黏土中两种不同直径单桩水平循环加载模型试验与分析

Model tests and analysis of single piles with two different diameters subjected to cyclic lateral loadings in clay

为探讨海上风机在风、浪等水平往复循环荷载下大直径单桩基础的循环弱化特性,设计了稳定输出长期循环荷载的机械加载装置,开展了软黏土中长期水平循环荷载下海上风电大直径单桩基础和传统长桩基础的模型试验对比研究。根据API给出的骨干曲线和Masing二倍准则构建循环荷载下的p-y(荷载-位移)曲线,并借鉴前人工作,采用累积塑性应变描述软黏土的不排水抗剪强度弱化,提出了分析大周数水平循环荷载下单桩基础循环弱化的理论方法。该方法将循环荷载次数、幅值等外界条件与桩周土体的循环弱化特性建立联系,以适应海洋环境复杂多变的水平循环荷载形式。通过模型试验和理论研究认为,大直径单桩基础因刚度较大,在同样的水平力循环荷载条件下,其抵抗循环荷载的能力明显优于传统长桩。在海上风机大直径单桩的设计中采用基于黏土残余强度的循环后稳定水平承载力更为合理。

Model tests are carried out on the large-diameter single pile and the conventional long pile under lateral cyclic loads in clay, which aims to investigate the behavior of pile foundations of offshore wind turbines under the action of cyclic loads from wind and wave. Based on the backbone by API and Masing rules, a cyclic p-y curve is formed, where p is load and y is displacement. The method is presented to calculate the cyclic degradation of a pile subjected to lateral cyclic loading, using a typical clay model in the literature, which modifies the undrained shear strength by accumulated absolute plastic shear strain. By relating cycle numbers and cyclic amplitudes of lateral load to the cyclic degradation of soil around pile, the method can consider various types of lateral cyclic load in offshore projects. The results by model tests and theoretical calculations demonstrate that, under the same cyclic load, the cyclic resistance capacity of a large-diameter single pile with larger stiffness is better than that of a conventional long pile. For the design of a large-diameter single pile foundation of the offshore wind turbine, it is more rational to consider the post cyclic lateral capacity of the foundation with the residual strength of clay.