Experimental research on load-carrying properties of composite foundation in top-down order

The complex foundation by top-down method is a new kind of foundation. It is necessary to study its bearing mechanics and working behaviors. The model tests on a single pile and a series of single-pile and two-pile foundations are designed to investigate the relation between bearing capacity and settlement, the load sharing ratio between soil and pile as well as the load carrying properties of complex foundation by top-down method. The results indicate that the complex foundation in top-down order, which first constructs foundation plate and a part of superstructure and then presses steel piles and seals the piles subsequently, can take full advantage of soil bearing capacity. The foundation plate tightly keeps contact with foundation soil which bears all the loads of superstructure before pressing piles; the rigidity of soil is strengthened after pressing pile, the settlement of foundation decreases and the bearing capacity is enhanced. The most of incremental loads are supported by pile until the pile reaches the ultimate bearing capacity, and the timing of sealing pile is responsible for load sharing between pile and soil and the behavior of foundation settlement. The pile cap makes distribution of axial force gently and frictional resistance decrease at the upper part of pile, meanwhile, frictional resistance at the rest part increases.