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 soil and pile of the composite pile foundation in top-down order.The results indicate that there are two inflexions that are corresponding to the time of sealing pile and the time of foundation collapsion 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 but 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.