Abstract: The nature of composite foundation is the load from the overlying shared by the reinforcement and ground soil via the deformation compatibility. Cushion plays a coordinating role of pile-soil deformation; however, its characteristics of the work and deformation characteristics are not yet clear. Designing cushion thickness still depends on experience or reference standard. It can not fully play the bearing capacity of foundation soil. The pile-soil deformation is usually adjusted by cushion in current composite foundation design. The pile-end piercing settlement coordinates pile-soil deformation and plays the role of foundation soil bearing capacity is ignored. Using pile-end piercing settlement to adjusted pile-soil deformation and bring foundation soil bearing capacity into full play, the cushion thickness is reduced or not to set cushion, and the designed pile length is shortened in order to reduce the cost of ground handling and achieve the purpose of load shared by pile and soil finally. A design method for pile-soil self-balanced composite foundation is established through controlling pile-soil deformations adjusted by pile piercing settlement. Through contrasting with the cushion method and project examples, it is proved that the method can show the foundation soil bearing capacity better, and provide references for the optimal design of composite foundation.

Key words: composite foundation, pile-end piercing settlement, cushion, pile-soil self-balance, deformation compatibility