土塞效应对管桩纵向动力特性的影响研究

基于附加质量法,研究考虑土塞效应时成层地基中管桩的纵向振动问题。首先,根据桩侧土、桩端土的成层性,将桩土系统沿纵向划分为有限个微元段,并采用虚土桩法和附加质量法建立了桩土系统的纵向振动控制方程。然后,运用Laplace变换技术和阻抗函数递推法,推导得到了考虑土塞效应时管桩纵向振动的桩顶速度频域响应解析解和半正弦脉冲激振力作用下相应的桩顶速度时域响应半解析解。最后,分析了附加质量法中Voigt模型参数的敏感性区间,讨论了土塞效应对管桩纵向动力特性的影响规律,并通过模型试验验证了所提理论解的合理性。结果表明：①当附加质量法中的Voigt模型参数逐渐增大时,土塞与管桩之间的相互影响将逐渐增强；②在桩顶速度时域响应曲线上,土塞顶部界面位置处会出现类似扩颈桩段的反向反射信号；③由于土塞的存在,填充土塞桩段的综合波速会小于管桩材料的一维弹性纵波波速,且土塞高度越高,填充土塞桩段的综合波速越小。

Influence of soil plug effect on vertical dynamic response of pipe piles

Based on the additional mass method, the vertical vibration of pipe piles embedded in layered soils is theoretically studied by taking into account the soil plug effect. Firstly, allowing for the stratification of pile surrounding soil and pile end soil, the pile-soil system is divided into finite segments. By means of the fictitious soil pile method and the additional mass method, the vertical dynamic governing equations for pile-soil system are established. Then, by virtue of the Laplace transform technique and the impedance function transfer method, the analytical solution of velocity response at pile head in frequency domain is derived, and the corresponding semi-analytical solution of velocity response at pile head in time domain is also obtained when there is vertical half-sine pulse excitation force acting on the pile head. Finally, the sensibility intervals of the parameters of Voigt model in additional mass method are analyzed, and the influence of soil plug effect on the vertical dynamic response of pipe pile is also investigated. The rationality of the proposed theoretical solution is validated by means of model tests. The results show that: (1) with the increase of parameters of Voigt model, the interaction of pile and soil will be strengthened; (2) as shown in the time-domain curves of velocity response at pile head, there are reverse reflection signals at the upper surface of soil plug. It looks like there are expanding neck pile segments at the upper surface of soil plug; (3) due to the presence of soil plugs, the integrated velocity of the pile section filling soil plug is less than the elastic longitudinal wave velocity of pipe pile, and the higher the height of soil plug is, the smaller the integrated velocity of the pile section filling soil plug is.