Study On Pile Longitudinal Vibration In Saturated Soil Considering Three Dimensional Wave Effect

The dynamic soil-pile interaction has been a subject of considerable interest in past four decades. The theory of pile longitudinal vibration investigates dynamic responses of pile under vertical loads. It finds its applications in machinery foundations, pile driving and structures exposed to seismic excitation. And it is also the basis of any kinds of methods in dynamic pile testing. Although many soil-pile interaction models have been developed using a variety of analytical and numerical techniques, how to model soil layer accurately is still a major difficult in pile dynamics. Based on 3D axis-symmetrical soil model and the theory of saturated porous medium originally presented by Biot, an integral pile and pile with variable impedance embedded in layered saturated soil are analytically studied in this dissertation. The principal work includes four items.Firstly, dynamic interactions between an integral pile and saturated soil are studied. A dynamic interaction schematic of an end bearing or elastic bearing pile with arbitrary force at pile top is founded. By using Helmholtz resolution and the operator decomposition method, Biot's equations governing motions of a porous solid saturated with interstitial fluid are decoupled. Then the rigorous solutions for soil layer vibration are analytically derived by virtue of the separation of variables. By means of the orthogonal expansion technique, the coupling system solutions are finally obtained. Then the dynamic model of saturated soil layer caused by pile longitudinal vibration is founded. Incorporated wave propagations into saturated soil layer, the characteristics of soil resistance factor and the mechanism of the radial damping are analyzed, as well as distributions of shear stress and pore pressure in saturated soil caused by pile vibration. Meanwhile, dynamic responses at pile head are investigated. It is shown that the effects of pile slenderness, bearing stiffness of pile toe and the pile-soil modulus ratio on pile impedance are major whereas the ones of the permeability and the soil reaction coefficient are minor.Secondly, on the basis of the theory of Rayleigh-Love bar, the longitudinal vibration of a large diameter end-bearing pile in saturated soil is investigated considering transverse inertial effect. The vibration of pile considering transverse inertial effect is different from the one not considering this effect significantly at a smaller slenderness. Under the same conditions, the reflective peak of pile toe in time domain in the former is smaller than in the latter and decreases gradually with the increase of exciting frequencies.Thirdly, a simplified model neglecting the radial displacement of saturated soil is established and an analytical solution for vertical vibration of the soil-pile system is obtained. By comparison the solution with available viscoelastic solution, the differences are illustrated as well as its applications. The results show that there is significant difference between the solution considering and neglecting the radial displacement at lower frequencies but they are identical at higher ones. So, it is suitable to use the former for aseismic design of pile foundation but the latter for dynamic pile testing.Finally, dynamic compliances of a pile with variable impedance embedded in layered saturated soil are studied. A simplified layered model is put forward on the basis of the single layer elastic bearing model. By using the same method, analytical solutions in frequency domain hence semi-analytical solutions in time domain representing the dynamic responses at pile head are obtained. By comparison with the single layer solution, the rationality of layered model is verified. Based on these solutions, the dynamic responses of integral pile and pile with various impedances are investigated. The results show that not only variations of pile impedance but also parameters of soil layer can make effects on the dynamic compliances at pile head.The coupled soil-pile dynamic interaction model and the corresponding...