群桩水平非线性振动的理论与实验研究

In recent two decades, constructions of cross-sea bridges, offshore wind-power towers and offshore oil platforms are growths of blowout type in China. The horizontal loads caused by typhoon, tsunami, earthquake and collision of ship to the structures have become the main control factors in design of pile foundations. However, the dynamic responses’ properties of the pile group have not been understood deeply and systematically up to now because of complexities of interactions of pile-soil system. As a result, the pseudo static analysis methods are still applied to take the place of dynamic analysis in the most of engineering design projects. Hence, it is certainly worth researching perfect theories of analysis and methods of design for pile group excited by horizontal dynamic loads. This proposal, the formation of dynamic p-y curves of piles will be founded through large scale model tests and theoretical analysis. With the p-y curve, the deformation mechanism and transfer law of load along the pile for group piles forced by horizontal dynamic loads will be studied. This research is aimed to develop a generic class of rigorous, complete theoretical system and simplified analytic technique for horizontal vibration of group based on the considering the nonlinear feature of soil . Simultaneously, an equivalent dynamic p-y curve using reduction coefficients will be researched to analysis the dynamic response of group piles in practice engineering. The results of the proposal will be not only multiply the results of model tests for pile-soil nonlinear vibration, but also make the level of dynamic analysis for pile group in progress theoretically. A more rigorous and effective new theory for nonlinear dynamic analysis of group will be developed. The research of this proposal has high academic value and great significance for engineering applicationpile.

近二十年来，我国跨海大桥、海上风电、港口码头与采油平台等近海工程建设迎来热潮。在这些工程结构中，台风、波浪、地震、船舶撞击等形成的水平动荷载往往成为桩基础设计的主控因素之一。然而由于桩土系统动力相互作用的复杂性，目前对桩基础动力响应的研究还不够系统深入。其动力设计还主要是采用拟静力分析方法，尚未形成较完善的设计与分析理论体系。本项目将通过试验研究和理论分析，建立桩土动力p-y曲线并揭示水平动荷载下群桩的变形机理及其荷载传递规律，提出能够描述土体非线性变形特性及群桩效应的桩基水平振动严密理论体系及简化分析方法，同时探索研究适用于群桩动力响应分析的“折减系数”等效动力p-y曲线实用简便方法。本项研究将不仅丰富桩土非线性振动的模型试验成果，而且可以发展更为精确、有效的桩基非线性动力分析新理论，使得群桩的动力分析研究达到新水平。本课题研究具有较高的学术与工程应用价值。

近二十年来，我国跨海大桥，海上风电，港口码头及海上采油平台等近海工程迎来建设热潮，传统的高承台群桩基础因其承载力高，变形小而在上述工程中被广泛采用。这些工程的桩基施工或使用过程中，因水流、台风、波浪、地震、船舶撞击等形成的水平动荷载往往成为桩基础设计的主控因素之一。然而，由于桩土系统动力相互作用的复杂性，目前对桩基础动力响应的研究还不够系统和深入。动力设计主要采用拟静力分析方法，尚未形成较完善的动力分析与设计的理论体系。本项目针对水平受荷桩的动力响应问题，通过理论分析、数值模拟和模型试验等方法系统研究群桩水平非线性动力特性。主要研究成果包括：（1）基于虚拟桩的概念，根据虚拟桩和桩孔位置的土体水平位移协调，建立了求解桩-桩间相互作用所需要的第二类Fredholm积分方程，与桩顶边界条件联立求解水平受荷群桩的位移和转角的相互作用系数，该方法是对传统相互作用系数的改进，克服了传统相互作用系数分析法过高估计桩的相互作用效应而带来的计算结果偏差；（2）针对水平受荷桩桩土局部分离的几何非线性特征，基于Novak薄层单元理论，借助势函数、分离变量法、圆孔辐射应力混合边值解法、傅里叶级数卷积等，结合桩土接触面相互作用边界条件，提出一种可以考虑桩土接触面滑移和分离影响的桩土相互作用模型，给出简谐稳态振动、瞬态激振作用下求解桩土动力阻抗的解析解。研究激振频率、桩土刚度比，桩身长径比，桩周土压缩模量比和孔隙比、土层刚度随深度连续变化等对桩土动力阻抗的影响；（3）采用有效应力的方法，根据不排水过程中的土体应力应变关系，计算孔压变化，并利用UMAT子程序模块进行二次开发，实现考虑孔压生成的修正Mohr-Coulomb本构模型在数值模拟上的运用。结合桩土接触面条件，研究桩土局部分离、桩间距、加载频率对桩基动阻抗及孔压分布的影响。本项目研究成果进一步完善桩土动力相互作用理论，可为桩基础动力分析与设计提供理论参考。