中文摘要：

竖向循环荷载下，软土地基中的单桩承载及变形特性不同于静荷载情况。利用FLAC3D软件开展了单桩在循环荷载作用下承载及变形特性的数值试验，探究了不同循环荷载比、桩材料及桩端持力层对单桩承载及变形的影响规律。实验结果表明：桩侧摩阻力随着循环荷载比增加呈现衰减的变化趋势，当循环荷载比小于临界循环荷载比时，衰减趋势不明显。桩材料的不同对单桩侧端分担比（循环后桩侧阻力与循环后桩端阻力的比值）、端阻循环比（循环后桩端阻力与循环前桩端阻力的比值）影响较小，侧端分担比及端阻循环比随着桩端持力层模量的增大而减小。说明在工程实践中，通过控制循环荷载比小于临界循环荷载比，选择较大模量的桩端持力层对于改善单桩承载及变形特性效果明显，而提高桩材料的模量对其作用甚微。

英文摘要：

Under a vertical cyclic load,the bearing and deformation characteristics of a single pile in a soft soil foundation are different from the conditions under static load.Numerical experiments on the bearing and deformation characteristics of a single pile under the cyclic load were carried out using FLAC3D software.The influences of the cyclic loading ratio(CLR),pile material,and bearing stratum on the bearing and deformation characteristics of a single pile were studied.The results show:pile skin friction decreased with increase in the CLR,and the attenuation trend was not obvious when the cyclic loading ratio was less than the critical cyclic loading ratio.The influence of the pile material on the skin-tip sharing ratio(ζ:the ratio of pile skin friction and pile tip resistance after cyclic loading is applied)and the tip resistance cyclic ratio(η:the ratio of pile tip resistance before the cyclic loading is applied and pile tip resistance after cyclic loading is applied)is not obvious.In this case,ζandηdecrease with increase of the modulus of the bearing stratum.This indicates that in engineering practice,the bearing and deformation characteristics of a single pile could be improved by selecting a cyclic loading ratio that is less than the critical CLR,and selecting a bearing stratum with great modulus,but not by improvement of the pile modulus.