an existing engineering case firstly. On the basis of the secondary development of ABAQUS, a three-dimensional numerical model of piles in sloping ground is then further developed to analyze the influence of key parameters on the accumulative deformation of piles and the law of the soil weakening. Correspondingly, the model of soil weakening under low-cyclic lateral loads can be proposed by developing the strain wedge technique based on the results of the model test and numerical simulation. Finally, combined with the modified finite bar element method, the calculation method of pile-soil interaction of bridge foundation under low-cyclic lateral loads can be proposed.

斜坡段桥梁基桩桩土受力变形特性及计算方法较平地基桩更为复杂，目前尚未形成系统的设计计算方法。本项目拟采用室内模型试验、数值模拟与理论分析相结合的的方法，探讨反复水平荷载下基桩累积变形及桩周土体抗力机制与弱化特征，并提出相应理论计算方法。首先，以工程实例为原型，开展反复水平荷载下斜坡段桥梁基桩模型试验研究，以获得基桩累积变形与斜坡坡度、荷载作用次数及幅值之间的关系；其次，在对ABAQUS二次开发的基础上，建立斜坡段桥梁基桩三维数值分析模型，进一步分析关键参数对基桩累积变形及土体弱化规律的影响；最后，根据模型试验及数值模拟计算结果，对应变楔模型进行改进提出反复水平荷载下的土体弱化分析模型，结合修正有限杆单元法，提出反复水平荷载作用下斜坡段桥梁基桩桩土相互作用计算方法。

斜坡段桥梁桩基在我国山区高速公路和铁路中应用广泛，此类桩基受力情况复杂，有必要对其展开深入研究。本项目采用室内模型试验、数值模拟和理论计算分析相结合的方式，研究了反复水平荷载下斜坡段桥梁基桩与桩周土体受力变形特性及计算方法。首先，设计并完成了不同坡度及水平荷载幅值下斜坡段基桩承载特性室内模型试验，总结了桩身内力及变形规律，揭示了桩前土弱化规律。其次，在模型试验基础上，建立了数值分析模型，提出了可考虑斜坡坡度、水平循环荷载幅值及循环次数等因素影响的水平循环荷载下桩顶水平位移经验计算公式。最后，改进了传统有限杆单元方法，结合应变楔理论及土楔理论在斜坡地基上的修正，提出了斜坡段桥梁基桩内力及位移计算方法。本项目研究成果，可为类似桥梁设计和施工提供参考。