竖向下压循环荷载作用下单桩承载力及累积沉降特性模型试验研究

Model test on bearing capacity and accumulated settlement of single pile subjected to axial cyclic loading

竖向循环荷载作用下,单桩的承载力及变形特性均不同于静荷载情况。利用浙江大学自行研制的大型地基与边坡工程模型试验系统开展了单桩基础竖向下压循环荷载作用下的大比例模型试验,获得了不同侧/端阻比下桩基的循环承载力及桩顶循环累积沉降。试验发现:存在一最小循环荷载比,当循环荷载比小于该值时,桩顶不会发生循环累积沉降;一定循环次数内桩顶循环累积沉降基本与循环次数成正比,且循环累积沉降与循环次数的比值近似与桩顶循环荷载比呈线性关系。通过给定单桩循环破坏标准,绘出了模型桩的循环承载力曲线,发现侧/端阻比较大的桩基更易发生桩顶循环累积沉降;通过拟合桩顶无量纲沉降,可预测桩基循环累积沉降的发展。最后提出了长期循环荷载作用下单桩基础的工程设计方法。

The performance of the single pile under cyclic loading is different from that under static loading. A series of large scale model tests on cyclic axial response of the single pile in silt are described in this paper. The tests are carded out by use of the large foundation and slope engineering test system of Zhejiang University. Accumulated settlement of the pile is measured for different cyclic loading levels. A critical value of the cyclic axial loading ratio termed the minimum cyclic loading ratio is defined. Below this threshold value the pile performance will not be significantly affected by cyclic loading. It is found that the accumulated settlement of the pile is proportional to the number of loading cycles, and the ratio of accumulated settlement of the pile and number of loading cycles is varied linearly with the cyclic loading ratio. With the given failure criteria of the pile subjected to the axial cyclic loading, the cyclic bearing capacity curve of the pile is presented. It is seen that the accumulated settlement of flooding is more than that of the end bearing pile under cyclic loading. The non-dimensional settlement of the pile is proposed, and it can be used to predict the accumulated settlement of the pile in-situ. A design method of the pile under long-term cyclic axial loading is finally presented.