饱和土中端承桩纵向振动特性研究

VERTICAL VIBRATION OF AN END BEARING PILE EMBEDDED IN SATURATED SOIL

基于饱和多孔介质理论研究了三维轴对称条件下端承桩在饱和土中的纵向耦合振动,首先通过引入势函数对Biot动力固结方程解耦,采用算子分解方法及分离变量法求得饱和土层振动解,进而利用桩土完全耦合条件得到桩土系统定解,然后对桩顶的频率和时域响应进行参数研究,结果表明,桩的长径比和桩土模量比对桩顶动力响应有较大影响,而渗透力对其影响较小,最后将幅频及时域反射波理论拟合结果与桩基实测结果加以对比,结果表明理论曲线与实测曲线规律一致。

Dynamic interaction of pile and soil plays an important role in structure design. Although many researches have been carried out on the field in past two decades, the emphasis is mainly focused on pile vibration in single phase medium. Such a fact has been neglected that soil is multi-phase medium. The effects of ground water on the interaction are seldom discussed. In this paper, vertical vibration of an end bearing pile embedded in a saturated soil layer is theoretically investigated. The pile is assumed to be vertical and can be dealt with one dimensional elastic theory. The soil is considered as a linear saturated isotropic poroelastic medium and satisfies rigorous three dimensional poroelasticity. Potential functions are applied to decouple governing differential equations of the soil layer originally presented by Blot. By virtue of differential operator splitting and variable separation method, soil vibration displacement solutions with an undetermined constant are obtained at first. Under the assumption of perfect contact between the pile and the soil, the pile response to an arbitrary vertical load is analytically derived in a closed form. Then harmonic complex stiffness and admittance at the pile head are defined in frequency domain. And velocity response in time domain is gained by means of Fourier inverse transform. Based on the solutions, a parametric study is conducted to determine the main features of the soil-pile interaction in vertical vibration. As a result, the pile slenderness and the pile-soil modulus ratio are major on the pile dynamic response, while the seepage force has minor influence on the response. Finally, it is shown that the theoretical curves are in good agreement with those obtained from field test.