中文摘要：

为预测桩的极限承载力，对桩土临界位移进行了研究。选取了钻孔桩及管桩两种桩型的桩进行静载试验及内力测试。桩顶沉降量是由两部分组成的，一是桩身的压缩变形，二是桩的整体位移，用桩顶沉降量减去某一横截面以上桩身压缩产生的变形量后得到的位移是该截面的桩身实际位移。试验发现，对于超长的预制管桩，桩身压缩产生的变形量在桩顶位移中占重要比例，应以桩身实际位移进行桩土临界位移研究。根据试验结果绘制了各土层侧摩阻力与该土层处桩身实际位移的关系曲线，根据这些关系曲线可知：桩侧摩阻力随桩身实际位移的变化可分为快速增长阶段、平缓阶段及下降阶段，不同深度土层的侧摩阻力发挥不同步。采用“假想悬臂梁模型”对试验现象进行分析，得出某土层的桩土临界位移随桩土界面强度的增大而增大、随土层自身强度的增大而增大、随土层所受的周边土层向上的限制作用的增大而减小的结论。

英文摘要：

In order to estimate the ultimate bearing capacity of pile, the critical displacement of piles is researched. The static load tests and internal force tests of a drilled pile and a pipe pile are carried out. The top displacement of a pile includes two parts ： one is the compression deformation of the pile, the other is the displacement of the pile section. The displacement of a pile section can be obtained by subtracting the compression deformation above the pile section from the top displacement of the pile. It is found that for the long pipe piles, the compression deformation is very distinct, so the research of the critical displacement should be carried out with the displacement of a pile section. The relationship between side soil resistance and pile-soil displacement are obtained based on the test data. The relationship shows that the change of shaft resistance of pile along with the displacement variation of a pile section can be divided into three stages ： stage of fast increase, stage of slow increase and stage of decrease. The appearance of ultimate shaft resistance in different depth soil layers is asynchronous. A model of ＂imaginary cantilever beam＂is used to explain the phenomenon. It is concluded by the analysis that the critical displacement will increase with the increase of the strength of pile-soil interface or the strength of soil, and will decrease with the increase of the circumjacent restriction of the soil.