Pile groups under cyclic horizontal loading

根据EA-Pfähle (EA-P) (DGGT 2012)，循环荷载定义为桩的重复荷载，其中不需要考虑作用在桩-土系统上的惯性力。在土木工程的各个领域，如海上和陆上风力发电机组或交通基础设施结构中，桩基的循环荷载是很重要的。对于海上风力发电机，主要采用单桩（即大直径的单桩）或大桩间距的夹套结构（即桩间相互作用不重要）。然而，桥台往往是建立在相对较小桩间距的桩群上。这种由若干相互作用的桩组成的地基随后被称为群桩。例如，由风和波浪（海上风力涡轮机）或温度引起的约束（没有接头和轴承的整体桥梁）引起的循环载荷。根据EA-P，对于循环荷载作用下的桩只有有限的知识。为了考虑整体和半整体桥梁的循环温度约束，通常在设计过程中采用或多或少任意选择的折减系数。因此，该项目的主要目标是对循环水平荷载作用下的群桩承载特性进行基础研究，并对结果进行定性和定量评价。在本研究中，对地基条件、桩群几何形状和荷载条件等参数的影响进行了实验和数值研究。群桩几何形状和荷载条件应以整体和半整体桥梁的典型结构为基础。详细地说，以下主题将被处理：-识别在循环水平荷载下影响群桩承载性能的主要参数。-检讨EA-P中有关静力荷载下一组桩内的桩荷载和温克勒模量分布的减少系数，并在重大循环荷载下调整这些系数。-基于Tasan（2011）的增强应变楔模型（ESWM）开发了一个分析模型，该模型允许确定以下参数：+桩头水平位移的累积。+群内各桩的温克勒模量沿桩身的分布。+群内各桩沿桩身的弯矩和剪力分布。

According to EA-Pfähle (EA-P) (DGGT 2012) cyclic loading is defined as a repetitive loading of piles where forces of inertia acting on the pile-soil-system do not need to be considered. Cyclic loading of pile foundations is of importance in various fields of civil engineering such as offshore- and onshore- wind turbines or structures for transport infrastructure. For offshore wind turbines mainly monopiles (i.e. single piles with large diameters) or jacket-structures with large pile spacing (i.e. interactions between piles are of minor importance) are constructed. However, bridge abutments are frequently founded on groups of piles with relatively small pile spacing. Foundations of this type comprising a number of interacting piles subsequently will be termed pile groups. Cyclic loadings are caused for example by wind and waves (offshore wind turbines) or temperature induced constraints (integral bridges without joints and bearings).According to EA-P there is only limited knowledge available for piles under cyclic loading. To consider cyclic temperature induced constraints for integral and semi-integral bridges, frequently more or less arbitrarily chosen reduction coefficients are applied in the design process. It is therefore the main objective of the project to carry out a fundamental study on the bearing behaviour of pile groups under cyclic horizontal loading and to evaluate the results qualitatively as well as quantitatively. Within this study the influence of parameters such as subsoil conditions, pile group geometry and loading condition are to be investigated experimentally and numerically. Pile group geometries and loading conditions are to be based on configurations typical for integral and semi-integral bridges.In detail the following topics are to be treated:- Identification of the main parameters influencing the bearing behaviour of pile groups under cyclic horizontal loading.- Review of the reduction coefficients documented in the EA-P for the distribution of pile loads and Winkler modulus within a pile group under static loading and adjustment of these coefficients for significant cyclic loading.- Development of an analysis model based on the Enhanced Strain Wedge Model (ESWM) by Tasan (2011) which allows the determination of the following parameters: + Accumulation of the horizontal displacement at the pile head. + Distribution of the Winkler modulus along the pile shaft for the various piles within the pile group. + Distribution of bending moment and shear force along the pile shaft for the various piles within the pile group.