Abstract: In practical engineering, pile foundations are often subjected to dynamic loads. For example, piles under high-speed railway are subjected to cyclic loading induced by train movement. Studying on the dynamic bearing characteristics of pile foundations under cyclic loading is of great importance in engineering design. The X-section pile is a new type of technique improved based on the traditional circular section pile. Its load-bearing mechanism is different from traditional circular section piles. The objective of this paper is to make further study on the dynamic characteristics and load-settlement relation of the X-section pile under cyclic loading; and then large-scale model tests on the performance of the X-section pile subjected to axial cyclic loading in sand are conducted. The results show that cumulative settlement of X-section pile is induced by the cyclic loading; and the settlement increases with increasing amplitude and frequency of the cyclic loading. At the initial period, the dynamic stiffness of X-section pile decreases and the axial stress of the pile increases. Furthermore, the friction resistance at the pile side decreases. After the initial period, they tend to be stable. These indicate that the dynamic performance of the X-section pile is better than the circular section pile; moreover, the friction resistance of the X-section pile is larger, the cumulative settlement of the X-section pile under long-term cyclic loading is smaller. The study results may provide some guidelines for the engineering design of the X-section pile under dynamic loading.

Key words: large-scale model test, X-section pile, sand, axial cyclic loading, bearing characteristics