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实际工程中桩基经常受到各种动荷载作用,如高铁路基中的加固桩长期承受列车行车时产生的循环动荷载作用,桩基在循环荷载作用下的承载特性研究对动荷载下的工程设计至关重要。X形桩是一种在传统圆形截面桩基础上发展而来的新型异性桩技术,其承载机制不同于传统圆形截面桩。为了深入研究X形桩在循环荷载作用下的动力特性和荷载与沉降规律,开展了砂土中X形桩竖向循环加载大比尺模型试验。试验结果表明,随着循环加载的进行,X形桩顶产生累计沉降,且循环荷载比越大,加载频率越高,桩顶沉降越快;循环加载初期,X形桩顶动刚度降低,桩身轴力响应增大,桩侧摩阻力发生弱化,之后逐渐趋于稳定,且桩身下半段侧摩阻力较大;在同等加载条件下X形桩与等截面圆形桩相比,承受动荷载能力较强,桩侧摩阻力较大,长期循环加载作用下产生的累计位移较小。研究结果可为X形桩在动荷载作用下的工程设计提供参考依据。
In practice, the pile foundation is often subjected to various kinds of dynamic loads, such as the reinforced pile in high-speed railway embankment long-term to withstand the cyclic dynamic load caused by train driving, the bearing characteristics of pile foundation under cyclic loading, It is very important. X-shaped pile is a new type of pile technology developed on the basis of the traditional circular section pile, whose bearing mechanism is different from the traditional circular section pile. In order to further study the dynamic characteristics and load and settlement law of X-shaped piles under cyclic loading, a large-scale model test of vertical cyclic loading of X-shaped pile in sand was carried out. The experimental results show that with the cyclic loading, the cumulative settlement of X-shaped pile top produces cumulative settlement. The higher the cyclic loading ratio is, the higher the loading frequency is, and the faster the pile top settles. At the initial stage of cyclic loading, the dynamic stiffness of X-shaped pile decreases, The response of body force increases and the friction of pile side is weakened, and then gradually stabilizes, and the lateral friction of the lower half of pile body is larger than that of X-shaped pile under equivalent loading. The dynamic load capacity is strong, the pile side frictional resistance is larger, and the cumulative displacement caused by long-term cyclic loading is smaller. The results can provide a reference for engineering design of X-shaped piles under dynamic load.