大直径变径桩竖向承载特性模型试验研究(I)

变径桩在桥梁桩基和软土地基处理得到了一定程度的应用，对其承载特性和工作机制的研究十分必要。通过室内大型模型试验，对大直径变截面单桩的荷载与沉降关系、桩侧摩阻力分布形式、桩身内力和桩端、变截面处的破坏模式等问题进行了探讨，试验结果表明，在桩顶截面相同的情况下，变截面桩竖向承载特性受变截面比影响显著，变截面比越小，竖向极限承载力越小。模型试验P-S曲线不存在最优变截面比，变截面比设计受桩横向受力特性的控制。变截面处土体挤土效应的发挥是以牺牲桩顶位移为代价，在只有到达一定桩身位移时，才体现明显的挤土效应，使承载力提高。

Model testing study of vertical bearing behaviors for large diameter pile with variable cross-section (I)

Large diameter pile with variable cross-sections is applied to the region of bride engineering and foundation treatment.It is necessary to study the vertical bearing behaviors and working mechanism.The relation between vertical bearing capacity and settlement & distribution of the axial forces and skin friction along pile and failure mode of the pile are discussed based on laboratory test.According to the test,it is concluded that it is clear that the vertical bearing behaviors of the pile is affected by the ratio of variable diameters b value;the b is more smaller,the vertical bearing capacity is more smaller.It is proved that how to choose the b is controlled by the lateral bearing behaviors.The squeezing effect is not clear to improve the vertical bearing capacity unless the top displacement of the pile reaches a certain value.