基于不同地震动强度的液化土中直斜桩动力响应特征及规律研究

As the application background for the lateral bearing capacity and seismic design method of the pile, through dynamic tri-axial test, the dynamic centrifuge model test and numerical simulation, the influence on internal forces of straight and batter pile were studied by considering sandy soil liquefaction and inertia coupling effect from the supper structure. The dynamic response characteristics and soil attenuation coefficient distribution regularity of the pile were analyzed by changing liquefied soil layer thickness and the ground motion intensity. The similar rate for centrifugal test model was studied in order to determine the material of pile body and soil, and then the centrifugal model tests were conducted. The p-y curve was got based on the cyclic stress strain of the soil parameters according to the vibrating tri-axial test for saturated sandy soil physical parameters in accordance with the centrifuge test, and then the simplified seismic calculation model of pile was established by using OpenSees software; three-dimensional finite element model for numerical simulation research was established by selecting suitable sand liquefaction large deformation constitutive relation. After that, the simplify calculation results were compared with centrifuge test and numerical simulation results to verify the reliability of the simplified model; through comparing the centrifuge test and numerical simulation results of pile, such as deformation and bending moment distribution and straight batter pile p-y curves, the differences of horizontal bearing mechanism and seismic performance were evaluated for straight and batter pile in liquefied soil. The study results will provide the raw data for scientific research, but also enhance the level of seismic design of pile foundation in liquefied soil and provide scientific suggestions for practical engineering application.

以液化土中桩基水平承载特性及抗震设计方法为应用背景，通过动三轴试验、动力离心模型试验和数值模拟相结合的途径，研究砂土液化和上部结构惯性作用对直斜桩内力的影响，分析不同液化土层厚度和地震动强度下桩基动力响应特征及土层衰减系数分布规律。研究离心模型相似率，确定土体和桩基模拟材料，进行离心机动力模型试验；按照离心机试验饱和砂土物性参数进行振动三轴试验，依据砂土的循环应力应变参数获得p-y曲线，通过OpenSees平台建立桩基抗震简化分析模型；选取合适的砂土液化大变形本构关系，建立三维有限元模型进行数值模拟研究，将简化计算结果与离心机试验和数值模拟结果进行对比，验证简化模型的可靠性；通过对比离心机试验和数值模拟结果中的桩身弯矩分布和直斜桩p-y曲线等指标，评价液化土中直桩和斜桩水平承载机制与抗震性能差异。成果将为科学研究提供原始资料，提升液化土中桩基抗震设计水平，为工程应用提供科学建议。

桩基础是液化场地建筑物基础的主要应用形式，液化场地中群桩基础动力响应规律一直是建筑物抗震领域研究的热点。近年来，许多学者对砂土液化场地中直群桩动力响应进行了大量有价值的研究工作。然而，对于饱和砂土场地条件下斜群桩动力响应规律以及直斜群桩抗震性能对比研究的内容比较少见。鉴于此，基于离心机振动台试验、三维数值模拟结合理论分析的方法，对饱和砂土场地土层和上部结构动力响应特征、土-直斜群桩-承台结构动力相互作用机制、直斜桩身弯矩分布规律和直斜桩周土刚度衰减关系进行研究，主要内容及成果包括：（1）基于离心振动台试验，研究液化场地中群桩-地基土的相互作用机理，探讨不同地震动强度作用下直斜群桩承台加速度、不同深度处地基土层加速度和超静孔隙水压力在砂土液化过程中的动力响应特征。（2）将频谱分析方法首次应用于饱和砂土场地高承台群桩桩身弯矩分析，描述土体在液化前后直斜群桩桩身弯矩分布规律，为地震作用下桩身内力分析方法提供了一种新思路。（3）基于ABAQUS软件平台，建立了土-群桩-承台结构二维数值模型，深入研究了不同峰值加速度作用下饱和砂土地基超静孔隙水压力变化规律。然后，基于FLAC3D数值模拟方法，从多个角度对桩基础动力响应特性及桩身弯曲变形分布规律进行深入研究，为实际工程中饱和砂土场地高承台桩基抗震设计提出合理的建议。（4）根据弹性地基梁和桩土相互作用理论，构建了饱和砂土场地直斜群桩动力p-y曲线，并提出了一种基于动力p-y曲线的直斜桩周土液化衰减系数计算方法，丰富了桩土动力相互作用理论研究成果。