Kinematic response of end-bearing piles in inhomogeneous soils under P-wave excitation

抄録

This paper presents a novel elastodynamic model for the kinematic response of single, end-bearing piles embedded in vertically inhomogeneous soils, excited by vertically propagating P-waves. The response in terms of displacements is expressed in the form of a generalized Fourier series, and extends a previous work of some of the authors to account for soil inhomogeneity. Contrary to formulations for homogeneous soils, the associated Fourier coefficients are now coupled, and can be obtained as a solution to a system of algebraic equations of rank equal to the number of soil modes considered in the analyses. The pile is modelled as a rod, using the strength-of-materials solution, and the soil as an approximate continuum of the Tajimi type. For the axisymmetric problem at hand, the Tajimi approximation lies in adopting the physical motivating assumption that the vertical normal and vertical shear stresses in the soil are controlled exclusively by the vertical component of the soil displacement. This approximation results in reducing the number of governing elastodynamic equations to one, which satisfies the equilibrium in the vertical direction. The proposed model can predict the steady-state and transient response of piles in inhomogeneous soil strata over a rigid rock, subjected to vertically-propagating harmonic compressional waves and actual earthquake recordings, respectively. The predictive power of the model is verified through comparisons with finite element analyses. Results are presented in terms of a kinematic response factor which relates the motion of the pile head to the free-field surface motion. It is shown that a pile foundation may significantly alter the motion transmitted to the base of a structure.