This paper is aiming to find a simple method for the settlement calculation of flexible pile composite foundation under embankment load. Firstly

the side frictional distribution of pile is simplified into a piecewise linear model based on the existing research results. Then

according to the relationship between the length of pile and the critical length of pile

combined with the coordination conditions of stress and compression deformation at the interface of pile-soil-cushion

settlement calculation formulas of flexible pile composite foundation reinforcement area are deduced by using the unit element method

and the settlement of underlying layer of composite foundation is calculated by layer summation method. Finally

the proposed approach is used to predict the settlement of an engineering example

and it is found that the predictions are in accordance with measurements

demonstrating that the approach is available in reflecting the working behavior of the flexible pile composite foundation under embankment load better. Further analysis shows that within the critical length of pile

the bearing capacity of soil between piles in composite foundation is maximized by the interaction of piles and soil. In addition

due to the drag effect of the negative frictional resistance

the axial force of pile at the position of the neutral plane reaches the maximum. Therefore

the concept of critical pile length and neutral plane should be highly valued and applied in engineering design.