轴力作用下液化土中端承桩的水平振动特性

将地震液化场地土层分为非液化表层土、中部的液化土层和底部的基层，基于饱和多孔介质理论和Novak薄层法，研究轴向压力作用下液化黏弹性土层中端承桩的水平动力特性。利用Helmholtz分解和变量分离法，得到液化土层对桩水平振动的阻抗。利用矩阵传递法，在频率域得到轴力作用下液化土层中端承桩简谐振动的解析解和桩头复刚度的表达式，并进行参数研究，分析轴力、桩-土模量比、桩长径比、液-固耦合系数等对桩头动力刚度和阻尼的影响。结果表明，在轴力作用下，不同长径比、桩-土模量比、液-固耦合系数时的动力刚度绝对值均比无轴力作用时减小，但随频率的变化趋势相同；轴力对桩水平振动的动力阻抗影响显著，随着轴力的增加，桩的水平振动动力刚度因子的绝对值减小，若轴力继续增大，其绝对值趋近于0，桩发生失稳破坏；桩长径比和桩土模量比对桩的水平振动动力阻抗有显著的影响，而液-固耦合系数的影响较小。

Characteristics of horizontal vibration of end-bearing piles in liquefied soils under axial force

Regarding the soil profile in seismic liquefied deposits as being composed of a non-liquefied crust layer at the ground surface, a liquefied layer in the middle of the deposit and a non-liquefied base layer, and based on the theory of saturated porous media and Novak’s thin layer method, the dynamic behavior of an end-bearing pile in liquefied viscoelastic under axial force soil layer is investigated. The horizontal dynamic impedance of liquefied soil was obtained using Helmholtz decomposition. The analytical expressions of the harmonic vibration and dynamic complex stiffnesses of the end-bearing pile in liquefied soil under axial force are obtained with the transfer-matrix method. A parametric study was conducted to analyze the influences of the axial force, the slenderness ratio of the pile, pile-soil modulus ratio and the coupled coefficient of fluid and solid phase on the dynamic stiffnesses and dampings. It is shown that, with different slenderness ratio of the pile, pile-soil modulus ratio, coupled coefficient, the absolute values of the dynamic stiffness of pile with axial force are smaller than those of pile without axial force; and the change tendency with frequency are the same. The influence of the axial force on the dynamic impedance of the horizontal vibration pile is remarkable. The absolute values of the dynamic stiffness factors of the horizontal vibration of pile are approaching to zero; and the pile will buckle with the axial force increasing. Furthermore, the influences of the slenderness ratio of the pile and the pile-soil modulus ratio on the dynamic impedances of pile are notable; and the influence of coupled coefficient of fluid and solid phase is trivial.