Machine-Induced Vertical Responses of Single and Pile Groups

The main objective of this study is to understand the dynamic characteristic of pile foundations subjected to machine-based vertical vibrations. To accomplish this objective, forced vibration field tests are performed on hollow steel single and pile group to obtain the vertical responses of the pile foundations. It is found from dynamic frequency-amplitude response curves that the resonant frequencies are decreases and resonant amplitudes are not proportional when excitation forces are increases which indicate the nonlinear characteristics of soil-pile systems. The values of resonant frequencies are found higher and resonant amplitudes are found lower when the number of piles is increased due to an increase in soil-pile stiffness. For theoretical study, the continuum approach method is used to determine the analytical response curves of piles, and further, it is compared with the field test results. To understand the behavior of pile group, the variations of group efficiency ratio with varying frequencies are also predicted form the analysis.