Abstract: Based on the linear distribution model of the side friction of pile, the theoretical value of pile side friction will far exceed the actual value when the pile is comparatively long. Consequently, the calculation of neutral plane depth and pile-soil stress ratio of the rigid pile composite foundation is quite different from the reality and needs modification. Therefore, the distribution of pile side friction was assumed to be piecewise linear, with influence of negative friction and behavior of pile upward and downward puncture deformation taken into consideration. According to the cushion-pile-soil deformation compatibility condition, a theoretical calculation model was created to obtain the neutral plane depth and pile-soil stress ratio on the top surface and neutral surface of pile. Finally, the calculation method was verified by field measurement as well as model test results of the rigid pile composite foundation, and theoretical values agreed well with the experimental data.

Key words: rigid pile composite foundation, neutral plane depth, pile-soil stress ratio, deformation compatibility, negative friction