Abstract: Researches on the depth of pile penetration into the cushion of composite foundation is a part of understanding the foundation settlement and load transfer, which would further complete the theory of  composite foundation settlement. We performed model tests on composite foundation under different working conditions to obtain the working mechanism of cushioned composite ground, and to investigate the pile-soil stress ratio and the behavior of pile penetration into the cushion. It was found that with the increase of load, the pile-soil stress ratio tended to be stable. When pile diameter increased, the pile-soil stress ratio and the penetration reduced, while the load bearing ratio of pile rarely changed. Therefore, it's uneconomical to add pile diameter (replacement ratio) to improve the bearing capacity of piles. The rise of cushion thickness helped reduce the pile-soil stress ratio, while intensified the penetration. The test results provide data support for the design of composite foundation.

Key words: composite foundation, cushion, model test, depth of penetration, pile