考虑土体三维波动效应的现浇大直径管桩纵向振动

考虑土体三维波动效应和桩-土耦合振动,把桩看作一维杆,把土体看作三维轴对称黏弹性介质,对黏弹性地基中现浇大直径管桩纵向振动频域特性进行了理论研究。首先通过引入势函数对土体振动方程解耦,采用Laplace变换和分离变量的方法求得了桩周土及桩芯土频域响应解析解,进而利用桩土完全耦合的条件得到桩振动响应解。将所得解完全退化到实心桩的解,验证了解析解的合理性,并与未考虑三维效应的简化解对比。分析了桩底刚度系数、桩长以及桩径等对桩顶复阻抗的影响,得到了各参数对桩振动特性影响的规律。分析表明：桩底刚度系数增大,共振频率增大,且复阻抗的振荡幅值增大。无桩芯土时复阻抗的振荡幅值比桩周桩芯土都存在时大,无桩周土时复阻抗的振荡幅值比无桩芯土时大。桩长增大,桩顶复阻抗的振荡幅值和共振频率均显著减小,当桩长增大到一定长度的时候,增加桩长对桩顶复阻抗基本没有影响。外径增大或内径减小,桩顶复阻抗的振荡幅值增大。

Analytical solution to vertical vibration of cast-in-place concrete large-diameter pipe piles by considering 3D wave effect of soils

Considering 3D wave effect of soils and soil-pile coupled vibration, treating the pile as one-dimensional rod and the soils as three-dimensional axisymmetric viscoelastic medium, the frequency-domain vertical dynamic response of PCC pile in viscoelastic soils is investigated. The potential functions are adopted to decouple the governing equations for the soils. The analytical solutions of soils in frequency domain are obtained by using the Laplace transform technique and the separation of variables. Under the assumption of perfect contact between the pile and the soils, the pile response is derived. The solution is compared with that of solid pile to verify the rationality. Furthermore, this solution is compared with the simplified solution to verify the correctness of the simplified solution. Moreover, the effects of the stiffness coefficient of pile, pile length and pile radius on the complex stiffness are analyzed. The oscillation amplitudes and resonant frequencies of the complex stiffness of the pile decrease steeply with the increase of its stiffness coefficient. The oscillation amplitudes of the complex stiffness of the pile without inner soils are larger than those with outer and inner soils, and those without the outer soils are larger than those without inner soils. The oscillation amplitudes and resonant frequencies of the complex stiffness of the pile decrease steeply with the increase of the pile length. When the pile length increases to a critical value, the effect trends to vanish. The oscillation amplitudes of the complex stiffness of the pile increase with the increase of the outer radius or decrease of the inner radius.