Abstract :

This thesis contains the results of a systematic study aimed at providing a rational framework as well as a set of practical tools for the dynamic analysis of piles and pile groups under multi-directional dynamic loading. In the context of three-dimensional elastodynamics, a rigorous formulation is first presented for a single pile which is modeled as both a beam-column and a thin-walled cylindrical shell. By virtue of integral equation methods and ring load Green's functions, it is shown that the requisite traction and kinematic compatibilities on the contact surface, singular stress concentrations at the pile ends, and the three-dimensional energy radiation conditions can be observed exactly for general static, dynamic, and incident wave loadings. The problem is reduced to a set of coupled Fredholm integral equations. By an analysis of the kernels involved, the detailed nature of the stress singularities is rendered explicit, and incorporated into an efficient numerical procedure. Numerical results are used to evaluate the accuracy of existing analyses. The problem is also extended to the case of a pile under incident seismic waves. For general applications, the singularity analysis on the basis of the governing differential equations has also been developed which can be used for a body of revolution under general asymmetric loading in a linear elastic and poro-elastic material. This asymptotic analysis can be extended to a general system of piles.
With the attention shifted to pile group behaviors, an exact formulation using the elastodynamic point-load solutions is derived for the pile-soil-pile interaction problem. With the capability of dealing with general variation of the interfacial load transfers in both the angular and axial directions for each pile, the analysis leads to a set of governing integral equations which can be solved numerically. The computation is facilitated by the recognition that the integration of point load solution in the axial direction can be performed in closed form. The numerical results furnish a basis upon which the merits and inaccuracy of the few existing approaches can be assessed in a rational manner. The results also compare well with an experimental study.
With the current solution as the background, effort is directed to the development of a simplified method for practical applications where a large number of piles might be involved. On the basis of a reduction of the rigorous mathematical formulation, it is shown that a practical method of analysis is feasible by which one can accurately predict all the essential features of the pile group problem.