Nonlinear Characteristics of the Pile Soil System under Vertical Vibration

In this paper, the inverse problem of the nonlinear vibration of pile foundations has been studied. The methodology proposed by Novak is used to identify the parameters of the soil-pile system from the measured response displaying nonlinear features. A comprehensive study involving both vertical dynamic testing of piles and theoretical analysis is described. The dynamic tests are carried out on single and 2 × 2 group piles in the field under varying levels of vertical harmonic load. From the measured nonlinear response curves, the effective pile-soil system mass, stiffness and damping are determined using the methodology of Novak assuming nonlinear restoring force and linear damping force. It is found that the stiffness of pile-soil system markedly decrease with increasing exciting intensity but the damping increase with exciting moments. Finally the dynamic responses of piles are back-calculated using the estimated nonlinear parameters. It is found that theoretical nonlinear response curves agree well with that obtained from vertical vibration tests.