Behavior of piled raft foundations subjected to static horizontal loading and seismic loading

本研究的主要目的是：1)为桩筏基础的设计提供静水平荷载和动（地震）荷载作用下桩筏的综合实验数据；2)建立一种简单可行的桩筏和群桩的变形和荷载比分析方法。为了实现这些目标，我们对桩筏进行了一系列的离心建模，得出如下结论：桩筏中单桩的刚度和极限阻力与孤立单桩的加载试验结果存在较大差异。在桩筏设计中，在评价桩响应时应考虑荷载通过筏基传递引起的桩周围应力的增加，以及各构件之间的相互作用效应。与筏板竖向荷载和筏板基座与土的摩擦系数计算结果相比，筏板构件在桩筏中的极限摩阻力较小（刚性桩头连接）或较大（铰接桩头连接）。认为筏板下土体受桩的约束，可减小筏板基部正下方土体的剪切变形，从而使界面处的动剪应力较小。在各构件所承担的水平荷载比例上，筏板最初承担的荷载大于桩，在刚性桩头连接的桩筏中，桩的位移大于筏板。在铰接桩头连接的桩筏中，桩的贡献要小得多。然而，总体而言，该比例高度依赖于桩筏位移，因此在桩筏基础设计中考虑这种非线性响应是很重要的。在桩筏设计中，位移（沉降、水平位移、倾斜）和构件所受荷载比例的评估是最重要的因素。本文对上述因素的动力行为进行了深入的研究。即使桩筏受到较强的输入运动，桩与筏基之间的竖向荷载分担与水平荷载相比变化较小。少

The main objectives of this research are 1) provide comprehensive experimental data for pile rafts subjected to static horizontal loads and dynamic (seismic) loads for design of piled raft foundations, 2) develop a simple but workable analytical method for deformation and load proportion of pile rafts and pile groups. To achieve these objectives, a series of centrifuge modeling of pile rafts was extensively conducted and some conclusions are shown below:1. The stiffness and the ultimate resistance of the single pile in the piled raft are highly different from those observed in the loading test of the isolated single pile. The increase in the confining stress around the pile due to the load transferred through the raft base should be considered in the evaluation of the pile response in the piled raft design, as well as the interaction effects between the components.2. The ultimate frictional resistance of the raft component in the piled raft was smaller (rigid pile head connection) or a … More lmost the same (hinged pile head connection) compared with the estimates from the raft vertical loads and the coefficient of the friction between the raft base and the soil. It was thought that the soil beneath the raft was constrained by the piles which may reduce the shear deformation of the soil just beneath the raft base, and thus the mobilized shear stress at the interface was smaller.3. As for the proportion of the horizontal load carried by each component, the raft initially carried more load than the piles, with larger displacements the piles more than the raft in the piled raft with rigid pile head connection. In the piled raft with hinged pile head connection, the contribution of the piles was much smaller. Overall, however, the proportion is highly dependent on the piled raft displacement, and it is therefore important to consider such non-linear response in the designs of piled raft foundations.4. In the piled raft designs, evaluation of the displacement (settlement, horizontal displacement, and inclination) and the proportion of the load carried by the components are the most important factors. The dynamic behaviors of the above factors were intensively examined in this paper.5. The change in the vertical load sharing between the piles and the raft base was relatively small compared with the horizontal load, even when the piled rafts were subjected to relatively strong input motion. Less