逆作法复合桩基承载性能的室内模型试验

通过对单桩、两桩以及四桩的逆作法复合桩基室内模型试验,研究在极限荷载作用下逆作法复合桩基的荷载与沉降关系及桩、土荷载分担特性。试验结果表明:逆作法复合桩基的荷载-沉降曲线具有两个拐点,分别对应封桩结束并加下一级荷载时刻和基础破坏时刻;逆作法复合桩基封桩前的沉降量介于浅基础与复合地基的沉降量之间,桩不直接参与分担上部荷载,只起到改善土体刚度的作用;合理选择封桩时机可以控制桩、土的荷载分担比;封桩后基础总体刚度大幅度提高,基桩不但参与基础受力而且控制基础沉降;在基桩达到极限承载力之前,基桩分担了大部分复合桩基阶段的荷载,基础的沉降也得到了明显的控制;在基桩达到极限承载力之后,上部荷载又大部分由地基土承担。

MODEL TEST ON BEARING CAPACITY OF COMPOSITE PILE FOUNDATION IN TOP-DOWN ORDER

The model tests on series of single-pile, two-pile and four-pile foundations were designed to investigate the relation between bearing capacity and settlement under ultimate load and the load share ratio between soft and pile of the composite pile foundation in tep-down order. The results indicate that there are two inflexions that are corresponding to the time of sealing pile and the time of foundation eollapsion on the load-settlement curve. The settlement of this kind of foundation is less than the shallow foudation's but more than the settlement of the composite foundation and the pile didn't share the load hut changed the stiffness of the soil before sealing piles. The time of sealing piles selected in reason could control the load share ratio between pile and siol. The study also shows that the stiffness of the foundation after sealing pile enhanced in large extent and the pile not only bearing the large part of the load in this step but also controlling the settlement very well, and after reaching the pile' s ultimate load, the soil turn to be the main body to bear the load.