三维饱和层状土–虚土桩–实体桩体系纵向振动频域分析

Frequency analysis of longitudinal vibration of a three-dimensional system of saturated layered soils,virtual soil piles and solid piles

为分析饱和土中浮承桩纵向振动特性,基于Biot波动理论提出一种桩底饱和虚土桩模型,并建立三维饱和层状土–虚土桩–实体桩耦合纵向振动体系定解问题。采用势函数法、桩–土耦合条件及阻抗函数传递性求解得出桩顶纵向振动动力阻抗解析解答,并通过多元退化验证所提出解析解的正确性。在此基础上,对浮承桩纵向振动特性影响因素进行参数化分析,结果表明:当桩底土饱和性显著且排水性较差时,桩底土单相虚土桩模型会过低估计阻抗曲线共振频率,宜采用饱和虚土桩模型和所得相关解析解答分析浮承桩纵向振动特性。桩周饱和软(硬)夹层对桩顶动力阻抗曲线振幅水平影响显著,而桩底软(硬)下卧夹层则对桩顶动力阻抗曲线影响很小。桩周饱和表层土体孔隙率仅对桩顶动力阻抗曲线共振幅值产生明显影响,而桩底饱和土层孔隙率对桩顶动力阻抗曲线共振幅值和共振频率均影响显著。

In order to study the longitudinal vibration characteristics of floating piles in saturated soil,a saturated virtual soil pile model based on Biot′s wave theory was proposed,and a coupled longitudinal vibration system of three-dimensional saturated layered soil,virtual soil piles and solid piles was established.The analytical solution of the displacement of saturated soil was derived by potential function method,and the vertical dynamic impedance at the pile head was obtained by using the pile-soil compatibility conditions and the transfer method of impedance function.The validity of the obtained solution was verified by degrading to existing solutions,and parametric analyses were performed to investigate the effects of the parameters of the saturated soil on the vibration characteristics at the pile head.The results show that,when the saturation of soil layers beneath the pile toe is remarkable and the drainage is poor,the saturated virtual soil pile model and the relevant analytical solution is more suitable to analyze the longitudinal vibration characteristics of floating piles.The longitudinal interlayer of surrounding soil has obvious effect on the amplitude of the dynamic impedance at the pile head,but the effect of longitudinal interlayer of soil beneath the pile toe on the dynamic impedance at the pile head can be ignored.The porosity of saturated surface surrounding soil has obvious influence only on the resonance amplitude of the dynamic impedance at the pile head,while the porosity of saturated soil beneath the pile toe has significant effects both on the resonance amplitude and the resonance frequency of the dynamic impedance at the pile head.